Several of the radios I have been working on play fine except a nearby station appears several places on the dial where it is not supposed to be. I'm calling this station overload, but there may be a better name for this problem. I suspect that tuning in the rf section is the problem, but I can't seem to tune it properly to eliminate the overload and leave this station where it should be on the dial. Any suggestions?

Might be an image? What is the freq of the station and where do you pick it up on the dial, and what is the IF freq?

Might be an image? What is the freq of the station and where do you pick it up on the dial, and what is the IF freq?

The radio I'm working on at present is an American Bosch, model 510, and the IF frequency is 465 kc. The station giving the problem is about 1550 kc and it appears at about 6 locations on the dial. Some places signals are very strong and some are not.

Dick,
Since you have several radios with the same symptom, might be a dirty transmitter putting out harmonics. Might even be something unique to your house wiring, if these are all AC powered sets. Try the same test with a cheap battery powered set.
marv

:Several of the radios I have been working on play fine except a nearby station appears several places on the dial where it is not supposed to be. I'm calling this station overload, but there may be a better name for this problem. I suspect that tuning in the rf section is the problem, but I can't seem to tune it properly to eliminate the overload and leave this station where it should be on the dial. Any suggestions?

:Several of the radios I have been working on play fine except a nearby station appears several places on the dial where it is not supposed to be. I'm calling this station overload, but there may be a better name for this problem. I suspect that tuning in the rf section is the problem, but I can't seem to tune it properly to eliminate the overload and leave this station where it should be on the dial. Any suggestions?

I see the exact same thing from my local AM station. It's strong on some parts of the dial and weaker on others. I've seen it on multiple radios. I have an 1934
copy of Radio Engineering on hand and will see if it mentions anything.

:Several of the radios I have been working on play fine except a nearby station appears several places on the dial where it is not supposed to be. I'm calling this station overload, but there may be a better name for this problem. I suspect that tuning in the rf section is the problem, but I can't seem to tune it properly to eliminate the overload and leave this station where it should be on the dial. Any suggestions?

Hello Dick,

You may try constructing an adjustable series wavetrap and hooking it up between the antenna input and ground. The wavetrap can be constructed using an adjustable core universal antenna coil or adjustable loopstick antenna coil covering the broadcast band and a variable condenser of around 360 pf. Hook the two components in series with the coil going to the antenna terminal and the condenser (shell) going to ground. Adjust the coil core and variable condenser for minimum interference from the station causing interference. I have not tried this with radios that have internal loop antennas and no antenna terminals. Perhaps this may be the solution to your problem.

Radiodoc

Radiodoc,
I don't recall these severe measures being introduced in yesteryear, except in the case of an untrained, sloppy HAM operator. Presumably, faulty components have been replaced and a good alignment performed. Shields were placed on especially sensitive tubes, and I don't know of any radio stations operating on 456kHz, except illegally. If there is an especially strong station with its tower operating nearby, that can be a problem with unshielded tubes. Unfortunately, dirty connections in any of the hardware, can act like a diode detector of an AM signal, propagating it throughout the entire audio system. I suggest that if the listener is an AM audiophile, your suggestions are appropriate, but if the problem lies outside his/her spectrum of expertise, other technical measures are required.
marv

::Several of the radios I have been working on play fine except a nearby station appears several places on the dial where it is not supposed to be. I'm calling this station overload, but there may be a better name for this problem. I suspect that tuning in the rf section is the problem, but I can't seem to tune it properly to eliminate the overload and leave this station where it should be on the dial. Any suggestions?
:
:Hello Dick,
:
:You may try constructing an adjustable series wavetrap and hooking it up between the antenna input and ground. The wavetrap can be constructed using an adjustable core universal antenna coil or adjustable loopstick antenna coil covering the broadcast band and a variable condenser of around 360 pf. Hook the two components in series with the coil going to the antenna terminal and the condenser (shell) going to ground. Adjust the coil core and variable condenser for minimum interference from the station causing interference. I have not tried this with radios that have internal loop antennas and no antenna terminals. Perhaps this may be the solution to your problem.
:
:Radiodoc
:

:Several of the radios I have been working on play fine except a nearby station appears several places on the dial where it is not supposed to be. I'm calling this station overload, but there may be a better name for this problem. I suspect that tuning in the rf section is the problem, but I can't seem to tune it properly to eliminate the overload and leave this station where it should be on the dial. Any suggestions?

