08-03-2011, 12:10 PM
Bob, I've been out of town, so I didn't see the description of your additional problem until now. Have you made any progress resolving it?
From your post of July 2, it doesn't sound like your main problem then was alignment, so I wouldn't yet try the alignment I suggested UNLESS the stations you can receive are offset on the dial from their actual frequencies. Say the station you receive at 1530 on the dial has an actual frequency of 950, or something like that. In that case dial alignment is called for.
You can test your signal generator calibration fairly easily. Did you get a manual? It should have a way to do the initial calibration, since it is a kit. If you didn't get a manual, here is how I would try it.
1) Take a piece of scrap wood or plastic about 3 or 4 inches across. Size is not that important. Wrap 3 or 4 turns of wire around the wood, leaving a long lead to plug into the signal generator.
2) Connect this lead to the signal generator through a .1uf capacitor. This cap isolates the coil you have just made from any high voltage coming from the output tubes of the signal generator.
3) Place the coil you just made very near the antenna of any radio that is working properly. Lean it against the side or back of the radio if possible. A radio with digital tuning is preferable. Tune this radio to a quiet spot on the lower end of the dial, say around 600 KHz.
4) Set the signal generator on the range appropriate to the AM band. Set the signal generator output to modulated RF. Set the RF and modulation levels to the mid point. Set the signal generator frequency to about the same frequency you set on the radio. Sweep the signal generator frequency up and down around this frequency until you hear a tone in the radio. If you don't hear a tone, adjust the RF and modulation levels up, and try sweeping again.
5) When you get a tone, check the correspondence between the radio dial and the signal generator dial. Write it down. You probably have an offset, but it shouldn't be too high.
6) Set the generator and the radio to another quiet frequency near the top of the dial, say between 1500 and 1600 KHz. Sweep the generator frequency until you get a tone. Note the radio and generator frequencies. If you are lucky, your offset is nearly the same at both ends of the dial, so you can simply offset the generator reading by this amount and call it good. If the offset is greater at one end of the dial, then you will probably want to make a table of the offsets at various frequencies and use this table when you align radios so you can be fairly close.
Actually, the dials of old radios like a 42-355 don't have very good resolution, so perfect calibration of your generator isn't necessary. If you know the offset at, say, 550 KHz, then you can use the same offset for 455 KHz and be accurate enough. If anyone has a better way to calibrate at 455, chime in!
From your post of July 2, it doesn't sound like your main problem then was alignment, so I wouldn't yet try the alignment I suggested UNLESS the stations you can receive are offset on the dial from their actual frequencies. Say the station you receive at 1530 on the dial has an actual frequency of 950, or something like that. In that case dial alignment is called for.
You can test your signal generator calibration fairly easily. Did you get a manual? It should have a way to do the initial calibration, since it is a kit. If you didn't get a manual, here is how I would try it.
1) Take a piece of scrap wood or plastic about 3 or 4 inches across. Size is not that important. Wrap 3 or 4 turns of wire around the wood, leaving a long lead to plug into the signal generator.
2) Connect this lead to the signal generator through a .1uf capacitor. This cap isolates the coil you have just made from any high voltage coming from the output tubes of the signal generator.
3) Place the coil you just made very near the antenna of any radio that is working properly. Lean it against the side or back of the radio if possible. A radio with digital tuning is preferable. Tune this radio to a quiet spot on the lower end of the dial, say around 600 KHz.
4) Set the signal generator on the range appropriate to the AM band. Set the signal generator output to modulated RF. Set the RF and modulation levels to the mid point. Set the signal generator frequency to about the same frequency you set on the radio. Sweep the signal generator frequency up and down around this frequency until you hear a tone in the radio. If you don't hear a tone, adjust the RF and modulation levels up, and try sweeping again.
5) When you get a tone, check the correspondence between the radio dial and the signal generator dial. Write it down. You probably have an offset, but it shouldn't be too high.
6) Set the generator and the radio to another quiet frequency near the top of the dial, say between 1500 and 1600 KHz. Sweep the generator frequency until you get a tone. Note the radio and generator frequencies. If you are lucky, your offset is nearly the same at both ends of the dial, so you can simply offset the generator reading by this amount and call it good. If the offset is greater at one end of the dial, then you will probably want to make a table of the offsets at various frequencies and use this table when you align radios so you can be fairly close.
Actually, the dials of old radios like a 42-355 don't have very good resolution, so perfect calibration of your generator isn't necessary. If you know the offset at, say, 550 KHz, then you can use the same offset for 455 KHz and be accurate enough. If anyone has a better way to calibrate at 455, chime in!
John Honeycutt
