[TenTec] OmniVI Plus Over Drive Amp

[Dr. Gerald N. Johnson]

On Wed, 2008-06-25 at 17:53 -0700, Jim WA9YSD wrote:
> I had to bring up the tolerance of the meter itself.  Could not resist
> cause it brings into focus real accuracy and the misnomers that
> tolerances play on it..  It is more accurate than 5% full scale and the
> SWR gets twisted some what when tolerances is talked about.  The design
> of the Bird had to have taken that into consideration.  Been to long
> since I heard this argument. Gotta be 40 years ago.

That meter tolerance is important. And the 30 microamp meter makes
errors more likely because of pivot or taut band friction. There's not
much horsepower available to fight the springs and pivot friction.

Then there's the special diodes without much forward drop. I have a 5 or
10 watt slug that I bought at a hamfest cheap. Cheap because the diode
was blown. With a Schottky diode it takes a certain amount of power,
like 5 or 10% of full scale before there's any DC to the meter. That's
not the right diode.
> 
> It has something to do with with the 1st, 2nd and 3rd part of the 
> scale and 33.3333333...% or 66.66... % exponentially and the non 
> linearity of the power curve.  Been too long to remember this stuff. 
>  Decay rates have a similar cure but inverted.  This is out of my realm. 
>  Please set this straight.

Well the power scale is not linear in power. It more like linear in
square root power. Thats what it would be for a perfect diode because
the diode is seeing voltage and that's linear and power is proportional
to voltage squared. Its complicated by the diode at low voltage acting
as a square law detector instead of a rectifier. I'm pretty sure the
Bird meter movement is linear in current at least I've not noticed
shaped pole pieces like have been used with thermocouple ammeters.
> 
>  Keep The Faith, Jim K9TF/WA9YSD
> 
73, Jerry, K0CQ