Friday, 22 August 2014

Ramp Up The Amps

After much deliberation, reading and checking, a couple of things occurred to me. First was that I should try varying the emitter resistor in the Wispy LO, to try and increase the drive to the receive mixer. Germanium diodes typically turn on around 0.3V, so with a drive of barely 240mV pk-pk, I doubt they were on enough. The resistor in circuit is 2k2. So I tried tack soldering another 1k in parallel. This brought the level up to closer to 300mV pk-pk. A bit more playing here and I should be able to obtain the right level of drive. It will probably mean though that the Tx chain will need completely realigning!

The other thing that suddenly popped into my head was why my LM386 audio PA seemed to overload so badly when fed from the Wispy audio chain. I suddenly thought, perhaps I had the gain control pot wired wrong? Indeed I had! So after changing the wiper of the pot to go to the input capacitor and not the input pin of the chip, all should now be well.

My little self contained LM386 audio power amplifier
Oooh! Look, Ive just realised how to add captions to my pictures! Expect more of that!

Emperor Mong Defeated!

Well, It seems my problems with the Wispy's audio stage have been to an unannounced visit to my workshop by the Emperor Mong. That and a crappy earth or earth loop between the test set and the variable PSU!

Using Roger G3XBM's AF strip design as detailed in my last post, and listening with a crystal earpiece, I set the test set to about -75dBm on a 28.1261MHz carrier. At first there was nowt but buzzing! Realising that this was probably an earth issue, I switched the supply to the AF strip and my mock-up for 'TennaLady' to a 12v SLAB. I now had a clean output but no tone! I again had to back the input right, right down, this time to nearly -20dBm!!!

Alas, It was but the Emperor, having one last play with me! I decided to swap the port on the test set, to see if that made a difference, and discovered I was feeding the project with the BNC to Croc clip cable, but the test set was connected to a BNC-BNC lead! I quickly swapped to the correct cable, and nearly had my ear blow out!

Reducing the signal level, after adjusting the frequency to something that gave a nice to listen to tone, I was able to go right down to -115dBm before I had to start on/off comparisons!

By doing on/off (switching on and off the RF output of the test set) I discovered that I could easily discern a -120dBm signal, and could just make it out down to -125dBm.

So, the audio strip works as expected. However, as far as the receiver goes, this is using my SBL-1 DBM based 'TennaLady' mock up, not the Polyakov mixer based Wispy. I will try the Wispy receiver chain later, after trying the AF stage hooked up to an LM386 based audio PA, which hopefully will drive a small loudspeaker.

Wispy AF strip rebuilt

The two transistor (common base - common emitter) audio amplifier strip for the Wispy transceiver beacon has been rebuilt as a self contained little module on a small precut piece of Veroboard. This makes a nice looking little module, especially since I took the time and trouble to add proper PCB pins for the external connections!

Common Base - Common Emitter AF amp

I have to confess however that the layout is not as compact as I had planned, due to an error in designing it. But it fits neatly on the little precut piece of board.

Following on from discussion last night with Roger about how he checked the audio level, I connected a high impedance crystal earpiece to this amp, and then fed it with an AF signal at 800Hz from my Marconi 2955. I could quite clearly hear the test sets 1mV signal, along with a lot of noise and other switching artifacts from the test set! (They're not the cleanest of machines!). Knowing i'm looking for about -120dBm sensitivity on the receiver, which equates to about 0.2uV, I decided to see if I could go lower. So, another previous project was put in line -

Homebrew 50 ohm Attenuator Bank

Now, this is of course designed for 50 ohm use, so some inaccuracy has to be expected, plus I'm relying on my own ears! But I found I could still make out the tone even with a further 28dB of attenuation switched in (possibly more, but thats the most I can be confident at), which is a signal level into the amp of around -95dBm, or ~4uV. I suspect with a cleaner input it could be lower.

Other bits of electronics on the go today included a 10m long control cable for my LDG RT-11 Auto remote ATU, this required soldering a pair of 9-way D-types, which is always a fiddly job. Ive also added a brass rod and plate (made from a 2p piece) to the gate input of the FET electroscope, which has tamed the beast somewhat!

Next task is to add more gain to the AF strip, to allow the direct drive of a small loudspeaker. I already have a small general purpose audio power amp for this, based on an LM386 chip. That should complete the audio stages of the Wispy project, and allow me then to move to the mixer again.

Thursday, 21 August 2014

Wispy receiver - really as bad as I think?

A thought occurred to me a while ago - is my Wispy receiver really as bad as I think, or is there something else ive forgotten to take account of?

Well, using my Marconi 2955, I get no noticeable reception until -50dBm, ish. BUT - Im using the test sets own 'scope and audio system, or my Hitachi 212 oscilloscope, what if the audio level from the receive chain is too low for these? Might it be that the level from the AF stages is not sufficient to drive either of them until this input level?

Somewhere, I read about how Roger determined his sensitivity figures, which were done much like mine by ear, but I think Roger listened directly to the output of the AF strip. Now, did he use headphones, or perhaps a Hi-Z crystal earpiece? Is this my problem - I dont have enough audio output to actually listen to to determine the sensitivity?

Im going to rebuild the audio strip as a self contained module on Veroboard. I can then test it to see how it works, and either feed an earpiece, or use it to drive another amp capable of giving enough level for a small loudspeaker.

Getting Nowhere - Time to Divide and Conquer

No matter what I try recently, Wispy will not work on receive for me. I seem not to have enough LO drive, but the buffer amp i've tried doesn't work! Likewise, I cant seem to get anywhere with the receiver aspect of 'TennaLady'.

It doesnt help that there could be issues with my test equipment again, not easy to prove one way or the other!

Ive also been playing with what should have been a simple 'battery low' indicator using a PNP transistor and zener diode, but even this wouldnt work! I do at least know now why this was the case, and have an appreciation of how such a simple circuit isnt necessarily the best solution.

