Thursday, 23 October 2014

Wrong again!

Oh dear, I do seem to get myself into some awkward situations.
In all innocence I earlier tweeted a picture of a commercial video coder/modulator. I was told in good faith that it should be suitable for use within the new 146-147MHz ham band allocation, when frequency translated from its current 70MHz. I should have followed my inititial instincts that it wouldn't be suitable when using QPSK modulation, even at rates significantly below 1Msymbols/sec. 

It seems I innocently walked into an ongoing debate between some parts of BATC and the RSGB. 

It can be done, but it seems that what was being proposed would be unsuitable in view of the difficulties of achieving a suitable SPD at the band edges and consequent potential interference to safety of life services operating above 147MHz and our fellow satellite enthusiast just below 146MHz.

Whilst not wishing to discourage anyone from using DATV in the new band ( or indeed 10 or 6m) it looks like more effort needs to be put into solving the spectrum occupancy issues. This is what radio amateurs are good at.

It seems to me that the current wish to use a number of free ex-commercial coder/modulators may be clouding the real issues. 

It should be added that I am referring to fast scan digital TV. Slow scan variants look fine but may not offer anything new or innovative and hence not enhance our case to keep 146-147MHz in the future, or indeed give us a bit more spectrum in this region.

I hope these issues can be overcome and a real solution found.

Finally, these are my personal views and do not represent those of any organisation.

Sam


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