craigm wrote:
wrote:

Hello everyone,
I buy the above book, quite useful it is too. There are one or two
things about it which I find hard to fathom. Why do they go on so much
about synchronous detector features on receivers? I own a dozen or so
receivers, some with and some without. The ones without the SD are not
that much more useful than a receiver with it. For example, my
ATS909/DX398 does not have it but my Sony SW7600GR does. For me, the
ATS is still, marginally a better receiver for my needs. My Sony SW77
does not really seem to be much better when the SD is on and on my AOR
7030, well the receiver is that good with a good antenna that I never
ever need it. With my Sat'800 it's also not that useful although on
occassions it has helped.


For some signals, the synchronous detector is very helpful at removing
distortion from selective fading. If you don't experience selective
fading, then you won't see the improvement.

Selective fading is a result of signal propogation and is different than
fading that affects all parts of the signal at the same time.

The sync detector can also help with some types of interference, but if
you are not experiencing them, you may not see the benefit.

For me, the sync detector is very helpful.



My other bug bear is that they plugged and plugged the Sat'800 when it
first came out and it was a pretty poor thing in my book. Much better
now and I would not sell mine but in the beginning they seemed blind to
it's quality control.



I would probably say it was Eton that plugged and plugged the Sat 800.
They are the ones who pay for the advertising space. (Either directly,
or via ad co-op with the resellers.)

You also have to admit there are very few new radios introduced, so when
something new comes along, it gets a lot of attention. When the
manufacturer hypes the product months before its release (as Eton
does)there will be lots of press visibility.


Oh and one more thing, why oh why do they harp on about receivers
showing the time and frequency at the same time? Useful, yes I know but
not that important. I own a watch and a clock and I am quite good at
using them. Moan over....


I don't understand that one either.

A selectable sideband sync' detector can be very effective for reducing
interference from stations on an adjacent frequency from the one you're
trying to hear. This is a very common problem with shortwave listening
and the sideband sync' detector is a good solution. Of course this only
works for AM signals not SSB.

As i understand it when a AM signal fades you can sometimes still hear the
modulation content but without the AM carrier to support it so it sounds
garbled like listening to a SSB signal on AM, so the SD circuit is adding
the carrier back to the signal sync'd to the original carrier so it does'nt
beat against the existing AM carrier and cause a heterodyne and then the
audio does'nt distort when it looses it supporting carrier because of the
receiver has generated it own carrier.
Correct me if i'm wrong.....




"HFguy" wrote in message news:OXuvf.1$7l4.0@trndny03...
craigm wrote:
wrote:

Hello everyone,
I buy the above book, quite useful it is too. There are one or two
things about it which I find hard to fathom. Why do they go on so much
about synchronous detector features on receivers? I own a dozen or so
receivers, some with and some without. The ones without the SD are not
that much more useful than a receiver with it. For example, my
ATS909/DX398 does not have it but my Sony SW7600GR does. For me, the
ATS is still, marginally a better receiver for my needs. My Sony SW77
does not really seem to be much better when the SD is on and on my AOR
7030, well the receiver is that good with a good antenna that I never
ever need it. With my Sat'800 it's also not that useful although on
occassions it has helped.


For some signals, the synchronous detector is very helpful at removing
distortion from selective fading. If you don't experience selective
fading, then you won't see the improvement.

Selective fading is a result of signal propogation and is different than
fading that affects all parts of the signal at the same time.

The sync detector can also help with some types of interference, but if
you are not experiencing them, you may not see the benefit.

For me, the sync detector is very helpful.



My other bug bear is that they plugged and plugged the Sat'800 when it
first came out and it was a pretty poor thing in my book. Much better
now and I would not sell mine but in the beginning they seemed blind to
it's quality control.



I would probably say it was Eton that plugged and plugged the Sat 800.
They are the ones who pay for the advertising space. (Either directly, or
via ad co-op with the resellers.)

You also have to admit there are very few new radios introduced, so when
something new comes along, it gets a lot of attention. When the
manufacturer hypes the product months before its release (as Eton
does)there will be lots of press visibility.


Oh and one more thing, why oh why do they harp on about receivers
showing the time and frequency at the same time? Useful, yes I know but
not that important. I own a watch and a clock and I am quite good at
using them. Moan over....


I don't understand that one either.

A selectable sideband sync' detector can be very effective for reducing
interference from stations on an adjacent frequency from the one you're
trying to hear. This is a very common problem with shortwave listening and
the sideband sync' detector is a good solution. Of course this only works
for AM signals not SSB.

wayne wrote:
As i understand it when a AM signal fades you can sometimes still hear the
modulation content but without the AM carrier to support it so it sounds
garbled like listening to a SSB signal on AM, so the SD circuit is adding
the carrier back to the signal sync'd to the original carrier so it does'nt
beat against the existing AM carrier and cause a heterodyne and then the
audio does'nt distort when it looses it supporting carrier because of the
receiver has generated it own carrier.
Correct me if i'm wrong.....

You're essentially correct. When the signal fades it changes the phase
relationship between the carrier and the audio sidebands, which produces
distortion. A sync' detector replaces the defective received carrier
with a locally generated 'clean' one.

http://www.hard-core-dx.com/nordicdx...al/fading.html

http://nitehawk.com/sm5bsz/linuxdsp/selfade/selfade.htm

HF Guy...

Good post and great links!

"HFguy" wrote in message
news:ZU2wf.979$ID1.548@trndny01...
wayne wrote:
As i understand it when a AM signal fades you can sometimes still hear
the
modulation content but without the AM carrier to support it so it sounds
garbled like listening to a SSB signal on AM, so the SD circuit is
adding
the carrier back to the signal sync'd to the original carrier so it
does'nt
beat against the existing AM carrier and cause a heterodyne and then the
audio does'nt distort when it looses it supporting carrier because of
the
receiver has generated it own carrier.
Correct me if i'm wrong.....

You're essentially correct. When the signal fades it changes the phase
relationship between the carrier and the audio sidebands, which produces
distortion. A sync' detector replaces the defective received carrier
with a locally generated 'clean' one.

http://www.hard-core-dx.com/nordicdx...al/fading.html

http://nitehawk.com/sm5bsz/linuxdsp/selfade/selfade.htm