BATC Forum

Do we know if there is going to be another NOV extesion for NB DATV on 2m ? I see last year it was decided early Ocotber to extend it to end October 24. Seen nothing on the RSGB website so far. I finally got some interest locally and have helped kit up another local station yesterday. Only to find the NOV runs out tomorrow. Did we the BATC get any contact from Ofcom / RSGB to discuss how it went ? Obviously there are concerns about interference etc..

John G8IKP

Well, I tried to renew and this is the problem:
Martin G8LCE

I asked Murray (RSGB spectrum manager) and the reply was:

It is hopefully getting somewhere
– but users really need to help the process out by send JR/HQ et al reports of its value/results/innovation a month before the deadline – so we can present a case to Ofcom in good time!!

He has a good point - WHENEVER we operate on the bands, but particularly 146, we should post a report either on the forum or Twitter, just so OFCOM and others can see we are using the spectrum which is continually under pressure from others....

Perhaps we could try some “in band” 2m DATV like they do at times in Holland …….i have moinitored between 144.500 144.650 and rarely hear anything ….ive tried with 9 ele yagi and a colinear …..QTH is about 300 ft asl plus 40ft mast in north Essex …so reasonable take off in most directions .

I have 9 ele yagi , mast head pre amp and a 1.2kw gemini amp …….but seriously it could be an option on a very underused part of the band ……in fact you rearely hear anyone on FM .

Found this from a Dutch station

http://www.itr-datanet.com/~pe1itr/144mhz/datv-2m.htm

That's what I was proposing. The other advantage being, we could use 1kW to a beam. Should go quite far.

Mike

g0mjw wrote: ↑

Fri Nov 01, 2024 1:50 pm

That's what I was proposing. The other advantage being, we could use 1kW to a beam. Should go quite far.

Mike

Hi mike

Gary G4GHD just messaged me and said this was discussed on the net last night ….which I didn’t see .

Sure it would work very well on 2m ……will have to dig out the portsdown out of the junk box .

For info the RSGB 146-147 NoV-app page has had this note added:

"A request has been submitted to Ofcom to extend this temporary allocation for another year and we are awaiting a response."

- and that has involved stats and a report for both 71 and 146MHz

73

Murray G6JYB

I did a few calculations and a signal of 18 ks/s would allow 30-50kb/s of data, which should be enough for video, but not audio. This would fit into a 25kHz channel.

That data bandwidth is more than enough for a contest exchange, it should support low rate video, though not full HD. That's what we did on 10m. Maybe this is the next experiment. On 2m we might be able to use higher order modulation, e.g. 8PSK as we would not have the EIRP limit we have in the extended band.

Anyone fancy testing this?

Receiving would need to be done in software. For the 10m tests we used SDR Angel. The main issue frustrating reception was the ionospheric multi-path, which should be less of a problem on 2m. Transmission can be done with the Pluto.

Mike

g0mjw wrote: ↑

Sat Nov 02, 2024 8:57 am

I did a few calculations and a signal of 18 ks/s would allow 30-50kb/s of data, which should be enough for video, but not audio. This would fit into a 25kHz channel.

That data bandwidth is more than enough for a contest exchange, it should support low rate video, though not full HD. That's what we did on 10m. Maybe this is the next experiment. On 2m we might be able to use higher order modulation, e.g. 8PSK as we would not have the EIRP limit we have in the extended band.

Anyone fancy testing this?

Receiving would need to be done in software. For the 10m tests we used SDR Angel. The main issue frustrating reception was the ionospheric multi-path, which should be less of a problem on 2m. Transmission can be done with the Pluto.

Mike

According to the tests the Dutch guys done it seems a SR of 125 got best results …..copy and paste from Dutch article


Practice Test

On July 12, I conducted a test with Joris, PE1GLX as a counter station. PE1GLX is 7 km away and was the receiving station. PE1ITR the sending station at 144.600 MHz. At the transmitter, PE1ITR we set the signal level at PE1GLX so that it was above the threshold at SR 125 kHz FEC 1/2. Level was 2.4 db. I was running 200 mW output.

In the test I tried different settings. A finding is that an SR 125 kHz with a strong FEC beats SR 66k with a less strong FEC. It turns out that you can put too little video information in a block at a low bit rate if you use a too strong FEC. It turned out that 66k FEC 3/5 was just going. But 66k FEC 1/2 resulted in no picture. The SR 33 KHz resulted in any case at the low signal levels at no image information at the receiver and proved useless in that sense.
So 125 kHz FEC 1/2 wins of 66 kHz FEC 3/5. And for the even lower signal levels, 125 kHz with FEC 1/3 and even 1/4 is also possible. So 125 kHz is a nice value for DATV DX-ing.

146/147 MHz
NOV is now available just renewed mine