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DRM 3995
The past few evenings I've tuned up to the top of the 75 meter band to see what
effect DRM on 3995 has on the band and it's atrocious. DRM = QRM dxAce Michigan USA |
In article , dxAce
wrote: The past few evenings I've tuned up to the top of the 75 meter band to see what effect DRM on 3995 has on the band and it's atrocious. DRM = QRM That's one of the neat things about technology is predictability. DRM claims about better audio in the same bandwidth is BS as are the non adjacent channel interference clams. -- Telamon Ventura, California |
Telamon wrote: In article , dxAce wrote: The past few evenings I've tuned up to the top of the 75 meter band to see what effect DRM on 3995 has on the band and it's atrocious. DRM = QRM That's one of the neat things about technology is predictability. DRM claims about better audio in the same bandwidth is BS as are the non adjacent channel interference clams. Yep, I just checked the signal a few minutes ago on 3995 and it wipes out at least the top 10 kHz of the band. dxAce Michigan USA |
In article , dxAce
wrote: Telamon wrote: In article , dxAce wrote: The past few evenings I've tuned up to the top of the 75 meter band to see what effect DRM on 3995 has on the band and it's atrocious. DRM = QRM That's one of the neat things about technology is predictability. DRM claims about better audio in the same bandwidth is BS as are the non adjacent channel interference clams. Yep, I just checked the signal a few minutes ago on 3995 and it wipes out at least the top 10 kHz of the band. How about below? The upper harmonics are a sure thing but I expect the DRM signal to spread out as far below the frequency transmitted on. Digital signals spread out above and below the frequency they are on. Upper frequency spread is from multiple carrier mixing products and higher frequency harmonics of the fast switching edges and phase noise or random jitter. The low frequency spread is from data dependent effects or data dependent jitter and the data mixing with the carriers. -- Telamon Ventura, California |
Telamon wrote: In article , dxAce wrote: Telamon wrote: In article , dxAce wrote: The past few evenings I've tuned up to the top of the 75 meter band to see what effect DRM on 3995 has on the band and it's atrocious. DRM = QRM That's one of the neat things about technology is predictability. DRM claims about better audio in the same bandwidth is BS as are the non adjacent channel interference clams. Yep, I just checked the signal a few minutes ago on 3995 and it wipes out at least the top 10 kHz of the band. How about below? The upper harmonics are a sure thing but I expect the DRM signal to spread out as far below the frequency transmitted on. Digital signals spread out above and below the frequency they are on. Upper frequency spread is from multiple carrier mixing products and higher frequency harmonics of the fast switching edges and phase noise or random jitter. The low frequency spread is from data dependent effects or data dependent jitter and the data mixing with the carriers. Well I did mention the top 10 kHz of the band. Apparently the signal is centered on 3995, and it is certainly audible both above and below that point. In the few times I've checked recently I've not noticed any amateur use of that range when the DRM signal is on. It's a mess! dxAce Michigan USA |
In article ,
Telamon wrote: How about below? The upper harmonics are a sure thing but I expect the DRM signal to spread out as far below the frequency transmitted on. Digital signals spread out above and below the frequency they are on. Upper frequency spread is from multiple carrier mixing products and higher frequency harmonics of the fast switching edges and phase noise or random jitter. The low frequency spread is from data dependent effects or data dependent jitter and the data mixing with the carriers. Huh? There're no fast edges. It's a COFDM signal that consists of hundreds of closely spaced subcarriers modulated as some slow baud rate (around 30-50 Hz). It shouldn't slop over much, but it'll fill up all the spectrum it's using. It's very similar to a FDM telegraph (Droning DC-3) signal, only about 5-20 times as wide. Mark Zenier Washington State resident |
dxAce wrote in message ...
