I tuned to a local station on 610kHz using my newly restored 1962 all American five radio and was greeted with quite a loud whistle. No other stations had this problem on this radio so it is apparent that the receiver is OK.
A little math solved this problem. The image frequency of a superhet receiver is Fimg = Fs + 2xFif where Fs is the tuned station and Fif is the receiver intermediate frequency. For 610kHz and Fif = 455kHz the image is 610kHz + 2x455kHz = 1520 kHz. The image frequency is one where if a signal is strong enough it will appear on top of the tuned frequency. 1520 kHz is the frequency I chose for my secondary transmitter. When I noticed the problem the transmitter was on and the radio was located 3 feet from the transmitter so the signal was very strong at 1520..
I am not concerned about disrupting my neighbors' enjoyment of the 610 station (the station does that with their programming) since the transmitter is using a 3 meter wire antenna with 70 mW input power and cannot be heard at the curb in front of my home. However if someone is transmitting within an apartment building it is possible that their signal might be strong enough to interfere with neighbors' reception if it is on an image frequency. This is possible even though the transmitted signal is perfectly clean since the failure is in the receivers.
If you get a complaint about interference check the image frequency. The only remedy is to change frequency and hope you are not on another image frequency.
Neil
Reading about Neil's "image frequency" I remembered noticing the same thing with the SANGEAN ATS-505 located 4-feet from my AM1550 Wintenna (metal window-frame as antenna for AMT3000). I hear a loud and clear image of the 1550 signal at 650, the frequency for WSM in Nashville often heard here even in the day.
So I put the GRUNDIG FR-200 in the same location but heard no image frequency whatsoever anywhere on the dial.
10-feet away I tried the C.Crane Radio Plus... no image at 650, only buzz from the nearby computer.
Went 25-feet away to the Zenith Transoceanic and heard a "putt-putt-putt plus whistle at around 650", but traced that disturbance to the battery charger on the other side of the wall.
Images are in short supply here in the Internet Building.
Carl's mention of different radios reacting differently reminds me that the image probably is not coming through the antenna but is entering directly into the mixer or I F stages. This was the case years ago when my ham activities would cause serious interference to our TV set.
The TV I F was in a shielded metal box but the box was not connected to chassis ground. Adding a simple ground strap from the box to the chassis solved the problem.
Neil
You're dating yourself LOL!
This thread verifies what I posted a while back about bad radios being the problem or some of the problem of interference.
But how can you tell people around you to get a better reciever?
When I was in an apartment on the 14th floor I couldn't listen to certain stations because of the radio picking up courier transmissions blocking out the program. I called Industry Canada at the time and was told basically to get a better radio as it was my reciever at fault, not the transmissions that I thought was interfering with the AM and FM bands.
Mark