That's about right. There's no reason (after some warm-up) that the oscillator
temperature should change by more that 0.5C (or whatever) over a 1 minute
transmission -- unless your oscillator is sitting close to the PA heat sink like the KX3.
The KX3, like most amateur radios, has a weasely frequency stability specification.
It says +/- 1 ppm typical over 0-50C. What's weasely about that?
1. "typical", to begin with. It means something like "your chances are pretty good
it's within +/- 1 ppm if you are a normal user." It's a weasel word, because you
would have a hard time proving that your radio did not meet this spec. (Problems?
Well, you're just not typical.) A more serious spec would be "worst case", but we
hardly ever see a worst-case spec in the amateur world.
2. What does 0-50C mean? A reasonable user might think that means ambient operating
temperature. But it might just as well mean indicated oscillator temperature, which
is around 38C for my idle KX3 at the moment, while my ambient is ~22C.
3. What is the timescale? A radio that flicks around +/- 50 Hz on 6 Meters would be
in spec, but nasty even for SSB. Most of us would probably assume that short-term
stability should be better than long-term. That would be true if we're talking about
drift due to slow temperature changes, supply voltages, component aging, or
whatever. The published spec does not give much insight as to what to expect in
practice. The one minute on / one minute off that we have in JT modes is awkward for
the KX3. The oscillator "typically" sees a large temperature swing over a minute's
transmitting -- several degrees C, depending on power setting.
For what it's worth, the Orion claims +/- 3 ppm stability (and accuracy - another
issue) over its operating range, but its short term (1 minute) stability is much
better than the KX3's. I assume the K3 would be similar to the Orion, but sadly
there is no K3 on my desk.
This sounds like splitting hairs -- a good description of JT9 decoding! The KX3 is a
fine radio for most applications, just not bleeding edge digimodes.
I admit to being fascinated by precise time and frequency. I particularly like the
new Flex 6500/6700's GPS stabilized option, 5 x 10**-12 over 24 hours, for a price.
That might support JT9 at 20 GHz. Even there, the devil is in the details. They
don't give fluctuation vs timescale info.
73
Martin AA6E
Date: Wed, 30 Jul 2014 14:02:30 -0700
From: "Wes (N7WS)"<[email protected]>
To:[email protected]
Subject: Re: [Elecraft] KX3 + JT9 -- any successes?
Message-ID:<[email protected]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Maybe he's holding the temperature to 0.5 deg C
On 7/30/2014 10:33 AM, Don Wilhelm wrote:
It is good that you are not complaining, but I just don't*get* it.
The specification is for ± 1ppm over a temperature range of 0 to 50 degC.
You say the mode being tried needs .05 ppm or even .01 ppm. Why would anyone
attempt to use a radio for that mode for which the specification is worse than
the needed stability by a margin of 20 to 100 times?
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