[TowerTalk] More from the M2 antennas quality control file

[Jim Lux]

On 4/13/15 7:33 AM, Lizeth Norman wrote:
> Thanks! I do understand. This makes the math a lot clearer.
>
> Regarding the orbiting signal generators, if the spacecraft is in LEO,
> then the accuracy of the tracking becomes "noise" on the measurement?
> Are there any spacecraft that you could suggest?

I'd look for any of the numerous cubesats that are up. AMSAT probably 
has a list somewhere on their website.
They're radiating in the ham band.. not at 432 (hopefully).

You point the antenna at a fixed position in the sky and let the 
satellite cross through the beam and log the power.  It will vary a lot 
due to a variety of effects, but averaging over multiple passes, etc. 
you can do pretty well.



>
>
>
> On Mon, Apr 13, 2015 at 10:25 AM, Jim Lux <jimlux at earthlink.net> wrote:
>> On 4/13/15 6:42 AM, Lizeth Norman wrote:
>>>
>>> Do have a question. How does one characterize an unknown antenna's
>>> parameters? If I understand it correctly, to characterize the "real
>>> world performance" (using the sun) of this type of antenna, G/T needs
>>> to be known.
>>>
>>
>> Some form of antenna range.  Sun Noise works, sort of, but the problem is
>> that unless your antenna has a very narrow beamwidth, the sun is "small"..
>> The sun is 1/2 degree wide.  If you have a 20 degree beamwidth (20dBi gain),
>> the sun occupies only 1/1600th of the field of view (400^2) so even though
>> the sun is, say, 5000K, it's swamped by the mass of 3K cold sky around it.
>> Get to a 30 dBi antenna with a 1-2 degree beamwidth, and then sun noise
>> starts to be a useful source.
>>
>>
>> There's a fair number of orbiting UHF sources these days, which provide a
>> decent far field point source (albeit not of calibrated signal strength, but
>> at least you could get good pattern cuts).
>>
>>
>>
>>
>>
>>
>