I've mentioned this scenario before (and I don't think anyone believes me), but years ago, back in the days of metal gutters, downspouts, rusted TV antenna, masts, etc. etc....that is, BEFORE PLASTIC...this sort of thing was not all that uncommon. There is a corrosive reaction that takes place between dissimilar metals exposed to weather, that will form a natural diode at the joint. A strong RF source nearby will be sucked up by this diode, and somehow be mixed with another source and retransmitted to a set nearby (radio or TV) on an odd-ball frequency. Some of the more scholarly among us can give you the real, technical information on this, but I assure you it can and does happen. I would be a wealthy man today if I had a penny for every case of TV interference I cured from a local 50KW FM station, by just convincing the afflicted homeowner to tear down that weatherbeaten TV antenna installation, and install a new one. A very good friend of mine (sloppy ham) was the scourge of his neighborhood while running only fifty watts on 3.7mHz. No amount of detective work could solve the problem. There were not enough low pass filters on the planet to solve the problem. Then his next door neighbor replaced his old, metal gutters and downspouts one weekend and the problem vanished. My friend had apparently been mixing with 910kHz one mile away. I used to live one mile from a 620kHz facility and could hear that thing all over the spectrum. It would cut in and out on windy days as whatever was causing the problem flapped around making and breaking connections.
Also, don't overlook the possibility of modern devices causing the problem. Try going around the house and disconnecting everything electric from all their connecting cables (including ac power source), while listening to the interfering signal on a battery operated portable. I find charging stands, wall warts, and DVD players to be a huge source of electronic trash in general. Ground any unused outside antennas. It is also possible that if you live in a densely populated area that one of your neighbors is the source. Good luck.

Precisely!! I chased interference problems for days, while restoring my Edison 7R TRF. Using an o'scope, it looked like 120Hz hum on the audio, so natural suspicion was radio problems. I took a cheap portable battery AM set throughout my home, and here is what I found. Modern electronics, even though OFF, are still somewhat active to allow instant on with a remote vs a physical closure of a mechanical switch. So in reality, they're always somewhat active. In my case, 1 computer de-glitch power strip, 2 std power strips, 2 TV's, 2 computers, a wireless modem/router, an XBOX and all flourescent lights were all contributors to my noise pollution. Only solution was to unplug them all from the wall. Bingo!! Noise gone. The diode detector from rusted, corroded, dissimilar metals thing is still valid too.
marv

:I've mentioned this scenario before (and I don't think anyone believes me), but years ago, back in the days of metal gutters, downspouts, rusted TV antenna, masts, etc. etc....that is, BEFORE PLASTIC...this sort of thing was not all that uncommon. There is a corrosive reaction that takes place between dissimilar metals exposed to weather, that will form a natural diode at the joint. A strong RF source nearby will be sucked up by this diode, and somehow be mixed with another source and retransmitted to a set nearby (radio or TV) on an odd-ball frequency. Some of the more scholarly among us can give you the real, technical information on this, but I assure you it can and does happen. I would be a wealthy man today if I had a penny for every case of TV interference I cured from a local 50KW FM station, by just convincing the afflicted homeowner to tear down that weatherbeaten TV antenna installation, and install a new one. A very good friend of mine (sloppy ham) was the scourge of his neighborhood while running only fifty watts on 3.7mHz. No amount of detective work could solve the problem. There were not enough low pass filters on the planet to solve the problem. Then his next door neighbor replaced his old, metal gutters and downspouts one weekend and the problem vanished. My friend had apparently been mixing with 910kHz one mile away. I used to live one mile from a 620kHz facility and could hear that thing all over the spectrum. It would cut in and out on windy days as whatever was causing the problem flapped around making and breaking connections.
:Also, don't overlook the possibility of modern devices causing the problem. Try going around the house and disconnecting everything electric from all their connecting cables (including ac power source), while listening to the interfering signal on a battery operated portable. I find charging stands, wall warts, and DVD players to be a huge source of electronic trash in general. Ground any unused outside antennas. It is also possible that if you live in a densely populated area that one of your neighbors is the source. Good luck.

......................or maybe a lot of the stations in your area got taken over by Clear Channel Communications. There used to be about 5 different stations in my area, both local and distant, that played the same programming. Thankfully most have changed programming. If you hear the same music but different call letters, then this is your problem. I have, however, occasionally had harmonic problems that came and went, where one station would show up in several different places. It isn't uncommon.

Thomas