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!