[amsat-bb] Re: [Mw] Dish reflector density (and Kaguya)

[Michael Fletcher]

Loren Moline WA7SKT wrote:

> Hello,

Hi,

CC:ing AMSAT-BB in case somebody wants to quit
the keyboard and do something cool for a change ;-)

> Is there anything that says what the maximum space or hole size in a not solid dish should be.

Depends on the thickness and hence fringe effects (the cutoff
is half a wavelength, but for all practical reasons (the
"thinness" of the material), you can take 10 - 20 % of the
freespace wavelength.

> I have been told that a barbque grill antenna works better if you cover with 1/4" or smaller hardware cloth adhering to the curvature of the original dish shape.

Well, the grill design is linearly polarised, so for
circular polarisation (with a suitable feed also),
making the reflector more complete can give you up to
3 dB gain (circular over linear).

Tonight I used a +- 45 degree linearily polarised
W-LAN patch, outer dimensions 8 * 10 cm, with a
commercial preamp specified at 1.2 dB NF; solid
copy with the naked ear, even through double glazing
(i.e. the antenna is seeing a lot of ambient noise
temperature too).

This thing is extremely difficult to make non-audible
by the ear. I just did pretty much the ultimate test
and used a QBFH omnidirectional: no problem hearing
Kaguya by the ear.

What this means is you can hear the 2.2 GHz carrier
from the moon whilst mobile, no DSP, SDR, nothing...

> Loren                                                                                                                                                    

Michael, OH2AUE

-- 
"Life is too short for Sudoku"