One thing I have built successfully though, although it doesnt work quite how i'd like for its actual intended purpose, is a FET Electroscope. This amazingly simple device simply detects static fields, and indeed does it very well.

Its intended purpose is as a 'twat-ometer' - An approaching person is detected and the level of meter deflection shows just how much of a twat they are! Its supposed to be a simple joke device for workplace amusement. I won't include the circuit diagram here, as they are all over the 'net, and its such a simple circuit.

So, with regards to the 10m receivers, I intend to build an audio stage next as a stand-alone module, which can be tested on its own. That will then be used with the other circuits to test them out.

Saturday, 16 August 2014

How Do They Do It? - Or, why I cant buy local

I like to support local, and UK business, as much as the next fella. But, when it comes to electronic parts these days, unless its something very specialist, or I need it instantly, I can rarely justify it.

Take, for example, a recent need for 9-way D-type connectors and shells. To buy a pair of connectors and a pair of shells at the local Maplin store (ok, yes, I know they are dearer than the likes of Bitsbox and Bowood) would have cost me nearly a tenner. For around the cost of just one of the connectors, I instead have purchased 10x female, 10x male, and 10x shells, from the far east.

I just dont understand how they do it! All these are free shipping as well. Likewise, my stock of 2N3904 transistors is running low. A quid has bought me 100 of them from China. Even not allowing for the percentage of that that must be the shipping, thats a penny a throw. Same with opto's, a hundred mixed red, yellow, green, 3mm and 5mm LEDs from the far east - £1.10.

The same seller has an offer of 10x red laser diode modules for a tad over a quid! Packs of mixed size/colour heat shrink tubing for a couple of quid, a few hundred mixed value ceramic caps, or electrolytic caps, for a couple of quid. Its really quite easy to stock up on the basics for next to nothing from China, leaving you cash free to buy the more specialist parts locally.

Some detractors will say 'oh, but the parts are likely to be Chinese knock-offs!', maybe, for high value parts, but these are low value, mass produced, OEM components, and are, whether  you buy them direct or from a UK stockist, all made in the same Chinese factories anyway!

For such low value, high volume parts, it isnt cost effective for me to buy locally. I will still support UK companies for the higher value or more specialised bits, particularly G-QRP club sales, who have bits I can't easily find elsewhere, and are in fact almost as competitive on the small parts they stock as the Asians!

One part I cannot source form the far east, and will have to get from a UK seller, are the inductors for Daz's Theremin! Unfortunately, they are only stocked by Farnell Element 14, not exactly the lowest cost merchant!

What a Muppet

Yesterday evening, I tried to test my 10m Wispy on my Marconi 2955 test set, with shocking results. This morning, whilst I had a few moments spare, I fed the test signal direct into the RF amp, bypassing the filters, but had no better luck. I then fed it direct to the mixer, with still no luck.

It wasnt until a good while later that the niggle at the back of my mind (which sadly has had to contend with quite a few niggles these past weeks) resolved itself, whilst I was reviewing the details of the operation of the Polyakov mixer - This mixer has good AM rejection!

Bugger! Ive been testing with an on-frequency AM signal!

Part of the problem for me, I think, is that I tried an off-air receive test first, and didnt get a single received signal. But, propagation is poor on 10m at the moment, and although I looked at WSPRnet and noted not many signals, I didnt really correlate the lack of spotting by stations in central and northern UK with my lack of success, leading me subconsciously to think I had a fault.

A look back through Roger G3XBMs design notes, showed he achieved a -124dBm sensitivity without an RF amp, but with over 70dB of AM rejection, the AM only becoming detectable at -50dBm or so. Compare then with my, unaligned, -22dBm detection point of a 60% AM signal!

So, when I next get in the workshop, I will retest - this time using an actual carrier! Rather than set the test set to the actual tuned frequency of 28.1246MHz with a 1.5kHz modulated AM signal, I will instead just set the test set, with modulation switched off, to 28.1261MHz.

I do hope this is the only real issue. The RF amp is a grounded gate FET, and Roger used an MPF102. I didnt have any at the time of building, so substituted a J310 FET. This shouldnt be a problem. The only other change is to one audio coupling capacitor, and a bit of additional screening.

Last nights 472kHz reception was just as good as the previous session, best DX again 1141km into Germany, and again spotting Rogers tiny 5mW signal from over 190km from the small hours and into daylight, finally losing him around 06:00.

Friday, 15 August 2014

Poorly Wispy

Wispy isnt quite ready to be let loose on the wide world of 10m just yet, its a bit poorly.

The receiver is not working as expected. Detectable receive audio starts at an input signal level of around -20dBm, which is frankly rubbish. I would have hoped for -100dBm at least.

The fact it is so poor suggests something fundamental. When I next work on it, i'll check the transistors (ensuring their the right way round!) etc, but also will remove the coax link from the LPF to the RF amp, in case this is upsetting it. I'll also bypass the antenna switching diodes and see what receive is like direct to the receiver input. This is something im likely to do anyway, since I wish to use a small linear amp to give me a few watts of power, and relay switching will probably be the way to go for that.

So for tonight, all is packed up. I will monitor 472kHz overnight again. Already some decent spots are coming in, from Germany and the Netherlands.

Wispy On Test - Fingers Crossed!

My 10m 'Wispy' is now on receive test. It took a bit of time to work out usable level settings for the laptops microphone input, but im now showing the correct 0dB noise level, which in this case is a mic level of 50 and a 20dB 'Mic Boost' setting. Unlike when using a normal rig, where no mic gain is needed, the receiver here is very basic and the levels very low.

All I need now is an actual signal in band at a level strong enough to decode, or at least, see on the waterfall! But conditions have been very poor recently, with no spots even using commercial equipment, so this could be a long wait.

I also, have as yet not aligned the receive chain with a test set signal. Theres only two trimmers to adjust, but I dont want to tweek them yet. Save that for the Marconi 2955! For now, I'll just soak test the unit, check no smoke comes out anywhere.

