[time-nuts] OT favorite signal generator?

Brooke Clarke brooke at pacific.net
Fri Jun 19 11:52:29 EDT 2009


Hi Patrick:

There are a bunch of signal sources that could be used.

The rack sized HP signal generators that weigh 50+ pounds were designed to have 
very low phase noise and although now many years old are still very good for that.

The HP 3325() is the only signal generator that has adjustable amplitude that's 
calibrated to a small fraction of a dB.  They still are the specified 
instrument for amplitude calibration of many other pieces of lab equipment and 
there is no newer instrument to replace them.  They don't have good specs in 
the frequency domain.

The HP 8648() series are reasonably small and light synthesized signal 
generators.  I got the 8648A Option 1EP which is specific for pager testing and 
includes many modulation enhancements. The prior versions of the 8648 did not 
have good enough specs to test pagers.
http://www.prc68.com/I/HP8648.shtml

A problem with injecting a signal into operating equipment is you may burn out 
the signal generator.  For example just touching a DC point feeds a step change 
back into the sig gen.  So it's good to have a series resistor and blocking cap 
to protect the sig gen.

You might be able to use a probe that generates something like narrow pulses at 
an audio rate as a universal signal source.

Have Fun,

Brooke Clarke
http://www.prc68.com

Patrick wrote:
> Hey everyone
> 
> Sorry for the off topic post. I have received great advice in the past
> with items for my little shop and I can't resist to ask again.
> 
> I am thinking about buying a signal generator. I suspect that I will
> mostly use it to inject low uV/mV signals into the amplification stages
> of the laboratory instruments I service.
> 
> Any feedback you have would be greatly appreciated-Patrick
> 
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