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Hi Stefan,
having the LF coil in parallel to the MF one
will not increase the losses at MF. But the open switch will have to withstand a
high voltage when operating LF, which is not trivial.
I had played with a diplexer here,
consisting of a loading coil which resonates the antenna
at sqrt(f1*f2) ~ 255 kHz. From this point, there was an
inductive low-pass branch for LF and a capacitive high-pass branch for
MF. In addition, each branch was equipped with an extra parallel
element to notch the other frequency.
This worked ok at low powers. But
the disadvantage was
that it largely increases the stored energy (loaded Q) at the MF
frequency, with associated narrow bandwidth and high voltages as on
LF.
Best 73,
Markus (DF6NM)
----- Original Message -----
Sent: Sunday, January 13, 2013 4:20 PM
Subject: Re: LF: Re: MF variometer
Hi
Albert and Gary,
Yes, here it is the same. The detuning due to wet soil
is higher than on
LF. Also the relative rise of the resistive losses are
higher than on
LF. It can make up to 3 dB here.
Now i think about a
switch that allows to switch from LF to MF remotely.
The idea is that the LF
coil remains connected to the antenna (i.e. is
not switched), only the MF
coil would be switched in parallel. There
will be some reactive current
through the LF coil when operating on MF
but it can be compensated and the
losses will be low. I still did no
calculations. At least the MF voltages
and currents are quite low
compared to LF...
73,
Stefan/DK7FC
Am 13.01.2013 11:28, schrieb Albert W:
> Hello Stefan
es Gary,
>
> The same here depending on weather conditions and of
course frequency
> change, using a relative small variometer (DC-motor
adjustable from
> the shack) in series with the fixed L.
>
>
73, Albert PA0A
>
>
>
>
>
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