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[Linrad] Re: Phase relationship V to H in Linrad RX

I learn something evey time I read a post here.  Many thanks, I think I 
have a better idea of what is going on.
73, John

---- Original Message ----

From: Leif Asbrink <leif@xxxxxxxxxx>
To: linrad@xxxxxxxxxxxxxxxx
Subject: [Linrad] Re: Phase relationship V to H in Linrad RX
Date: Mon, March 16, 2009, 18:41:00

Hi John,

> Is there a degridation of Linrad (or MAP65) if the H and V signals are
> out of phase.
NO. But you would loose information about what polarisation
you actually receive so the computation of the optimum transmit 
polarisation would become incorrect.

What Linrad does is the following:

1) Compute the correlation between H and V (a complex number
averaged over a long time) 

2) Find out what combination of H and V that would minimize
the correlation.

3) Compute the signal B using the data of step 2. The B signal
will contain noise only.

4) Compute the A signal with the combination of H and V that 
makes the correlation zero between A and B.

The combination of H and V uses one real and one complex number.
The phase of the complex number is the phase shift between H and
V for the spectral peak selected for the computation.

A and B are the results of an orthonormal transformation of
H and V. Having a minimum in B means that all the signal
energy is available in A. This is fine for weak signals in
a background of white noise. If one wants to use the algorithm
for suppressing a strong interference, one would click on
the interference signal and listen at an offset frequency
in the B channel. The desired signal would not be at maximum,
but in such cases having the interference kept at minimum
would be the optimum. Linrad does not have the code for selecting
polarisation based on another spectral peak than the one that
is selected for the output because nobody seems to ever 
have this kind of problem. It seems the number of WSE HFA units
on the HF bands is rather low....
> 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?
No. On HF you might as well use two V or two H antennas that are
well separated or pointing in different directions.
> I'm still thinking of this as diversity reception, perhaps a bad model
> but the only mental picture I have.
I hope it is different now:-)


Leif / SM5BSZ

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