5+4 Balance Plugs - Zippy Compact 7S 4000mAhr

I did say that once i'd worked the correct wiring details out I would post them here, so here they are

 

 

Yes, they are on a post-it note, but its easier to post a pic of that than to create a new diagram and risk an error. The wire colour code on the 4- and 5- way plugs are 'as is' on my battery. Note that the red wire on the 4-way is parallel with the black wire on the 5-way (i.e. both are from the 11.5v 3rd cell.) and the 7S balance adapter lead supplied by Hobbyking has no connection to the 4-way red wire, using instead the 5-way black wire for the 3rd cell. Note as well that all but the 0v connection on the adapter cable use red wires.

Balance Cable Challenge

A few of the items I need to rebuild the 4Ahr Clansman battery have arrived, and the crucial item, the Balancing Cable, is likely to pose a bit of a challenge!

The Zippy Compact 7s LiPo battery pack has two balancing connectors. The balancing cable adaptor supplied also has these two connectors, but one of them is missing a connection. Exactly what this signifies I have yet to discover. Is the missing wire a duplicate that is made up for on the other connector?

It seems that the manufacturer has no website, and theres no wiring info available for the battery!

Once ive worked it out, I will post the wiring details on the blog.

Im still waiting on the low voltage alarm and the temperature sensors. But I can now at least work on the main wiring of the pack, and how to safely mount the battery in the case, im considering perhaps fire resistant foam for this. The final thing to work out will be the fixings for the case lid!

Pye PF8 Conversion - Partial Success

With the new 70cm SU20 channel crystals in hand, I found time today to work on the conversion of the Pye PF8 to 70cm. Earlier efforts resulted in me effectively buggering it up, due to not following the procedure properly, and by not appreciating that modern crystals have just a pair of insulated lead outs rather than the whole base of the crystal being an insulator - with the result that I shorted the bloody thing out! I also inadvertently put a little more voltage on it than it likes, luckily it seems not to have killed anything, although I cant be certain yet!

With thin slivers of polythene cut and fitted as insulators under the crystals, I started the tune up. It was here that I hit a major problem. L13, part of the Tx chain, was broken. Both the ferrite core and the coil former were shattered. Replacing it required a complete strip down of the set, and some very careful desoldering and soldering. L13 is the 2nd can from the left below, shown after replacement.

And the original, knackered coil -

Since I had the whole thing apart, I also took the time to replace the lower microphone housing, which was split around the threaded insert.

I also removed C69. This capacitor is only needed when the Tx and Rx frequencies are more than 4MHz apart, but of course im converting this to simplex!

After following the official alignment procedure (mostly!), the set is now working on 70cm, admittedly though not as well as i'd like. For a 500mW set, if so far managed to coerce a mere 50mW from it. On receive, after a lot of fiddling ive got it to work at -85dBm, a far cry from the -118dBm im used to setting PMR squelch pots at!

Before I look at improvements based on trying to convert the U0 band (440-470MHz) components to T1 band (405-440MHz), I want to check that my lack of success is to be expected, and not the result of another fault somewhere.

Musings on LiPo protection

One of the big problems with Lithium Polymer batteries, and Lithium chemistry in general, is that if you get it wrong, it has a tenancy to bite! Overcharging, overdischarging, or piercing/scratching the cells can all lead to the lithium reacting violently and catching fire, and believe me, having used lithium, sodium, magnesium and caesium in the lab, reactive metal fires are NOT something you want happening in your radio!

Its one thing having a low voltage alarm monitoring module keeping an eye on your battery, but if your working an SSB transmitter, the current draw, and hence the cell voltages, can fluctuate rapidly, which could result in the monitor going into alarm fleetingly, and if your wearing a headset you might not hear it sounding. So, modifying the module to trip a cut-off relay is the way to go. But proper dual coil latching relays are expensive, especially with contacts rated for the sort of current I need to pass!

So, ive thought up a simple circuit that should allow me to do the cut-off with a normal non-latching relay. For this to work, the relay must be energized whilst ever the battery is at a good state of charge. Yes, this does mean that when not in use the protection circuit itself will slowly discharge the battery. To prevent this when the battery isnt being used, but still in the Clansman housing, a 'Trip' button will be provided that will de-energize the relay.

The concept is simple. A pair of NPN transistors control the relay coil. The supply to the coil comes through one half of the relays DPCO contacts. At start, the coil will have no supply. An 'Arm' button temporarily bypasses the contacts, putting bias on the transistor base and energizing the relay coil, this pulls in the contacts and the button can be released. A second transistor goes from the firsts base to ground, and is driven by the output of the alarm module. When the voltage drops to the cutoff alarm level, the alarm sounds, this transistor turns on, grounds the bias to the other transistor, which turns off, the relay de-energizes, the contacts open, and the battery output is disconnected. Attempting to re-arm the relay circuit will just result in the alarm module activating and tripping the protection again.

A 1N4148 or 1N40001 diode serves as back-EMF protection across the relay coil. A suitable fuse is also provided as close to the battery terminals as possible. A series resistor sets the voltage of the supply to the protection circuit suitable for the relay coil. It may be possible to eliminate this if a 24v relay is available.

I now need to find a suitable relay and to mock up the circuit to prove that it works as expected.

Clansman Battery Upgrade Progress

After waiting for what seemed like months, but was in fact about two weeks, I finally received an email telling me that the specialist Balancing Charger I require was back in stock. I jumped on the 'net and got it ordered, along with the Lithium Polymer battery. If i'd had a bit more spare money I could have gone with a much higher capacity (these are available at over 6Ahr!) but decided to save a few bob and stick with 4Ahr, the same as the original NiCd batteries.

The charger, a Turnigy Accucel-8 150W, is capable of charging and balancing up to 8 Lithium cells (8S), it can also handle up to 27 NiCd/NiMH cells, so will also do the original Clansman batteries, and it can do SLABs as well. The battery is a 7S 25C 4000mAh Zippy Compact Lithium Polymer (similar to the one pictured). This means it has a terminal voltage of around 26v. Its size is such that it will fit in the empty 4Ahr NiCd, but it only weighs about 650g - the originals are about 3kg!

