FlightAware Discussions

Watch those N male to SMA Adapters

A ‘public service announcement’. :wink:

If you use an N male from the FA antenna, to SMA for the Pro+ adapter, are you sure it’s a good/right one?

I don’t have ‘confirmed’ 50 Ohms adapters here. The pictures on the net are not enough for me to distinguish between the two. I just ordered two more that claim to be 50 Ohms. Let’s wait and see.

But here is the point of this post. I unscrewed the adapter almost half way out from the antenna. To my surprise, the number of planes and messages jumped up substantially. Who needs an LNA now?:wink:

I suspect the adapters I have are all 75 Ohms, even though they were listed as 50 Ohms.

Could a multi-meter help to determine the actual resistance?

Not by simply measuring it, like a resistor, not impedance.

Until I have a ‘true’ 50 Ohms N adapter in my hands, my suspicion is that the thinner 75 Ohms center pin is the reason for this ‘behavior’.

Check that the female socket on the antenna has not been splayed out. I think it is unlikely that your adaptors are 75ohm as sma is 50ohm. I have never seen a 75ohm N to sma adaptor. However if a PL259 to sma adaptor had been accidentally screwed into the antenna at some stage, that would splay the socket. I’ve seen this happen before.

Compare the pin with a BNC plug.
The pin of a BNC is the same as a 50ohm N plug.
Unlike N plugs, BNC plugs, both 50 and 75 ohm use the same size pin. With a BNC the difference between 50 and 75 ohm is achieved by the dielectric, not the pin size.

Enough ‘work’ for today, but I’ll check tomorrow. That said, how would that happen? The 75 Ohms N pin, if that is indeed what I have, is smaller than the 50 Ohms pin. If it’s 50 Ohms, then is the right size, presumably.