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[Linrad] Re: Phase relationship V to H in Linrad RX
- Subject: [Linrad] Re: Phase relationship V to H in Linrad RX
- From: Joe Taylor <Princeton.EDU; joe@xxxxxxxxxxxxxxxx>
- Date: Sat, 14 Mar 2009 22:43:54 -0400
Hi John, Ed, and all,
When used with a dual-polarization system, Linrad and MAP65 process
signals using full phase information. Feedlines and preamplifiers for
the two polarization channels do not need to be precisely matched... but
if they are not, you should go through a calibration procedure to phase
The best way is to find a signal that is more or less equally strong in
the two channels. As pointed out on Leif's web site, this is relatively
easy if your antennas are mounted in the "X" configuration -- you just
need a horizontal or vertical signal. With the more common "+"
configuration, the best test signal is an EME signal polarized at
approximately 45 or 135 deg. Then you add or subtract fractions of a
wavelength in the feedline for one channel or the other, until Linrad
reports that the circular polarization component vanishes. You want
Linrad to show pure linear polarization oriented at 45 or 135 deg to
orientation of the individual antennas.
MAP65 can do the phase matching automatically. After finding a JT65 EME
signal with approximately equal strength in both channels -- you can do
that by watching signals in Linrad's high resolution graph -- click on
menu item "Setup -> Fine Dphi". MAP65 will solve for the necesssary
phase shift, and you can then trim the feedline appropriately or simply
enter that value of phi on the "Setup -> Options" screen. (If you do
the latter, polarizations will be correctly measured and reported in
MAP65, but of course Linrad does not benefit from the correction.)
Beware of one potential trap: you can be 180 degrees out of phase and
get what appears to be a correct solution, whether by trimming cables or
by letting MAP65 do it mathematically. In this condition, everything
will work well except that the sense of increasing polarization angles
will be exactly wrong (e.g., clockwise instead of anti-clockwise. MAP65
and Linrad will then give you bad advice on the optimum transmit angle
to match a received EME signal. Add another 180 degrees or a hale wave
of cable to correct this error.
-- 73, Joe, K1JT
> Lief and Joe,
> Is there a degridation of Linrad (or MAP65) if the H and V signals are
> out of phase. I am thinking of HF rx for wisper, My H and V may have
> several wave lengths difference in feed line. Is this a problem?
> I'm still thinking of this as diversity reception, perhaps a bad model
> but the only mental picture I have.
> Tnx, John K1VBM
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