But, its of course not that simple! These batteries if handled or charged incorrectly can be very dangerous. There is a risk of fire. The fact it will be installed in a metal housing goes some way to protecting against this, but further specialist electronics are needed to make this into a safe and effective power system.

Firstly, I need adaptors. The chargers main connection is a different connector type to the battery, so I need an adaptor to connect to the charger, and one to connect to the case terminals. I also need one that converts the 5+4 balancing connections to a single 8 pin connector for the chargers balance port. Then, I need a protection device to prevent over discharge. The PRC320 and PRC351 would quite happily keep taking power beyond the safe discharge cell voltage of these batteries, which would lead to a risk of rupture and fire. So, it needs one of these

This is a low voltage alarm module suitable for up to 8S batteries. When the cells reach the minimum allowable voltage it sounds a loud alarm. I intend to modify this to drive a cut-off relay instead. All this kit will be fitted into the battery housing. Whether I then add panel connectors for the charger, and a window for the meter display, I havent decided yet. It would make charging convenient. I would also need a reset button to reset the latched cut-off relay.

 

The charger is also capable of monitoring the battery pack temperature with a probe based on the LM35DZ temperature IC. It makes sense to include one of these bonded to the pack inside the housing, and provide a connection point to it as well, as an extra level of safety when charging.

 

So im now waiting on the adaptors and the monitor board before I can proceed futher with this. In the meantime, I have a couple of bids on for other Clansman items that im missing, notably the 1.2m whip and the carrier frame for the PRC351.

 

I also have the Simoco PRP70 series radios to play with. I have had to buy a USB 3.5inch floppy drive to get the programming software onto the DOS machine from my main PC, which doesnt have a floppy! Next step there is to build a programming interface and then find a facilities plug for the radios!

Antennas, APRS, and storage

Its not often in amateur radio that several diverse problems can be all sorted out in a mutual way, but a few of the problems I currently have, that is, the poor reception of APRS signals at my QTH, my lack of directivity for 2m SSB operation, and my lack of segregated storage for components.

But it seems all these can be alleviated by grouping them all together into one task - create storage space.

The first part of this combined task will also remove one more thing that Julie has told me to sort - the growing number of empty butter tubs under the sink!

So, with as many of these as I can use now labelled up with their future contents, ive mostly used them up. But that leaves me facing another problem - lack of workshop shelf space. That problem can be relieved by a simple expedient - stop clogging the shelf up with a currently unused 144MHz Yagi in a box! And, at the same time, make some space by moving a 2m collinear out of the workshop!

So, If I do that to create space to put the butter tubs on the shelf, I need to put those antennas somewhere. And clearly, the sensible place to put them is up in the air! So I will change the layout of my 'test' mast (the only one currently available) to accommodate these two antennas. By putting them on the mast, I will improve my SSB capability to the SE, and at the same time my 2m FM and APRS reception!

It would help, of course, if I completed a few projects that are on the bench!

Much of the time at present however is taken up with testing and charging batteries, to get the Lions radios ready for use with the Christmas Sleigh. On the subject of batteries, ive finally had an alert that the special multpurpose charger, which will do the 7s LiPo's for the Clansman, is in stock. That is now ordered, along with the LiPo battery!

APRS

Its been quite a while since I played with packet! In fact, I probably havent used packet radio since the affair of Bobs laptop, way back in my teenage years. Now, Bobs laptop was in fact somewhat more - it was a complete portable packet radio station in a briefcase! Comprising of small handheld radio, SLA battery and charger, Antenna (mounted beside case handle), TNC (Baycom) and laptop. The affair refers to myself and Ian having to visit Bob to retrieve either the machine or payment for it!

But tonight I decided to see about setting up a packet radio system, in particular, an APRS system.

APRS is Automatic Packet Reporting System. Using the old packet radio methods, but with modern internet linking, it allows message services, transmitter tracking, etc etc. Ive become interested in this because I use the APRS systems ability to give propagation information for VHF/UHF at work to help track co-channel interference due to tropo. Ive noticed that many areas of the UK are not well covered for this!

Its been hard work though! Much of the online information is not well presented, many links dont work, and the software needed - clients, gateways, engines, all rather confusing. After a lot of asking about, downloading, and fiddling, ive now managed to get a packet soundcard TNC engine called Direwolf working, along with an IP and GUI front end called APRSISCE/32. On this I am seeing APRS stations around the north, but sadly only via the IP connection - despite having a working VHF radio feed into the system, theres not been a single packet decoded off-air, why, because theres no one within range transmitting it!!!

A bit more surplus

A few days ago, one of our engineers left me a note to say he'd found a few oddments of surplus PMR kit, that I could have if I could make use of it. Gimme Gimme Gimme!

Its mostly Philips/Simoco PRP70 series kit, which Ive not made much use of in the past, since most of what came my way was U0 band UHF stuff. But of interest here is the later model PRP76 on the right, which is E0 band - VHF Low Band! That means it would go on 4m. All the radios work, but theres only two batteries, and they are very dead. Im in the process of trying to rejuvenate one of them at present through a combination of high current burst, trickle charging, and pulse charging over several charge/discharge cycles.

A few years ago I did have proper charging equipment for them! But I passed it onto someone else. Even once I get a working battery, the next problem will be programming them! I will need to track down a facilities connector, then the required software, and then probably breadboard up a programming interface.

Theres also a rather nice little Yaesu VX2000V VHF 40ch mobile rig. This will probably go quite easily onto 2m, and might make a neat little set for special events, or maybe for APRS. Ive been considering setting up for APRS for a while. I use the Mountain Lake APRS propagation website to track active and potential UHF co-channel interference conditions at work, and would like to set up a fixed APRS unit up at Emley Moor to contribute to the propagation monitoring.

More pressing, is the need to build a crystal controlled oscillator for Sams school science fair project. Based around the big old 10X slab of quartz I got from Rishworth, we are going to perform an experiment where we will test the effect of grinding the crystal on its frequency. I of course already know the likely results, but Sam will discover this for himself. I just need an oscillator that will work with a crystal of this size, and to build some form of holder for it!

