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Re: LF: Re: The case of the missing amps

To: [email protected]
Subject: Re: LF: Re: The case of the missing amps
From: "Dick Rollema" <[email protected]>
Date: Thu, 17 May 2001 16:54:46 +0200
References: <[email protected]>
Reply-to: [email protected]
Sender: <[email protected]>
To All from PA0SE

Bob, ZL2CA  and Rik, ON7YD  wrote:


>Thanks to Dick PA0SE for doing further tests.  Replacing the antenna with
an increased capacitance from a vacuum variable has lower losses than the
"antenna circuit" but it is a reasonable approximation for gathering
measured
data.
What about replacing the antenna by a capacitor in series with a resistor,
would't that be a better simulation ?

For low power tests (as Dick did) a short piece of coax can be used as low
loss capacitor. Most 50 Ohm coax is 101pF/m, so a 1 to 3 meter length will
be sufficient. The coax cal be rolled up to get things compact, an
alternative is a number of short pieces in parallel. Cheap and flexible
coax such as RG174 will withstand up to 1.5kV (according to specifications
that tend to be rather conservative), RG58 even up to 2.5kV.
For those interested in high power testing : RG8 and RG213 are specified
at
5kV, RG218 at 11kV.
I don't see what advantage this would bring. In test B (without aerial)
I saw to it that the voltage over the coil (50V) was the same as with the
aerial. So from the coil's point of view the situation was identical with
and without aerial. As the voltage over the coil was the same  so must be
the current in the coil and the losses that occur as a result of that
current.

The purpose of test B was to isolate a possible current that
escapes from the coil to the surrounding and I think I managed to do that.

The current passed by the vacuum capacitor is a pure capacitive one. But for
all practical purposes that  is also  the case for the current in the real
aerial .

Please remember that my measurements were not precision ones but
they were good enough I think to draw the conclusion I mentioned and
which is now  also supported by Bob.

73, Dick, PA0SE




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