"Ken" wrote in message
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I am building the Ramsey Electronics DDF-1 doppler DF. This uses
four 1/4 wave whip antennas on the corners of a square approximately
1/4 wavelength on a side. These are connected to a rooftop switcher
that activates each antenna in sequence. See:

http://www.ramseyelectronics.com/cgi...ction&key=DDF1

My question is, How dependent is this rig on proper whip length to
function properly? Does sensitivity suffer if my whips are
significantly too short, or does the thing simply stop working
properly?

I want to use it for 6M. I have the room for the 55" antenna spacing,
but my antennas are only around 24" long.

Ken KC2JDY

Ken
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Ken,

Very familiar with the "Doppler" type system. You may very well be
better off with non resonant whips. When you have whips near resonance, you
are subject to the phase shift due to small differences due to being
slightly above or below resonance. A test should be to put all the whips
very close together, in a line and receive a signal from broadside (so all
antennas are equidistant from the source...assuming you have a single path
as from a nearby hand held) Then you verify that the pulses out of the
discriminator are non existent.

Shorter whips mean reduced sensitivity. Not all that desirable in a Doppler
since it suffers already. It is nothing other than receiving a 6M signal on
any other 24" whip.