Sorry for being such a RX newbie here. I guess I shoulda stayed awake
more during signals class. My expertise is very large switching and
resonant power supplies and transmitters.

So the multipath distortion causes fading of the carrier only?? This
makes some sense to me. A small set of the lower sideband frequencies
would also cause phase cancellation, but since the audio spectrum is
moving around so fast no one notices. I think I'm on the right track
here. So use another carrier slaved to the received carrier and you
get better reception during fade. Even if it wanders a few cycles
during fade you probably don't hear anyway. I guess that is how a sync
detector works.

I Imagine it would be a chore to build a sync detector from the ground
up, but I would also think it must have already been put into an ic
chip, no???

I like the link R2000swl posted to AmWindow for the precision full-wave
rectifier. I think I'll stick it on a pc board and give it a try. If
anybody wants a board let me know. They are very inexpensive.

bm, or anyone else, if you have good link to ELPAF or alternative RX
circuits then maybe I could throw that down on same board if not too
much room.

Details of board size at www.expresspcb.com I do the small one double
side and no silkscreen 3 boiards 60bucks.

You can contact me off board at

73
Bob
N9NEO





bm wrote:
Well, it works.

I have been playing with the ELPAF since last autumn; first on my
R-390A, which, despite having done the AF Deck mod, does have its
quirks with regard to audio quality. The ELPAF cleaned up audio
admirably. Mostly doing MW DX then. Then, this summer together with a
modified IC-703 mostly on SW. It practically eliminates the distortion
caused by fades, as well as high-frequency hiss and noise giving an
audibly better signal to noise ratio. The trade-off is of course a
more limited audio response. Personally I can live with that - I never
use bandwidths wider than 6-7 kHz anyway. My ELPAF has a bypass switch
so it is easy to compare audio quality.

I used to have an SE-3 as well, and enjoyed the excellent audio it
produced. The ELPAF does little less with regard to audio recovery. I
am thinking about doing an A-B comparison between the two later on.

BM

Back to the Future movie is on Radio tv.See if your radio has a Flux
Capacitor.According to the doc,that's what makes time travel possible.
Calling Art Bell,calling George Noory.I found the secret to time travel.
cuhulin

On 30 Jul 2006 09:28:29 -0700, "N9NEO"
wrote:

Sorry for being such a RX newbie here. I guess I shoulda stayed awake
more during signals class. My expertise is very large switching and
resonant power supplies and transmitters.

So the multipath distortion causes fading of the carrier only?? This
makes some sense to me. A small set of the lower sideband frequencies
would also cause phase cancellation, but since the audio spectrum is
moving around so fast no one notices. I think I'm on the right track
here. So use another carrier slaved to the received carrier and you
get better reception during fade. Even if it wanders a few cycles
during fade you probably don't hear anyway. I guess that is how a sync
detector works.

I Imagine it would be a chore to build a sync detector from the ground
up, but I would also think it must have already been put into an ic
chip, no???

I like the link R2000swl posted to AmWindow for the precision full-wave
rectifier. I think I'll stick it on a pc board and give it a try. If
anybody wants a board let me know. They are very inexpensive.

bm, or anyone else, if you have good link to ELPAF or alternative RX
circuits then maybe I could throw that down on same board if not too
much room.

Details of board size at www.expresspcb.com I do the small one double
side and no silkscreen 3 boiards 60bucks.

You can contact me off board at

73
Bob
N9NEO


http://users.adelphia.net/~alexmm/Prod_det/detector.htm

On 30 Jul 2006 09:28:29 -0700, "N9NEO"
wrote:

http://home.att.net/~wa1sov/technical/sync_det.html

David wrote:
On 30 Jul 2006 09:28:29 -0700, "N9NEO"
wrote:

http://home.att.net/~wa1sov/technical/sync_det.html

While this synchronous detector works quite well, there is a link
http://home.worldnet.att.net/~wa1sov/technical/allpass/allpass.html
to a filter that allows improved reception by "rejecting" signals other
then the desired signal. While this does improve reception, it isn't
quite as effective as some literature would suggest.

If you really interested in synch detectors, Tom Holden has an
excellent
page, http://groups.yahoo.com/group/Synch_AM/messages that has
some links to very good resources.

Terry

Thanks Terry, I just signed up.

regards,
Bob


wrote:
David wrote:
On 30 Jul 2006 09:28:29 -0700, "N9NEO"
wrote:

http://home.att.net/~wa1sov/technical/sync_det.html

While this synchronous detector works quite well, there is a link
http://home.worldnet.att.net/~wa1sov/technical/allpass/allpass.html
to a filter that allows improved reception by "rejecting" signals other
then the desired signal. While this does improve reception, it isn't
quite as effective as some literature would suggest.

If you really interested in synch detectors, Tom Holden has an
excellent
page, http://groups.yahoo.com/group/Synch_AM/messages that has
some links to very good resources.

Terry

N9NEO wrote:
So the multipath distortion causes fading of the carrier only?? This
makes some sense to me. A small set of the lower sideband frequencies
would also cause phase cancellation, but since the audio spectrum is
moving around so fast no one notices. I think I'm on the right track

No, a simple 2-path is effectively a comb filter with the separation
between
frequencies of constructive and destructive interference determined by
the
difference in propagation delay. With enough delay, this separation can
be
much less than the bandwidth of the desired signal, causing multiple
cancellations within the passband. The delay difference is not a
constant
due to the roiling ionosphere so the frequencies at which destructive
interference occurs and their separations are constantly changing. The
severest form of distortion is when a cancellation occurs at the
carrier
frequency but if you have ever heard of 'flanging' in the recording
industry, you'll know what the interference effect can be when a
cancellation occurs in the sidebands. It is is very noticeable.

So use another carrier slaved to the received carrier and you
get better reception during fade. Even if it wanders a few cycles
during fade you probably don't hear anyway. I guess that is how a sync
detector works.

That's basically it.

Tom