A previous edition (and maybe the current one) of the Low Band DXing book has several methods of detuning TX antennas...might be worth a look. Some can be done right in the shack.
73 Charlie, N0TT On Sun, 17 Jun 2012 13:37:55 -0700 Bob K6UJ <k...@pacbell.net> writes: > I am very interested in this subject, I am trying to figure out how > to detune my 160 inverted L. I am using a flag antenna for > receive and unfortunately > it is only about 50 feet from the base of the L. By itself the > flag works very well at reducing the local electrical noise, (which > luckily it is coming from only one direction) > When the L is strung up it the flag is useless, it reradiates the > noise like mad. I'm hoping to learn more solutions on detuning > xmit antennas during receive from the group. > Wouldn't it be nice if all we had to do was ground the feedline to > the xmit antenna during receive ? sigh................ I > guess the idea is to make the xmit antenna non resonant anywhere > near > the operating freq during receive. > > Bob > K6UJ > > On Jun 17, 2012, at 8:03 AM, W2XJ wrote: > > > There is no single solution for detuning an antenna it depends on > > > electrical length. For verticals a quarter wavelength or less it > is > > common to have a contactor between the network and the radiating > element > > and open the connection to float that element. This is the > practice in > > commercial directional arrays where some tower are not used in a > day or > > night mode. This does not work well on taller towers and I do not > know > > offhand how it would work with the T. It is easy enough to model > in EZNEC. > > > > On 6/16/12 3:02 PM, Shoppa, Tim wrote: > >> OK, several folks came back and recommended detuning my transmit > antenna in receive. > >> > >> Certainly any receive antenna I have is going to be in the shadow > of my transmit antenna, a 130-foot flat-top about 85 feet up, fed > against ground. (Really it's an 80 meter doublet fed with ladder > line. I tie the ladder line together at the bottom and feed against > ground.) > >> > >> Trying to figure out what "detune" is. > >> > >> I match the transmit antenna to 50 ohm coax with a L network at > the bottom. If I want to detune, then I can.... open up the > connection between the antenna and the L network at the bottom? > Unhook the L or C in the L network? Short out the antenna where it > comes into the L network? I could rig up a relay contact to do any > of those. > >> > >> Tim N3QE > >> _______________________________________________ > >> UR RST IS ... ... ..9 QSB QSB - hw? BK > >> > > _______________________________________________ > > UR RST IS ... ... ..9 QSB QSB - hw? BK > > _______________________________________________ > UR RST IS ... ... ..9 QSB QSB - hw? BK > > _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK