My SWRs got no nose - How does it smell?

Well,

You may recall the 6 Element LFA 2M Yagi I installed back here:

http://g0mgx.blogspot.co.uk/2014/08/this-is-even-more-bonkers-than-before.html

plus the masthead amplifier I built and installed back here:

http://g0mgx.blogspot.co.uk/2014/12/how-can-something-so-simple-be-so-tricky.html

There has been something very strange indeed going on with this antenna. Here's the evidence as I see it:

• The SWR varies - not while in use, but sometimes it's not as good as it was when I left it!
• It is either good or bad, I have never seen it go from good to bad while in use;
• When it's bad the Gemini linear trips with high SWR (which is good)
• The bad SWR does seem to be more present when it's cold
• When it's bad the SWR seems to be about 1.8:1
• Having had the antennas down many times to look at this problem, the only thing I am suspicious of is a "back to back" N-Type connector that's up in the air. Everything else seems OK to me.

When I installed the pre-amp, I didn't want to hard wire it in so it was a permanent installation - I therefore decided to hard wire it to the cable tail that connects to the antenna, and fit an N-Type connector to the other lead from the pre-amp. This other lead is connected to the Westflex 103 that feeds back to the shack by means of a "back to back" N-Type plus the N-Type fitted to the end of the Westflex - got it?

So - the connectors are all expensive (not that this means they are good quality, but they look good to me) and they are compression fittings. No amount of wiggling these connectors will make the SWR change. 

I have concluded that the only thing that might be causing my problem is the back to back N-Type connector. To remedy this I have purchased a Female N-Type in-line connector which I can fit to the end of the pre-amp tail, thus eliminating the need for the back to back connector. 

Today I brought the  antennas down and found that by adjusting the 2M antenna, I could reduce the SWR further than it was when I started. Now, due to my suspicions, this was the return loss trace from the 2M beam last time I finished fiddling with it:

So, according to this I had an SWR of 1.55:1 last time I finished with the antenna, after my fiddling today, today my AA-170 analyser is saying this:

which is a return loss of 22.68 dB and an SWR of 1.16:1. My return loss bridge on the spectrum analyser is saying this:

which is that the return loss is 22.12dB and an SWR of 1.17:1 - which is pretty damn close to the analyser or perhaps the AA-170 is close to the SA. What I am trying to say is that the results are astonishingly similar!!

This suggests that I hadn't adjusted the antenna properly when I finished with it last time - perhaps I just got bored? Who knows!

I haven't fitted the female N-Type and will wait and see what, if anything changes going forward. If I have any recurrence of this jumping SWR the pre-amp will have to come down and the female N-Type connector fitted.

Odd, egh?  

Transverting some more, some more

Well,

Following my progress last time:

http://g0mgx.blogspot.co.uk/2014/10/transverting-some-more.html

I've kind of finished (ready for test) the Anglian transverter.

Here's the finished article:

Here's the main transverter module:

This is the external DDS LO which stabilises the in-board LO:

And this is my hideous looking changeover relay for the 144MHz socket.

There's an Omeron relay on the underside of the board, even so it looks pretty hideous to me!

These are the things I am not so sure about:

• The case is metal but plastic coated. Have I got a good ground connection to the front, back and main parts of the case - should I add some specific earth tags on each part of the case?
• The changeover relay - need I say more!

Fun though, egh?

Transverting some more

Well,

You may recall my discussion a while ago on the best way to get a 144MHz capability here; should I continue to use my FT-847 or transvert from my TS-990.

The TS-990 has an external drive socket "DRV" documented to be a 0dBm output; that's not entirely true. What I have found is that:

• WITHOUT XVRT selected the output power on the DRV socket is variable from 0dBm to -15dBm with the front panel power control.
• WITH XVRT selected AND Advanced Menu item 8 ON the power is fixed at -15dBm.
• WITH XVRT selected AND Advanced Menu item 8 OFF the power is variable between 0dBm and -15dBm with the front panel power control.

However, the TS-990 also has a neat feature in that you can program the offset of the transverter into the rig, thus making the display read the transverted frequency rather than the IF.

So, I joined the list for an Anglian transverter from Sam, G4DDK:

http://g4ddk.com/

And after seeing him present the design at the RSGB HamFest, mine duly arrived.

Here's the basic transverter module in its screening box:

And the underside:

This will be stabilised by an external 116MHz Local Oscillator generated by a kit from ZL2BKC, based on an Analogue Devices ADF4351 DDS:

you can find details of this project here:

http://zl2bkc.com/projects/zlpll/

Then finally, there is an 8W PA module for the output:

This is based on the Mitsubishi RA08H1317M module. I've cut the input track and made a 6dB pad at the input on mine:

I haven't yet assembled the PA module, but I have made the heat spreader that the board is bolted too.

The next job was to build and test the low pass filter for the amplifier output stage, it looks like this:

It's pass band looks like this:

and the return loss like this:

All in all, the 2M transverter project is progressing nicely.

Pepper cat hasn't been helping much:

Fun, egh?