More CQ on them there Meteor Trails

Well,

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:

http://www.thedxshop.com/

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

Wel,,

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

http://g0mgx.blogspot.co.uk/2013/11/meteor-scatter-you-cant-be-serious.html

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?

Moving onwards and upwards....

Well,

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

http://g0mgx.blogspot.co.uk/2014/06/history-repeating.html

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:

http://homepage.tinet.ie/~ei9gq/bpf.html

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?

History Repeating....

Well,

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:

http://g0mgx.blogspot.co.uk/2010/11/radcom-dec-2010-ssb-exciter.html

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:

http://www.rsgbshop.org/acatalog/Online_Catalogue_What_s_New_26.html

and the authors website is here:

http://homepage.tinet.ie/~ei9gq/

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?

Say something then!

Well,

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:

http://g0mgx.blogspot.co.uk/2013/05/thatll-never-work-will-it.html

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:

http://www.tigertronics.com/slusbmain.htm

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?

More Mixer Musings

Well,

Following my total confusion over the KISS mixer, I decided to go back to basics and make certain my very little brain:

http://en.wikipedia.org/wiki/Winnie-the-Pooh

was up to speed and understanding the diode ring mixer as a starting point.

So, I made one of these:

Please accept my apologies for the simply appalling quality of the image above.

Now, the LO looks like this into 50R:

I make that 1.25V peak to peak which is 5.85dBm.

The RF input looks like this into 50R:

thats a whopping 2.36V peak to peak which is 11.44dBm (that's way too big!).

The output of the mixer looks like this (after a lot of fiddling with the 'scope):

So hopefully it's clear that ever time the LO (we could call it a switching signal) is negative the RF input is inverted on the IF output. If you then apply a filter to the IF output we can find a nice clean signal at the wanted frequency.

Now, if I keep the amplitudes as they are above, this is the output of the diode mixer on the SA:

I've put some markers on some notable signals; the 5.85dBm LO signal is visible at the output port at -32dBm. The RF input signal at 11.44dBm is at the output port at -20dBm and my wanted signals are at 1.7dBm. I also placed a marker on the harmonic at 40MHz - that's at -38.5dBm.

If I now add 30dB of attenuation to the RF signal, the output looks like this:

So now, the 5.85dBm LO signal is visible at the output port at -32dBm (no change), but my RF input signal now at -18.5dBm is visible at the output at -42dBm. My wanted signals are at -23dBm and my random harmonic is at -50dBm.

So, back to the KISS mixer confusion:

Let's look at exactly the same input conditions with the KISS mixer configured as per the schematic:

So, here we have the LO signal at 5.85dBm, the RF at 11.44dBm, with these input signals the bias pot has no effect at all that I can see:

and here, the LO signal remains at 5.85dBm but the RF signal is at -18.5dBm, with these signal levels I can make a slight change to the amplitude of the LO signal in the output with the bias pot - I have set it for minimum LO:

What does all this tell me? Primarily that I need to go out more!

I'm going to let those far cleverer than I draw the conclusions.

Interesting, egh?

KISS Mixer Musings

Well,

Part of the Minima transceiver I made back here:

http://g0mgx.blogspot.co.uk/2014/01/my-minima-is-alive-and-well.html

was the so called KISS mixer:

Above I have stolen the mixer part from the Minima schematic and labelled the ports. In my test setup I have the LO connected to a test crystal oscillator I had lying about, it's running at 20MHz (ish), the RF port is connected to my bench signal generator and the IF port is connected to the Spectrum Analyser.

Here's what the test setup looks like:

Now, the author of the Minima Farhan gave us some information on the KISS mixer here:

http://www.hfsignals.org/index.php/Minima#The_KISS_Mixer

and also a reference here:

http://www.phonestack.com/farhan/mixermusings.pdf

Now, here is what I see when I have a play. I have 20MHz LO, 15MHz set into the RF port from my bench sig gen and the spectrum analyser connected to the IF port.

Here's the output spanning 0 through 100MHz with just the LO (20MHz) signal:

This is just my oscillator and it's harmonics - so far so good. Now lets add in the 15MHz signal to the RF port and keep the 100MHz span:

So now we see the 20MHz signal plus harmonics, the 15MHz signal plus harmonics plus all the differences and sums which land at every 5MHz interval. So far so good.

Now, lets zoom in on one of the mixed signals at 35MHz:

Looks good to me.

Now, if I connect my x10 'scope probes to the gates of the FETs, here is what we see:

The 'scope struggles to trigger on anything here, because there is all sorts of frequencies in the signal, however, I think we can safely say that the two signals are the same but out of phase with each other as we would expect.

Now, if I look at the drains (my sources are connected together and the bias supply), we see this:

and if I add the LPF in the scope to bandwidth restrict the inputs:

If we replace the SA on the IF port with a 50R load, then look at the signals on the drains with the SA, here's drain one:

and here is drain two:

Now, in all of the tests above I have tried altering the bias pot and I can see no difference at all under any circumstances. If I look at the voltage at the wiper of the pot I can see 0-5V as expected. However the voltage at the sources read from -0.12 to -0.15V. That isn't what I expected either! If I remove the +5V supply the output doesn't change nor does it if I connect the sources to ground.

The FETs in the KISS mixer effectively replace the diodes in a more traditional diode ring mixer; this chops the RF signal thus providing the IF signal at the centre tap of the RF transformer.

So I replaced the single bias pot with one on each FET, under these circumstances I can alter the amplitude of the unwanted signals in the output but not make any difference to the wanted signals.

In my case the wanted signal is the 20 + 15MHz, here is the mixer output with the two bias pots adjusted to minimise the unwanted signals:

However, if I just remove the 5V line, the bias pots and just ground the two sources on the FETs, here's the output:

And these are the signals on the drains with no bias (the sources grounded):

Any volunteers to explain?