Chinese Airband Radio nears completion

Two issues with the LCD frequency counter module needed resolving before I could finish the electronics on this project. First of course was the detuning affect of body proximity. The second was a desire to ensure the radios voltage regulator was not working too hard.

The second issue was the easiest fix. Rather than draw an 8v supply for the LCD module from the airband radios own 78L08 regulator, I modified the LCD module by removing the power connector, and soldering in another 78L08 onto the board, its output pin going to the +ve connection pad and direct to the counters input diode and 5v regulator (which, it seems is only spec'd to 9 or 10v anyway!), its GND pin to the -Ve pad, along with the black 0v wire, and the red +ve wire direct to the new regulators input pin, with a bit of heat-shrink sleeving. The black blob of the regulator and yellow sleeve can just about be seen in the photo below, above the 'SQL' pot connections. The whole LCD unit now gets a direct 12v supply from the fuseholder.

Issue number one, the loading of the oscillator, was a bit trickier. To help solve this, I knocked up a little emitter follower buffer amp, using a 2N3904, on a bit of spare PCB material, with pads milled out of the copper using a Dremel. This was mounted directly to the LCD module by removing the signal input connector and replacing it with PCB pins, the buffer PCB soldering to these. It can be seen above, sitting above the main PCB at a slight diagonal. The pink wire is the input, which taps the oscillator of the NE602 IC from a pad of one of the capacitors on pin 7.

Body proximity effects are now reduced to about 20kHz shift when close, which I think could only have been improved by using a metal case. This is still well within the IF passband! So even when detuned slightly, a selected station is still receivable.

The LCD frequency counter module was then secured in place with hot melt glue. The final tasks are to drill a grid of speaker holes in the lid and mount the loudspeaker, and to find a 10k switched pot to replace the volume control, so I have an on/off/volume function. In fact, it took a while to find a speaker that didnt cause too much detuning when in close proximity to the VFO!

Another task I need to get on with is a controller for the dew heater strap for my camera when taking astro photos. I got this cheap LED dimmer unit from the far east

 which claims to be a PWM circuit. I have to say I had my doubts, so opened it up. Inside, as well as a potentiometer, there is a small PCB, but no visible components!

But, on removing the PCB it does turn out there is some electronics on the other side. Ive tried to see the thing in action on the oscilloscope, but its playing up again (must be and earth thing!?) so instead I proved it does indeed dim an LED by putting one and a 4k7 resistor across its output.

Next step with this is to attach the heating strap, and monitor the temperature.

Shack Refurb - Antenna Patch Panel

When Julie decided a new carpet was required, I decided to rebuild the shack. This involved some drastic redesign of the desk, which is still in the process of being repopulated with equipment. This will take some time, as new power runs and cable control is needed.

As part of this, and in order to get away from the interminable jungle of thick coax behind the desk, which makes connecting anything up a nightmare, I decided that all coax coming into the shack will go to a patch panel, and from there, flexible short jumpers will be used to the equipment.

The panel is cut from 3mm sheet aluminium, and will be mounted on a wooden frame. The wall cutout behind will need expanding somewhat, forming a cone shaped entry. Four N-type bulkheads, plus one BNC bulkhead, are provided for the main antennas, plus a little bit of expansion capability. A 30mm diameter grommeted hole allows other cables, such as temporary antenna feeds, DC cables, control cables etc, to be fed through.

Boxing the Chinese Airband Receiver

Today was the annual G-QRP club Rishworth convention. Although I didnt have a particularly long list of things I wanted, I did have on the list a box of some sort to build the Chinese Airband receiver into. This, as it turned out, was one of the few items on my list I actually managed to get!

I got a fairly generic, basic black ABS box from Bowood's stall. Another stall furnished me with a little ABS box ready to build a regulator unit that Bob has asked me to make for him. I thought it felt a bit heavier than expected, but it was taped up so thought no more of it. Once home I found that as well as the screws for the lid, it also had a number of new connectors inside! Clearly someone had started acquiring bits for a project that never happened. I also found a small, ancient card box labelled as containing a 3.6MHz crystal. On opening, inside was a wad of tissue paper, within which I found a big square quartz crystal slab! But, it was marked as being 900kHz. I bought it anyway for 50p - a nice teaching aid I thought. On looking closer once home, I found two smaller bits of tissue underneath, each containing another crystal blank!

I also grabbed a pair of channel crystals on S16 (2m - 145.400MHz) marked as for Burndept. Ive no idea which Burndept radio, but couldnt resist for another 50p!

Once home, after a detour for myself and Sam to devour copious quantities of fried chicken, I set to on boxing up the airband receiver. This took some thinking about. Sam decided on the front panel layout, and I set to marking out and drilling

The big problem when doing these sorts of projects is the need for the square cutout for the display. This inevitably comes down to drilling lots of little holes, punching out the excess, and then spending a long time filing and checking, until the desired hole is created.

In the photo below, the front has been mocked-up to check everything looks right. The big knob on the right is the tuning control, on the left, the top knob is the volume, and the bottom one squelch.

Despite the space in the box, getting both the receiver board and the frequency counter module fitted took some doing. For a start, all the sockets and controls had to come off the board, and be replaced with panel mount parts. In most cases, the PCB mount component could be reused. Ive added a fuseholder as well, since its likely this will be powered off a 12v SLAB. In order to get the main PCB right to the back, I had to cut the base of two of the PCB mounts in half.

The frequency counter module was then taken out again to be modified (it needed some hex studs removing and sockets replacing with direct wiring) and the wiring added for the front panel controls.

With the various controls wired, and the wiring looms twisted in bundles, I clipped on a temporary 12v supply and powered the receiver up. The first problem to sort was that the volume pot AND the squelch pot were working backwards! I'd got them wired up wrong, and had to swap the wires over. With that done, I found I couldnt tune in a test signal on 125MHz. I guessed that the tuning pot wiper was wired wrong. Checking with my meter, this proved to be the case. That corrected, I could find the test signal, but on increasing it by ten MHz to 135, found I had to tune backwards to find it! I changed the wiring yet again, and now have all the controls working properly. Even finding a few planes whilst I was at it!

