[time-nuts] L1 L2 choke Ring Question

Attila Kinali attila at kinali.ch
Sun Nov 20 15:37:45 EST 2016

On Sun, 20 Nov 2016 19:48:42 +0000
Tom Knox <actast at hotmail.com> wrote:

> I recently purchased a used L1 L2 Choke ring antenna AeroAntenna
> AT2775-20W-000-05-26-NM, it has an AT2775 aircraft antenna with a 3.3" x 
> 1.8" bolt pattern at it's heart.

Do you have pictures of the antenna module?

Have you tried to take it apart?
It is likely to be a standard passive antenna with a simple LNA.
As long as the antenna isn't mechanically damaged, it is likely
that just the LNA is fried (lightning strike?). One should be
able to replace the LNA chip or the whole LNA module.

> Sadly the antenna is dead. I have been looking into the possibility of
> replacing the aircraft antenna portion and was wondering what the critical
> specs were and the approximate tolerances. I found an antenna from another
> manufacturer with the exact bolt pattern, but it appears the phase center is
> 1-2mm lower.
> Any thoughts would be greatly appreciated.

That shouldn't be a problem. The chocke ring acts like an high impedance
area around the antenna. You can see it as an "isolator" or resistor
for electromagnetic waves. I.e. if you are a bit lower, you will get
less from the reflections from the ground and proably have less reception
in the lower elevations. It could be, that an antenna that wasn't designed
for a choke ring will be slightly detuned. But that should pose any problem.
I'd guess the signal los would be minuscule.

> Or if anyone has a AeroAntenna AT2775 aircraft antenna with a 3.3" x 1.8" 
> bolt pattern they would be willing to sell or trade contact me off list.

The AT2775 is a whole family of antennas. One would need a bit more information
about which it actually is. They do pop up on ebay from time to time.

			Attila Kinali

Malek's Law:
        Any simple idea will be worded in the most complicated way.

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