# Antenna Separation

Team,

I have both flightaware antennas for 1090 and 978 which i’m planning to mount next to each others. can someone tell me what is the minimum separation I should have between the two antennas?

Regards,
Antoine

1 foot is about a wavelength, so anything more than that is probably enough.

As these are “receiving only” antennas, the normal rules don’t really apply.
If they are very close together, they will de-tune each other and there will be some shadowing as well.
While ‘more is better’, it’s very much a matter of diminishing returns.
If you can manage 1 foot, that’s great. If you can manage more, you probably won’t notice the difference.

I originally had these 1/4 wave ground plane antennas (1090 & 978) mounted together in the middle of this box but the experts in this forum suggested at least a 1/4 wave separation to minimize antenna performance degradation (impedance & VSWR). If you’re using full-wave antennas, I would guess the experts would recommend at least a full-wave separation.

What is a “full-wave” antenna?
(I understand the words, but mathematically, it doesn’t make sense)

I’m far from an antenna expert but what I’ve learned is that 1/4 wave for ADS-B (1090MHz or 978MHz) is about 2.5 inches so full-wave would be ~10 inches. I’m guessing the FA antennas (26 inches) are dipole full-wave with a 10-inch section stacked on another 10-inch section.

I remember seeing pictures where the 2 are mounted at least 12 inches apart (as suggested above).

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Engineering a system to do what mobile phones do and just installing antennas is something completely different.

Anyway, i’d say minimum half a wavelength, better more.
Or even better install one higher than the other.
This way, one of them has a perfect view.

Then install the second antenna half a foot or 15 cm or better more away from the mast.

and cellphones are just trying to receive a signal from a nearby cell tower, not an aircraft +100 miles away.

And those are patch antennas. No sure if the same rules apply. In any case, receiving is not as bad as transmitting, I guess.

I have RX and TX antennas only feet apart, and they are for HF. I have RX input protection, in case I TX while another RX is ON.