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Friday, 27 June 2014

More CQ on them there Meteor Trails


Further to my earlier post, I found after about 8 or so TXs on JT6M, my linear was tripping out due to "over temp" today.

I dropped an email to the DX Shop:

And within about 5 mins I had a very helpful reply!

Under instruction from the manufacturers I have adjusted the trip level. This involved removing the cover of the amplifier, wow, what neat construction:

Here's Freddie, who seems to be resting in a plant pot today:

Impressive, egh?

CQ on them there Meteor trails


Been fiddling around this morning in the shack and doing some MS on 50MHz.I do this from time to time:

I thought you might be interested to see the setup operating, so have made this very rough and ready video:

My Nixie clock is about right but and the video quality is rubbish, you'll get the idea. I'm calling on 50.230 and listening on 50.245 (so I am calling CQ 245 G0MGX).

Fun egh?

Monday, 23 June 2014

Moving onwards and upwards....


Following on from my last post, I've been making some more bits and bobs to go with the SSB exciter:

I've made the Triple Balanced Mixer:

As is becoming an apparent recurring theme, my isolation between the different ports isn't measuring as good as the author, however I can measure LO-RF and LO-IF isolation of about 40dB and more like 50dB of RF-IF isolation; which isn't at all bad.

The mixer uses 5 bifilar wound inductors, each of 12 turns on a FT37-43 and two well matched sets of diodes.

I have then added the post mixer amplifier and constructed the first of many band pass filters. This one is for 40M or 7.0 - 7.2 MHz.

Information on the filters is here:

which includes a link to a spreadsheet credited to John Charlton G3VRF which is an excellent calculator tool.

When I first built this filter is was too low in frequency (the yellow trace below) so I reduced the inductors by one turn each to get the purple trace. The markers are at 7.0MHz and 7.2MHz:

So the filter, at least, is now looking rather good.

I've had another good look at the exciter from last time but still I can't see why my output level is so much lower than the authors; will have to look again tomorrow!

Good, egh?

Sunday, 22 June 2014

History Repeating....


I've bought myself a new RSGB book; it's called "Building a Transciever" and is actually a reprint of a load of RadCom Homebrew columns. Those of you been here a while may remember I actually made the exciter from these articles a while ago back hare:

Now, there has been a lot going on here since then and I probably have a bit more experience in these matters, so, to cut a long story short, I am planning to start again from scratch and have a go at the books contents.

The book itself is here:

and the authors website is here:

So, today I have made the exciter (again):

I could be a bit critical of this book (well actually I am and have told the RSGB so), here's why:

  • The photos in the book are exceptionally small (even compared to the original magazine copy)
  • They are black and white making component identification impossible in some cases
  • Some of the book schematics dont have all the component values in th picture or the text (crystal frequencies for the SSB exciter oscillator and also the Op-Amp in the Mic amp) - and that's just so far
Here's the output of my exciter on LSB with a 2KHz audio signal injected into the Mic amp and the carrier adjusted for what I think will be about right. Each of the SA images includes a sweep of the crystal filter - I have no real idea why the top of the passband has appeared to be so wibbly wobbly - could it be an impedance thing? The filter is 450 ohm ish and the SA is 50 - but I doubt it somehow.

I've used a GQRP club SSB filter 10.7MHz and the two carrier crystals that match it; however, my USB carrier point was **way** too high in frequency so I have had to add an inductor into the circuit to pull the crystal downwards (this is why I would like to know what frequency crystals the author used). Here's the exciter in USB:

Also the output of my oscillator is no where near the amplitude the author suggests he had from his. We will see.

Here's another shot showing the actual frequencies of my USB and LSB carriers:

I used a TL072 op-amp in the mic amp and here are the gain figures I measured:

So, all in all a good start I think.

Here's the latest two additions to the household (the dogs not the wife - she has been around for quite a while):

Good, egh?

Monday, 9 June 2014

Say something then!


A while since I have posted; primarily because I am spending far too much time in foreign parts for my employer, rather than playing for me!

Anyhow, been rummaging around in the shack today and finally got round to configuring my MS station for 6M and 4M.

I have the antenna I put up back here for both bands:

And today I have got the digital interface working to my satisfaction into the FT-847:

You will see that I have used a SignaLink USB thingamabob to connect the radio to the PC:

Now, the FT-847 has caused me a load of trouble in the past when dealing with digital modes; primarily in an unsatisfactory delay going back from TX into RX again. I have always interfaced the radio like this:

So here the PTT is combined with an audio line which is then decoupled using the capacitor you see in the graphic above.

This time I have interfaced into the Mic socket and used the PTT and audio in feeds available there:

Now, further inspection of the FT-847 manual today, and I find this:

which looks infinitely more sensible again!

So, I may yet change things once more to enable an easy switch between digital and voice operation.

I'm still using the amplifier I bought from Linear Amp (the DX Shop):

I'm scared stupid I'm going to overdrive this amplifier; I would like to find a way to restrict the output of the 847 permanently to 25W - any suggestions? I may well ask the question on the appropriate owners forum.

Fun egh?