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Old 20-04-2015, 17:48   #1
Digger
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AIR on 7550 kHz from Bangalore

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!

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.
Attached Images
File Type: png 7550-150420-1743-2229-Terje@SE.png (47.1 KB, 1111 views)
File Type: png 7550-150420-2026-2110-Terje@SE.png (40.9 KB, 1034 views)
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Last edited by Digger : 21-04-2015 at 05:37.
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Old 20-04-2015, 20:31   #2
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April_20

Strong signal about 60dBuV, SNR reached 20 dBs, bad IR, no audio.
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Old 21-04-2015, 21:10   #3
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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.
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File Type: png 7550-150421-1753-2106-Terje@SE.png (44.7 KB, 1004 views)
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Old 22-04-2015, 20:44   #4
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64% decoded audio in tonight's log. I stopped the log after 164 minutes of hick-hack audio.
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File Type: png 7550-150422-1756-2040-Terje@SE.png (45.3 KB, 1012 views)
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Old 23-04-2015, 18:27   #5
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Strong signal but only short pieces of the 2 audio channels decoded
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Old 23-04-2015, 20:50   #6
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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.
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File Type: png 7550-150423-1743-2040-Terje@SE.png (43.6 KB, 1076 views)
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Last edited by Digger : 23-04-2015 at 20:52.
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Old 24-04-2015, 20:40   #7
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Report from 24.04.2015:

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
audio.

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.
Attached Images
File Type: png 7550-150424-1721-2023-Terje@SE.png (40.2 KB, 929 views)
File Type: png 7550-150424-1730-1856-Terje@SE.png (41.3 KB, 1016 views)
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Old 25-04-2015, 20:40   #8
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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.
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File Type: png 7550-150425-1718-2030-Terje@SE.png (38.0 KB, 1066 views)
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Old 27-04-2015, 05:41   #9
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26 apr 2015

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.
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File Type: png 7550-150426-1747-2229-Terje@SE.png (42.0 KB, 1054 views)
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Old 01-05-2015, 19:48   #10
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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.

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Old 02-05-2015, 06:29   #11
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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.
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File Type: png 7550-150501-2210-2229-Terje@SE.png (39.9 KB, 817 views)
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Old 02-05-2015, 13:42   #12
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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.
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Old 03-05-2015, 20:37   #13
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No DRM this evening except for a few short bursts in the beginning at 1745 UTC.
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File Type: png 7550-150503-1834-2026-Terje@SE.png (27.4 KB, 798 views)
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Old 03-05-2015, 22:01   #14
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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.

Alan.
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Old 04-05-2015, 05:02   #15
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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.
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