Like many hams, I tried to marry an ICOM transciever with the
KPA500/KAT500. For the most part, it works. But there is an annoying
problem. I have two antennas. When I pressed "tune" on my radio after
changing bands, the KAT500 would tune before changing antennas. It
would then memorize the the tuning result (for the wrong antenna). A
second push of "tune" caused the KAT500 to switch antennas and then tune
again. This happens whether the KAT500 is set to Manual or Automatic.
There are several notes on the web on how to deal with this -- up to and
including transmitting a memorized tone from the radio after changing
bands. The KPA500 and KAT500 both see the signal, measure its
frequency, and adjust appropriately.
So I designed a circuit that detects any band changes on the ICOM using
the "band voltage" available on the auxiliary jack. After a delay of
1.5 seconds, it keys the transmitter to transmit its tune signal (10
watts) for a half second. This only generates RF, there is no tune
command to the KAT500. The result is that the KAT500 measures the
frequency, sets up the antennas correctly, and sets its relays to the
tuning result memorized for that frequency. It's automatic. If I need
to actually tune, I can then press the tune button on the transceiver or
on the KAT500 to match the antenna.
Why the 1.5 second delay? That's because wsjt-x takes that long to set
up the split frequencies on the radio. If the radio is keyed to emit
the tune signal, it interferes with the frequency setting.
The circuit uses an LM399 comparator and two 555 timer IC's (yes I could
have used a 556 but rather than rewire, I added a second 555 when I
discovered the need for a delay). It connects in series with the
antenna tune connection from the radio and in series with the "SEND"
signal -- to prevent the KPA500 from transmitting the 10 watt tune
signal. A third connection is to pick up the band voltage, 12 volts,
and ground from the AUX connector.
If anyone is interested in the circuit, please send an email directly to
me at
[hidden email].
73, Art K0AIZ
--
Arthur I. Zygielbaum, K0AIZ
ARRL Midwest Division Director
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