phantom transmitter?

[nautlynch]

A few minutes ago I turned my analog scanner on and I get a close call alert. I have a pocket radio turned on to some news station as well. I can hear the pocket radio through the close call as if the radio is transmitting. What is going on with this? It seems like a bug of some sort.

video of this: VID 20180428 222422 - Sendvid

 

[Voyager]

Your Close Call actually picked up the local oscillator (tuned frequency plus the IF) of the pocket radio.

Were you listening to 101.1 FM? (just guessing at the IF, as I don't know it)

If so, the oscillator might be 111.900 MHz, not 111.850 MHz, but that's close enough.

 

[nautlynch]

Thanks for explaining that. Do you know why it picked up the oscillator? Is there some fault with one or the other radios?

 

[Voyager]

Well, it's odd for the oscillator to be SO strong (it takes 20 dB above the noise floor or any other signal to trigger a hit), but no fault that I can see from your description. Well, other than the video being upside down. :wink:

I've never seen a LO CC hit, but I knew it was possible. And I was surprised that it's so strong in your FM radio - especially being in the Aircraft band.

 

[nautlynch]

I don't know why the video became upside down. It also appears "squished". The video host has something to do with this.

This little pocket radio is also a shortwave radio.

 

[iMONITOR]

A few minutes ago I turned my analog scanner on and I get a close call alert. I have a pocket radio turned on to some news station as well. I can hear the pocket radio through the close call as if the radio is transmitting. What is going on with this? It seems like a bug of some sort.

video of this: VID 20180428 222422 - Sendvid

You're probably picking up an internal oscillator signal from the pocket radio.

Turn off the pocket radio/news, and see if you still hear anything. Make a new and different type of noise and see if you're hearing it in the scanner.

 

[jwt873]

Thanks for explaining that. Do you know why it picked up the oscillator? Is there some fault with one or the other radios?

An oscillator is the basis for a transmitter. It's what creates the RF frequency. The image below shows the block diagram of a very simple CW transmitter. Note that it starts with an oscillator, it gets amplified then goes to the antenna.

For superhetrodyne receivers the oscillator is used to convert the incoming FM signal to an IF signal. The RF from the local oscillator is mixed with the incoming signal to produce the IF. Just because it's part of a receiver doesn't mean that it doesn't create an RF signal.

In your case, you're hearing the un-amplified signal generated by the local oscillator in the receiver.
.

 

[nautlynch]

You're probably picking up an internal oscillator signal from the pocket radio.

Turn off the pocket radio/news, and see if you still hear anything. Make a new and different type of noise and see if you're hearing it in the scanner.

If I turn the radio off the scanner stops picking it up. I have tapped on the radio and I can hear the tapping and handling of it in the scanner.


@jwt873 - Is the radio "leaking" RF a bit too much and picked up by CC?

 

[SCPD]

My DYNEX LCD tv transmits on all sorts of frequencies,
It creates strange "birdie" frequencies that randomly change day to day..as long as my tv is off,there are no bizarre frequencies.
Same thing happens with my EPSON bubblejet.Scanners,receivers pick up on this.
Even a cellphone wall wart can make strange oscillations.

 

[lmrtek]

10.7Mhz IF frequency being added to the frequency.
Very common among all receivers.
Scanners are also good signal generators.