F300-25 sudden RF decoding issue

Hi All,

Im just checking if anyone else has seen this issue.

I have an F300-25 that suddenly is very sensitive to 5200mhz (center frequency but is good from 5160 to 5240) but is almost useless in any other portion of the band until it detects the signal at about -70 then it will add the AP to the list but still won’t connect until about -59.
I have an AP 15ft away and have turned it up in 1db increments and the power needs to be quite hot before the SM connects, but if I set to 5200mhz then it connects at -89!

It is very odd that the radio is selective in what frequency that it can easily receive and decode. The only reason this became apparent was because it picked up another radio link.

I do not suspect this radio suffered any mishap as there is no physical damage and a quick radio swap and the location was back running.

In my short time working with Cambium equipment, I’ve not seen this, but I have seen it in other gear, even going way back to GE’s VHF and UHF base stations. Some times, when the antenna switching leaks transmit energy from the transmitter into the receiver (due to much lower isolation between the transmitter and receiver), the mixer can ring, or oscillate while the transmitter is on. It can affect the receiver’s SNR, and, when the level is high enough, add modulation to the outgoing transmitted energy. I’ve only seen this in discrete component radios, but I suppose it could happen in SoC devices since filters are external.

In my VHF / UHF days, every once in a while, you’d hear a 2 way radio with a very low frequency hum while transmitting. It was a sign that there was a PIN diode issue in the antenna switch. When the signal level was really low, the FM modulation was bad enough that you could barely understand the operator of the distressed radio. Repair the antenna switch, and clean up the receiver front end filter - problem solved.

This sounds very similar, with registration not occuring until well over 30 dB SNR is achieved. The fact this is frequency sensitive screams filter to me. Changing the radio and it worked tells you it had nothing to do with the environment.

Just my 2 cents!

Coming from VHF/UHF myself I had the same thoughts, but what gets me is using the SA function, it hears the whole spectrum, just 30 to 50db lower except the one range centered around 5200mhz.

To me this screams intermediate frequency issue, but a shorted high pass capacitor would have similar effects.

Since I have not opened this radio yet (not sure if this one still has warranty left), I was just checking if there is a commonality between this one and others that we could look at a manufacturing run issue?

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