Drew,
For BCB operation using a 100 ft wire for an antenna (hopefully you also
connect to some form of ground screen), I would expect the inductance in
the KAT3 to be quite low. I would suggest adding a supplemental
inductor in series with the antenna wire. I am not going to suggest
just how much, but you can experiment. Using an antenna analyzer might
be informative if you can find one that goes that low.
73,
Don W3FPR
[EMAIL PROTECTED] wrote:
Ok, Chuck, thanks alot. That explains all. I was thinking it was a pi
with two capacitors.
So anyway, for BCB reception, the capacitor doesn't do much and you
would pretty much want to have maximum L, right?
73,
Drew
AF2Z
On Sat, 19 Jul 2008 09:03:02 -0700 (PDT), Chuck, AE4CW wrote:
Vic and Drew,
The ATU in the K3 is a low-pass "L" design which has a series inductance and
*either* an input (Ct) *or* output (Ca) shunting capacitance. There is only
one capacitance in this desigh, not two. The single capacitance is switched
between the input (Ct side - transceiver) or output (Ca side - antenna) of
the inductance. So, when you are in CONFIG:KAT3 --> LCSET --> ATU TUNE,
tapping ANT switches the capacitance between the input and output of the
inductance. You can hear the relay switch when tapping ANT and sometimes
hear a distinct difference in the received signal.
In general the capacitance will need to be on the input (Ct) side when the
antenna impedance is below 50 ohms and on the output side when the antenna
impedance is greater than 50 ohm.
You can look at the circuit design in the K3 schematics (documentation page
on the web) if you would like to get a more detailed understanding. Or,
you could also look at a program like TLW (transmission line wizard) that
will calculate and show you a picture of the correct values for a low-pass
"L" ATU with any given values of antenna impedances.
Hope this helps! 73,
Chuck, AE4CW
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