[Boatanchors] Leonard R. Kahn

[Sheldon Daitch]

One of Kahn's more interesting works is  "Comparison of Linear Single Sideband Transmitters with Envelope Elimination and Restoration Single Sideband Transmitters",- pp 1706-1712 Proceedings of the IRE, December 1956.

Below is a partial list of US patents involving some of his work:

2989707

3350645

4194154

The first two are more related to the use of AM transmitters, CLass C power amplifier, being capable of transmitting an SSB with carrier signal.

As Richard notes, VOA did use some of Kahn's equipment, but as to the best of my memory, at Greenville, the sites were using some units built by Art Brown, based on Kahn's design.  I do remember the Kahn units in the racks, between the MCR console and the area where the three Gates HF-50C units were located.

Been far too long ago, and I have no idea if any of the manuals are still around at Greenville.

73
\Sheldon

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      Some time around the 1960s a fellow named Leonard Kahn
began making a system for transmitting SSB through an AM
transmitter.  He wrote a number of technical papers in peer
reviewed journals and has a pile of patents.  He based his
system on the theory that all modulation is a combination of
amplitude and vector modulation (I have that term wrong but
can't pull the right one out of my head).  Essentially the
system converts whatever is put into it into a frequency
component and an amplitude component. Both can be put
through an AM transmitter. When the outputs are combined
they reform whatever the original signal was. I believe the
VOA used some of these things on their transmitters and may
well have used them for single sideband with carrier. At
least two local broadcast stations used the Kahn system for
SSB with carrier; one was KBIG, which as that time was a
10KW daytime only AM on Catalina island (at 740Khz).  The
other was a station somewhere like San Bernardino that was
causing monkey chatter on an LA station. They also used SSB
with carrier to remove the modulation products that were
causing problems.  One or both of these stations also used
off-set carrier so that the channel center was on the
assigned carrier frequency.  KBIG was always funny sounding
as was its FM counterpart KBIQ.  The owner was also the CE
and who knows what odd-ball stuff was in the air chain.
KBIG, now KBRT had an antenna with a large reflector built
on the side of a cliff. They covered an enormous area with a
weak but steady signal.  They lost the lease on the property
and have moved to Costa Mesa in Orange County. The
difference is that they now interfere with KCBS at night.
     One can make a creditable antenna using the "lazy-H"
arrangement.  This is a very simple curtain antenna,
essentially two half-wave dipoles stacked with a phase
inversion between top and bottom. It is bi-directional but a
second antenna of similar type can be placed just behind it
as a reflector. This gives a reversable pattern with the aid
of a relay.  Lazy-H antennas have reasonably high gain and
are reasonably economical to build.
     Rhombic antennas can work very well but have the
disadvantage of requiring a lot of realestate.  The pattern
is affected by other antennas or conductors like power lines
that are at some distance.  The need for a dissipating
termination can be eliminated by using two rhombics on the
same poles but spaced a little with one being a reflector
for the other.  The price is a reduction of bandwidth.
However, the bandwith of a rhombic is mostly a matter of
constant impedance, the directional pattern varies
substantially with change in frequency.  A good book on
traditional type antennas, including rhombics is "Antennas"
by Edmund La Port. La Port was an engineer for RCA for many
years. The book has photos of things like huge insulators
for 100KW antennas.

--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com

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