I have the opportunity to get a hold of a couple of HP Signal Generators

[Polaraligned]

The HP 8640B is the best non-synthesized signal generator they made. Extremely low phase noise. It covers 500 KHz to 1 GHz. They made a down converter for it to drop the low end coverage. Does AM and FM modulation. Weak points are the gears that are shrinking and cracking (but can usually be repaired) and the little metal fingers on the switches that sometimes fall off. These sell for a few hundred dollars in good working order.

I am not familiar with the 8654A. I have 4 or 5 other synthesized HP generators, the best is the 8662A by far. Sweeps and has 5 programmable markers.

Yes, most HP SG's are good if they are working.

[vortalexfan]

Originally Posted by Polaraligned

The HP 8640B is the best non-synthesized signal generator they made. Extremely low phase noise. It covers 500 KHz to 1 GHz. They made a down converter for it to drop the low end coverage. Does AM and FM modulation. Weak points are the gears that are shrinking and cracking (but can usually be repaired) and the little metal fingers on the switches that sometimes fall off. These sell for a few hundred dollars in good working order.

I am not familiar with the 8654A. I have 4 or 5 other synthesized HP generators, the best is the 8662A by far. Sweeps and has 5 programmable markers.

Yes, most HP SG's are good if they are working.

Well I picked up the HP HP 8640B on Wednesday and I got it home and hooked it up to try it out and it doesn't seem to be wanting to put out a test tone (400 hz or 1kHz tone) ar the frequency dialed in on the frequency readout (for example I tried to dial in .45500 MHz on the readout or 455 kHz), and when I tried to tune to the low end of the AM band on a known working AM radio the test tone couldn't be heard and neither could the RF signal unless I went up almost 35 kHz on the readout on the signal generator.

Any ideas as to what's going on here? Is my radios IF Freguency that far off or is there something wrong with the calibration of the signal generator?

[Polaraligned]

Originally Posted by vortalexfan

Well I picked up the HP HP 8640B on Wednesday and I got it home and hooked it up to try it out and it doesn't seem to be wanting to put out a test tone (400 hz or 1kHz tone) ar the frequency dialed in on the frequency readout (for example I tried to dial in .45500 MHz on the readout or 455 kHz), and when I tried to tune to the low end of the AM band on a known working AM radio the test tone couldn't be heard and neither could the RF signal unless I went up almost 35 kHz on the readout on the signal generator.

Any ideas as to what's going on here? Is my radios IF Freguency that far off or is there something wrong with the calibration of the signal generator?

What test equipment do you have at your disposal? An oscilloscope and frequency counter would be nice. Maybe modulation is not working? How are you coupling signal into radio? The readout on these is just a frequency counter as they are not synthesized, so the internal cavity oscillator is working, but you still may not be getting output if the attenuator is not working. It is just hard to say from what you are describing without trying to look for signal output on oscilloscope. These are very difficult units to work on as is ALL HP equipment. If you are not experienced with these it may just be better getting a working unit. Did your friend say the unit was working? You NEED the service manual to repair these. HP has flow charts for troubleshooting, but that also requires test equipment to do so.

[vortalexfan]

Originally Posted by Polaraligned

What test equipment do you have at your disposal? An oscilloscope and frequency counter would be nice. Maybe modulation is not working? How are you coupling signal into radio? The readout on these is just a frequency counter as they are not synthesized, so the internal cavity oscillator is working, but you still may not be getting output if the attenuator is not working. It is just hard to say from what you are describing without trying to look for signal output on oscilloscope. These are very difficult units to work on as is ALL HP equipment. If you are not experienced with these it may just be better getting a working unit. Did your friend say the unit was working?

I do have an oscilloscope, would I just hook the output of the signal generator up to one of the inputs on the 'scope and see if it picks up a signal?

As for how I was coupling it up to the radio, I was using some 50 ohm BNC clip leads and clipping them to the proper coupling points on the radio.

[Polaraligned]

Originally Posted by vortalexfan

I do have an oscilloscope, would I just hook the output of the signal generator up to one of the inputs on the 'scope and see if it picks up a signal?

As for how I was coupling it up to the radio, I was using some 50 ohm BNC clip leads and clipping them to the proper coupling points on the radio.

Yes, you should be able to see a clean sine wave on the oscilloscope with modulation turned off. If your o-scope has a 50 ohm input use that, otherwise a high impedance input is ok but the amplitude will be a little off. Sinewave should still be clean.

Clipping the 50 ohm output to the radio is dangerous for the signal generator. You should use a .01uF or so capacitor to isolate the signal generator from the radio.

[vortalexfan]

Originally Posted by Polaraligned

Yes, you should be able to see a clean sine wave on the oscilloscope with modulation turned off. If your o-scope has a 50 ohm input use that, otherwise a high impedance input is ok but the amplitude will be a little off. Sinewave should still be clean.

Clipping the 50 ohm output to the radio is dangerous for the signal generator. You should use a .01uF or so capacitor to isolate the signal generator from the radio.

Ok. I've got a BNC to BNC cable I'll try hooking the signal generator up to the 'scope and see if I get a clean sine wave.

[vortalexfan]

It took me a while to figure out which hookup on the 'Scope to hook the signal generator up to to test the signal generator, but I was able to figure out that the signal generator is indeed working as I was able to get a clean sine wave onto the 'scope.

See picture below.