How to generate drive to generate drive

Or perhaps I should call this post "recursion, see recursion".

I finished testing the phasing of the transformers on the linear amp board, you can see from this pic that the input gets split nicely into two signals that are out of phase with each other. These are effectively the inputs to the gates of the FETs. The output transformer is then doing a good gob of mixing these two signals back together again:


So, this suggests that the transformers are wound and installed correctly. So I've installed the FETs on a heatsync that is a little below the board, that bit's worked out OK I think:


I can bias the FETs as expected, I measured the idle current and then increased the FET bias voltage until each FET drew an additional 10mA, the board with the relay engaged and the FETs both biased on is now drawing about 50mA.

The problem I have now is that the board includes a RF sniffer to close the relay, my signal generator (homebrew of course) only generates about 150mV pk-pk output which isn't anywhere near enough drive to close the relay, if I use a cable to drive the relay (i.e. short out the relevant bits of the circuit), I'm not seeing much gain in the FETs as I dont think the drive is enough for them either.

So I need to build an RF amplifier for my signal generator before I can test my RF amplifier - recursion see recursion.

Hence another small project is born.

HF Linear

Well, yet another project has started today; I've been collecting bits for the WA2EBY amplifier. This design claims 40W from a 1W drive accross all HF Bands. I got the PCB's from Far Circuits in the USA http://www.farcircuits.net, the toroids came as a pack from Kits and Parts in the USA also http://kitsandparts.com/. I've bought from both of these suppliers before and their dispatch to the UK is very reasonable and fast.

I've had to order a load of Silva Mica caps from Rapid electronics in the UK for the Low Pass Filters, as I didnt have anything suitable in stock; they are supposed to arrive today, but aren't here yet.

The main amplifier board is going to look a little scruffy, but here are a few picks from the build so far:






The last image shows the board under test, I havent inserted the finals yet and I've just stuck a 1nF capacitor between where the Gate and the Drain will go on each FET. This should allow me to check the phasing of the transformers and the other bits before I smoke any expensive parts! I've just watched the realay explode as I thought it was a 24V coil, but it seems it was a 5V coil and it didn't take too kindly to having 28V accross it!!!

I'll post more when I've got a replacement relay, I don't have one right now.

Would you Adam and Eve it?

Well,

As big a believer in QRP as I am, I'm not sure I'm able to actualy get my head round this. 6V p-to-p out of my QRSS beacon, that's about 100mW. This feeds through my ATU (mainly to convert from BNC to PL259!) then half way round the house in RG213; then up the side of the house and into a Windom.

Here is my call very readable at the QTH of ON5EX, thanks Johan! Thats a whopping 420km distance. Not half bad! The beacon frequency looks quite steady too! I'm well impressed:

QRSS Beacon Alignment

I've had a go at aligning this QRSS beacon today. The output from the small transmitter seems very clean and I've set it to the recommended level of just over 6V p-to-p. I did manage to set the output pot completely to max when I first powered it on, lots of heat but no smoke before I realised! I dont seem to have done any damage though...

I've stuch a 50R load on it and a scope probe, here's the output, very clean:

I've adjusted the frequency output to as near as I can to where I want it to be, and I've also watched the output using the Argo software and set the frequency shift of the callsign transmission.

So I guess it's time to connect the antenna and leave it running. There are quite a few grabbers on the internet, so I need to understand that a little more and then find out if and how far my 100mW is getting!

QRSS Beacon

I've been building a QRSS beacon kit that I purchased from Hans Summers:

http://www.hanssummers.com

It's a neat little package, which came as a complete kit. Mine is built for 40M.

Here's the kit with only the IC holder in place:

And here the kit is neary complete; only problem is I have L1 and L2 the wrong way round!


I've added some veroboard as a wider board to fit into the box I had in mind for the project, and included a 6V regulator in there to enable me to power this from the same source as all the other junk in the shack:


And here is the kit boxed and ready for alignment, I've also added a power switch and power on LED, plus a switch to put the keyer into 12wpm CW for testing or 6s dot length for QRSS running. Theres also a second LED to indicate that the kit is running in QRSS mode:


I've had a poke about with the scope and all looks as expected, I need to align the output frequency and spend some sime setting up the frequency shift.

I'll post more as I do that.

Mark.

Huff n Puff

I've been considering having a play with Huff n Puff VFO stablizers for quite some time; there are plenty of resources out there to explain this concept:

http://groups.yahoo.com/group/HuffPuffVFO/

http://www.hanssummers.com/huffpuff/minimalist/2chip.html

I've been reading with interest the experiments done by Hans Summers:

http://www.hanssummers.com/

And have had a go today at building his 2-chip VFO + Huff Puff; which is an exceptionally clever design.

Here's a picture of the schematic as drawn by Hans:



I've built it using veroboard, and paid no real attention to layout:



Now the output from this VFO is, as you would expect, rock solid:



What I'm planning to do is build a QRSS beacon and receiver for the shack:

http://www.sdrham.com/

Next is to build a Huff Puff stablised VFO on 10.140MHz for the QRSS receiver, and then think about how to build the beacon....

More will follow.

Let it Snow

Really bad weather has hampered progress a little; I've had no post for days as I guess they cant get very close to the house. Here's some pics of my chief technical assistant, plus the damn crazy dog. This is geddy cat, he tries to help, but doesn't succeed much...

This is Saki the dog, You can see just how deep the snow is; half of the dog is missing!


I'll post more when I receive some of the parts I'm waiting for.