In the meantime, I cannot use the main station for any HF work, since Wispy is on the main antenna! So, Ive moved back onto 6m to see what if anything might be doing in JT6M

UPDATE: Well, not a single spot received. I suspect that the band is pretty quiet anyway, which makes things harder when testing 'on-spec' like this.

However, I do know that the receiver works, at least after a fashion. The main station antenna is directly over the workshop. So, with the Wispy set up on receive in the shack, Ive set up my Marconi 2955 communications test set to give a signal on 28.1246MHz, with 1.5kHz modulation. Unfortunately, Im not lucky enough to own a test set that can produce SSB, so its a 45% modulation AM signal, and the maximum RF levelis 5dBm, into a telescopic whip. This is however just enough to detect as an AM envelope on the WSPR software!

Wispy Complete?


I have just finished building, to Roger G3XBM's design, the receive chain. This is a very simple direct conversion receiver, based around a f/2 Polyakov mixer, fed from the same 14MHz oscillator that drives the doubler for the transmit side.

The lower half of the board is the receive side. The mixer and RF amp is to the left, with the oscillator above. This is followed by an audio amplifier chain. The only change I have made to Rogers design, apart from the bit of coax from the Tx/Rx diode switch to the RF amp, is to use a 220nF cap to couple between audio stages, where Roger used a 470nF. This is simply due to the fact that I have no more capacitors higher in value than 220nF left!

I will rig her up for testing in a little while.

A tidy bench is the sign of a diseased mind

I admit i'm not the tidiest person in the world. Im not even the tidiest person in the house today (and theres only me and Sam here!), but I blame this on my bit of youthful gunsmithing - so long as you knew where your smokelamp was, everything was fine.

This is my work bench. Yes its incredibly untidy, but I usually have several projects on the go at any time, and they are often very long in the doing! On here at the moment is Wispy, in the foreground being worked on, my 'Manhattan' pads in the butter tub to the left. Theres an 80m Pixie in an Altoids tin, and the 'TennaLady' mock-up over by the multimeter. The tidiest part of the bench isn't shown, and thats the test bench to the far left

On the right hand side of the bench, its often a bit tidier, but today its stacked up with tubs full of salvaged components awaiting sorting, something im doing a bit of today.

When sorted, usable parts go into a growing collection of buttertubs! Each holds a particular kind of part, broken where necessary into ranges, for instance theres a tub for 'Opto' which contains LEDs, small bulbs, LED and LCD displays etc, and associated mounting hardware. Theres two for non-electrolytic capacitors, with a range break at 1nF.

Its not perfect, as I still need a lot more tubs to fully sort everything into suitable homes, and as I do, the lack of shelf space will also start causing problems!

Lashed up MF antenna but some good DX

Overnight, I left my FRG-100 tuned to 472kHz (474.2kHz to be exact) in USB mode, and the PC on running WSPR. The antenna was a serious bodge job

After the failure some time back of the random wire that fed both the FRG-100 and Sams VOLMET 5MHz receiver, all that was left feeding the Hi-Z port of the receiver was about two feet of speaker wire. With no time to fiddle (It was gone 22:00 by this time!) the best I could do was switch the ATU to bypass, can croc-clip the bit of wire to the center pin of the patch lead I use to the antenna switch for connecting up such things as Wispy or my SWL PSK-20.

Some fiddling was needed to get the audio into the PC as well, but I was remarkably surprised to see stations coming in. I left the whole lot running overnight. 13 different stations copied! Including, finally at about 03:00, including Roger G3XBM

 G7MRV  IO93ks 
 G7MRV  IO93ks 
 G7MRV  IO93ks 
 G7MRV  IO93ks 
 G7MRV  IO93ks 
 G7MRV  IO93ks 
 G7MRV  IO93ks 
 G7MRV  IO93ks 
 G7MRV  IO93ks 
 G7MRV  IO93ks 
 G7MRV  IO93ks 
 G7MRV  IO93ks 
 G7MRV  IO93ks 

New Modes and New Bands

With a few days with time on my hands recently, Ive spent more time playing with the WSJT suite of digital modes, particularly more WSPR on various bands, and a play with the JT6M mode for 6m meteor scatter. As yet, I havent made a full QSO in MS, but have been received a few times, and had part QSOs. Its just a matter of refining my technique, and being more patient.

Playing with WSPR, Ive had no luck on 6m, and very limited success on 10m. I have got a bit further with Wispy though. The photo below shows the experimental parallel transistor amplifier, supposed to be 1W, on the left, and the new LPF on the right

The new 7-pole Low Pass Filter is very effective. Built as an add-on board, I can easily test the levels of harmonics before and after the filter, and it is quite clean post filtering. Ive had far less luck with the parallel transistor amp though. I can see that it is amplifying, as can be observed using the spectrum analyser, but the output is just 10s of mW! Its not even enough to raise the meter!

Why this should be I dont yet know. Perhaps its something to do with the biasing or quiescent current, or maybe its the emitter resistors and emitter bypass capacitors.

Ive also, as can just be seen in the lower right of the above picture, made a bit of progress on the receive chain. The two red components are 470nF capacitors, which due to not having that value I had to rob from Daz's Theremin project! I need another, but dont have one anywhere, I will have to try something like a 220nF in its place and hope its value isnt too critical.

One thing I noticed today about 6m WSPR is the number of stations that are only listening! Today when I was active, out of a slack dozen of stations, less than a third were actually transmitting at all! For a propagation beacon network this is poor. It relies on each station transmitting in order to establish the propagation paths.

In light of this, and after reading Roger G3XBM bemoaning the lack of stations active at MF, I have considered today looking at ways to get onto 472kHz. This is an altogether different proposal to most HF/low VHF work. The best I can manage at present is to set up my FRG-100 receiver for 472kHz, and, in the absence of a random wire for that Rx at present, Ive had to take what left of the high-Z input wire (about 2ft of 7/.32 stranded speaker wire!) and using a croc clip lead, patch it to the main doublet antenna via the center pin of the antenna switch port, and set the ATU to bypass. I also have found that the audio feed into the PC is a bad fit, but after much juggling, have managed to feed the audio from the FRG-100 to the PC.

