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Tuesday, 10 March 2015

My SWRs got no nose - How does it smell?


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

plus the masthead amplifier I built and installed back here:

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?  

Thursday, 5 March 2015

TS-990 on 2M 144MHz - no way!


I've also created this video this morning showing the TS-990 being used with my homebrew transverter for 2M from here:

and the masthead amplifier from here:

All works rather fantastically, even if I do say so myself!

This is a video receiving the GB3VHF beacon on the TS-990:

Local conditions.

Meteor Scatter with the TS-990 - Are you sure?


Fiddling around in the shack this morning and I thought I would share with you a video of the TS-990 being used in conjunction with Gemini 4 linear for Meteor Scatter in JT6M mode.

Local conditions.

Wednesday, 4 March 2015

DSTAR GPS Connections - Really?


You may recall last time I was musing about connecting a GPS receiver to my IC-7100 to complement the DSTAR mode.

Anyhow, I tested the electronics I threw together and found my voltage regulator to be highly suspect so I threw it in the bin. I hadn't got any 7805 regulators, so I had to construct a 5V supply using a LM317 I had. There's a really handy calculator here:

And I soon concluded that a value of R1 =  330R and R2 = 1000R would give me a 5.04V regulated output.

I built the 5.0V regulator and coupled it up to the GPS receiver; a GPS antenna that has been sitting on the porch roof for some time was connected to the antenna socket and a scope to the data output line.

Here's what I saw:

Now, clearly I can't read or interpret this stream of pulses, but it certainly looks like a RS-232 type data output to me.

So, I decided to connect it to the radio and see what happens.

Guess what? Nill, zero, zip, nada.

Now, there are a few variables here that I have to fiddle with. Firstly the data jack on the back of the radio, what is the pin out? There's nothing in the manual to tell me. I assume the ring of the connector is the ground, so we have two options there. The TXD and RXD could be one of two ways round. Lets' try the two options....

Guess what? Nill, zero, zip, nada.

Additionally there is the baud rate of the GPS data - is it 4800 baud? 9600 baud? Again I am not too sure.

I think the best thing for me to do is to hook the GPS receiver up to an Arduino board and see what the data actually looks like before going any further.

So here is a very Basic Arduino Scetch to read a byte from the GPS receiver and write it out to the Serial Monitor:

And this is the output:

So, this confirms that the GPS receiver is spitting out GPS data at 4800 baud.

So now I think I need to focus on the connection to the radio. There is NOTHING in the manual at all to tell you what the pin out of the DATA1 connection on the radio rear panel is. Time for some research....

I dropped Icom UK an email asking about the connections to the DATA1 port and very quickly received this image from then by means of reply:

Now, the radio is definitely configured for an External GPS connection at 4800 baud.... but still Nill, zero, zip, nada.

More head scratching required me thinks....


It's just come to me in a flash! My GPS receiver output is TTL and the IC-7100 needs an RS232 input. I need to convert one to the other!

Earlier on today by some total coincidence, I stumbled across the TTL to RS-232 converter I made back here for the FT1000D:

Not that finding this made me think that this could be the problem here! Anyhow, I've hooked the board from that project to the output of my GPS:

And this is the input and output of the converter on the 'scope:

And low, and indeed behold, this is the output connected to the IC-7100:

It works!

Local conditions.

Tuesday, 3 March 2015

DSTAR - D what?


Not being one for newfangled technollogy, I've done no experiments whatsoever with the DSTAR capability in my IC-7100..... until now....

I wondered if I could hear the not so far away repeater GB3IN in Matlock, Derbyshire. It's a DSTAR note. I listened on an analogue radio and found regular bursts of what sounded very much like data.

This is GB3IN:

I started by reading the IC-7100 manual, that didn't help much at all, then I found this video on You-Tube which is most excellent:

Good job Julien, N3FJ!

I was also sent an idiots guide which I have made available on the interweb here:

Idiots Guide

These two resources explained a whole pile of stuff to me. Here's the radio configuration for local CQ through GB3IN:

And this repeater configuration includes the Gateway callsign information for making Gateway CQ calls.

I'm still very much new to this and haven't figured all things out yet, but the pieces are slowly falling into place.

One of the accessories available for the IC-7100 is an external GPS - there is a 2.5mm jack socket on the back for connecting the receiver.

Now, a while back I did some fiddling with GPS receivers when I made the GPS disciplined frequency reference for the shack:

So I am thinking it should be easy to connect one of the GPS receivers I have here to the IC-7100. This is how I think it should work and what the actually thing looks like in reality:

I'll connect it all together tomorrow and report back on what happens.

Dogs looking confused; my mum thinks he is almost asking if he should wake up the cat?

Fun egh?