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 <k6uj@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
|