The WSPR software is not at all happy at being fed a 24dB noise floor, and the hum is atrocious, but surprisingly some decent decodes are coming through -

2238 -23 -0.9   0.475749  0 DH5RAE JN68 23
2240 -22 -0.1   0.475684  0 DK7FC JN49 30
2240   2  0.2   0.475739  0 PA3ABK/2 27
2244 -19 -1.1   0.475641  0 DK2DB JN48 27
2244 -14  0.5   0.475653  0 G3WCB IO91 23
2244 -18 -1.5   0.475697  0 DC0DX JO31 33
2244 -12 -0.7   0.475725  1 GM4SLV IP90 23
2244 -21 -1.1   0.475762  0 G6AVK JO01 10

Best DX so far is DH5RAE at 1,141km!

Of course, ive yet to hear Roger!

UPDATE :  Managed to eliminate the hum by swapping from the USB soundcard, which it  seems doesnt like mono jacks, to use the on-board mic input. This has brought the noise floor on WSPR down to a more manageable 17dB. Unfortunately, all the messing about has upset the program, which now is crashing out a bit!

Tuesday, 12 August 2014

Perseids Meteor Shower Peak Soon - Lets Try JT6M!

Something ive thought about doing but never tried before, is Meteor Scatter. This, just like EME and the various QRP HF modes, is something that with the advent of fast computers, and particularly with Joe Taylor K1JT writing amazing software and developing amazing weak signal modes, is now within the grasp of even the smallest station.

The Perseids meteor shower is due to peak over the next couple of days, with average ZHRs of about 20-30, but with the severe disadvantage for visual observing that theres a full moon, which will wash out all but the brightest bolides. But the full moon doesnt affect VHF!

So, whilst Whispy gently toasts its PA transistor running all night on 10m, Ive downloaded Joe Taylors WSJT software suite, and am listening on 6m for JT6M meteor pings

Although not shown in the screenshot, I have picked up a few pings, along with a horrid pulsing noise which seems to come from the computers mouse, and annoyingly covers around 40kHz of the 6m band, centered right on top of the MS window!

Another thing of course with meteor scatter, is that it will work in daylight, something that is very rare for visual observation of meteors!

I dont yet fully understand the system, or procedures, so will need to see a good few received pings first before I decide to try for a QSO.

Monday, 11 August 2014

10m Wispy Tx running overnight

The Wispy beacon Tx is set up to air via my ATU on the main station antenna, Toshiba laptop providing the audio drive WSPR signal at a 50% Tx cycle.

Its running from a 12v 7Ahr SLAB. As it uses pretty much the same current, and runs at the same temperature, regardless of whether its actually on Tx at the time or not, I am going to put it to 80% Tx overnight, and hope that at some point, perhaps morning grey-line, some propagation occurs that at least gets a spot to somewhere!

Wispy on test!

After finally discovering that I had simply not been driving her hard enough, I have the 10m Wispy beacon transmitter testing to air.

Several problems had to be solved to get this far. First, I found the laptops clock is woeful! I now have Dimension4 running on both the laptop and the desktop to keep the clocks happy. Since doing this, my own decoding of the beacon (via the main station) is almost solid. Second, the main antenna, during high winds this morning, failed. The wire snapped right at the feedpoint, necessitating some quick repair work to get the antenna back in service.

The picture shows my own decodes of the beacon. From this, and some other test information I now now that the Wispy Tx takes around 30mins to stabilize during warm-up, after which its drift rate is negligible, but the initial drift during warm-up is about 60Hz. I  also know that the Tx takes a tad below 160mA, even in standby. This is due to the amplifiers always being powered. I might, later, add a Tx relay so the amplifiers can be off and allowed to cool when not in use, but that will add the complication of needing either a PTT input or a tone detector circuit, like in the FT-857D Interface.

Prior to any of that, I'd like to play with the biasing and see if I can lower the quiescent current somewhat. I also want to play with the drive and the output filtering to further reduce the harmonics in the output. If I can reduce the spurii going into the amplifier, then I can ensure that as much of the power consumed as possible is being used to generate my wanted 28MHz DSB signal.

To this end, Ive added the little 28MHz bandpass filter to the output of the SBL-1 DBM on the 'TennaLady' mock up, as well as adding the necessary parts to convert the oscillator to 14MHz self-doubling to 28MHz. If I can kill the spurii prior to the amplification chain then so much the better.

Another little beastie im looking at is a 28MHz 1W Power Amplifier, using parallel small signal bipolar transistors. Roger G3XBM has used this approach in the Tx only version of Wispy, plus in his 'tenbox' AM set. With 4x 2N3904 NPN transistors, Roger gets 500mW DSB, 250mW SSB equivalent. So, Im going to try with 8x transistors! Hopefully giving me an equivalent of 500mW SSB.

The photo just shows two transistors fitted, which would give the same output as the single 2N3866 im currently using in Wispy.

Unfortunately, so far my Wispy beacon has not yet been spotted. Ive had her running most of the day, but the propagation on 10m at present is dire. I'll let her run over night, and into the morning. Depending on the wind, I might put the 10m J-pole up and run her to that tomorrow, see if having a resonant antenna and not having to go through an ATU and long feeders makes much difference. At 100mW I think every little helps. At some point however I want to work on the receive side, so if I make decent progress on TennaLady tomorrow, I might try her to air for a bit while I do the Rx chain on Wispy.

Sunday, 10 August 2014

WSPR, Window, and Rain

It seems the window line section of my antenna isn't too keen on the endless rain we've had overnight. After I discovered that WSPR had crashed sometime in the small hours, probably when the antivirus decided to tell me it was due to expire, I restarted on 20m, but found not a single person was hearing me!

