Whistle on specific frequency, but only certain equipment

[grosporina]

I've been listening to the local air traffic on my scanners for several years, but I just bought a new tri-band transceiver and am trying to use it's scan function for the same purpose and am getting a whistle that comes and goes on one specific frequency. I'm trying to figure out if it's something about the transceiver, or just something I had not picked up on my scanners due to limited fidelity of their audio.

There is one specific frequency, 132.800 MHz that on my transceiver when I am receiving there is often a persistent whistle, on long transmissions I can hear it sometimes slowly changing pitch and it seems stronger when I am receiving a tower transmission compared to when receiving a plane's transmission. It's not absolutely all the time I hear it, probably 75% of the time but on days I do hear it it is persistent. I would just chalk this up to some sort of interference but if I set one of my scanners and my transceiver side by side and listen to the same transmission the scanner will never pick up this whistle while the transceiver does.
Does anyone have similar experience of have a suggestion as to whether I should suspect some issue with the transceiver? I just got it a week ago so if this is something equipment-specific I'd like to deal with it while I can. Listening to aviation frequencies was not the main reason I bought it but it was a factor in my selection of make and model. I wouldn't be surprised if it was something there in the signal and the scanners are just filtering it out or it's outside their audio bandwidth but it seems weird.

I've gone searching online for similar discussions and found nothing, and there's no related discussions I can find for this transceiver model to hint at some known design flaw. It's a Kenwood TD-D74A by the way, while my scanners are both several years old Unidens, a BC296D and a BC-95XLT (the NASCAR branded one, bleh, but the price was right).

 

[majoco]

If you're only hearing it on your new receiver, I would suggest that it's a 'birdie' from within that receiver. Not sufficiently strong to lift the squelch but as soon as there is another carrier to beat with you hear the beat tone on that one frequency. You could try sniffing for it with another scanner with a bit of wire for an antenna draped over the new receiver and tuned to the 132.800MHz - open the squelch and you may hear the noise decrease as you tune through 132.800MHz on the new receiver. If you have one of the cheapo USB stick receivers, you may be able to see the birdie on the spectrum display.

Unfortunately there's probably nothing you can do about it - receivers generate a multitude of frequencies within themselves and it's a difficult job to stop them getting out! When the warranty runs out you could take the covers off and go round every screw you can find and check that they are all tight but other than that you're stuck with it!

Nice transceiver, your new TD-D74A, nice to see a proper keypad and not have to wade through scads of screen menus!

 

[grosporina]

Thanks for the suggestion, yes overall aside from the mystery whistle I am impressed so far by this unit and the full keypad was another of the deciding factors in choosing this unit.

VA3USO