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Old 23-02-2005, 08:10   #1
dk8cb
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BR Ismaning, 6085 kHz

BR Ismaning is currently testing on 6085 kHz.

Audio level is much too low. There is a strong residual carrier, perhaps a converted non-linear transmitter and a Telefunken DMOD 2 exciter are being used.

A few minutes ago, transmission was carried out with spectrum inverted.

Now (09:05 UTC), they have switched back to AM.

Roland
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Old 23-02-2005, 08:10   #2
Radioratte
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Bayerischer Rundfunk 6085

My first record from BR 5 on 6085 kHz! Just five minutes of test ransmissions, and with a lot of blackouts.

Vy 73

Radioratte
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Old 23-02-2005, 08:26   #3
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There will be more tests starting March 1st.
Regular transmissions on 6085 kHz may start on March 7.
73, Klaus
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Old 23-02-2005, 18:13   #4
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Hi all,
here are my results for BRīs tests this morning, only an unattended log, but great to see another member of the ARD start test transmissions in DRM !
73, Simone
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Old 06-03-2005, 14:38   #5
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Hi all,
if everything runs as it is planned, there will be again a DRM test on Monday, 7/3 between 8.00 and 09:00 UTC.
73, Klaus
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Old 07-03-2005, 09:35   #6
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Hi all,
much better audio quality today, but still with a carrier.
See screenshot.
73, Klaus
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Old 07-03-2005, 09:46   #7
dk8cb
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Quote:
Originally posted by Baldo34
... but still with a carrier.

Hi Klaus,

this is normal, if a modified AM transmitter with a class-C final stage and the original anode modulation transformer is used. Some time ago, it was thought, that such a setup would be totally unsuitable for DRM. But with Telefunken's DMOD2 modulator, a linearity correction circuit has allowed to use such transmitters for DRM as well. One cannot expect a high SNR under such circumstances however. Also, the overall transmitter efficiency will not be as good as on a "real" DRM transmitter.

Roland
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Old 07-03-2005, 13:59   #8
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Hi all,
here are my results of the test transmission this morning, good results only in the last minutes, also quite good SNR for this modified transmitter then.
73, Simone
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Old 08-03-2005, 07:24   #9
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Hi Roland,
thanks for this information. But the relatively low SNR causes problems in practice. Because of the unstable propagation conditions on shortwave (geomagnetic disturbances, fading etc..) the necessary reserve for a troublefree decoding is missing.
AFAIK the Junglinster transmitters are much older. How did they manage these problems?
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Old 08-03-2005, 18:30   #10
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Quote:
Originally posted by Baldo34
AFAIK the Junglinster transmitters are much older. How did they manage these problems?

There is some information about the transmitter on these pages:
http://www.drmradio.co.uk/html/junglinster.html

http://members.aon.at/wabweb/radio/rtl.htm

On the latter page, one can find information that the transmitter is not running in its normal non-linear class-C AM configuration with full power but instead with the tube operating in linear (class-A) mode at much reduced power.
In this mode, transmitter tuning is different, voltages have to be changed and the AM modulator has to be switched off. Perhaps some permanent modifications are also required.
I guess that, if the transmitter is to be used for both AM and DRM in a switchover mode as is done on 6085 kHz, a linearity correction using a DMOD2 is much easier to implement.

But perhaps someone from the station can give some more information on that. (lx1nw?)

Roland
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Old 08-03-2005, 20:24   #11
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Hi Klaus,

Quote:
Originally posted by Baldo34

... But the relatively low SNR causes problems in practice. Because of the unstable propagation conditions on shortwave (geomagnetic disturbances, fading etc..) the necessary reserve for a troublefree decoding is missing.
Interestingly my experience was quite the opposite, unfortunately the results from the early days are not available anymore on the forum, but whenever there was a problem limiting the SNR at the Tx I got better decoding ( as long as it was not at the threshold of the required SNR for a given coderate). Maybe the software decoders handle a more stable but even lower SNR better.
73, Simone
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Old 06-04-2005, 06:52   #12
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Hi all,
next test transmission on 6085 kHz today (April 6th) between 10:15 UTC and 11:15 UTC, again with a carrier. The carrier will be eliminated at the end of May.
73, Klaus
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Old 06-04-2005, 10:31   #13
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The signal strength is ok, up to 9+ 30dB.
Because of the carrier SNR is low with many dropouts.
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Old 06-04-2005, 10:33   #14
dk8cb
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Local reception in Munich (Sendling Westpark)

Hi,

it seems that the audio level is a bit too high. Compared to BBC 7320 kHz, audio is much louder.
There also seems to be some audio distortion.

Even at this short distance, reception is clearly mostly ionospheric with strong fluctuations, see attached impulse response.

Roland
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Old 06-04-2005, 12:52   #15
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Hi all,
lots of dropouts on BRīs test this morning, also very high audio levels, see attachment
73, Simone
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