On Sat, 20 Dec 1997 18:29:08 Pete Smith <firstname.lastname@example.org> writes:
>In my case, the amp makes a huge difference. Just measuring with my
>transceiver, if I measure through the amp my lowest SWR on 20 falls
>above the band - 14450 or thereabouts - while measuring without the
>falls at about 14200. My Autek tracks very well with the transceiver
>this respect. Quantitatively, the minimum SWR readings are similar,
>with the amp and without. Clearly, these are transmission line
>"transformer" effects, intended or not. If your feedline isn't
>matched and a multiple of a half wave at the operating frequency, the
>way to see real resonant frequency is to measure at the antenna. At
>antenna, the resonant frequency is 14175.
>73, Pete Smith N4ZR
The reason that the observed SWR changes through an amplifier
is usually that the coax switching is performed by OPEN FRAME RELAYS
and there are moderately long spans of open wire to and from the relay,
thus CHANGING the effective Zo of the "transmission line" inside the
amplifier. This effect can often be compensated for by adding an
appropriate amount of capacitance (10 to 30 pf) to ground at the relay.
Be sure to use capacitors with adequate voltage and current ratings.
de Tom N4KG
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