Playing with the ATU showed it was very difficult to get a decent match anywhere, suggesting the now soggy vegetation near the balun is probably drooping onto the window line section and detuning it. I have managed to get a usable match on 40m, so have popped up there at 2W. The system went straight into transmit with the results as below

Now into the receive cycle, lets see where I can get today 

UPDATE: The rain has stopped (mostly) so I managed to get out and take the shears to the mass of Ivy that has, seemingly in the last 12h, utterly overgrown my balun and lower section of window line feeder. With that cleared I can once again get a match on 10m, so have QSY'd up there to see what can be done.

Thursday, 7 August 2014

WSPR - A fantastic mode, so long as someone uses it!

Yesterday, I set up the main station to beacon in WSPR mode on 10m. This was sometime just after lunch.

Around 21:30, I retasked the system to 40m. Not one, single, solitary spot on 10m! Neither hearing nor heard. It seems there were less than a bakers dozen of us on 10m on the entire planet! This is simply rediculous. There were nearly 200 stations on 20m, a band whos characteristics mean it really doesnt need any propagation investigations. This is just people who want to do something without actually having any real involvement in it.

On tasking the system to 40m, as soon as I came out of idle the system went into transmit, and was immediately received in Tasmania!

Today, shortly after 15:00, I started beaconing, 10% Tx/Rx cycle, at 2W on 6m, beaming SE. I dont hold out much hope, as theres fewer than ten stations around the world on 6m today! And, although I dont know whether to believe it or not, the WSPRnet site says most of them are running 0%, i.e. Receive only!

Monday, 4 August 2014

FT-857D Digital Interface Mk2 (Rebuild)

Yesterdays successful test of the digital interface for my FT-857D did unfortunately leave me with a rather convoluted collection of bits of circuits all cobbled together. Todays task then was to build the Mk2 interface - in other words, get it all on the one, neat and tidy board, ready to be boxed.

Last night I drew out the schematic, planned a Veroboard layout, and selected a suitable hunk of board. The only minor change was to include a level control potentiometer on the receive path. Not really needed for WSPR, but perhaps useful for other modes.

The picture above is how it all looked at close of play yesterday, not including the opto-isolator. The board to the lower right is the single transistor audio amplifier, that drives the audio detector and PTT switch (right hand side of main board). The modified el-cheapo Chinese USB soundcard hanging off the whole lot to the left.

This is the new board. As an odd off-cut the sizes actually turned out to be pretty good for the job, with the longer, lower section fitting the PTT system nicely. Here the audio isolation transformers, DC switch and opto-isolator are installed, along with the radio side ground connections. 

Further on, the Tx 10:1 audio divider, computer side grounds, and the audio rectifier diode doubler are installed. What can't be seen, is the continuous run of track breaks under the transformers and opto, forming a complete separation of the two signal sides.

And, finally, the completed board, in use. The USB sound card is affixed onto the board with hot melt glue. This is during final testing. Im pleased to say all the testing went well, with good receive spots from around Europe, and some decent DX 'heard by' spots into Isreal and the USA, all at about mid-day here in the UK on 20m.

The schematic is shown below. There is nothing new, or original in this design, and it borrows much from KK7UG's interface. The audio activated PTT circuit is a mish-mash of several designs found around and about the internet.

With a couple of simple mods for serial port controlled PTT etc, this could easily be made into a 'universal' digital modes interface.

The final two tasks are to replace the sound-cards USB plug with a wired USB connector, and to put the whole thing into a case.

Sunday, 3 August 2014

Mobile WSPR - Finally!

Well this took some flippin' doing! The audio isolation needed to make an effective interface was really quite simple, the trouble came about when trying to use the radios own Digital VOX circuits to control the transmitter. It would work, so long as the audio input was high enough, but that level was always far greater than the power output I wanted, and always driving up into the ALC action region! No matter what settings I used, adjusting the soundcard level, the interface level, the VOX level, or the Digital Gain control on the rig, I could not get the 1-2W I wanted AND have VOX PTT!

So, I had to work on a hardware solution.  This seemed simple - both channels of the soundcard carry the same audio signal at around 4Vpk-pk, it should have been a simple job to rectify this and drive a switching transistor. Er, no. The output of the diode doubler used only generated 0.3V, no where near enough to switch the PTT transistor.

So, some head scratching, and internet searching later, I added a single transistor audio amp to the detector circuit. Yeah! It switches!

Only trouble was, I had to use the 5V supply from the USB soundcard to power the amp, so I now no longer had the isolation between the radio and the computer! The photo above shows the interface in this state of development! I now had to add yet another little bit of veroboard, this time with a 4N25 optoisolator and a resistor on it.

That done, I got out to the car, connected everything up - and it wouldn't Tx! Arrgh! I'd forgotten to put the ground connection from the opto to the rig on! Back to the workshop, telling Julie that 'This is definately the last trip!' and then back to the car, and finally, a working audio driven PTT line!

So, the time now being around 19:00, and with a fully recharged laptop battery ready to give me its whole whopping 20mins capacity, I set up the Tx level to about 3-4W, sync'd the clock with an internet time server, and started WSPR, with one Rx period followed immediately by a Tx period. First spot, both heard and heard by, was HS0ZKM Thailand!

So what remains now is to rebuild the interface with everything, including the USB soundcard and the opto-isolator, all on the one compact board!

Show Cards and Yaesu WSPR

After a slight delay of just about 11 months, I finally took delivery of the QSL cards for GB2LDS this week. They are all now written, along with a few remainders from the year before, and ready to be sent off to the bureau. Thats around 150 cards.

Ive taken the time to check for QSL status, so as not to waste a card on someone who doesnt want one anyway, or who only accepts them direct but who hasnt sent one direct to me. If you havent sent a direct card in 11 months then clearly your not going to send one!

With just a month to go before GB0SML, the final preparations are underway. The main antenna now has actual wire on it, and just needs a trial on site to trim the elements. The digimode interface for the FT-857D is made and due to be tested today, im just waiting for the laptop to charge up!

