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

In article ,
(Mark Zenier) wrote:

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

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.

--
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