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Author Topic: Signal generator help  (Read 1132 times)
WU0L
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Posts: 9




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« on: May 05, 2009, 04:33:54 PM »

I recently acquired an HP 675A sweep signal generator cheap but I don't have a manual.  Seems like no matter what I do, or settings I use, it puts out two different RF signals of slightly different frequencies.  I can observe these on the oscilloscope but my frequency counter cannot resolve between the two and gets all confused.  I have never used a "sweep" generator before, but I think I have the sweep turned off and set to "CW".  Any suggestions?

thanks   Mark    WU0L
meyerfin@hotmail.com
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WX7G
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Posts: 5945




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« Reply #1 on: May 06, 2009, 09:51:29 AM »

Do you have FM or AM modulation activated?
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WU0L
Member

Posts: 9




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« Reply #2 on: May 06, 2009, 12:39:13 PM »

The AM modulation is turned off.  There is no FM modulation control available as near as I can tell.  Thanks for the help.

Mark WU0L
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WB2WIK
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Posts: 20558




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« Reply #3 on: May 07, 2009, 09:32:14 AM »

Do you have a marker turned on?  I don't know this model specifically, but most sweep generators can also produce a marker signal, so if you run with the marker on, it's producing two signals, at different frequencies, simultaneously.

WB2WIK/6
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WU0L
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Posts: 9




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« Reply #4 on: May 08, 2009, 07:45:45 PM »

The marker is turned off, so this is not the problem.  Thanks for the suggestion.

Mark WU0L
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KC9KEP
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Posts: 208


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« Reply #5 on: May 14, 2009, 12:52:34 PM »

Mark,

I went to the "Agilent" WEB page (Agilent owns
the HP stuff) and looked under Test & Measurement,
but it only tells me that the HP 675A is discontinued and they have no archived manual.  They do provide a list of links that may have old manuals.

Sounds like your unit is "stuck" maybe in a two-tone test mode?  (I don't know the HP 675A).

You should be able to set the starting and ending sweep frequencies and how radiply the generator sweeps from start to end.

And, it should be "easy" to display on a scope .. i.e., you should see a sin wave that compresses & snaps back repeatedly :-)

Sorry I can't offer more help ..



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WU0L
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Posts: 9




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« Reply #6 on: May 15, 2009, 10:40:27 AM »

Thanks for the tips.  Using your suggestion, I did observe the "sweep" affect between the start and stop frequencies.  I can only get it to sweep once in the "auto", "manual" or "retrace" mode.  I would think in the "auto" mode it would periodically sweep.

Do you know what the "F/delta F" mode would be? The "delta" being represented by a triangle symbol on the dial. This is the control that has "Start/Stop", "F/deltaF", "CW", and "External Control" for modes.  Then another control allows you to set the "delta F" to various kHz or mHz settings. I can observe no changes in output no matter where it set the "delta F" when in "F/delta F" mode.

Gradually I am learning a few things about this machine, and also it seems to be coming to life a bit more as I keep it powered up.  Probably it had been retired for a long time.

Thanks,  Mark  WU0L  
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KE4DRN
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Posts: 3721




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« Reply #7 on: May 18, 2009, 06:28:45 PM »

hi Mark,

try the hp yahoo group, I'm sure
you can find a pdf manual no cost.

http://tech.groups.yahoo.com/group/hp_agilent_equipment/

73 james
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WU0L
Member

Posts: 9




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« Reply #8 on: May 19, 2009, 01:04:48 PM »

Thanks for a good idea.

Mark WU0L
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W6IEZKEN
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Posts: 29




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« Reply #9 on: June 14, 2009, 02:26:16 PM »

The Delta sign refers to the amount of change between two frequencies.The first could be 10Mhz and the second could be 15Mhz, so the unit would sweep between 10Mhz And 15Mhz.This is useful for determining bandwidth and shape factor in I.F.'s. or filters.A manual would be the best solution to your questions and keep in mind the reason you don't see a change when switching is that circuit may not be working.Get the main circuit working and then go to each sub-circuit function.A manual of any sweep generator from HP in that period of time will at least help you understand the functions even if there are differences.If you can't find a free manual you can buy one from the commercial manual suppliers for about $30.
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WU0L
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Posts: 9




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« Reply #10 on: June 21, 2009, 10:59:57 AM »

Thanks.  I gotta get a manual.

Mark
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VE3CLD
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Posts: 2




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« Reply #11 on: July 24, 2009, 05:41:40 PM »

I have also recently acquired a 675A with the 676A Phase/Amplitude Tracking Detector.  A manual came with the 675A but unfortutately it is not of much use when used with the 676A - hopefully someone can help out there!  There is very little info available on the net besides an application note that is rather vague about how everything is connected...

I would be happy to copy/scan the 675A manual if required.

Now I am looking for some help with the 676A!

73 de Dan VE3CLD
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WU0L
Member

Posts: 9




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« Reply #12 on: July 29, 2009, 06:00:13 PM »

If it wouldn't be too much trouble please scan the manual for the 675A.  Hopefully that will help me get this thing running correctly.

Tnx

Mark
WU0L
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VE3CLD
Member

Posts: 2




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« Reply #13 on: July 29, 2009, 06:35:55 PM »

Sure - it will take me a while but if it helps someone I will be more than
willing to.  Turns out my problem was a bad contact in the crystal oven.

By the way - I got mine working with the 676A Tracking Phase/Amplitude
Detector and it works like a charm.  Very handy for tuning filters for traps
and tuned circuits!

To use your 675A - the frequency on the left side display is the one that should be generated in the CW position and in the delta f position, the frequency will sweep plus or minus the selected variation (selected on the delta f dial)around the frequency set here.  The only time the right hand freq display is used is when you are in start/stop mode and then is sweeps from the left hand freq to the right hand freq.

Hope that gets you started in the meantime...

I also purchased a 8407A Network Analyzer so hopefully will be able to do
stuff up into the low VHF region - just waiting now on my 8601A Sweep Gen to
arrive.

Regards,

Dan VE3CLD
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