W2VW
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« on: January 18, 2011, 09:34:14 AM » |
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Anyone know how much audio it takes to drive the HP 8640B AM modulator to 100% modulation. No option 004 IIRC.
I tried +10 dBm and was only showing 20% on the 8640 meter. The internal tones work FB.
TIA.
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Steve - K4HX
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« Reply #1 on: January 18, 2011, 10:07:49 AM » |
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It's been a long time, but I think it's on the order of a volt or two.
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WD8BIL
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« Reply #2 on: January 18, 2011, 10:33:08 AM » |
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I have an 8657A here Dave. The ext. input is labeled 1V Peak.
Lemme do a quick test to see how much'll give me 100% on a scope!
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Steve - K4HX
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« Reply #3 on: January 18, 2011, 10:41:45 AM » |
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10 dBm is about 700 mV. Dunno if the external mod input is 50 Ohms.
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WD8BIL
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« Reply #4 on: January 18, 2011, 11:39:50 AM » |
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OK Dave, here's what I got....
Freq. 3885Khz (of course)
for 100% mod.
1KC - 2.15V P-P
2KC - 2.17V P-P
5KC - 2.21V P-P
10KC - 2.22V P-P
I know these 2 generators are different beasts but I wonder just how different their schemes are?
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Steve - K4HX
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« Reply #5 on: January 18, 2011, 12:33:23 PM » |
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I checked the manual. Nominal voltage to the external AM input is 1 V peak (0.707 RMS). Max voltage is 5 V pk. The impedance is 600 Ohms.
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W2VW
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« Reply #6 on: January 18, 2011, 03:47:12 PM » |
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Thanks Steve and thanks Buddly for checking.
I'll hit it with a medium source impedance and report back.
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WD8BIL
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« Reply #7 on: January 18, 2011, 04:00:40 PM » |
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Dave, I did hafta set the mod level on the generator to 99% before I could get full mod. Otherwise it was limited to whatever level was displayed no matter how much audio I pumped in.
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W2VW
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« Reply #8 on: January 18, 2011, 04:06:44 PM » |
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Ok. I had this working once before with a 3 diode setup and a transformer. I just grabbed one and it worked. Now I forgot exactly which stuff I used. Test equipment is all starting to look the same....
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WA1GFZ
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« Reply #9 on: January 18, 2011, 10:12:49 PM » |
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Dave,
I know the FM input works at about 1 volt. I build the phase locking circuit from the service manual for checking phase noise and drove the FM input with LC filtered output from a double balanced mixer. Bama had the manual but I can burn you a copy if you need it.
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W2VW
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« Reply #10 on: January 19, 2011, 01:04:30 PM » |
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Thanks Frank, I will get a little time to try this again an a day or two. I found manuals and even read part of them : ) Dave. Dave,
I know the FM input works at about 1 volt. I build the phase locking circuit from the service manual for checking phase noise and drove the FM input with LC filtered output from a double balanced mixer. Bama had the manual but I can burn you a copy if you need it.
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W2VW
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« Reply #11 on: January 20, 2011, 05:26:52 PM » |
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Self imposed fail.
Forgot about the limiter!
Now getting 100% positive with .250 volts of voice.
Thanks.
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W3SLK
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« Reply #12 on: January 20, 2011, 07:44:18 PM » |
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Dave said: Self imposed fail.
Forgot about the limiter!
Now getting 100% positive with .250 volts of voice.
Good! Now you can be like Ken, K8TV and hook it to your antenna to see how many people can hear you! BTW I heard him do this on 160 one night when he was out in OH and I was here in NEPA. |
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Mike(y)/W3SLK
Invisible airwaves crackle with life, bright antenna bristle with the energy. Emotional feedback, on timeless wavelength, bearing a gift beyond lights, almost free.... Spirit of Radio/Rush
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