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

G4TMV 04-05-2015 22:07

Hi Terje,

It certainly is, the only way they (and us) will ever discover what does work and what doesn't is by doing tests like these and seeing what happens. Makes things a bit more interesting for us anyway!:D

Let's hope they keep the tests going and try a few more different settings so we can compare the results from all of them.

It's still coming in here yet, but I'm starting to get a few more drop outs now than I was earlier.

Cheers for now, Alan.

mitajohn 04-05-2015 22:27

May_04
 
2 Attachment(s)
Here is and unattended log for about 3 hours...no good at all.

PS: Can anybody explain to me why SODIRA sw shows a sample rate of 12 kHz? is this correct?

Digger 05-05-2015 07:44

1 Attachment(s)
Hi all,

Last night (4th May) there was a change of Protection Level to the better. It was changed to PL 0/1 instead of the less robust 3/0. This caused a major increase of the decoded audio. However, the propagation is not favourable. This can be seen in the Channel Impulse Response, which is very flat. When I left the receiver around 2050 the CIR had improved somewhat, and the decoded audio did also increase at this time.

The bitrate was a little bit lower last night with 10.24 kbps. It would be unwise to go lower, as the audio spectrum will be limited. The audio in the Regular Service was quite good, but the Test Music channel sounded a little bit muffled.

In the beginning around 1747 UTC there was English in the Regular Service and poular-sounding native music in the Test Music channel.



PS: Just after writing this I got a message that AIR will try a different configuration tonight.

peter-s-drm 05-05-2015 08:02

Hi Terje an all,
AIR used Mode A (:rolleyes: ). This isn't the right mode for DRM in ionospheric propagation conditions. Mode A is a good choice for broadcasts on long- or mediumwave, realy not for shortwave, I think.
Cheers, Peter

Digger 05-05-2015 09:34

Hi Peter,

True. But way back we sometimes experienced good results over long distances using Mode A. It seems like the rulebook is not always right. I suggested that they should try Mode B tonight and try to keep the Protection Level as it was last night. We just have to wait and see what changes they might do.

F1BJB 05-05-2015 11:00

Very bad results here .
In spite of identification of the 2 audio channels barely any audio at all.
I wonder why they use such a high bit rate to transmit 2 audio channels
that very few can receive in a rather poor audio quality.

Digger 05-05-2015 11:14

At least there is no hum on this transmission :D

On air now with Mode B and 8.72 kbps on both audio channels. SNR now at 1747 UTC is well above 20 dB and audio with the occasional short dropout.

There is a massive front with thunderstorms coming my way, so I'm not sure how many hours I'll be able to log tonight.

mitajohn 05-05-2015 18:06

May_05
 
2 Attachment(s)
I receive it good this evening with audio decoding, both services. There is a change in BR as well as a new mode. That's a real difference...see the images for details.

Later I will post a log.

G4TMV 05-05-2015 18:10

1 Attachment(s)
Getting very good reception this evening with Mode B, and the audio sounds good too, as Terje said, no hum at all and a lower bit rate.

It will be interesting to see how well it holds up throughout the evening now. No sign of any thunderstorms here, I'm more worried about my aerials blowing away in the strong winds!:D

Alan.

F1BJB 05-05-2015 20:23

Very big improvement here too.
In fact I have 100% audio now.
There is a kind of hum on the "regular service"
"Test Music" is perfect
The quality of audio is quite good at such a low bitrate.

mitajohn 05-05-2015 22:41

May_05
 
2 Attachment(s)
Here's the log. Great improvement at ~ 98% CDA for 4 hours and 44 mins. The results turned bad towards the end of log.

Digger 06-05-2015 07:46

5th May
 
1 Attachment(s)
There was a big improvement in the decoded audio last night with Mode B. The rulebook won - this time. :p

The decoding was perfect during the 294 minutes I logged. There were only 22 errors in the Main Service Channel which did not disturb the reception very much.

The Channel Impulse Response was not very good last night either. The log was mostly unattended. The Test Music channel featured more light music than what was played on the Regular Service. I was worried that I had to cut the log short because of a severe front with thunderstorms south of Sweden, but it did not head directly in my direction, so I let the receiver log until the end. The bitrate was low, only 8.72 kbps. Still the audio was acceptable, not the best but not too bad. At least there is no hum on this test transmission!

mitajohn 06-05-2015 18:19

May_06
 
1 Attachment(s)
BR 8.08kbps to night but almost flat CIR, no decoding, no log. If it will turn better I will post a log.

Digger 06-05-2015 18:24

Now at 1818 UTC it is perfect reception-wise and has been like that since I started th log at 1738 UTC. So far, 100% CDA.

Log later (or tomorrow morning).

G4TMV 06-05-2015 21:18

Same here as well, I've been listening to the test channel all evening, and it has been almost perfect, looks like they've got it cracked now.

It will be interesting to see if this latest X-Class flare has any effect on the 7 MHz Band over the next few days, and if it does, how well the DRM signal holds up to it.

Alan.


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