Well, after giving the lappy a brief session on the charger, it lasted long enough for me to establish a working receive path. With the car parked on the drive, and just the mobile 20m whip, good Rx spots were straight away coming in!

Now to get Tx working! This is less straightforward, as it requires some fiddling of levels and power settings. With the Tx PWR setting turned right down to 5W, and the DIG VOX setting right up to 100 (not greatest but will do for now!) ive managed to get the radio to trigger to Tx from the WSPR software. Using FM mode and a dummy load and power meter, Ive set it first to ensure the meter was calibrated at 5W, and then set the audio drive level to give 1W output.

This is all with the DIG GAIN level set to 50, and without reference to the ALC meter! I will probably let a bit more drive into the radio, and adjust the DIG GAIN to set the actual modulation level. However, for now, flat battery stops play! The lappy is back on charge.

Saturday, 26 July 2014

Cheap Chinese WiFi Yagis - Avoid!

Well, Ive generally found the cheap Chinese imports to be alright, but it seems I lucked out on the WiFi Yagis.

I ran a test, comparing these to a standard 'whip' wifi antenna, and these are actually worse! The more I look at it, the more I realise I should have known from the start!

The main problem I think is that the driven element is so far out of the plane of the antenna.The boom is also far too wide, and the elements far too thick.

 I will see about a mod to put the driven element correctly in the plane. I have two of these and if I dont get them to work im effectively out of pocket by about a tenner (yes, I know its not much for two antennas, and in fairness, the U clamps they came with are probably worth a fiver themselves)

Its a shame, as the little cheapo wifi dongle I bought to improve the laptops connection works quite nicely! Its only about 10dB better than the laptops internal antenna, but since it has an antenna port, it means I can connect a directional antenna to it - If I can get a working one!

I have looked at various homebrew wifi yagis, and will probably make one now and see how it works.

 I finally have the spanner for the Larkspur mast! Thanks to Chris G6HTH.

Ive looked around online and made use of a yagi calculator to create a set of dimensions for a 15dBd gain 2.4GHz yagi, using simple materials that I have knocking about. It should take about 2h to knock one up.

Monday, 21 July 2014

Playing around with Jenny

Jenny, like many of us, takes a little bit of caressing to really get going, and Julie doesnt mind me playing around with her. Of course, Jenny, or 'Genny', is short for generator.

This is the machine I picked up at the rally. After Sam and I had enjoyed our morning of Canadian canoeing, and a fried chicken lunch, we headed to ASK to pick up some two stroke oil for her. She needed a while for the oil and fuel to work into her, but soon she was throbbing away. She does like a little squirt of carburettor cleaner/easy-start to help get her going, and she runs a bit lean, so likes just a touch of choke to keep her from 'hunting', but other than that she works quite well.

She's shown above feeding a small 7A 13.8v linear PSU (it does slightly over volts anyway). 
The blocking diode needed to allow parallel battery operation was lifted from an old PSU card, I think from a transposer. Its a dial diode, each leg rated 15A. It was one of a half dozen semiconductors all mounted on the same block of aluminium, so I also took that ali block to mount it on.

A pair of lengths of my heavy duty DC cable provide the connections to the diode. A layer of tape, and then liberal coatings of liquid insulation, sealed and insulated the +Ve rail.

A small piece of heatshrink tubing, pumped full of hot melt glue, seals the -Ve rail through connection. The whole assembly was then wrapped in 3M PVC electrical tape. The red smudge isnt, for once, my own blood (I managed to save cutting myself for later!) but is actually tamper evident varnish, used to seal the thread on the bolt.

By setting the PSU feeding into the diode such that the output voltage at the diodes cathode is 13.6V, this will allow the big 38Ahr SLAB to be charged and act as a reservoir for the peak current demanded by the radios. An added bonus of this scheme is that the generator can be stopped for refueling without having to stop radio operations.

Ive managed to get a bit further with the WiFi repeater, but need to do a proper air test soon. Still to do is making up the datamode lead for the Yaesu, the 6-pin miniDIN plug I have isnt wired properly. Being a sealed plug, its not easy to change, so ive ordered a plug. I can probably get away with the old plug as a test until the new one arrives.

Sunday, 20 July 2014

Finningley ARS Rally

Sorry, another post with no photos!

Today was the 1st Finningley ARS Rally at Sandtoft, near Doncaster. Myself, Sam and Mike arrived not too early with our selections of bargains (ok - junk) and were directed to an outdoor pitch.

Once we had our stall set up, the other vendors were beginning to make use of 'trader privilege' to seek out bargains before the punters arrived, and I was already taking money before i'd finished unloading!

The target of the day was to raise enough money to cover the insurance costs and some running expenses for the CHOTA station. This was more than achieved! Oddly, the vintage stuff i'd expected to sell easily didnt, and the RF PCBs I thought might be hard to shift went well!

My own wanted items I couldnt find! So I will have to order the dipole center and the 6-pin MiniDIN (unless the old mouse one does work) online. Most of my days purchases were to feed and water my eldest son, who happily had the price of a can of pepsi and a tray of chips from me. But, one bargain I couldnt resist was a small 2-stroke petrol generator for £25! I didnt actually pay that, I paid £20, and the stallholders wife (he was away at the time - it turns out looking at MY stall!) said ok, as she didnt want to cart the bloody thing home! I think the fella might have been a bit disgruntled at this, as she told me later he came back and said "you sold that genny for £20! I know, 'cos the fella that bought its bragging about what he paid!" I have yet to see if it actually works (no two-stroke oil!) but if I have bagged a bargain, i'll be very well pleased.

But, the potential to have a small genny available gives me a bit of a problem - Its regulation might not be great, so I would prefer any sensitive kit - such as HF transceivers, to be run from it via a PSU AND a parallel battery. However, to do this I need a blocking diode capable of taking the full, peak, forward current! This is about 22A! As luck would have it, one of the PCBs I didnt manage to sell today has a pair of suitable diodes on it!

