[Linrad] Re: 90 degree hybrid

[Leif Asbrink <sm5bsz.com; leif@xxxxxxxxxxxxxxxx>]

Hi Jeremy,

> May I use a 90 degree hybrid device to split simgle signal from RF generator. 
> 
> My question about this may seem easy, but I can see the hybrid supplies near 90 phase difference but also a similar time difference at the -90 port. I am thinking this would be similar to a circular polarity signal on a XPol boom, but not that of a more traditional side by side array of V and H elements, where unlike XPOL, all drivers (H/V...whatever) are the same distance from source, supply 0 and 90 but less the time difference? True or no true? 
Yes, true.

> So me thinks this might be a silly question, but can I begin to refine my WSE converter with a signal generator split through a 90 degree hybrid? Will this testing represent what the WSE will see from my seperate V and H antennas? 
> 
> Does the whole time factor make no never mind and just not even important?
I do not quite understand what you want to do.
I usually use just a T-connector to feed the same signal
into the two channels for e.g. calibration. The 90 degree
hybrid will be perfectly OK also.

For your system refinement, i.e. the preamp and second RF
amplifier you would need if your preamp has normal gain
you should test the channels one by one.

In real life it is hard to make the phase shift equal
in all amplifiers and (long) cables so the best solution
is to just set things for equal gain (and equal noise 
floor) in the two channels. Then you measure the appearent
phase shift on a signal that is approximately equal
in both RF channels. Easy if you have X configuration
but difficult in case you have the more common
+ configuration. 

The linear 45 degree signal you would need for phase
calibration on a + configuration must be an EME
signal with the moon at high enough elevation for
no ground reflection to occur.

Phase errors only affect the polarisation readout,
the sensitivity is always 100%. Just find out if
the pol. indicator shows a circle or an ellipse 
you should change one of the cable lengths until 
it becomes a narrow ellipse or ideally a line at
those times when the EME signal is about equally
strong in H and V.

(With the X configuration, any normal H or V signal
from some local station would be fine. Just make
sure your antennas point towards each other. Side
reflected signals often have twisted polarisation...)


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

73

Leif

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