There's another difference - the dollars are a LOT larger on those than on
the GDO.
73, Jim
----- Original Message -----
From: "Jim Lux" <jimlux@earthlink.net>
To: "Jeff Carter" <towertalk@hidden-valley.com>
Cc: <towertalk@contesting.com>
Sent: Thursday, March 20, 2008 6:33 PM
Subject: Re: [TowerTalk] Using a dip meter
> Jeff Carter wrote:
> > I've been following this thread with interest, largely because I'm
> > ignorant about the utility of these meters. Jim, your description
> > fits with what I had concluded about them, that being if you had
> > pretty much anything else to use, it would be better. I understand
> > how they work but using a GDO always seemed pointless.
> >
> > I have seen these things on eBay for years, but I still cannot think
> > of a single instance where it would be of more utility than more
> > modern antenna tools, so I never bought one.
> >
> > My question is, am I wrong? Is there some situation I have not yet
> > encountered where only a GDO will do? Jim, you said that for some
> > systems it's convenient. I can't picture one for the life of me.
>
> The GDO has two aspects that are convenient:
> 1) It's inherently a narrow band detection process, so interfering
> signals (a real issue if you're trying to dial in a 160m antenna and
> there's a pesky AM broadcast station near by)
> 2) It's not oriented towards a 50 ohm system in particular. You can
> adjust the coupling ratio to suit the measurement (granted, more an art
> than science).
>
> >
> > I usually use a HP network analyzer for general things, and the little
> > Autek boxes for spot checks.
>
> You should be able to use the VNA.. Set it up to measure S11, then run
> your coax up to a coupling network of some sort. In theory, you'd want
> a transformer to transform the 50 ohms to whatever the loop resonant R
> would be, but in reality, since you're going to be using loose coupling,
> that will set the magnitude. I've used some turns of magnet wire on a
> BNC connector (and you can add and remove turns by hand) You'll see the
> bump in S11 magnitude at the resonant frequency of the system under test.
>
> (of course, the VNA's probably not handheld. Anritsu has a handheld
> (2hands) device that does this sort of thing, though, if you have a few
> tens o'kilobucks laying around. It's pretty neat)
>
>
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