Larry Dighera wrote:


This is a first draft. Critique, corrections, and suggestions for
improvement and inadvertently omitted information welcome.





AM Synchronous Detector Review: Sony ICF-2010 vs RL Drake R8B

Two terrific SWL receivers with comparable performance up to a point.

Operating technique differs between these two synchronous detectors.
Because a synchronous detector is phase-locked on the station's
carrier frequency, it is able to overcome phase distortion introduced
in the incoming signal by dynamics and irregularities in the Earth's
ionosphere and magnetosphere.

The distortion is caused by selective fading where the carrier is reduced in
amplitude resulting in the equivalent of an over modulated signal. It is
the effective overmodulation that results in a distorted signal when using
a peak detector.

The restoration of the signal's phase
relationship results in a significant increase in readability. Both
receivers' synchronous detectors are enabled by pressing the
respective 'Sync' button.

Rather than 'restoring the phase', you are switching from a peak detector to
a product detector which does not rely upon receiving a carrier to
demodulate the signal. A product detector has two inputs, one being the
received signal, the other being a locally generated frequency (I choose
not to say carrier). In a sync detector, the locally generated frequency is
phase locked to what remains of the received signal's carrier. (Note, by
using SSB you are doing the same thing, EXCEPT the locally generated
frequency is not locked to the incoming signal. Thus fine tuning is needed
when using SSB. I don't call this ECSS, because the you do not Exhault the
Carrier.)

The difference in their operation occurs
when adjusting the other signal enhancing function of this remarkable
AM detector.

One of the primary tools employed by the radio operator is the
selection of bandwidth appropriate to the current reception
conditions. Narrowing the bandwidth is effective in removing two
additional types of signal degrading effects: atmospheric noise, and
adjacent channel splatter and heterodyne. T?he AM synchronous
detector provides the means to continue the exploit of this bandwidth
narrowing philosophy significantly by providing the means to further
restrict the detection envelope to only a single sideband of the
inherently double-sideband AM signal

Without the sync detector one can still narrow the bandwidth to include one
sideband and the carrier.

snip

Hope this helps

craigm