Sunday, 19 October 2014

144MHz transverter construction

Now that I have finished my 'run' of talks on the Anglian, I have stripped out my temporary homebrew 144MHz transverter unit, ready to add in the PA and the 116MHz GPS locked LO.
Both these units were used as demo pieces for my talks.
I have mounted a small (40mm) diameter fan to the rear panel so as to blow or draw some cooling air across the PA components as the PA will be mounted to one of the case side walls. There will be no external heat sink on the case. At 4W PEP out and class AB operation, the aluminium case wall should be sufficient to dissipate the heat of the PA with quite acceptable temperature rise inside the case.
I will post a picture of the finished transverter on here later this week ( optimistic?).

Sam


Saturday, 18 October 2014

More on the Anglian

I have almost cleared the backlog of orders for the Anglian 144MHz transverter, thanks to sterling efforts by G7OCD to get the boards assembled.
If anyone is interested in one of the transverter kits, featured in DUBUS 3/14 and covered in my RSGB Convention talk, I am now able to take more orders.
The cost of the transverter has deliberately been kept low, and assembled boards offered, in order to allow more amateurs to build their own high performance 144MHz transverter, rather than relying on commercial 144MHz black boxes with their (usually) indifferent performance!



Sam

Thursday, 2 October 2014

144MHz set up

I have now added a Gemini 2 to my 144MHz set up. It is currently being driven by my K3 and internal K144VX transverter.
I will be migrating the 144MHz over to my Anglian transverter after the RSGB Convention. I don't have a spare Anglian 8W PA whilst my demo one is slated for show at my Anglian talk!
The Gemini gives close to 300W saturated output for 5W input. 
It is small and convenient and sits well on the operating bench, next to the K3.




Sam

Sunday, 14 September 2014

Some results from using the Anglian with K3

One of the things I dislike about the internal K3 144MHz transverter is the number of birdies that appear in the DX part of the 2m band. This has always tended to put me off using the K3 on 144MHz.

I spent some time testing yesterday with the antenna replaced by a 50R load.
Rather that use an objective set of measurements such as an analyser at the IF output, I used the simpler technique of just listening. After all this is what most operators really notice!
Incidentally, not all the birdies seen on the P3 or other SDR attached to the IF output are audible at the receiver output and are possibly due to shortcomings of the SDR in the P3 or other SDR (SDR-IQ in my case).

Tuning from 144.00 to 144.500MHz, with the internal transverter, I recorded about 10 significant birdies. Some weak and some medium strength. There were no strong birdies.

With the Anglian selected as an external 144 to 28MHz transverter the number of birdies dropped to under half those with the internal transverter and many of those that remained dropped in level to barely noticeable. I have therefore decided that the Anglian is a better choice for Dxing. Well, I would, wouldn't I?

I suspect that the problem with the internal transverter is more down to lack of screening than anything else, although the extra IF output filtering incorporated in the Anglian also probably helps.

I plan to do some objective testing in due course.



Sunday, 7 September 2014

Red in beak and talon

Just been watched a Goshawk kill and devour a starling in the garden.
Fierce looking bird!


Saturday, 6 September 2014

144Mhz results

I took the opportunity to listen and operate during the 144MHz Trophy contest.
100mW is not a lot to use during such a contest and indeed I worked one ON using the 100mW and he told me he was using 1kW! There was a slight difference in the reports with 40dB power difference......
What was interesting was the difference in ability of some stations to hear me and others to not even notice that anyone was calling them. How much was down to receiver blocking at their end and how much to shear QRM will never be known. 
An interesting evening.
Sam


144MHz antenna




After my recent changes to the YU7EF 9 element 144MHz long yagi feed point I changed over the 6/4m yagi for the 144MHz one.
I wanted to check out the new preamp on the 2m antenna.
The first thing I noticed was how quiet the YU7EF yagi is. As long as I don't beam towards the house ( approx 10 to 20T) the back ground noise is extremely low, although punctuated by the usual pulse noise from a nearby electric fence and some computer/data equipment carriers.

The plot above shows the return loss ( match of the yagi directly at the feed point. This was achieved by the usual calibration procedure at the yagi, using short,open, term.
A across the range 144 to 145MHz the return loss is around 20dB. I'm not so happy about the way the match starts to deteriorate rapidly above 145MHz.
The original 6/4m feeder is Ecoflex 10. There is now a short length of RG213 beteen the EF10 and the yagi feed point. This will be replaced with something of lower loss once the masthead preamp is installed.


The feed line loss is 1.9dB. Measured as half the two way loss from the shack to the yagi with a cal short circuit replacing the yagi. This is a great way to check installed cable.

Sam