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-   -   AIR on 7550 kHz from Bangalore (http://www.drmrx.org/forum/showthread.php?t=2647)

Digger 01-05-2015 12:39

The tests will continue!
A message came in the mail this afternoon where the Spectrum Manager's office gives orders that the tests should continue until further notice.

So please listen again and send reports to the Spectrum Manager' mail address.

G4TMV 01-05-2015 18:08

It's coming in here now in english, though I'm still getting a lot of drop outs, the waveform looks a bit mangled so I think I might try it on my 7030 and see if the narrower IF filter helps at all.

Still, an improvement on the other evening, at least I'm hearing audio now.

Thanks a lot for the news that the tests were continuing Digger!


Digger 01-05-2015 19:00

Grrr...! My receiver was tuned to the wrong frequency. Thanks Alan for your mail info! No sound here - they still insist on P3/0. SNR is below 20 dB here now at 1900 UTC.

Doppler is getting better (<1 Hz) now after 1910 UTC. Perhaps the low Sun activity will do some good...

Log follows in a new post on Sunday.

G4TMV 01-05-2015 19:48

I managed to get some audio out of them this time, but it was still dropping out a lot here. It has dropped down to about 11db at the moment (1940utc), it was at 19.0db earlier. Maybe the signal will improve a bit now that it's going dark here, we shall see. At least it didn't seem to have the usual AIR 'hum' when it was audible.


Digger 02-05-2015 06:29

1 Attachment(s)
Like I mentioned, I had tuned my receiver to the wrong frequency last night and noticed it around 1855 UTC. I think that a more robust Protection Level would increase the chances of decoding. As it is now, only SNR higher than 20 dB produce audio. Even then, with 20 dB SNR, the audio is chopped up. After 2210 UTC until the end of the log I got 49.5% decoded audio.

G4TMV 02-05-2015 13:42

I noticed that the upper side of the DRM waveform looked very distorted throughout the broadcast, and when they went off air at 2229 UTC, it was very noticeable that there was some sort of digital 'multiplexer' signal (probably military) covering from about 7552 to 7559 kHz, and I'm wondering if this was having a negative effect on the signal? It wasn't noticeable under the DRM noise whilst the station was on air, and I wouldn't even have guessed that it was there during the broadcast. It would be good if they could move down to 7540 kHz to avoid it and see if that made any difference to the quality of the decodes.

Digger 03-05-2015 20:37

1 Attachment(s)
No DRM this evening except for a few short bursts in the beginning at 1745 UTC.

G4TMV 03-05-2015 22:01

Hi Digger,

It came on late. I thought there wasn't going to be one tonight, but when I checked again at 2130 UTC it was back on in DRM again.

Still just getting bits and pieces, but the signal seems up a little bit on last night.


Digger 04-05-2015 05:02

Hi Alan,

Thanks for noticing. I gave up and switched off all my equipment last night. Did you notice what mode they used? Those few bursts I saw were Mode A and the usual PL 3/0.

G4TMV 04-05-2015 16:37

Hi Digger,

Yes, it was:

DRM Mode/Bandwidth: A/10 kHz
SDC /MSC Mode: 16 QAM / SM-64 QAM
Prot.Level (B/A): 3 / 1

The only difference to previous nights seems to be on the Prot Level, pity they don't try using the same setting as they use on 9 MHz.

In comparison to other nights, the signal actually came up just before they pulled the plug, and I was hearing lots of talk in english.

It will be interesting to see if they come up on time this evening, and if they've changed anything at all.


Digger 04-05-2015 17:44

I see P 0/1 just now and a slightly lower bitrate. CIR is bad as usual, but that's not their fault.

Oops... its gone... (1741 UTC)... and back on again at 1747.

Log later.

PS: I also have noticed some kind of sawmill in the channel....

G4TMV 04-05-2015 18:12

Same here, and I noticed that they've dropped back to 10.24kbps again.

Looking at their waveform, that 'multiplexer' type signal is on again and covering from 7552 to 7559, I'm not sure if this has any negative effect on their signal at all.

I'm getting a bit of audio in english, though the signal strength seems to be well down on last night, hopefully it might improve a bit later on.

mitajohn 04-05-2015 19:00

2 Attachment(s)
Bad CIR, Signal ~ 65dBuV, BR 10,24 kbps the rest on the image...

EDIT: I added the label.

BTW now I receive some audio...

G4TMV 04-05-2015 20:02

1 Attachment(s)
It has really improved here now, with almost continuous audio, it looks like changing the protection level has made a difference, though I'm still a bit surprised that they're not using Mode B, I thought Mode A was mainly for MW use?

Digger 04-05-2015 20:49

Hi Alan,

Perhaps my problem, I asked them to try something els instead of Mode C, a mode that never proved very successful. Tomorrow morning I'll suggest Mode B and the same P/L. By the way, in the past Mode A gave good results over multiple hops from Santiago de Chile with 17 kW DRM into Switzerland. I think the DRM manual is a bit to theoretic. So far I'm surprised that AIR has been brave to try different parameters. And, isn't that what testing is all about?

Again, my log follows tomorrow, as I let this run unattended from now (2046 UTC).

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