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Old 14-04-2004, 14:42   #1
jbriggs
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7320 kHz (BBC from Rampisham)

Hello DRM's
From today we are starting a new experiment. Single Frequency Network (SFN) tests. But this means the data transmission has stopped for a few weeks
Now we use 2 senders and 2 antennas to transmit on the same frequency (for some of the time, not all the time) from Rampisham.
Today the second antenna had a bearing of 61 degrees (Baltic/Norway/Sweeden). The original antenna points on 105 degrees (Austria)
Question, can anyone see the difference between using 1 Sender and the periods when 2 are used?
James
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Old 14-04-2004, 15:39   #2
dk8cb
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Hi,

I listened today for about 50 minutes from 10:00 UTC to 10:50 UTC and noticed two breaks in reception at around 10:40 (I don't have my log here at work, so I can only guess the precise time of the event), when the spectrum suddenly looked very strange as if there was additional noise on the signal but only within its own bandwidth. At first, I thought, that there were adjustments being made at the transmitter.
Dream lost sync during that time but recovered quickly.
During the rest of the time, reception was very good with 100 % correctly decoded audio at 20.96 kbit/s.

dk8cb

Last edited by dk8cb : 14-04-2004 at 15:57.
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Old 14-04-2004, 23:18   #3
dk8cb
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Hi,

here is the corresponding screenshot.

It would be interesting to know, if those breaks correspond to a change at the transmitter.

dk8cb
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Old 15-04-2004, 08:03   #4
jbriggs
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Hi dk8cb,
I think the change in reception was when we only had 1 transmitter working.
Today I will make some careful notes of the exact times we make changes and post them here.
James
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Old 15-04-2004, 11:02   #5
dk8cb
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Hi James,

here is today's first 55 minutes. Sorry, have to leave and must switch off.
Very bad at the beginning.
The missing station label in the screeenshot is due to the fact that I started logging before the broadcast actually began.

dk8cb
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Last edited by dk8cb : 15-04-2004 at 11:07.
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Old 15-04-2004, 11:26   #6
jbriggs
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Thanks for the replies, here are the events this morning

0958 On air 61 degrees only
1019 SFN both Tx's on air, 61 and 105 degrees
1022 1 transmitter on air, 105 degrees only
1032 0 transmitters!
1033 1 transmitter, 105 degrees only
1041-1043 Tune up 61 degree transmitter giving interfering AM carrier
1044 SFN both transmitters on
1047-1048 adjust delay between transmitters by up to 3mS
1049 1 transmitter only on, 61 degrees
1050 SFN both transmitters on
1115 1 transmitter, 105 degrees only

James
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Old 15-04-2004, 13:44   #7
dk8cb
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Hi James,

thanks for the information,

Quote:
0958 On air 61 degrees only


I already suspected that, because signal strength was a lot less than usual. My location should be almost in the centre of the other beam.

Quote:
1041-1043 Tune up 61 degree transmitter giving interfering AM carrier


At that time, the carrier was clearly visible in the spectrum, but nevertheless reception continued.

When interpreting the screenshot, one should keep in mind, that the values shown are always delayed by one minute, i.e. the interval over which values are summed.
I clearly noticed the break at 10:32. The reason, why the SNR doesn't reflect that and doesn't go to zero (as does audio) might be due to the timeconstant involved in calculating this value.

dk8cb

Last edited by dk8cb : 15-04-2004 at 13:54.
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Old 15-04-2004, 16:14   #8
simone
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Hi all,
with my location (91° from Rampisham) being in between the 2 beams, results are not as I expected. On the 61° beam I only got a very weak signal, the 105° beam worked quite good but no improvement that I could see in the results at the times when both transmitters were used, see attachment
73, Simone
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Old 15-04-2004, 16:19   #9
simone
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Hi all,
... and the results later today, another SFN test at 14:05?
see attachment
73, Simone
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Old 15-04-2004, 19:21   #10
carknue
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Hi James,

here is my complete log.

Wouldn´t it make more sense to do SFN from two different sites? e.g. Rampisham and Juelich.
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Free DRM Tools for analysing, controling and automating your DRM reception and logging
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Old 15-04-2004, 19:51   #11
simone
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...and here is today´s logfile, still wonder about the improvement in the last hour.
73, Simone

@Carsten: Transmissions from different sites beaming at the same target area would be interesting.
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Last edited by simone : 15-04-2004 at 19:56.
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Old 16-04-2004, 11:19   #12
dk8cb
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Hi,

here is my log of half an hour of today's transmission. (Sorry, I could not log for a longer period of time)

There was a carrier before DRM transmission began, but it was not visible any more in the spectrum after DRM transmission had begun.

dk8cb
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Old 16-04-2004, 11:33   #13
simone
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Hi all,
I could only do a logfile of the first 22min, good results, I can´t say if it is one or two transmitters, btw I often get red sync/data lights and never reach 150 sync frames, see logfile attached
73, Simone

@James: Will the SFN tests continue over the weekend?
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Old 16-04-2004, 13:15   #14
jbriggs
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Quote:
Wouldn´t it make more sense to do SFN from two different sites? e.g. Rampisham and Juelich.
Hi Carsten
Yes you are correct. This is the intention, we may be able to do a SFN from Rampisham with RNW in Bonaire soon. But before we send the equipment to Bonaire, we thought it would be a good idea to test it first!
With some more development we can also start tests with modulator equipment from different manufacturers. Then a test with Rampisham and Sines or Rampisham and Juelich is possible.
This (in theory) could improve reception reliability.
However, I think same site SFN has a future as well.
James.
PS no SFN transmissions today, just 105 degrees.
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Old 16-04-2004, 15:23   #15
simone
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Hi all,
strong and stable signal this afternoon, see attachment
73, Simone
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