I have a 13 foot x 6 foot flag and a 60 foot base loaded vertical on
a smaller lot than Remi's, and I have found that the decoupling issue
is exceedingly important, especially since the flag gives such a
modest (but generally worthwhile) improvement in S/N.
On 160m, my flag is about 0.05 wavelengths away from the vertical. I
have a convenient built-in ability to detune it because the antenna
has matching networks for 30m and down selected by a motorized rotary
switch... I set up a footswitched T/R system to move the switch a
half-position to disconnect the vertical from the loading coil, and
when I A/B the flag with the resonant TX antenna connected and
disconnected I can get between a 3 and 7 S-unit difference for signals
off the rear of the flag! (Sorry I don't have that in dB... I didn't
measure it, I just wanted to eliminate it).
The situation is better when the TX vertical is located directly off
the back of the flag, but there's still a major degradation of the
pattern from what I can hear. No surprises here. EZNEC shows that
the flag + vertical pattern is almost completely omnidirectional for
most orientations of the flag. It's got some directivity if the flag
is pointed directly away, but it's significantly degraded.
I bet a DPDT relay (sped up ... plenty of discussion here lately) at
the dipole feedpoint would suffice to get the TX antenna out of the
picture as far as pickup and reradiation goes. QSK is tough but 10WPM
QSK at least relaxes the speed requirements a little. A couple of
floating quarterwaves won't cause trouble.
The tower probably needs a resonant detuning section... sending a copy
of Low Band DXing along really does sound like a great idea... all
this is in there.
For what it's worth, the flag is really starting to shine now that
major thunderstorm activity is cropping up in the states. I've been
using it more on 80m than 160 and listening to EU and it's nice to
have your back to the QRN, so to speak.
73,
Dan
_______________________________________________
Topband mailing list
Topband@contesting.com
http://lists.contesting.com/mailman/listinfo/topband
|