[Boatanchors] Grid Dip Oscillator (GDO) Info Request

[hwhall at compuserve.com]

The meter change over its tuning range is normal, it just means the GDO doesn't put out the same level over the entire range of operation.  Normal stuff.  A tip is to tune for the dip in the direction of increasing grid current.  A dip is harder to spot when the meter is already moving downward.  

Coupling well enough to get a reading on a trap inside a metal housing like the R-7000 seems to use is a real problem. Might have to run a wire across the trap with one or two small turns to get indications - just don't expect the dip to be in the exact right place, due to the extra inductance of that jumper/turn.  I think if it might have been damaged, as you indicated, I'd bite the bullet & open it up.

 

 Wayne
WB4OGM

 

-----Original Message-----
From: D C _Mac_ Macdonald <k2gkk at hotmail.com>
To: boatanchors <boatanchors at mailman.qth.net>
Sent: Fri, Jun 1, 2018 12:20 pm
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, OK​
USAF Retired 61-81​
FAA Retired 94-10​



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