Final act for tonight was to add a fuse. I found a 2A fastblow 20mm, which will do for now. I'd rather it was smaller, maybe 500mA, but its all I have at present. Next task is to add a buffer amp for the counter, and wire that in. I will probably give it its own 5v regulator as well, so as not to draw too much on the receivers regulator.

Ex-PMR collinears - Preparing to test

It was a bit inconvenient of the riggers to just cut the connectors off, i'll have to say! But, you cant look a gift horse in the mouth, no matter how bad you think its teeth may be.

So, the first task was to get a connector onto one of these antennas. I happened to have some in-line female N-types ideal for the job

With only about three inches of cable to work on, I had to make sure it was right first time! The corrosion hadnt had time to get very far, thanks to our handyman informing me of these being available very shortly after they were decommissioned. Baring the cable back just 3/4 of an inch gave me good clean braid and inner conductors. The connector I had chosen has an insert that pushed into the braid to make the outer connection. With this in place, I trimmed off the excess braid strands, then cut away the excess dielectric.

By now the soldering iron was nice and hot. Tinning the center conductor allowed me to cut it to length for the center pin, which with its PTFE insulator was added next

Before going further, I hoovered up the cut off strands of the braid, and made sure there were none still present that could cause a short. Then, with the aid of a pair of adjustable spanners, the outer body was added and the securing nut tightened on.

So, I now have an ex-PMR UHF 440-470MHz collinear, with a short but usable connector attached, ready to be tested.

I would suggest to the riggers in future that they dont cut the connectors off, but leave the antenna attached, pull the whole feeder off down to the equipment cabin, coil the feeder and antenna up, and let me have the lot!

I need the weather to improve slightly now in order to rig up to test the antenna. Theres a lot of jet aircraft noise today in my area, which unfortunately is overcast, so it seems a good day to scan the UHF airband! Ive already found one active frequency with American accents asking for weather info for various UK airfields. I suspect from the S9 signal strength that this may be an AWACS controlling the exercise.

Ex-PMR antennas on ham bands

Many years ago, when I was first starting out in amateur radio, at our local club (Mexborough ARS) there was much fuss over a supply of ex-PMR VHF collinears, known as 'Sam's Specials' as a result of the supplier! Quite a few of us around the South Yorkshire region had these for 2m, I think he charged £15 for them. I dont know what band they were cut for, but one of the standard 'Pye' bands covered 2m.

Ive now acquired a pair of ex-PMR UHF collinears. These are marked as being 440-470MHz. Just how well they will work on 70cm I will need to find out by testing. Sadly, the antenna guys decided it was too much effort to remove the weatherproofing and disconnect the coax, so they have just been cut off above the connectors.

The weather has attacked the end of the coax, but luckily, its not spread more than a few mm into the cable. Theres just about enough cable to put a connector onto, so long as I get it right first time! I decided to use this one as the test antenna, despite the fact that the other one has much more cable to work with (about six inches!) and this one is the hardest to work with, since I wanted to see just how bad the corrosion had got. I know that, if the antenna proves useless on 70cm, ive wasted the effort.

If they are no use as is on 70cm, then they will be opened up and either modified, if thats possible, or a different antenna built inside them.

Ive also today, taken the plunge and ordered a channel crystal pair for the Pye PF8. Ive opted for the 70cm calling frequency 433.500MHz. I wont be able to ragchew on it, but decided for general rally use etc the calling channel was probably the sensible option.

The Agony of Choice

So, ive received a quote for a pair of custom ground crystals to get my Pye PF8 running on 70cm. This was never going to be a cheap option! Im not going into pricing specifics but suffice to say that the cost of a Tx/Rx crystal pair for one channel is about that of a Chinese dual band low end handheld of the UV-5 type! Of course, I always knew this would be the sticking point, so I do have feelers out hunting down a spare channel pair hopefully in someones junkbox that they would be happy to let go.

Crystals for the PF8 are of the HC45/u variety. These are reduced height varients of the HC18/u, as shown above. These are very small when compared to the FT243 WW2 vintage rocks! The HC-6/u crystals above are the size that would be needed to convert similar 1960's/70's era mobile sets such as the Pye Westminster. Nowadays of course, such things can be done with off the shelf Direct Digital Synthesis modules! But, theres no space in a PF8 for such things! So, single rock-bound channel it is!

I received today the above book - 'Surplus 2-way Radio Conversion Handbook' by Chris Lorek. This is a must for anyone with a fancy to refurbish and convert these old radios. It details the conversion of the PF8 plus many more, including the quite unusual PF9 - a reversion to the old PF1 Tx/Rx separates style! It seems some users just couldnt get used to an 'all in one' handheld radio!

Carrier	Tx Xtal	Rx Xtal
433.4	48.15556	46.96667
433.425	48.15833	46.96944
433.45	48.16111	46.97222
433.475	48.16389	46.975
433.5	48.16667	46.97778
433.525	48.16944	46.98056
433.55	48.17222	46.98333
433.575	48.175	46.98611

 

So, unless someone finds and offers me a channel crystal pair, i'll have to fork out for a custom job. Which leaves me with a dilemma - which channel to choose? This is not a choice to be made lightly at these prices! I want a simplex channel, since I dont wish to be tied to a local repeater, nor to have to add a CTCSS unit! But which one? Theres effectively eight to choose from, between 433.400MHz and 433.575MHz in 25kHz steps. 433.550MHz is often used, as is 145.550MHz a band lower, for rally talk-in stations. Now, admittedly fewer rallies offer this facility these days with the advent of in-car satnav and smartphones running Google Maps, but since plodding around rallies and events if where im most likely to use the PF8, its probably still best to avoid this channel.

So that leaves seven to choose from. I could of course put it on 433.500, the calling frequency. That will allow me to hear calls, reply, etc, but not to hang about and natter. I could go then to one of the other frequencies where I would be free to ragchew, but unless previously notified or announced, no one would know to call me there, and of course, if its occupied at the time...

