[TenTec] Tuning Amp on 17 meters

[Robert Mcgraw]

Stuart makes a very good point about SWR bridges in general.  One thing
that contributes to error is the fact there may be current flowing on the
outside of the coax.  I have found this fact contributes to errors. 
Therefore using a UNUN or length of coax with a series of ferrite beads
to form an RF choke used between the SWR bridge and the antenna/load does
a lot in minimizing this issue.

Accurate SWR measurements depend not only on the instrument but and often
more importantly the technique that is used for the measurements.

73


> Taken with my previous post, just remember this about SWR and resonance.
>   Resonance is just the frequency where the inductive reactance cancels
> the capacitive reactance, BUT, some of the total may not be from the
> antenna alone.  That can be seen where the SWR does not null at the same
> frequency where reactance is zero.  And some of that could be imbalance
> in the SWR bridge measuring circuit.  Items like Bird wattmeters are no
> more accurate than 5 per cent generally, and
> if SWR bridges are that good, feel lucky.  There must be a reason you
> generally don't see them rated for accuracy.  For one thing they can be
> frequency dependent, depending on quality of bridge construction.
>
> Stuart
> K5KVH
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