[Elecraft] SWL with KX1

Fri Dec 5 00:47:01 2003

Just as a correction, synchronous detection doesn't imply receiving only the
upper or lower sideband.  Synchronous detection means that the receiver
generates it own constant-amplitude carrier which is phase-coherent with the
incoming signal's carrier.  This locally-generated carrier is used to feed
one input of a product detector, with the second product detector input
being the received signal.

During selective fading of  AM signals, it's common for the carrier to fade
but at least one sideband remains strong. The advantage of synchronous
detection is that it eliminates the severe distortion caused by selective
fading (which results in a received modulation index greater than 1.0)
because the received carrier amplitude is constant.

Many receivers that employ synchronous detection also allow you to select
the sideband, which can substantially minimize interference in some cases.
An SSB receiver can serve as a pseudo-synchronous detector by carefully
tuning for zero beat.  But the SSB receiver's BFO and the incoming carrier
can never maintain phase coherence, so you'll always have some distortion
(worse with music where the IMD really shows up).

Scott
N7NB

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Phil Wheeler
Sent: Thursday, 04 December, 2003 20:41
Cc: [email protected]
Subject: [Elecraft] SWL with KX1

First, I appologize for not having as yet any quantitative comparisons
to my SWL receivers.  A minor point, but none of them have BNC
connectors.  So my assessment is pretty qualitative.  More will follow.

I've spent three evenings listening (casually, while doing other things)
to a variety of stations on 31 meters using my 30 m dipole.  Lots of
audio (no surprise).  Audio quality is very nice with filter set to full
width .. better than I expected.  Both usb and lsb are good.  And that
brings up a major point: One of the high-end features of pricy SWL
receivers is "synchronous detection" which simply means you can listen
to ether the upper or lower sideband.  This feature is inherent in the
KX1 design.

When I get more serious with this comparison, I expect the following:

o SWL receivers will be more sensitive with very short antennas (4-6 ft)
o The KX1 will hold its own on any antenna capable of ham ops (e.g. 20
ft wire)
o SWL receivers will overload on such antennas (all but the best of them)
o The KX1 will show much better selectivity (e.g., rejection of that
station 5 KHz away)
o SWL receivers will work much better on LW/MW/FM bands (not tunable
with the KX1)

Soon I will test the KX1 and several SWL receivers (Sony ICF SW-100,
Sangean ATS-909, etc.) and the KX1 with the sort of antenna I use when
backpacking and in European hotels: Reel-type antennas in the 8-16 ft
range.  Whatever the results, the KX1 will be with me in the Sierras
(Yosemite and Mammoth) in Feb and in Greece in May.  The very best SWL
receivers are not great for making CW contacts :-)

73, Phil

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