If I do select a discrete channel, then which one? Either side of the calling channel would seem the best option, but these do tend to become occupied soonest, but the further out frequencies, whilst likely to be clearer, mean its less likely that I would just be stumbled on by people having a quick tune around, for instance if I decide to try the PF8 out on SOTA.

Im leaning toward 433.500 MHz if im honest. At least on the calling channel i'll find some activity!

Thanks...

I would like to thank these people publicly for their help with my refurbishment of the Pye PF8

Firstly, Alan C, from the Vintage Radio Repair and Restoration forum, who supplied me with the radios to start with!
Then theres Dave Hicks G8EPR, of the Pye radio museum, who sent me the initial scans of the service information, and Dylan85, also off the vintage radio forum, who is sending me a copy of Chris Loreks 'Surplus 2-way radio conversion manual'.
And finally, special thanks to Roger Lapthorn G3XBM, who has supplied me with a PDF of the complete comprehensive Service Manual, and without who the PF8 itself would never have been created.

And of course, several others for advice, encouragement, general derision and routine piss taking - you know who you are!

Great news - PF8 Non-fault

I had expected a long, drawn out fault finding task with the PF8 receiver, something I wasnt looking forward to on account of its revolutionary, and probably unique, dual PLL frequency system.

The PF8 uses dual, linked Phase Locked Loops in the receive chain, providing an unusual level of AFC, where both the channel crystal and the IF CIO crystal are pulled to correct errors in the receive signals frequency. However, in the case of this unit, the marked receive frequency should have been 453.200MHz, but was in fact 454.35MHz, and the Rx crystal was marked 49.88888MHz - a value that doesnt result in either receive frequency!

Adjusting L6, the rx crystal tuning, did not pull the receiver to 453.200MHz. So, I decided to do the obvious quick test, and swap the crystal for the rx crystal from the donor set. This is on 49.5638MHz, and should give 456.775MHz as the receive frequency...

...which it does! And, rather than the previous -30dBm minimum detectable signal (with the proviso that this is from an untuned whip antenna!), suddenly the receive MDS is -80dBm, and roughly -75dBm for 12dB SINAD, under the same test. If this was a radio with an antenna socket, im confident i'd have an industry standard -118dBm receive! I set the squelch level RV2 to break at about -70dBm in this set up.

Flipping the sig gen output level to 0dBm (1mW), I went for a walk down the garden, all the time with the 1kHz modulation tone purring loud and clear from the PF8!

So receive works fine, transmit works fine, although could do with the frequency trimming a little, as its about 2.5KHz high. squelch works fine, volume control is fine, both PTTs and mics are fine (deviation limits at about 3.5KHz)

What I need now are a pair of crystals for 70cm. This radio is clearly a U0 model 440-470MHz, rather than T1 405-440MHz as really needed for 70cm, but the service manual shows which parts are different, and I dont think there will be any problem with the conversion.

The donor set is proving very valuable!

In many ways, these were remarkable radios for their time, which it seems led to their demise. Incredible in the level of miniturisation, long before the advent of surface mount technology, they utilised very small components on plug in modules, or hybrid 'thick film' modules, and uniquely a multilayer PCB. Power is derived from just 2.4v (2x sub-C 1.2v NiCds) using an inverter circuit, when most other handhelds were using 9v NiCds or 9 to 12v packs. With the use of Roger G3XBMs skeleton plate antenna, there was no external aerial to get broken (as in the case of the PF1's telescopics) or catch on anything. The dual microphone system allowed it to be used almost like a mobile phone! These two features - the internal antenna and the mic at the base away from the speaker, would not be re-adopted by the cellphone industry for nearly quarter of a century!

The radios main downside is its low transmit power. In an era where handheld radios were putting out 1-3W, and many breaking the 5W barrier, its fixed 500mW was limiting. But this was never a radio intended for 'user-to-user', but for use with a high power base station, with antennas located high and clear, or a network of linked repeaters.  Its compactness, when compared with contemporary units in use by the UKs police forces, meant it was ideal for CID and other covert users, being discretely hidden away in the inside pocket of a jacket or the back pocket of the coppers Farrahs. A feature which almost certainly got it noticed by the producers of The Professionals - its exactly the kind of discrete radio that CI5's commander Cowley would have specified!

Pye PF8 - The difficulties begin

Well, no one said it would be straight forward! A set of this vintage is bound to have some issues. With the battery terminal fixed and the cells given a very gentle and cautions charge, ive been able to test the radio out 'on air'. Using a whip antenna on my Marconi 2955, I was pleased to discover that apart from being a little temperamental on the lower PTT control, she transmits quite nicely. Deviation is also acceptable at about 3.4kHz.

She also receives, the squelch, which seems very tight, breaking at -30dBm - but bear in mind thats over the air with the radio a few inch from the antenna! Volume is good and distortion is low. But - theres a problem!

According to the radios frequency plate, it should receive on 453.2MHz. According to the receive crystal, she should receive at 459.7MHz (same as Tx!), but she actually receives at 454.35MHz!

I suspect its an alignment issue. These are 3rd overtone crystals, so it might just need pulling in

Inside the PF8

The first task with the boxed Pye PF8 was to open it up and inspect it for completeness. Inside these radios, which are incredibly compact for their age, considering there are no modern 'surface mount' devices, everything is hidden away under a screening plate. In typical Pye form, this plate allows access to all the adjustment points, and labels them very clearly

Removing the plate reveals the electronics. Great use is made of hybrid and thick film modules in Pye's compact handheld transceivers. Whilst in this state, I attempted to apply battery power and measure the voltage at the radio's input. In doing so I discovered the first issue that required attention - the corroded battery terminal.

The 'donor' set had a nice clean terminal, so the whole unit - terminal, insulator, spring and wiring, was removed from each and swapped over.

This time, the test revealed 1.19v at the radios battery input. Good, DC is now getting to the circuits. Rebuilding the radio, and inserting both batteries into the case, I turned on and gave it a go!

And got a very brief flash of the Tx light on PTT before the batteries, which probably havent seen a charger for a couple of decades, went flat! But - It did show the radio working, even if just for a moment!

