What am I seeing?
Dave3825us, Mon Oct 21 2019, 08:41pm

I was scanning around and ran across 465.482. It nxdn so I popped on dsdplus and it showing as cc 453.5625 and that's for Nassau Suffolk Communications (NEXEDGE)
001 (1) Farmingville Suffolk 451.8625 452.3875 463.5625 464.950 462.945

So is this an input or something? Site is in Farmingville and I am in East Islip. Why would 465.482 run perfect as a cc for the 246 system?

Re: What am I seeing?
GTR8000, Mon Oct 21 2019, 10:12pm

First clue is that 465 is in the input range, not the output range (460), so it wouldn't be carrying a control channel. The control channel input does not carry a steady stream of data like the output; only burst transmissions from the subscribers communicating with the controller.

Second clue is that 465.482 is not a valid frequency. The nearest valid frequencies are 465.475 or 465.4875.

You're almost certainly receiving an image of 463.5625 with the dongle. Try lowering the gain.

Re: What am I seeing?
Dave3825us, Tue Oct 22 2019, 11:52am

That makes sense . Gain was low when I first saw a faint signal. Then after boosting it, that's when it id'd as 246.1. Seeing another image, this time a cap plus system. Seems to be town of Islips.

Interesting that different receivers see images differently. Sdr# showing 468.443 (470.3625) but fmp24 does not see it even with gain maxed out...

Guess I am going to edit my scan ranges in SDR# to exclude inputs.


Re: What am I seeing?
GTR8000, Tue Oct 22 2019, 09:00pm

Yeah, it can be frustrating. The GRE/Whistler made scanners can be some of the biggest culprits when it comes to false images, thanks to their lousy front ends. For years we had people swearing they were finding trunked system control channels in the high 700 MHz range, when in fact they were images of control channels in the 851-860 range.

A bit of advice would be not to rely on external tuners like SDR# when using DSD+. I understand that SDR# makes it easy to snoop around the airwaves to find stuff, but ultimately you should confirm newly found signals with FMP24/FMPA coupled to DSD+ before putting much faith in those signals.

And of course any control channels you find within the UHF/T-Band/700/800/900 standard input blocks is going to be an image.