Rather than charge Mike his share of the booking fee (I took the pitch booking fee of £5, so Mike's fee was just £2 for an additional trader pass) I just made him brew bitch for the day!

Thursday, 17 July 2014

1st Sandtoft Rally - This Sunday

This Sunday sees Finningley ARS hold the 1st Sandtoft Rally. This is on the grounds of the old Sandtoft airfield, near Doncaster. See their website for more details Finningley Rally

I shall be there, along with a considerable quantity of junk to sell. Please come along and buy some of my junk! It will be mostly RF circuit boards, mainly UHF, with some very nice RF parts on; but also cable, various loose bits, some odd bits of untested equipment etc. All proceeds towards the CHOTA station's expenses.

Come along and support us and the rally! I believe rally entry also gets you free entry into the Trollybus museum!

In the meantime, the WiFi repeater progresses. The 5v regulator board is now fitted.  A power on test with the unit connected by LAN cable to my laptop showed the board to be working, at least as far as logging in and configuring, and able to see some local WAN networks. Oddly it didn't seem to see my own network, but then in the workshop neither can my phone! Even with the yagi's, there probably isn't sufficient signal penetrating into the workshop to pick up.

The regulator board looks very home-made, but this is in order to get the decoupling capacitors as close to the 7805 regulator as possible.

It turns out that the antenna port at the lower left of the photo is the 'source' network antenna, which means it is the antenna port on the right of the unit when viewed from the front. This is ideal, as in my mind the source signal should be on the right, and the destination signal, or new network coverage, to the left.

Still to do, is the U-clamp plate for the lid of the case, and an actual 'air' test - I have to prove that not only will this pick up and connect to a network, but it will also generate a new, relayed network.

Sunday, 13 July 2014

WiFi Repeater Progress

The box has been completed, the board modified, and all installed into the case

The purple wire is the thinnest I have at the moments. Unfortunately its not thin and flexible enough and has led to one of the pads coming off the board. Luckily, this was for the WAN  LED, which was to have been the green one. I can live without this, but subsequent wiring was done with far more care! It had proved impossible to remove the original SMD LEDs, so these had to be destroyed in situ, to prevent running parallel LEDs and ramping up the current. One of the coax's also had to be redone as the dielectric melted and shorted out.

With care, the remaining two LEDs (PWR and RF) were connected up, along with the reset switch and fitting the RP-SMA connectors. I dont know if the LEDs are wired correctly yet, that will become apparent when the unit if finally powered up. Apart from the sheet of insulation behind it, the board is only currently held in place by hot melt glue along the edge and around the LAN connector. Much more hot melt will be added to the top corners later.

The device bolted to the side of the case is a 7805 5v regulator. A set of bypass capacitors are still needed on this before the board can be wired to it, and the DC socket connected up. Prior to this, the antennas will be fitted temporarily and the boarded fed 5v from the variable PSU on the bench, with the laptop connected, just to prove the board is still operational.

When the 2nd repeater arrives, i'll meter out the WAN LED connections and find a way to reconnect the LED.

Apart from the PSU and testing, there remains the mounting plate. This will bolt to the lid of the case, and hold two U-clamps. With this in place, a section of pole with a base plate attached will be fashioned to allow a free standing repeater unit to be set up.

Hopefully testing of the unit can start in the next day or two.

Saturday, 12 July 2014

WiFi Repeater Ruggedization Build

The project to build a ruggedized WiFi repeater ready for the church station is underway. The RP-SMA connectors and the extra Yagi have both arrived from Hong Kong,

The repeater has been removed from its cheap plastic shell, and the outrageously poor SMPSU removed and discarded. The two silly little PCB dipoles have also been removed.

The PCB pads for connecting the new antenna connectors are not very big, but just about workable. The hot melt glue holding the original coax in place was very carefully peeled off, and the coax cut to leave just the smallest bits soldered to the board to unsolder. Attention then turned to the new housing

This is a die cast aluminium 'Eddystone' box ive had kicking about for a long time waiting for a suitable project. Some very fine needle file work and we have a snug hole for the LAN connector. Holes were then marked for DC power input, the two antenna sockets, a reset switch, and the status LEDs.

The reset switch on the board is a tiny push button, this is being replaced by a good sturdy toggle - latching one way and momentary the other. The momentary contact will be used as the reset control, but the latching side will be used as a 'parked' position, helping prevent resets due to the switch being knocked.

The LAN socket cutout is so arranged that the whole board sits a few millimeters above the case, and will be held in place by hot melt glue. Other spacers will be used to ensure the board cannot short to the case.

The 5v regulator circuit will be installed against the left hand side of the case, and the three status LEDs through the bottom surface, in a vertical row. These are likely to cause the greatest headache, as the LEDs on the board are incredibly small, and i'll have to remove them and wire the case LEDs in their places.

Once complete and tested, the lid will be fitted. But the lid itself will have been heavily modified - It will have a plate bolted to it through which pass a pair of U clamps. This will make it possible to fasten the repeater and its Yagis to the same short pole, with the battery underneath.

Sunday, 6 July 2014

'Jaybeam' Slim JIM

Many of us began our ham radio career as the then Class B licensees, confined to the frequencies above 50MHz, and for many of us, our first antenna will have been the ubiquitous 'Slim-Jim'. Some of us, those with money, might have bought a commercial antenna, but those like me, impoverished school kids with an agonising paper round, spent our birthday money on a radio, and built an antenna. My first radio was a Kenpro KT-22 2m Handheld. This was actually stolen off my belt in Doncaster market, but one day i'll get another for nostalgia!

To go with this, I built my first slim jim. This was made from mains wiring stapled to the cardboard backs of several A4 notepads. Incredibly crude, but it worked, stood against my bedroom wall. I only abandoned it after it folded over whilst on air on night, across my bare arm!

