Bill is touching on an issue I've raised before: A way to select
multiple ATU settings for the same frequency and antenna output. I had
to build a tri-band tuner to switch between my two tribanders so they
would both present the amplifier with the same impedance. The internal
ATU would have been able to do that, if only there were a way to store
and recall two different sets of settings. In the case of automated
antenna switching systems like mine, there also has to be a way to
electronically tell the amplifier which settings to use: Having to press
a front panel switch is not acceptable, as that would require two
operations to switch antennas, which is way too slow. (I sometimes have
to flip the antenna switch several times during a call to determine
which antenna to use.)
73,
Scott K9MA
On 11/19/2019 13:02, K8TE wrote:
Another issue not explicitly mentioned is using an external antenna switch
with different conjugate matches already trained withing the KPA1500 ATU.
Those different matches mean when one selects a "new" (different) antenna
than already selected on a particular frequency (same band or not), the
KPA1500 doesn't know this fact until power is applied. Then, due to a high
VSWR, the amplifier faults.
With just two antenna ports on the KPA1500, there are only two quickly
accessible tuning solutions per frequency if using both ports. If using
only one port and an external antenna switch, a common choice in many
stations, finding the correct tuning solutions can't be done fast enough to
prevent a fault.
As alluded to in previous messages on this topic, perhaps the solution,
unfortunately, is an external box that could contain the appropriate data so
that, when a new frequency/antenna combination, that has a previously tuning
solution, is selected, the external box will tell both the KPA1500 ATU to
select the appropriate solution and transceiver to make appropriate power
level adjustments, both PRIOR to actually transmitting.
This is done (approximately, but with no power level changes) by the KAT500
in selecting one of the three antenna ports and the appropriate tuning
solution. This assumes no other antenna choices on each of the three ports
for the same frequency. The KPA1500/K3S combination is (currently) not
sufficiently "smart" to accomplish this.
Of course, if we had "perfect" antennas that provided resonant matches on
all bands/frequencies, we wouldn't be discussing this. If we had those, we
wouldn't need the KPA1500 ATU either. 73, Bill, K8TE
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