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Re: Re: Is hardwire RHCP OK?




I watched Bob point that 3-element yagi toward the sky during a 9600
baud demonstration this past weekend at the AMSAT Symposium.  As he 
was pointing it toward the sky, I made the comment that the signal 
polarization was typically in the vertical plane.  As I made that statement I 
turned toward John, N5DF,  to observe a reaction.  Each time Bob twisted
his wrist to put that little beam in the vertical plane the signal increased 
dramatically and packets from the 9600 baud bird were decoded.  It was 
amazing to see that little Kenwood HT with the built-in TNC receiving the 
9600 baud downlink signal so well.

Several years ago I ran an experiment over the course of a few months
with UO-22 and KO-23.  I found that the polarity of the signal favored the
vertical plane from Huntsville, Alabama.

Bascially, the experiment used a linear polarized antenna that was mounted
in the vertical and horizontal planes during the course of the data capture.
The increase in data was significantly noticed when the antenna was mounted
in the vertical plane.

As Bob mentioned in his note, there is no percepable circular polarization.
Since the bird is moving so rapidly relative to the ground, then you would
not expect to see a true right or left hand polarization. The reasoning is
that
the antenna is not pointing directly toward you for the entire pass.  That 
being the case, then you would not expect to see an RHCP or LHCP sense.
The polarization sense that is perceptable on the ground would be constantly
changing, but not exhibiting any real left or right hand circularity.  With 
that being the case, you may never see a true left or right hand polarization 
sense.  Even if the antenna on the bird were circular polarized or not, it 
would make little to no difference unless it were precisely pointed toward
you during the entire pass.  The odds of that happening are very remote
due to the low orbit.

Left or Right ?   It probably does not matter.  You may stick with Right Hand
Circular Polarizarion as a default , that is what I tend to select when I had
to make that choice on my 2MCP22.  When Phase 3D takes the sky, then
polarization may make a difference since it will be very high in orbit and the
antennas would be pointing toward the earth for longer periods of time.



73's de Tim - N8DEU
Huntsville, Alabama



In a message dated 10/19/98 12:51:14 AM Central Daylight Time,
bruninga@nadn.navy.mil writes:

> > > need to ever switch to left hand cp?  If I encounter trouble with cp 
>  > > switching could I just wire it in RHCP and I if  so what would I miss? 
>  > 
>  > I hardly ever use LHCP but its there if I want it. You wouldn't miss
much.
>  
>  Since I got my new Kenwood prototype dual band HT with built in 9600 baud
>  TNC, I have spend many passes outside with a handheld 3 element beam
>  copying passes of the 9600 baud satellites.  I can say, that
>  I have never seen any detectible circularity on the downlink. 
>  
>  Again, with a handheld 3 el linar beam, I can instantly rotate my wrist to
>  get a peak signal.  In ALL cases, I can rotate the antenna 90 degrees and
>  the signal *always* disappears.  As the satellite pass progresses, of
>  course, the polarity does change slowly, so a cross polarized antenna that
>  is *not handheld* is a must.  It would appear to me then that it doesnt
>  make any difference about L or R circularity, because there is none that I
>  have been able to detect.
>  
>  bob
>  
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