Most people these days build them from a length of ladder line, which is what ive done here. 300 ohm window line. I used dimensions from G0KYA's blog, where he discusses a problem found when converting from 300 ohm ribbon to window line, with the velocity factor. To prove a point, I started with the original measurements, then swapped to his new set of 53" overall length, 16" for the matching section.

The insulation on this stuff is quite thick, and takes some baring back. Once about 1/4" is bared at one end, its tinned, folded over and soldered together. This is done at both ends of the section of line.

The bottom few inches are also bared back to provide a location for the feedpoint. This is found experimentally, and is usually the most tedious part of the build - this one being no exception! A sharp knife is needed to expose the wires.

The gap cut into one side, which separates the 1/4 wave matching stub from the 1/2 wave folded radiator, usually makes the whole thing go floppy, here ive reinforced it by taping a wooden coffee stirrer splint over it! This is a 1" gap cut 16" from the bottom.

I used an offcut of RG-58 with an N-type plug on it for the feeder, about 2" long. After a lot of experimentation, I found that 2" from the bottom gave me an acceptable match, 1.6:1, when the antenna was enclosed in its fibreglass tube.

Now, a word about enclosing these antennas. Im using the remains of an old commercial antenna, but even so, putting the antenna into the tube drastically detunes it! So much so that the resonant frequency of my antenna is about 138MHz. Attempts to compensate for this by cutting the antenna for 145MHz resonance when in the tube failed, im not at all sure why, but I reverted to the original dimensions and found a workable feedpoint.

 The antenna is now in its fibreglass tube, with the metal mounting hardware attached. This is being reattached using epoxy filler. Once cured, four bolts will firmly attach the mounting, and the bottom of the tube will have some sealant pumped in.

I also found time to get around to sectioning the 4" Heliflex feeder offcuts. The outer copper on this stuff is so thick that in the end, it was removed with an angle grinder!

 I now have the two sections with connectors sectioned, and apart from a bit more filing to remove some swarf, they are ready for classroom use.

Saturday, 5 July 2014

New 2m Vertical

Its about time I had a portable vertical for 2m FM work. Now, I do have one, but its extremely heavy! Ive used it on the Clansman masts at the show before, but it takes some serious effort to raise.

So ive decided another Slim Jim is in order. Like the last one, this one will be made from 300 ohm window line, but this time enclosed in the radome of a now defunct Jaybeam collinear.

The antenna itself is now built, and the collinears fibreglass tubing cut to size. However, I have not yet had it on the analyser to see where the correct match feedpoint is. Thats a job for tomorrow.

Friday, 4 July 2014

Laptop power

OK, so this really belongs on the CHOTA blog....but I suppose it comes also under the general radio and electronics stuff I do...

I have an old(ish) Toshiba Equium A200 laptop, this is alright for general radio use, but the battery is shot, and I cant justify paying the price of a new battery! Now, I really want to be able to use this in the field, or car. Ive tried it on a 12v SLAB, but it wouldnt power at that low a voltage. The specified supply is 19v (although its battery is rated 10.8v???). So ive decided to invest in a 'car charger', like this one 

With any luck, this will solve the problem of running the machine from a 12v DC supply. This will allow me to run WSPR etc mobile (well, parked up!), and especially at the church station. I will have to measure the current taken when running just WSPR on the laptop, to work out what battery capacity I really need for a days working.

New blog for CHOTA

I have decided, since theres a lot of information and a lot of tests involved, that this blog was getting a bit cluttered with posts about the St Marys CHOTA station, and so ive started a new blog just for CHOTA

On there you will find the info and pictures of the various antennas, masts etc, and of the church itself, as pertains specifically to the GB0SML station.

On here though, there might still be some stuff related to Lead church! This is because, the landowner, Simon, has been nice enough to allow me to use his field for the Backpackers contests! Of course the same ban on ground penetration still applies! So, im now considering how best to get my little 3 element 2m beam in the air from the church! I would normally use a 5.4m Clansman mast, but these need guying! Time to see if the 10m fibreglass mast can take it! It will be nice to get the FT-290 back out portable!

Saturday, 28 June 2014

Transportable WiFi Repeater

Testing the Chinese import WiFi repeater yesterday revealed a few good features, but also one very major and disappointing one. On the plus side, it is actually rather easy to set up, although it is easier to do so using the RJ45 LAN port than by wireless, if only due to the fact that as soon as its connected to a network, it becomes 'transparent' and cannot be 'seen' by the devices on the network! This means you cannot reconfigure it without a hard reset, as you can't access the devices IP address!

The big downside is its power supply. Physically, the two pin mains connector is very poor, and is so loose in an adapter for UK mains that just knocking the device causes it to reboot. I feel that this is a dangerous situation and have complained to the supplier.

Today was Toms birthday party, and with less than an hour to go, we found that the professional audio system we had for the music would not work. It seems it runs on internal batteries, and these were dead. Both the mains and the DC power input are charge circuits, neither bypasses the batteries and allows the unit to run! It is also a 24V system. So I had to desperately strip the unit, disconnect the batteries, find a way to bring the cables out, and rig a temporary 24V DC supply

The spade terminals I had were too big, so I had to cut them down using tin shears. The power came from two 12V 38Ahr SLABs in series.

In order to build the proposed transportable WiFi repeater, I need some suitable coax connectors to allow connecting various 2.4GHz antennas. Notably, in order to use collinears or Yagis. The old Hirshmann TV transposer cards on my shelf yielded two short SMA coax leads, as seen in the photo below

 These are ideal. All I need now is a 12V to 5V regulator board, a 7Ahr SLAB, and a suitable metal box with a handle to build it into!

I have also finally installed the coax switch in the shack. This is mounted above the ATU and is between the ATU and the transceiver. It will allow me to connect other radios, in particular my MKARS80 and the PSK-20, to the main antenna. This switch has a center position which puts everything to ground as well, so when im not present I can ground the station and antennas for safety.

I still need to find an old PS/2 mouse (or keyboard) to yield a data cable for my FT-857D, plus a spare USB lead to finish the USB soundcard that will be boxed as part of this interface.