[amsat-bb] Re: Polarity questions

Nate Duehr nate at natetech.com
Fri Sep 19 23:56:56 PDT 2008


On Sep 19, 2008, at 11:24 PM, Tony Langdon wrote:

> At 09:23 AM 9/20/2008, n3tl at bellsouth.net wrote:
>
>> I don't-at-all disagree with the concept that working AO-27, AO-51
>> and SO-50 isn't terribly difficult with a handheld station. Frankly,
>> that has really (and pleasantly) surprised me. However, I do believe
>> that adjusting polarity when hand-holding the Arrow provides
>> improved performance during many passes.
>
> It makes a big difference in many cases.


I'm kinda sitting here chuckling that people have "opinions" on how  
physics works.  :-)

Tony's right: Of course polarity makes a difference.  It's well proven  
physical science at this point in our RF history.

When the physics don't match the real-world experience, look for  
variables that might be affecting the test.

For example, most FM receivers aren't linear in their response from  
"noisy" to "quieting" on weak-signals.

If the satellite is moving, rotating, and generally "messing up" the  
test, it's hard to always see the results of polarity changes -- mix  
in trying to do it by hand, and different people's tolerance for  
listening through noise, different receiver sensitivities, higher and  
lower gain antennas, and pretty soon -- the whole test is pretty non- 
objective.

Some people may say "not switching polarity works fine" and on a  
particular day, with a particular rig, antenna, satellite orientation  
or motion, and a different set of between the ears DSP filters (ears)  
than the next person, their perception may be accurate for their  
experience -- but it doesn't change the physics... 20 dB loss is still  
20 dB of loss due to a polarity mismatch.

This is just the difference between the practice of radio  
communications, and the hard science of it all...

--
Nate Duehr, WY0X
nate at natetech.com


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