signal generators

To: mail11:;-at-msd26.ENET.dec-dot-com (-at-teslatech)
Subject: signal generators
From: "I am the NRA." <pierson-at-msd26.ENET.dec-dot-com>
Date: Fri, 15 Dec 95 17:17:58 EST
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>2. Series resistance does make a difference.  I have a 0-10 mHz 
>Hewlett Packard signal generator that has 75 ohm and 600 ohm 
>outputs.
	I DO NOT know about the specific generators in question.  BUT!
	I have been "bit" by generators with a connector marked "mumble" ohms
	AND THE OUPUT WAS NOT MUMBLE OHMS!!!!.  When pressed, the vendors usual
	excuse was that the generator met its spec with "mumble" ohms connected
	TO THAT PORT.  Which is not the same thing at all as having a "mumble"
	Ohm port.

	Before assuming a port labelled 75 ohms is 75 ohms (or whatever)
	_verify_:
		Set source to convenient level.
		Measure voltage.
		Attach 75 ohms (if labelled as 75 ohm source).
		Voltage should drop by 1/2.
			If its not, its not a 75 ohm source.
		A little ohms law fiddling will yield the approximate output
		impedance.  This figure may vary with frequency or with
		amplitude setting or .....

	One approach to a low z source would be a transformer, home brew, if
	needed, to step "down" the Zo of the generator...

	regards
		dwp