[Premium-Rx] Comparing AM Synch Detection to AM Product Detection

[Gary Geissinger]

Hi Guys,

I agree with Tom.  There are times when I like both as well.

The SAM detector can follow drifts in the apparent received frequency.
Also, it stops the "woosh-woosh" sound (sounds like a phaser/flanger on
an electric guitar) when the transmitter is not exactly on the right
channel.  The Sherwood SE-3 is high fidelity; it sounds really, really
nice on music!

The SSB detector is a better choice for weak signal / interference
cases.  For example, listening to 100 watt station IDs in the tropical
bands.

I've compared several:

Sherwood SE-3
WJ HF-1000
Drake R-8B
Icom R-75 with/without Kiwa mods
Homebrew analog from QEX article
Homebrew DSP (future article I want to write)

The Sherwood unit is a little harder to drive (must offset tune Rx for
good results), but the fidelity is great.
The HF-1000 (USB ONLY) is just okay.  It can get screwed up by
propagation, interference, and weak signals.
The Drake R-8B is easy to use and pretty robust.  Probably the best out
of the box for an internal SAM unit.
The R-75 stock SAM is marginal and can get fooled (like HF-1000), but
much better with the Kiwa mods; then about equal to R-8B.
The QEX article SAM unit is actually quite good, once you get used to
using it.
My homebrew one locks on and stays locked, but the fidelity is not as
clean as a good analog SAM detector.  Sample rate is relatively low, so
there is some phase noise to contend with.

I hope this helps,

Gary WA0SPM



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-----Original Message-----
From: premium-rx-bounces at ml.skirrow.org
[mailto:premium-rx-bounces at ml.skirrow.org] On Behalf Of Tom M.
Sent: Friday, May 20, 2005 6:45 AM
To: Ahmet Gundes; Premium-RX
Subject: Re: [Premium-Rx] Comparing AM Synch Detection to AM Product
Detection


Depending on the rig, the sync detector may offer a bit more advantage
as the lock range may as high as +/- 2 KHz or so.  In product detection
you're pinned to the frequency of interest.  Adjacent channels that are
a problem can be partially avoided by the sync detect lock range (i.e.
if you're desired freq is 870 Khz and you have adjacent channel on 860
Khz, sync detector may allow you to tune 872 Khz and still remain locked
on.  

Also, if the frequency generation device drifts at all, product
detection will noticeably change freq while the sync detect will stay
locked on and you won't notice it in the pitch of the sound.

All this said, product detection still works perfectly fine.  Gives one
the opportunity to fiddle with the dials.  

The sync detect adds a bit of gee whiz factor.  I have rigs with both
and like both.

73 Tom N5OFF
--- Ahmet Gundes <ahmet-m at usa.com> wrote:
> 
> Hello everybody.
> 
> I am wondering how Synchronized AM Detection would compare to regular 
> Product Detection of AM signals (detecting it as SSB signal).  The 
> only difference in the Synch detection is
> basically RF and LO at the Product Detector are in Phase.  Does this
offer
> any
> added benefit such as improved Audio quality, better fighting
Fading,... etc
> ?
> 
> The reason of this question is that I am comparing the two methods and

> I am not sure if there really is any difference as far as my ears can 
> distinguish. The Sync detection being
> a more complicated circuitry and requires better design, is it worth
the
> effort ?
> 
> I am not too sure but I think the mathematical formula for both 
> methods comes down to same after the multliplication.
> 
> Regards to all.
> Ahmet
> 
> 
> 
> 
> 
> --
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