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Odd BNC device

M

maus92

Well Known Member
I found this device attached to the old GPS antenna in my plane. Can anyone identify it? Is it some sort of attenuator? The GPS was a Garmin 250XL.

2qbsto0.jpg
 
It's a notch filter to prevent the harmonics from your comm radio from interfering with your GPS.
 
It is a NOTCH FILTER and is used to attenuate unwanted frequencies that may be presented to the receiver.
 
You put it inline with the antenna to prevent that water hammer noise you'd get if you end a radio transmission to abruptly. :D
 
Mel said:
It's a notch filter to prevent the harmonics from your comm radio from interfering with your GPS.
Click to expand...

Even the later Garmin navigators need checking for this interference to meet their STC requirements.

For the early 430 units the frequencies to check are -

121.150
121.175
121.200
131.250
131.275
131.300

With the ADS-B accuracy requirements coming up you certainly don't want to lose that certified 2020 GPS position when you transmit on one of the above frequencies. :)

Re-install the notch filter with your present GPS, it can't do any harm, and check your installation manual for the specific critical frequencies for your present GPS unit.
 
Interesting. I will reconnect it. But it raises a question about the new GPS 20A position source that I am installing. The existing antenna is mounted on the glare shield, which will feed the GPS in the GDU 460, and will serve as the backup GPS source. The new GPS antenna for the GPS 20A necessary for ADS-B integrity is mounted behind the canopy slide rail. Will it require a notch filter as well?

C.
 
Last edited:
maus92 said:
Interesting. I will reconnect it. But it raises a question about the new GPS 20A position source that I am installing. The existing antenna is mounted on the glare shield, which will feed the GPS in the GDU 460, and will serve as the backup GPS source. The new GPS antenna for the GPS 20A necessary for ADS-B integrity is mounted behind the canopy slide rail. Will it require a notch filter as well?

C.
Click to expand...

Check the installation manual for post-installation testing, but since it's a new device specifically for ADS-B compliance it probably has a good filter internally.
 
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