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Measuring RF output impedance

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May 5th 04, 11:21 PM

Paul Burridge

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On Wed, 05 May 2004 18:45:36 GMT, (John Crighton)
wrote:

From an attenuator a large range is undesirable. The opposite
is what you want.

Oh, is that because the attenuator's maybe in parallel with the output
signal and earth?

Lets just call the RF output Z for this unit 75 ohms Nominal. :-)
And you have crappy pots to put up with. Not good.

Not good but not serious! I can always just replace the pots with ones
of equal values to the old ones - and better quality too.

This unit is a bit cheap in the attenuator department.
Pots for both course and fine controls. I don't like that idea.
I prefer a switched attenuator for course and a pot for fine.
I'd much prefer a switch for fine also but that would be
too expensive.

My Marconi uses two rotary-switched attenuator controls, actually.
What's the problem with pots? Switches can go noisy too...

Do a simple leakage test to see if this particular AVO
sig gen is worth keeping. On the bench beside the signal
generator place a radio and see if you can pick up the
signal from the generator. If a signal roars into the radio
then it is next to useless for serious or even hobby radio
work. Shield the RF output connector or short it.
( attenuator set to minimum output)
If it leaks RF and the frequency drifts a lot then you
might as well forget it.

Er, I *do* have a scope. Might that not be better or are you looking
for something a scope wouldn't show up?

Regards,

p.
--

The BBC: licenced at public expense to spread lies.

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