Hi all,
The KX3's standard VFO temperature compensation is adequate for nearly
all operating modes. However, JT65 and some other narrowband digital
modes can benefit from better tracking with temperature, especially on
the highest bands.
I have a new revision of KX3 field-test firmware available that can
meet this requirement. It includes a custom VFO temperature
compensation feature that accurately matches the temperature/frequency
curve to each individual radio. After performing the calibration
procedure, long-term (key-down) VFO frequency change can be as low as
about +/- 2 Hz on 20 meters.
There's a catch, however: You'll need a very stable signal source that
can provide an RF carrier on about 50.1 MHz, at a level of S8 to S9+20
dB. A temperature-stabilized or reference-locked signal generator is
preferred, although a ham-band transceiver covering 6 meters can be
used, assuming it can be keyed for 15 to 20 minutes at low power
output without appreciable drift. (One tester successfully used a K3
as the signal source.)
The procedure takes about half an hour to complete. I still consider
it experimental, but if you're a serious JT65 operator and don't mind
putting in the effort, I'll be happy to send you the new firmware and
instructions.
One other important note to those considering JT65 and other modes
where key-down times can be very long: You may need to keep power
output level down to 3 watts or lower. (Modes like CW and SSB have a
far lower duty cycle and can be used at up to 12 watts.) The maximum
sustainable JT65 power level can be determined by experimentation.
73,
Wayne
N6KR
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