[TenTec] Colliins SWR Bridge.....I'm also interested in EWR-PWR instrumentation.

[Ken Brown]

>
> I'm not overly impressed with the commonly accepted Bird meters in the ham
> community. I am looking for something much better, for sure. Guess I should
> look into this Collins Bridge 312B-4 or go to calibrated occiliscopes.
>   
Not sure what you mean by this. A calibrated oscilloscope, with a 
properly compensated probe, may be able to make a more accurate RF 
voltage measurement. If you want an indication of the ratio of forward 
and reflected RF power, you will still need to connect the scope to some 
type of directional coupler or bridge.

Last time I checked oscilloscope voltage measurement accuracy 
specifications, good ones were on the order of +/- 1%. (That was a long 
time ago, so maybe they are a lot better these days. But then if you're 
thinking of using a used oscilloscope.....) When using that figure to 
calculate power, assuming a known impedance, using E squared/R, you are 
going to get hardly better than +/- 2% accuracy. If you include 
imbalances in the directional coupler forward and reflected coupling 
factors, pretty soon you're going to be back down to Bird model 43 
wattmeter accuracies.

Anyway, when it comes to checking an antenna system VSWR, super high 
accuracy is not needed to determine whether the SWR is low enough, nor 
is it needed to adjust a matching device, or the antenna, for minimum 
reflected power.

DE N6KB


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