Next step then is to get the batteries recharged, and to test the radio against the test set. This I can do using the bench PSU. Testing it might be the trickiest part. These radios use an internal skeleton plate antenna designed by Roger G3XBM, with no external antenna connector. To start with at least, testing will be indicative only, but at this stage all I really want to see is if it will receive, and if it transmits!

37 to 45

After longing for one for a long time, I have today thanks to Alan C on the BVWS forum, acquired not just one Pye PF8 radio, in its original polystyrene packaging and including a pair of seemingly good NiCd's, but TWO! The second missing its baseplate and knob, and with one dicky PTT switch, but seemingly otherwise complete.

For those who dont recognise it, this is a Pye PF8 Pocketfone single channel UHF FM handheld transceiver, a revolutionary product in the early 1970s, and an iconic item, since its use by Mssrs Bodie and Doyle in the popular TV series The Professionals. Julie wouldnt let me acquire the other two iconic items from that series - namely the Ford Capri, or the L1A1 SLR service rifle!

The second radio will serve as a donor for spare parts. All I need now is a service manual! Since both radios still have their original channel crystals, and the ID plate is engraved with the Tx and Rx frequencies, and knowing they have a 10.7MHz IF (as confirmed by the IF oscillator crystal), it was little effort to deduce the oscillator multiplication factors needed to work out new crystal frequencies (x3 x3 for each)

A quick test has failed to get the set working, but a multimeter check seems to show that the battery isnt making contact. This is probably just due to the tarnishing of the positive contact, but might be down to physical positioning or size of the contacts. I'll power the radio directly with 2.4v clipped to the terminals to see. Hopefully the inverter circuits are sound.

Tropo, and another fault

Over the past week, there has been a high pressure system over Scotland. This, combined with conditions for strong radiative ground cooling over night, led to widespread morning fog - and strong tropo!

For me, this was mostly a nightmare. I was working nights, and the enhanced tropospheric propagation of VHF and UHF signals meant massive amounts of co-channel interference to the DTV network! The one saving grace was that, as I left for home on friday morning, 2m FM was buzzing! By the time i'd reached the M62, i'd worked SM7YES in Sweden! Now, Per has a very, very good VHF set-up, but even so, it takes some seriously good conditions to work Sweden on 2m FM from the middle of Yorkshire! Bob, M1BBV, over in Doncaster, even worked him on a 5W handheld!

On reaching home, I quickly rigged up my FT-290Rmk1, 30w Linear amp and assorted ancillaries, to see what could be had on SSB. A couple of Germans worked and I began to notice something was amiss. It seems the 290 has a fault on USB only, a strange tone/carrier that jumps up in level when the rig is keyed, then slowly decays, before sometimes coming back up again! Im totally stumped as to whats causing this.

I visited Hornsea rally today. Sadly I didnt find much I wanted, but I did acquire the battery extension cable for the Clansman radios. I can now power them even when open for repair or alignment. More pressing now though is the need for a charger!

Chinese Airband Receiver Kit - Now with Digital readout!

Ok, so, its NOT a synthesiser, its not even a PLL, its still a free running LC VHF oscillator under varicap DC control. But, it is now much easier to put on frequency, or at least, close enough that the wide IF bandwidth means i'll hear the signal im listening for!

Chinese Airband Receiver with LCD Frequency Counter module

A couple of points here. First, the connections are only tag soldered onto the underside of the PCB at present, and the LCD is powered from the 8v regulator. I need to check that the additional current load isnt too much, although I doubt that the whole shebang takes the 100mA limit of the regulator. Second, the signal input to the counter is at present a single wire, eventually that will be replaced with a length of thin coax. Incidentally, the plugs and wires as supplied with the counter are such that the signal input is a black wire and its ground is a red one! Something to be wary of! I might modify the LCD module to allow the backlight brightness and the contrast to be adjusted.

On the back of the counter module are two push buttons. These allow the display to be changed between 1kHz or 100Hz resolution. Ive set it to 1kHz here, as the oscillators stability isnt up to 100Hz! The buttons also allow setting of an IF offset frequency and direction. By setting it to -10.7MHz, I have a readout of actual receive frequency, or as close as makes no odds.

If its of any interest, here its tuned to Leeds East Airport.

More musings on the Chinese Airband Receiver kit

After a fair bit of testing, several negatives have come to the fore with this kit. None is a really major problem, and for most builders just wanting to have a pootle about the air band they wont be of any consequence. These are as follows -

1. Sharp crackles from the loudspeaker if the antenna touches anything, or nearby switches are operated
2. IF bandwidth is about 800kHz!
3. A bit low on sensitivity
4. Squelch isnt very good
5. Tricky to tune - whole 118 - 136MHz in just a 270degree turn!


Addressing these in turn, no. 1 is of no real worry, and such noise susceptibility is to be expected working on AM. I expect a bit of extra front end protection is needed, maybe a high value resistor to ground or an RF choke. No. 2, well, ok, it means I receive several channels at once, but lets face it where I live the band isnt exactly crowded, I might have the ceramic filter in the wrong way around, although I thought they were bidirectional! No. 3, only really an issue picking up the ground station, and I can hear both my local airfields towers on it. No. 4 is a bit annoying, but really, see no.3!

So, no. 5 is the issue that is most problematic. With the supplied 10k pot the whole coverage is in a single turn, which means its very easy to miss a signal by tuning right over it. I considered replacing the oscillator with a DDS unit, but mine is only good to about 40MHz, far too low. A simple fix, which ive done, is to replace the 10k pot  with a 10k 10-turn precision potentiometer.

Tuning is now much cleaner, but more time consuming! And, since the knob goes around ten times, impossible to know what channel your on except from ID'ing the traffic! I could add a turns counter. But, instead, my thought is to add the el-cheapo LCD frequency meter module I have! I have yet to see if connecting it to the oscillator will cause unacceptable pulling, but will try it out. It might need a little FET buffer circuit.

With the addition of a multipole switch, and a bank of 10-turn presets, I can tune in several local frequencies to switch between.  And from there, its not much more effort to add a simple timer and stepping system to allow scanning.

