Topband: Detuning transmittting antenna

[Paul Elliott]

My QTH is a 129 x 120 foot city lot in SE New Mexico.  The transmitting
antenna is an inverted L, exact length unknown but longer than ¼ wavelength.
By trial and error, it was made that length which, when the inductive
reactance is tuned out by a capacitor (about 180 pf), the SWR is 1:1 at 1827
kc (oops, kHz) as close as my crude instrumentation can tell.  It does
reradiate enough noise, if not detuned, to mask weak signals on my receiving
antennas:  two small EWEs, a 12 foot diameter untuned loop, and a 100 foot
piece of wire 2 feet off the ground 6 inches from a concrete block fence.
(FWIW that piece of wire was the only antenna on which I could receive
HB0/DL2OBO when I worked him on160 m about two weeks ago).  I have detuned
the antenna by using a relay to open the connection between the capacitor
and the coax feedline when receiving.  I would like to get the relay out of
that high current point-- and also I do not want to transmit into an open
load if the relay fails.

 

I would like to do the detuning at the shack end by connecting some detuning
network to the coax with a small relay when receiving.  Can someone please
tell me a good starting point and/or procedure—thereby possibly saving me a
lot of time?  I do not use QSK so timing is no problem.

 

Today, on the 70th  anniversary of the date of issuance of my first ham
license, I thank those who have shared their knowledge and expertise—a
special thanks to W4ZV for this reflector, to W8JI who helped me from the
time I started on topband about 12 years ago,  and to N5UL for his many
insights and patience  It has been fun!—149 DXCC topband on the books, three
more cards in hand and waiting for two more.

 

73 Paul W5DM