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tom
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 Posted:
Fri Mar 18, 2005 7:54 pm Post subject:
home-brew vswr meter |
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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
home made VSWR meter, for someone who doesn't have access to a store-bought
one, basically.
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Active8
Guest
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| Posted:
Sat Mar 19, 2005 1:52 am Post subject:
Re: home-brew vswr meter |
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On Fri, 18 Mar 2005 13:54:01 GMT, tom wrote:
| Quote: | 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
home made VSWR meter, for someone who doesn't have access to a store-bought
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 |
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Fred Abse
Guest
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| Posted:
Sat Mar 19, 2005 2:18 am Post subject:
Re: home-brew vswr meter |
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On Fri, 18 Mar 2005 13:54:01 +0000, tom wrote:
| Quote: |
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
home made VSWR meter, for someone who doesn't have access to a store-bought
one, basically.
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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)
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tom
Guest
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| Posted:
Sat Mar 19, 2005 2:20 am Post subject:
Re: home-brew vswr meter |
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I'm not sure I understand your point Mike --- what do you mean by, "Oh,
yeah. Is google's server down or something?" |
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dB
Guest
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| Posted:
Sat Mar 19, 2005 3:30 am Post subject:
Re: home-brew vswr meter |
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"tom" <cyberhun@shaw.ca> wrote in message news:<Z3B_d.711235$Xk.444675@pd7tw3no>...
| Quote: | 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
home made VSWR meter, for someone who doesn't have access to a store-bought
one, basically.
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A directional power meter (s.w.r. meter) will not differentiate
between the two cases. |
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