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

Digger 20-04-2015 17:48

AIR on 7550 kHz from Bangalore
2 Attachment(s)
AIR Test transmissions from 20 April to 30 April 2015. A strong signal, but CIR is bad. Chopped audio. And - they have forgotten to switch on the hum tonight! :p

21 dB SNR and chopped up audio...

A 286 minutes long, partly unnatended with 54.6% decoded audio. Max SNR was 28.48 dB at 2045 UTC.

The second attachment is a 45 minutes segment from 2026 UTC. Despite an average SNR of 25 dB the decoded audio was only 96%. There must be a better configuration?! I believe that the bad CIR is the biggest problem to the decoding.

mitajohn 20-04-2015 20:31

Strong signal about 60dBuV, SNR reached 20 dBs, bad IR, no audio.

Digger 21-04-2015 21:10

1 Attachment(s)
A little more decoded audio (74.66%) tonight in this 193 minutes long log. I must admit that this is the first transmission I've heard from India without hum on the audio.

Digger 22-04-2015 20:44

1 Attachment(s)
64% decoded audio in tonight's log. I stopped the log after 164 minutes of hick-hack audio.

F1BJB 23-04-2015 18:27

Strong signal but only short pieces of the 2 audio channels decoded

Digger 23-04-2015 20:50

1 Attachment(s)
57.6% decoded audio during the 177 minutes long log. If the one hour drop-out wouldn't have been, then the decoded audio would have hit about 87%. The mode used does not deliver any uninterrupted audio even with 25 dB SNR! The only thing woth mentioning for this test is that it is probably the first time I have heard AIR with audio without hum and hiss in the modulation. :D

Digger 24-04-2015 20:40

Report from 24.04.2015:
2 Attachment(s)
The transmission started early. I noticed TEST MUSIC with music at 1720 UTC and the REGULAR SERVICE was silent at that point. Soon after at 1723 UTC the RF signal disappeared. Around 1730 UTC the signal came back on the air.

A strong signal with 55 dBuV into my receiver, but the Channel Impulse Ratio
is again very bad. Chopped up audio all the time. And after 1856 UTC there
was no decoded audio at all despite this strong RF signal. Now at 2012 UTC
the SNR hovers around 18 dB, but like I wrote above, there is ZERO decoded

A 182 minutes long, partly unattended with 25.25% decoded audio. Max SNR was 24.21 dB at 1732 UTC.

Despite an average SNR of 22 dB the decoded audio was only 50.6% between
1730-1856 UTC. There must be a better configuration?! I still believe that
the bad CIR is the biggest problem to the decoding here in Scandinavia.

Digger 25-04-2015 20:40

1 Attachment(s)
The transmission started early today too. I noticed TEST MUSIC with silence at 1718 UTC and the REGULAR SERVICE was silent too at that point. Soon after at 1721 UTC the RF signal disappeared. Around 1740 UTC the DRM signal came back on the air.

A strong signal with 60-67 dBuV into my receiver, but the audio was chopped up all the time if there was any audio at all. After 1755 UTC there
was virually no decoded audio at all despite the strong RF signal.

A 122 minutes long, partly unattended with 3.15% decoded audio. Max SNR was 22.28 dB at 1751 UTC.

Digger 27-04-2015 05:41

26 apr 2015
1 Attachment(s)
The transmission started with AM today. I was surprised to hear this, but I left the radio on the frequency and at 1747 UTC it switched to DRM. A strong signal with >60 dBuV into my receiver's antenna, but the audio was slightly chopped up all the time despite the relatively high mean SNR of 24.5 dB for the whole transmission. Is the protection level 3/0 the best they can do with this configuration?

A 282 minutes long, mostly unattended with 91.5% decoded audio. Max SNR was 29.5 dB at 2117 UTC. The Doppler was lower tonight with an average of 0.32 Hz. This, plus the slightly better Channel Impulse Ratio might have helped to produce more decoded audio.

A programme announcer mentioned "Non-Stop Express" at 2030 UTC on the TEST MUSIC channel followed by light Indian music. The Regular Service started in English, but later on I heard native language(s) and typical Indian music like the transmissions on 9.950 MHz.

peter-s-drm 27-04-2015 08:40

The problem with the high needs of SNR to decode is Protection Level 3. AIR should test with Protection Level 1 or 2 and possible only one audio stream.

Digger 27-04-2015 21:12

1 Attachment(s)
Hi Peter and all,

I suggested the Spectrum Manager at AIR to set a more robust protection level (if possible with what they are doing) but got only an answer with a request for my full address (given to them a couple of times) to send me a QSL card. A QSL card is very welcome, but I think, especially as they call it a test transmission, they should then experiment a little with the settings.

But the propagation was much better last night compared to now. Only 17.5% decoded audio and the SNR was 18.7 dB on average. It would have been about 4-6 dB better if I had remembered to set the AGC to "slow". The Channel Impulse Response was pretty awful this evening adding to the bad result.

mitajohn 28-04-2015 18:20

1 Attachment(s)
The signal is strong >60dBuV and stable but the CIR is terrible, no decoding possible.

Digger 28-04-2015 19:00

AIR tests on 7550 kHz, 28 apr. 2015
2 Attachment(s)
...and Mode C doesn't do any good either! But the CIR is completely hopeless. Propagation is a mess in 7 MHz this evening...

It started out pretty bad, but after 1930 UTC the propagation conditions improved and from 2050 UTC the reception was perfect until the end in my log at 2229 UTC.

I logged the transmission with two receivers. The log taken with the Newstar DR111 looks much the same.

Digger 30-04-2015 09:53

1 Attachment(s)
Hi all,

Last night (29th April) the DRM transmission started late. Before 1947 UTC
there was AM on 7550 kHz. Suddenly the DRM signal appeared. Maximum SNR
reached 27.59 dB and the average SNR for the log was 23.48 dB. The average
Doppler was 0.55 Hz. Despite the high SNR the audio was very chopped up,
probably because of the lack of robustness. The result was less than 75%
decoded audio.

Enclosed is my log from last night until my DRM Log-Plotter switched the
system down at 2230 UTC.

Digger 30-04-2015 18:28

30th April ended with a flop
2 Attachment(s)
Hi all,

So far (until 1822 UTC) it seems to me that they have either forgotten to plug in the audio source(s) or the propagation is down the drain. SDC is red and MSC is gray. The RF signal received here is around S9+20 dB which in my case means an input level of +58 dBuV which is more than 0.5 mV into the antenna socket.

The SNR was around 5 dB until 2115 UTC when, after a few breaks in the DRM transmission, the SNR suddenly rose to more than 20 dB and the labels appeared. The bitrate was 11.72 kbps on both channels. Propagation wasn't good and the CIR was flat. At 2125 UTC I noted the comment "Non-stop Express", which seems to be a music programme with light native popular music.

They used Mode A for this transmission, but the P3/0 was not robust enough. What they were up to from 1752 until 2115 I have no idea. Probably they had managed to have chosen a bad DRM configuration. :confused:

If this was the last transmission in the test, it was a disappointment. We just have to wait for the next test.

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).

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

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

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


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.

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