Shack Teardown

Starting this evening, everything on the shelves in my 'shack' will be packed into boxes. The rigs will be disconnected and boxed, the cables coiled, and the desk itself dismantled.

No, im not closing down! But im finally getting a carpet (rather than random offcuts) in the shack, and the desk, which is attached to the wall at one side, has to come out. When its rebuilt, it will have two sides, and be movable, so I can access the cables at the back.

The only thing that will be left connected will be the MVT-7100 scanner and the coax to the discone, so I still have airband monitoring for tomorrow. Other than that, its handhelds, manpacks, or mobile for a while!

Airband receiver kit complete - first thoughts

So, on arriving home I got out to the workshop and cracked on with the Chinese Airband radio. I had only intended doing the electrolytics and the connectors, but it took no time at all to solder those in, so I got on with the diodes, then the transistors and the 78L08 regulator. This done I tested it with 12v but without installing the ICs, and checked I had an 8v DC rail.

All was well, so I depowered and installed the ICs. The kit as supplied has a3.5mm jack socket audio output, so I tag soldered a loudspeaker across it for testing. Power applied, I was relieved to find that I had noise from the speaker, and that it stopped when I adjusted the squelch control.

With it connected to my Marconi 2955B and being fed a -100dBm 125MHz AM signal (1kHz at 70%), a bit of tweaking and I located the signal. This was quite poor, but much improved after adjusting the IF transformer. Ive pretty much left the band pass filter alone for now, as my to hand trimming tools dont fit.

It isnt quite as sensitive as i'd hoped, 12dB SINAD being around -105dBm, but its not too bad. After a lot of fiddling I managed to adjust the VFO coil to put 118MHz at the extreme of the tuning control, although I couldnt go any lower as the coils slug was all the way out. The tuning is varicap controlled by a 10k pot, and the range is so wide (top end at least 136MHz) that in its current form finding a signal is very tricky. Several ways might solve this, I could modify the circuit for a smaller bandspread, or swap the control for a 10 turn precision pot and a turns counter dial. Or, I could replace the VFO with a DDS synthesiser!

Even as is, mooching about with the control and with a 1m telescopic antenna, it pulled in several aircraft comms signals, ranging from late evening long haul ATC traffic, to my local field with a request that 'as were the last landing you can turn off the lights'!

Next step is to get the frequency counter on the VFO and see exactly what the bandspread is. If need be i'll modify the circuit to reduce this. Ideally, I want to modify the VFO anyway to get coverage down to 108MHz.

But, all in all, for about £12 its a fun little project.

A bit more done on the Airband kit

I had a few moments spare last night to progress building the Chinese airband receiver. The ceramic capacitors, ceramic filter, and inductors are now fitted.

(just realised that photo is before I fitted the IF can!)

I'll add the electrolytics, connectors and controls tonight, and if ive time might get onto the semiconductors. At this rate, I might have it operational for saturday morning, which is the day of the inaugural East Leeds Airshow. Despite being only a few miles up the road at RAF Church Fenton, I shant be attending this time, the number of ground exhibits, aerial displays and stalls doesnt to me justify the £50 family ticket price tag!

The only aircraft I really want to see that will be displaying is Vulcan XH558 - and I should be able to easily see her from my own garden!

4m FM - where's the activity?

After trying each lunchtime from work to make a contact on 70.450MHz FM using the PRC-351, I decided today to try the same using my FM-1100. This uses the same magmount antenna as i'd been using with the '351, but at 15W rather than 4W, and is capable of 12.5kHz steps, giving me the whole of the 4m FM allocation.

But not a sausage! Where has all the 4m FM activity midday gone? There used to be at least a couple of stations monitoring that i could reach from Emley!

Chinese Airband Receiver

Well, this finally arrived today! And it rather distracted me from my principle task of checking and adjusting the PRC-351's deviation, which is what I was meant to be doing since ive yet to manage a QSO with it, however I do think that might just be down to low power and low activity.

 

First impressions are good. It was all shipped in resealable plastic bags, all the parts are present (and as usual, a few extra!), and the PCB is high quality, through hole plated, with, as seems normal for Chinese kits, the groundplane on the solder side. The band pass filter components were already installed. Im not entirely sure why, but as the coils are the most tricky part for a less seasoned constructor, perhaps its actually for the best.

Ive installed the resistors, a couple of ferrite chokes, the molded coil, and the IC sockets. I'll do the capacitors and maybe a few more bits over the next few days.

Ive also had the PRC-320 open for its first inspection since coming into my ownership. Partly this was to allow inspection of the PSU module and the dreaded tantalum capacitors. I found that the case bolts were rather easy to unfasten, so thats something I need to ensure when im finished - that the case is up to correct torque. Some of the internal modules could also do with their screws nipping up a bit.

I was quite impressed by the build quality, especially the antenna tuner, which uses a permeability tuning technique. The module to the top left in the above picture is the synthesiser. This is where my attentions will be, along with the decade switches, when planning the VFO control system.
The picture below shows the underside, and the main board. The turret tuner is the big cylindrical block in the middle.

Taking the lid off the PSU module revealed that im too late! 

Instead of the MoD issue module with its dodgy tantalums, I found instead three modern DC-DC converter modules and a nixie type high voltage PSU module. So the PSU has already been thoroughly converted.
I have only one slight worry, and that is that this bit fell out -

and ive no idea where from! The radio works perfectly without it! I suspect its a locating stud from a module thats come loose.

Incidentally, if anyone who reads this blog is located either close to Selby or close to Emley Moor, and has 70MHz FM equipment, I really would appreciate a sked to get a check on my deviation level!

A quick note about Clansman radios

The chances are that if your reading this blog on a regular basis, what im going to mention here is irrelevant. But, you might be considering getting an ex military radio, and might be wondering which of the Clansman range to go for.

I am not going to mention the vehicle sets here, as I have little experience of them. I will only talk briefly of the suitability for amateur use of the 'manpack' radios.

As far as the manpack Clansman radio go, there are six choices. Not all are any use to us!

