On Thu, 06 May 2004 17:27:52 +0100, Paul Burridge
wrote:

On Thu, 06 May 2004 04:12:58 GMT, (John Crighton)
wrote:

You are not following me here, I am talking about accuracy here.
Stick your ohm meter on your Marconi generators RF output
connector and click through the ranges. You will see a nearly
constant resistance reading. A small variation in resistance
reading is acceptable. No variation is prefection. A large variation
in resistance reading, such as short circuit or open circuit in any
attenuator switch position means it is stuffed. Just for interest
tell us what you measure.

Okay, well the vast majority of the positions are bang on 50 ohms.
About 7 are 51 ohms and after that point, the very end of the range
goes one ohm at a time up to 56 ohms as the worst instance. I guess
that's acceptable?

Yes, that is fine. You are laughing with that unit. Great! :-)


The thing is, John, I rather like the *look* of my AVO. What's
stopping me from just hooking up an external, switched attenuator?

Nothing! That is an excellent idea.

And you say the use of pots is cheapo, but this is an ex-military
piece of kit withe MOD record stamped on the front. The military don't
buy junk - well, apart from Nimrod, that is.

Heh heh heh, I can see where you are coming from. Military
buying junk is a whole topic on its own.


It does. There's no leakage whatsoever from the case. Nonetheless, the
attenuator appears to be shot to bits. I either get full output or
nowt but jitter. But I can't bear to junk it so I'm going to (in due
time) try to replace the pots. You can't really blame me, can you?

I like to see old stuff preserved and working too.

It'd be a sin to chuck one of these onto the trash heap. It would also
make a very nice looking ornament for the mantlepiece; looks a lot
nicer in real life than that photo I took.

Yes it would be a sin to chuck it. Just don't expect a lot from it.



I thought I would be helping a beginner who is
struggling with filters and may need a second good sig gen.
I'll get out your hair now. :-)

I was a "beginner" 35 years ago. Obviously I'm not making much
progress. Thanks for the advice, anyway, it's always valued.

I should have said helping a fellow beginner and hobbyist. I am
in the same boat as you, continually struggling. So I know what
it is like being in the dark and feeling my way. :-)

Getting back to your external attenuator idea.
I often buy dud damaged boat anchor sig gens, for a few dollars
at ham meetings/trash and treasure buy and sells, in the hope of
finding a nice attenuator. I have humped a few monsters home
only to find rubbish inside. I have been lucky a couple of times.
There are plenty of ready made attenuator units for sale
usually for big dollars from a hobbyists point of view.

Have a look at this one.
http://cgi.ebay.co.uk/ws/eBayISAPI.d...2959 880&rd=1
How far is Farnam from you? Postage is 4 quid.
No information as to the maximum frequency but if you can
pick it up for a tenner it might be a good buy even if you use
it for low frequncies for something else. I am sure you spend
more that that at your local. Take a chance! Bid 10 max. :-)

Regards,
John Crighton
Sydney