[Linrad] Re: 90 degree hybrid

[Jeremy Alexander <w7eme.org; jeremy@xxxxxxxxxxxxxxxx>]

Aloha Leif,

The source of my curiousity stems from: does the two signal when it finally arrive at Linrad really matter in any domain except phase to the Linrad? Looks as No?

I am testing channels now independently, mahalos for the advice. 

Jeremy w7eme


--- On Wed, 2/4/09, Leif Asbrink <leif@xxxxxxxxxx> wrote:

> From: Leif Asbrink <leif@xxxxxxxxxx>
> Subject: [Linrad] Re: 90 degree hybrid
> To: linrad@xxxxxxxxxxxxxxxx
> Date: Wednesday, February 4, 2009, 12:27 PM
> 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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