The past few evenings I've tuned up to the top of the 75 meter band to see what effect DRM on 3995 has on the band and it's atrocious. DRM = QRM dxAce Michigan USA What is DRM?? Some kind of digital communications?? Steve P.S. sorry if this is a dumn question. |
Steve wrote: dxAce wrote in message ... The past few evenings I've tuned up to the top of the 75 meter band to see what effect DRM on 3995 has on the band and it's atrocious. DRM = QRM dxAce Michigan USA What is DRM?? Some kind of digital communications?? Yes, it is radio transmitted digitally. Give a listen up on 3995 in our North American evenings and listen to the QRM. And then try and imagine what that sort of thing will do to the other shortwave broadcasting bands. dxAce Michigan USA |
Screw DRM,
If I want to listen to digital radio I'll just buy an XM radio or listen to internet radio. For me, I like my shortwave analogue since it's an escape from all the digital stuff. |
Ok, yeah, I used to talk with a group on 3985 in the evenings and I
always noticed that from about 3995 on up it the band was trashed.. Steve dxAce wrote in message ... Steve wrote: dxAce wrote in message ... The past few evenings I've tuned up to the top of the 75 meter band to see what effect DRM on 3995 has on the band and it's atrocious. DRM = QRM dxAce Michigan USA What is DRM?? Some kind of digital communications?? Yes, it is radio transmitted digitally. Give a listen up on 3995 in our North American evenings and listen to the QRM. And then try and imagine what that sort of thing will do to the other shortwave broadcasting bands. dxAce Michigan USA |
In article , dxAce wrote:
Steve wrote: dxAce wrote in message ... The past few evenings I've tuned up to the top of the 75 meter band to see what effect DRM on 3995 has on the band and it's atrocious. DRM = QRM dxAce Michigan USA What is DRM?? Some kind of digital communications?? Yes, it is radio transmitted digitally. Give a listen up on 3995 in our North American evenings and listen to the QRM. And then try and imagine what that sort of thing will do to the other shortwave broadcasting bands. You don't have to imagine, just tune to 9800 from about 21:00 to 2:00 UTC. That's RCI's Sackville DRM transmission. Mark Zenier Washington State resident |
In article , dxAce
wrote: Steve wrote: dxAce wrote in message ... The past few evenings I've tuned up to the top of the 75 meter band to see what effect DRM on 3995 has on the band and it's atrocious. DRM = QRM dxAce Michigan USA What is DRM?? Some kind of digital communications?? Yes, it is radio transmitted digitally. Give a listen up on 3995 in our North American evenings and listen to the QRM. And then try and imagine what that sort of thing will do to the other shortwave broadcasting bands. The acronym stands for Deception Radio Mondiale. -- Telamon Ventura, California |
In article ,
Telamon wrote: In article , (Mark Zenier) wrote: Huh? There're no fast edges. It's a COFDM signal that consists of hundreds of closely spaced subcarriers modulated as some slow baud rate (around 30-50 Hz). It shouldn't slop over much, but it'll fill up all the spectrum it's using. It's very similar to a FDM telegraph (Droning DC-3) signal, only about 5-20 times as wide. Mark Zenier Washington State resident There are not hundreds of carriers. I believe the number is sixteen. It is not the rate that they are switched at but how fast they actually turn on and off. Think dV/dT. The unfortunately vague article I found (Elektor Electronics, Dec. 2002) said that the (sub)carrier spacing is 66.666 Hz, and that they use 64 QAM modulation. So there are somewhere around 160 subcarriers in a 10 kHz wide signal) and at 6 bits per baud the baud rate must be in the 20-40 Hz range. (As I understand it, the signal is around 40 kBPS). (There's more tolerant form that uses 16-QAM). Mark Zenier Washington State resident |
In article ,
(Mark Zenier) wrote: In article , Telamon wrote: In article , (Mark Zenier) wrote: Huh? There're no fast edges. It's a COFDM signal that consists of hundreds of closely spaced subcarriers modulated as some slow baud rate (around 30-50 Hz). It shouldn't slop over much, but it'll fill up all the spectrum it's using. It's very similar to a FDM telegraph (Droning DC-3) signal, only about 5-20 times as wide. Mark Zenier Washington State resident There are not hundreds of carriers. I believe the number is sixteen. It is not the rate that they are switched at but how fast they actually turn on and off. Think dV/dT. The unfortunately vague article I found (Elektor Electronics, Dec. 2002) said that the (sub)carrier spacing is 66.666 Hz, and that they use 64 QAM modulation. So there are somewhere around 160 subcarriers in a 10 kHz wide signal) and at 6 bits per baud the baud rate must be in the 20-40 Hz range. (As I understand it, the signal is around 40 kBPS). (There's more tolerant form that uses 16-QAM). Any time you digitally modulate RF it will spread out from the carrier frequency. Now you can use a system like QAM -16 or 64 to minimize this but it still spreads out and occupies more spectrum than the bandwidth allocated. Their are many switching and mixing products that cause digitally modulated RF to spread out above and below the carrier frequency. From plots I've seen you are at best *(averaged) 60 dBc 30 KHz away from carrier center. This means it will easily wipe out the adjacent channels and weak signals 2 channels away from it. * Peak is much worse. For weak signal work that's 40KHz of spectrum with digital buzz for a 9-10 KHz DRM signal and that is when things are working right. -- Telamon Ventura, California |
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