[Boatanchors] Grid Dip Oscillator (GDO) Info Request

[K5MYJ]

The current will change smothly with tuning if not coupled to a resonat 
coil.

If you have current in the meter the GDO is working.

But to measure a coil the coil must have a capacitor in parrellel.

In antennas there are two kinds of coils used.

A coil without a parrellel capacitor is to make the antenna look longer. It 
won't dip.

A coil with a parrellel capacitor is a TRAP. It is used to shorten an 
antenna. It will dip.

Bob Macklin
K5MYJ
Seattle, Wa.
"Real Radios Glow In The Dark"
----- Original Message ----- 
From: "Jim" <Jbrannig at verizon.net>
To: "D C _Mac_ Macdonald" <k2gkk at hotmail.com>; <boatanchors at mailman.qth.net>
Sent: Friday, June 01, 2018 11:58 AM
Subject: Re: [Boatanchors] Grid Dip Oscillator (GDO) Info Request


> For starters, the signal from the GDO should be heard on any unshielded 
> receiver.
>
> Next, find or calculate the inductance a coil.  Add a capacitor in 
> parallel and calculate the resonant frequency. (I suggest a mid HF 
> frequency. 40 or 20M)
> Put the GDO coil in close proximity, windings parallel, to the coil and 
> sweep the frequency.
> There should be a pronounced dip on the meter at resonance.
> Proximity to the coil will influence the depth of the dip.
>
> If no signal and no dip at resonance, then you have to trouble shoot the 
> GDO.  Start with the tube and work until it produces some RF, as heard on 
> a receiver.
>
> Good Luck,
>
> Jim
>
> -----Original Message----- 
> From: D C _Mac_ Macdonald
> Sent: Friday, June 01, 2018 2:20 PM
> To: boatanchors at mailman.qth.net
> Subject: [Boatanchors] Grid Dip Oscillator (GDO) Info Request
>
> I am trying to repair a Cushcraft R-7000 vertical which suffered a damaged 
> first (bottom) trap when the antenna folded over at the tubing of that 
> trap in a windstorm.  I found some rather detailed help with a Google 
> search that described how to check traps with a GDO.  I have two Millen 
> GDO units, but I am not sure either is functional.  The grid current 
> varies as I tune the GDO across each frequency band, but that is in "free 
> air" without an L/C circuit near it.  Coupled to an L/C circuit, I find NO 
> dip other than what is seen without being coupled.  Supposedly I should 
> see a dip with the coil close coupled to the in-line tubing of a trap.
>
> I don't know if I have an instrument problem or an operator problem.
>
> Suggestions welcomed!
>
> 73 de Mac, K2GKK/5(Since 30 Nov '53)Oklahoma City, OKUSAF Retired 61-81FAA 
> Retired 
> 94-10______________________________________________________________
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