The PRC-349 and PRC-344 are of no amateur use. In fact, unless you are a cadet instructor, using them on-air is illegal. Entirely. Dont even consider it!

PRC-349 is a 'handheld', yeah right. About the size of a house brick sliced in half lengthways, it covers 37 to 47MHz. These are still MoD frequencies, although the radio is a mere 250mW, so you probably wouldnt get caught, its illegal to use in the UK, even by amateurs. Yet strangely, working 349s sell for rather a lot of money, I do wonder who's using them...

PRC-344 is a backpack UHF AM transceiver for forward air control and operates on the military airband. Dont even think about it! You'd probably get away with a 349 if you were no where near an exercise, but this will get you DF'd and an Ofcom van and a scuffer jam sandwich outside your house in pretty short order!

This leaves us with the PRC-320, PRC-350, PRC-351 and -352.

Of these, perhaps the most useful and most popular, but also most expensive, is the 320. This is a HF manpack covering 2 - 30MHz in 100Hz steps, AM, CW and USB at 30W. It can be easily modified for LSB. Its only drawback is its decade switch tuning. These sets were not designed for trawling the bands! Its built in manual ATU and standard antenna wire spools and masts however make this a potent set.

Next up is the 350. Covering 36 to 56MHz at 2W FM, these are usable on 6m. They sell for low prices as they are low powered, of limited use, and use a 15V battery which is non standard. They are a bit smaller than the 351

The 351, as seen in my earlier post, covers 30 to 76.995MHz FM in 25kHz steps, 4W out. It can be used on 6m and 4m. Although heavier, its more practical than the 350 as it shares its battery options with the 320. The audio ancillaries are also all interchangeable. You will see these with a 'SURF' unit attached - dont bother unless you really want to, or your set came with one. The SURF, or Selector Unit Radio Frequency, is essentially a pre-selector. Its intended to allow two or more radios to operate in close proximity. Nice to have but not necessary for normal amateur use.

Last on the list is the 352. Giving out 20W, this is simply the 351 with an add-on amplifier block! It is not for use with the whip antennas used with the 351 though, and is for use with the various 'Ground Spike' antennas.

A word about antennas -
The 351 can use a 50cm 'battle' whip flexible antenna, or a 1.2m sectional antenna. It can also use the Ground Spike, Elevated Ground Spike, and vehicle whips. The 352 should always be used with the Ground Spike or Elevated Ground Spike.

The 320 can use a 2.4m sectional whip, or, pretty much any normal (or even abnormal) form of wire antenna - dipoles, slopers, random wires.

So there you go. As an amateur, the 320, 350, and 351/2 are useful sets. If your not an amateur, then all of them will make you a nice display of military comms kit, but theres nowhere you can legally transmit on them.

But dont let me put you off!

Hello Zero, this is Sunray

Ok, so maybe not quite. But I have now obtained a Clansman PRC-351 VHF FM company level manpack radio, which is the very type of radio that 'Sunray', that is, the company commander, would be using. Luckily, I never had to carry one of these too far or often. They might not be as heavy as the PRC-320, but they're not exactly light by modern standards!

As a basic FM radio, its capably of roughly 4W out, on any 25kHz step channel from 30 - 76.975MHz. Frequency is set by thumb switches on the side by the antenna. It therefore covers 6m and 4m, but because those bands use 10/20kHz steps, it doesnt match exactly. This is more awkward on 6m where the FM calling channel is 50.510MHz.

It does have many features that are not immediately useful for amateur radio though. Its two volume settings, Loud and Whisper, also vary the mic sensitivity. On Whisper, the mic is more sensitive and the volume lower, helping avoid being heard by the enemy, perhaps useful for late night ragchewing when the XYL is in bed? Likewise, a pair of terminal posts, and a handy wire stripper built in, mean that the radio can be attached to a remote handset and operated by line from up to 3km away! It can also work as an intercom between the local handset and the remote handset. Perhaps there are some amateur uses for those features!

But these radios are also designed for use as a 'Rebro', that is, a re-broadcast, or repeater, system. Two radios linked by field telephone cable (DON-10) and on different frequencies can be set to act as a repeater automatically, but, to do so require a 150Hz tone. Much like most modern amateur repeaters!

When I got it, it was pretty mucky. Now, contrary to usual thinking, a well bashed and mucky field radio usually means its been reliable in the field. A clean radio always begs the question - why was it left in the comms stores? So, ive given it a bit of a clean.

Because of the 150Hz rebro tone, these radios can get bad audio reports on amateur bands, where the tone isnt expected. In this case, the tone deviation was over 1.7kHz!!! Luckily, its not hard to turn this tone down, which I did by adjusting R9 on module 13, and made it deaf in the process!

Now, the reason for this is, that these radios dont use a normal noise gate squelch circuit, they use a tone squelch, but in order for them to be inter-operable with non-NATO/Clansman users, an internal 160Hz tone is generated that defeats the squelch on the users behalf. By turning the 150Hz Tx tone right down, I'd also turned down the 160Hz internal tone.

This can be corrected by adjusting various tone signal path presets, but to to so would require having the set powered whilst open, something I cant do yet as I dont have a battery extension cable. So, with a bit of intuition from 5yrs servicing public safety radios, I blind set the Tx tone to a low value that I hoped would work and not be annoying on air. With the radio back together, I tested it again, finding now that the squelch worked properly again, and that the 150Hz tone on Tx was now at a comfortable 500Hz deviation.

A check of receive at 70.450MHz shows a sensitivity for minimum discernible signal of about -123dBm, and the squelch break at about -118dBm, pretty much how I used to set Kenwood TK-349s for the prison service! Tx power at this frequency is about 3.3W, reaching a tad over 5W at 30MHz, and a bit over 4W at 76MHz. The only thing I really want to adjust now is the Tx deviation, which is a bit high for my liking and may cause distortion in modern narrow band amateur receivers.

Ive yet to have a QSO with it, and I fully appreciate that its low power means I need to get a good take off location to do so. As for claiming the callsign Sunray - I only manage 'Sunray Minor' in this house...