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# home-brew vswr meter

tom
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 03-18-2005, 01:54 PM

How minimal of circuit would be required to tell the difference between
whether a load was inductively reactive or capacitively reactive at
frequencies between 100mhz and 200mhz, and in the 5 to 100 watts range? A
one, basically.

Active8
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 03-18-2005, 07:52 PM
On Fri, 18 Mar 2005 13:54:01 GMT, tom wrote:

> How minimal of circuit would be required to tell the difference between
> whether a load was inductively reactive or capacitively reactive at
> frequencies between 100mhz and 200mhz, and in the 5 to 100 watts range? A
> one, basically.

A VSWR meter won't tell you that, just that there's a mismatch.
Start longer and prune for best VSWR. That's as simple as a couple
of diodes, a meter, and some resistors and/or a pot - maybe a power
range switch in leiu of the pot and a switch for forwared/reflected
power. Additionally you'd need some type of directional coupler - 2
parallel PCB traces... or a piece of insulated 24 AWG wire threaded
under a length of coax braid... or a torroidal coil with the coax
running through it. Unless you can get a crossed-needle display,
you'll have to calculate the VSWR from the fwd/rev readings or just
prune until the reflection are minimum. Knowing the VSWR would help
you compare with other antennas.

Oh, yeah. Is google's server down or something?
--
Best Regards,
Mike

Fred Abse
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 03-18-2005, 08:18 PM
On Fri, 18 Mar 2005 13:54:01 +0000, tom wrote:

>
>
> How minimal of circuit would be required to tell the difference between
> whether a load was inductively reactive or capacitively reactive at
> frequencies between 100mhz and 200mhz, and in the 5 to 100 watts range? A
> one, basically.

If, by "VSWR meter", you mean the usual directionally sampled line
arrangement, it won't tell you. What it actually measures is forward and
reflected *current*, hence power. Whether the mismatched load is
resistive, capacitive, or inductive, it neither knows nor cares.

Google for "VHF bridge", and see if that gives you any ideas

--
"Electricity is of two kinds, positive and negative. The difference
is, I presume, that one comes a little more expensive, but is more
durable; the other is a cheaper thing, but the moths get into it."
(Stephen Leacock)

tom
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Posts: n/a

 03-18-2005, 08:20 PM
I'm not sure I understand your point Mike --- what do you mean by, "Oh,
yeah. Is google's server down or something?"

dB
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Posts: n/a

 03-18-2005, 09:30 PM
"tom" <(E-Mail Removed)> wrote in message news:<Z3B_d.711235\$Xk.444675@pd7tw3no>...
> How minimal of circuit would be required to tell the difference between
> whether a load was inductively reactive or capacitively reactive at
> frequencies between 100mhz and 200mhz, and in the 5 to 100 watts range? A
> one, basically.

A directional power meter (s.w.r. meter) will not differentiate
between the two cases.

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