Dear Topbander,
as having got more than several requests for information about my full size
dipoles 4SQR for 160m a'la K8UR which photos have been found by enquiries on
my pages www.ok1rd.com in connection with my previous comments on Topband
Digest sides, let me shortly answer them this way.
Somebody maybe know that I operate instead of home QTH a remote controlled
QTH too on low bands mainly. I found soon that I need more de-excitation
power there on remote site to balance excellent reception conditions from
Beverages field. A shunt fed tower produced power on not enough level as
needed. Increasing power by PA output was not efficient too because mains
coming there to telecommunication cot from near-by village offers just 16kVA
input. So being pushed on the idea to reach 300 DXCC countries on the
Topband as soon as possible / now with 4SQR help 295cfmd and 298 wrkd / the
only way was to build directional antenna system for 160m band. Because each
of us has a different conditions on Topband, having a 45m high tower there I
quickly decided that dipoles 4SQR would be the best solution for my case. I
heightened tower up to 60m of height built dipoles and phased them by
phasing system a'la Comtek on 90deg. phasing shift. The system worked but
nothing much so I found in popular ON4UN's Low bands Dxing ( thanks John )
better phasing system 0-137-263degs.so called cross-fire with optimised
phasing. I set up this system accurately using Mini VNA on needed phasing
terms. I found unbelievable change, first of all the system started to
listen almost as well as over 400m Beverages and statistically measured F/B
suddenly was 26dB and F/S much better close to 30dB ( maybe against physics
). I don't want to bore you but if somebody has chance to build this system,
go ahead soon because it is worth to build one for sure.
A few practice notes to avoid research work I had to pass:
1/ the dipoles should be trimmed separately always one by one up to support
2/ tune each dipole on 1790 kHz frequency exactly identical
3/ phasing leads ( coax ) 1/4 WL on asking operation frequency - do not
forget use for both measuring proper coax lenght
4/ each coax feeder must have on the dipole end a good balun; in my case a
big Amidons cores laced on coax to reach inductance over
100microH on 160m and further you should take care about connection into the
dipole centre
5/ set up phasing box exactly into correct magnitude phases, the VNA or
similar analyser is must
6/ matching from phasing box to 50 Ohm coax feeder is recommended
If kept the notes above one would be recompensated by excellent directional
antenna for Topband I am sure. In conjunction with proper Beverages
listening system I would not see better low bands tool except 9 circle, I
guess ( next year maybe Hi ).
Good luck to all courageous best Dxing and
73 Jarda, OK1RD&OK7XX
_______________________________________________
Topband mailing list
Topband@contesting.com
http://lists.contesting.com/mailman/listinfo/topband
|