[Linrad] Re: 90 degree hybrid

[Joe Taylor <Princeton.EDU; joe@xxxxxxxxxxxxxxxx>]

Hi Jeremy and all,

Jeremy Alexander wrote:
> May I use a 90 degree hybrid device to split simgle signal from RF generator? ... 

Leif has already provided the answer that matters most.

It might be useful to add, however, that if you're using the 
Linrad/MAP65 combination, MAP65 already provides the "software solution" 
that Leif must have in mind when he writes

> Some day it might be an adjustment in software....

MAP65 defines a parameter called Dphi that can be entered on the 
Setup->Options screen:

- Dphi (deg): Phase shift to be applied to vertical signal to compensate 
for a hardware phase shift relative to horizontal

"Dphi" defaults to 0.  If your system has equal phase shifts in the X 
and Y (normally horizontal and vertical) channels, you can leave it 
alone.  However, if your X and Y feedline lengths are different or 
something else introduces a significant differential phase shift, you 
can correct it here.

In version 0.8 and later, MAP65  provides a means to determine the phase 
difference between channels.  Find an EME signal that produces roughly 
equal signals in the X and Y channels.  Set the QSO Frequency and DF to 
this signal, and reduce "Tol" so that no other signals will be decoded; 
then click "Find Delta Phi" on the Setup menu.  MAP65 will decode the 
signal 13 times in quick succession, using assumed values of Dphi = 0, 
30, 60, ... 360 degrees.  The resulting output in the main text window 
should look something like this:

Freq  DF Pol  UTC   DT  dB  Decoded message      KV  DS Dphi
------------------------------------------------------------
110   -9  60 0746  2.1 -19  LX/PA3FPQ W0HP         1 204   0
110   -9  74 0746  2.1 -20  LX/PA3FPQ W0HP         1 173  30
110   -9 108 0746  2.1 -20  LX/PA3FPQ W0HP         1  53  60
110   -9 121 0746  2.1 -19  LX/PA3FPQ W0HP         0  17  90
110   -9 124 0746  2.1 -18  LX/PA3FPQ W0HP         0  11 120
110   -9 124 0746  2.1 -18  LX/PA3FPQ W0HP         0  11 150
110   -9 120 0746  2.1 -19  LX/PA3FPQ W0HP         0  17 180
110   -9 106 0746  2.1 -20  LX/PA3FPQ W0HP         1  58 210
110   -9  72 0746  2.1 -20  LX/PA3FPQ W0HP         1 177 240
110   -9  59 0746  2.1 -19  LX/PA3FPQ W0HP         1 204 270
110   -9  56 0746  2.1 -18  LX/PA3FPQ W0HP         1 203 300
110   -9  56 0746  2.1 -18  LX/PA3FPQ W0HP         1 203 330
110   -9  60 0746  2.1 -19  LX/PA3FPQ W0HP         1 204 360

     Best-fit Dphi = -46 deg

Of course, -46 deg phase shift is equivalent to +314 deg.

You would then enter -46 for the value of Dphi.

Keep in mind that this correction is used in MAP65 but is not sent back 
to Linrad.  As a result, Linrad's polarization fitting and polarization 
display will not be corrected.  That's why it's better, overall, to make 
the correction in the way that Leif described -- by adding or removing a 
bit of cable so as to make the fitted polarization "ellipse" collapse 
into nearly a straight line

	-- 73, Joe, K1JT

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