[Boatanchors] Grid Dip Oscillator (GDO) Info Request

[Jim]

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 
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