Radios in office buildings, and general radio interference

[RetroHacker]

Well, I was rather disappointed a bit ago. This weekend I found a little cheap plastic AA5 tube set at a flea market, broken. One dollar later, I brought it home, dismantled it, and scrubbed and cleaned the case, and replaced the capacitors. This is a simple little RCA Victor All American five set, using miniature tubes. (12BE6, 12BA6, 12AV6, 35W4, 50C5). It's incredibly cheap, mid 60's I'd say. White plastic case, light blue knobs affixed to the front of the cabinet by little black metal retaining rings so that they can't be pulled off (the 'chassis' must be pulled off the knobs, rather than the other way around). The radio is built on a circuit board, mounted in the case at an angle so that the tuning dial can be vertically centered on the cabinet.

I replaced the paper caps, some resistors, and the failed electrolytics, cleaned up the board, and it worked first try. It's a small set, and looked rather good after a lot of scrubbing and cleaning the filthy case, so I brought it into work. In at the office, however, I can only get one station (a religious talk radio station...), and lots of different pitced hums across the dial. With some careful tuning, I could get one other station faintly, but with distortion. I am guessing that I'm picking up interference from the computers, lights, and everything else in the office. So much for listening to Oldies 1240.

So... this leads me to my question - how to get a simple, All American Five set to recieve well (or, at least, somewhat better) in interference-laden areas? I've seen the site on "hot rodding" AA5's, and I think I may try some of his tricks, but I'd like to get the opinion of some of the experts here too.

I'm still keeping a lookout for a simple FM tube set I can bring in, hopefully that will work better. Any reccomendations on what to look for in one of those? I know they made many little cheap FM-only sets in the same manner as the AA5's. I'd love to find one of those. Is there a standard FM circuit for those, as with the AM sets, or is there more variation?

-Ian

[OvenMaster]

1. I have bad indoor interference on AM on my Yamaha T-80 here at home, thanks to computers, VCRs, TV sets, and my PC's battery backup. There are only four solutions that I know of for this problem: shut off the devices causing the interference, move the radio away from the interference, put the radio next to a window, or have an outdoor antenna with a shielded lead-in, where the shield is grounded. The first two are out of the question. The third may be impractical. The fourth one worked when I had to have an outdoor longwire feeding my shortwave radios here at home to kill off dimmer and oil burner noise.

2. Here's a site full of FM-only radios: http://www.somerset.net/arm/fm_only.html

[Old1625]

Your situation is pretty hopeless as far as reception of either AM or FM signals;

1) Most office bldgs have a lot of metal in their construction, making it an effective shield can.

2) Practically everything in the bldg except perhaps the water cooler generates spurious RF over a wide band of frequencies.

With a commercial tuner--one that is completely shielded, and with an rf coil instead of a loop on the back cover or a ferrite loopstick, and with a coaxial fitting on the back for antenna input--would do well in such environment if the pure, uninterfered signal is piped in from a remote (perhaps on the roof) aerial through a properly connected and dressed coaxial cable.

Back in the '60s--unless the Gestefax was busy perforating a mimeograph stencil, or there was a plethora of flourescents nearby--your nifty table radio would've worked fine. Today is a whole new can o' worms--sorry to say.

[jeffsod]

You might have luck with a late 50's or early 60's German set. But If you cannot locate it anywhere near a window I would say you are probably out of luck no matter what you use. I brought a Motorola B1W to work which is FM only and it receives a few stations when located near a window without having any work done to it. It does have a hookup for a 300 ohm antennea which helps.

[Chad Hauris]

I have found a GE superadio gives the best performance in an office building. I am lucky enough to have an office with a window now on the 13th floor but I used to have an interior office with no window and the Superadio was able to pick up fairly weak stations. Performance with the Superadio in the window is excellent. I can pick up a 900-watt AM station about 30 miles away and it's still listenable..also a very low powered public radio FM translator about 10 miles away comes in quite well too.

The tube type plastic AM table top radios I have found are the absolute worst in picking up interference. They seem to need to be operated in a pretty "clean" environment fairly far away from noise sources. For some reason the GE Superadio will get a fairly clean FM and AM signal where many other radios have problems.

[RetroHacker]

Originally Posted by Chad Hauris

The tube type plastic AM table top radios I have found are the absolute worst in picking up interference. They seem to need to be operated in a pretty "clean" environment fairly far away from noise sources.

Yeah, I figured as much - the All American 5 design was well known for it's ubiquity and low cost - not it's performance.

I was just amazed at how drastically the performance went away when I brought it into the office. It worked very well at home, and picked up weak stations, and sounded clear, even in my workshop, across from the computer. But at the office - static and hum.

I'm going to keep an eye out for a small FM-only set.

-Ian

[jeffsod]

Funny you should mention the GE superradio we have one at our office that supplies the music for calls on hold. I brought it in when they had exactly that trouble. Couldn't get a decent signal with any other radio in the location they had it setup (closet). I have owned three of these. Bought my first GE Superadio 1 when I was a teen and brought it everywhere! Pretty much killed that one and bought a superradio 2. Love em.

[Chad Hauris]

Originally Posted by RetroHacker

Yeah, I figured as much - the All American 5 design was well known for it's ubiquity and low cost - not it's performance.

I was just amazed at how drastically the performance went away when I brought it into the office. It worked very well at home, and picked up weak stations, and sounded clear, even in my workshop, across from the computer. But at the office - static and hum.

I'm going to keep an eye out for a small FM-only set.

-Ian

I did a test with a Westinghouse 5-tube small AM radio with ferrite bar antenna and a GE Superadio 1 in the same location. These were in the second story window of a downtown brick and concrete building.
The Westinghouse had all electrolytics replaced...other caps were ceramic.

The GE got a good quality AM signal where the Westinghouse picked up a lot more noise. There were no computers or TV's turned on in the area...the only interference was from fluorescent lights.
I think some of this noise must be coming in on the power lines and maybe directly into the tube filaments? It's kind of a puzzle why one radio can be really noisy and one can be clean in the same location. Both were using just the internal antennas.

[Old1625]

The Superradio IIRC has at least one tuned RF amp stage, where as the All American 5s almost never did. That preselector can filter out a lot of spurious noise, and peak up the desired carrier to a level much above the noise.