Steve Thompson wrote:
>>
>> Does anyone know how to adjust a Bird 1000H slug (1kW 2-30MHz)?
>>
>> It's reading only 400W when a known good slug reads 1000W, but there
>> seem to be no trimpots or other adjustments inside.
>If it's that far out it might need repairing rather than adjusting.
Thanks to everyone for all the suggestions.
The good slug is not mine, so I can't open it up. However, this morning
I finally got the brain into gear, and checked the DC resistances of the
bad and good slugs. They weren't the same, so I took the bad slug apart
to get at the diode itself. It is not completely destroyed, because it
is partly detecting RF, but it has a lot of reverse leakage.
The markings say "5-154-2 M/A", so what type would replace it? Unless
the threshold voltage and internal resistance are the same as the
original part, the calibration will be wrong.
That brings me back to the question of adjustment. The HF slug is not
the same as the VHF types because there is a rectangular ferrite core
that completely fills the space inside the loop. That core has a
multi-turn secondary winding, and the diode measures the voltage
developed across it (roughly speaking - the circuit is too hard to
describe in words).
There's no possibility of bending the loop in any big way, but the
grounded end is secured by a screw and can be moved just a little. I
guess that must be the adjustment, because there isn't anything else.
Oh boy. Even if I can find a replacement diode, re-calibrating this
thing is going to be *big fun*...
--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek
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