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From: email@example.com (carltons)
Subject: Re: Improving a Grid Dip Meter
References: <firstname.lastname@example.org> <email@example.com>
User-Agent: NewsWatcher-X 2.2.3b2
NNTP-Posting-Date: Wed, 01 Jan 2003 11:00:27 GMT
Date: Wed, 01 Jan 2003 11:00:27 GMT
In article <firstname.lastname@example.org>, LA8AK,xnd@Online.NO wrote:
> I read in sci.electronics.design that email@example.com (carltons)
> wrote on Tue, 31 Dec 2002 01:26:34 GMT :
> >John Woodgate wrote:
> >> I read in sci.electronics.design that carltons
> >> wrote (in >> om>) about 'Improving a Grid Dip Meter', on Sun, 29 Dec 2002:
> >> >The idea is sound, but I believe the
> >> >implementation to be faulty in that the circuit be measured would pull the
> >> >test instrument off freq. rendering the reading off by the length of the
> >> >pull.
> >> No, with *loose* coupling and the GDO tuned for minimum grid current,
> >> there is no pulling. The circuits are synchronous.
> >Very loose I would imagine and probably not a dramatic effect to note.
> it is better to use a signal generator with a coax cable to a probe
> consisting of 2-5 turns dependent on frequency, and measure the
> voltage drop on the output from signal generator when 'dip' occurs.
> You could also use a potmeter to vary the impedance between the
> generator and voltage detector with coaxcable
> It was described in QST May 1986
> Hayward "Simplified Scalar Network Analyzer" p.14-20
> (with attachments for various measurements)
> (Feedback Aug p.40)
> "Beyond the dipper(using signal generator) W7ZOI QST"
> Just keep the HP651B for the purpose since it is easier with a
> continous variable generator than a thumbweel tuned SG.
> remove ,xnd to reply
This makes more sense, Jan-Martin. I guess my problem with the whole
thing revolves around the fact that the concept of grid dipping is good
for approximate use, but not too good if you have limited resources (i.e.
equipment and advisors) and are trying to build a project. I used a gdo
in the Navy which was considered at the time to be state of the art (I
think it was the military version of the James Millen gdo), but my results
did not provide much help in determining inductance values. I got all
kinds of dips and peaks everywhere, some of which were not too dramatic in
depth. I would suspect that much of the problem was due to outside
interference at frequencies near the measurement. I ended up building a
bridge and those results were a difference of day and night. Moral of the
story is that the right tool will do the job, not to mention the fact that
doing the project is very educational in itself. :-)
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