[TowerTalk]Tuner Losses & Bird ratings

[Tom Rauch]

> << 
>  The most accurate way to measure loss in a tuner with different 
>  source and load impedances is to measure the temperature rise in 
>  the tuner, not the power levels. >>
> 
>  . 73, Tom W8JI
>  w8ji@contesting.com
> 
> Right on Tom.  Basically, if a tuner can match the Z at the end of the
> feedline (1:1 SWR is obtained at the input of a tuner), 100% transfer of
> power occurs to the antenna less the losses in the feedline which are
> predictable and the losses in the tuner as measured by the "heat test." 
> There are exceptions.  I had a load that the Johnson MtatchBox matched 1:1
> but wasn't transferring all the power without getting warm--with 100 W as
> the inductors were heavy.  With 1 KW I had arcing which tipped me off of a
> problem but no apparent heating with short tests. 

For a low power test, if you placed the tuner in a styrofoam 
container and measured temperature rise in the box over a period 
of time, you could measure the power loss.

Of course high power, as you found out, shows the problem right 
away.

Most tuners can only dissipate 50-100 watts without severely 
overheating or failing, because that loss is concentrated in one or 
two components. So if you are running several hundred watts or 
more and nothing is melting, you can be sure efficiency is high.

Arcing can be a different issue, arcing is not related to loss. It is a 
voltage breakdown problem. Arcing does not necessarily mean 
losses are high.


73, Tom W8JI
w8ji@contesting.com

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