Posted by
Mooneer Salem on
Jan 22, 2020; 7:48am
URL: http://elecraft.85.s1.nabble.com/KX3-temperature-compensation-experience-tp7657857p7657994.html
Hi all,
Here are some answers to questions that came up after I emailed my initial
post:
*1. How was transmit inhibited on the KX3?*
I set the power output to 0.0W as per the temperature compensation
instructions.
*2. Was any attenuation used during the procedure?*
Yes, a step attenuator set to approximately 40dB.
*3. Which GPSDO was used for the procedure and what is the power
specification of its output?*
https://www.tindie.com/products/nsayer/gps-disciplined-ocxo/. I used the
square wave output, which produced ~1.5Vpp per my oscilloscope prior to
performing the procedure.
Also, I performed some additional experimentation as to which frequency is
the best to perform the reference calibration from. I performed reference
calibration at 10/20MHz (both produced the same result for REF CAL), 30MHz
and 50Mhz and ended up with the following REF CAL numbers and their
frequency differentials:
*10/20MHz:*
*REF CAL:* 114.326.78
*50MHz:* 49.999.970 (-30hz => -0.6ppm)
*30MHz:* 29.999.993 (-07hz => -0.4ppm)
*20MHz:* 20.000.000 (+00hz => +0.0ppm)
*10MHz:* 10.000.000 (+00hz => +0.0ppm)
*30MHz:*
*REF CAL:* 114.326.81
*50MHz:* 49.999.986 (-14hz => -0.3ppm)
*30MHz:* 30.000.000 (+00hz => +0.0ppm)
*20MHz:* 20.000.004 (+04hz => +0.2ppm)
*10MHz:* 10.000.002 (+02hz => +0.2ppm)
*50Mhz:*
*REF CAL: *114.327.85
*50MHz:* 50.000.000 (+00hz => +0.0ppm)
*30MHz:* 30.000.010 (+10hz => +0.3ppm)
*20MHz:* 20.000.012 (+12hz => +0.6ppm)
*10MHz: *10.000.006 (+06hz => +0.6ppm)
Based on the above, performing reference calibration using a 30MHz
signal/harmonic seems to produce the lowest magnitude ppm differences in
frequency across the KX3's range. 50MHz is probably the next best
signal/harmonic to use, especially if one wants to avoid negative
differentials.
Anyway, let me know if you have any additional questions.
Thanks,
-Mooneer K6AQ
BTW, I also tried performing reference calibration using a 150MHz signal.
I'm not 100% confident of the values but that seemed to produce the worst
results for HF (bumping up pretty close to Elecraft's 1ppm spec). However,
for those who primarily use it as a transverter input, there may still be
some value in doing so.
On Wed, Jan 15, 2020 at 4:10 PM Mooneer Salem <
[hidden email]> wrote:
> Hi all,
>
> I recently redid temperature compensation on my KX3 using a GPSDO that I
> purchased to see what kind of results I could get. (I last did it a while
> ago with the XG50 and didn't have any complaints about operation afterward,
> but I also pretty much only used 20 meters and below.) Below is what I did
> and what I observed.
>
> *Device info:*
>
> KX3 purchased February 2013 (revision D RF board, S/N in the 3000 range),
> 2 meter, battery charger and roofing filter options installed
> VE7FMN heatsink installed
>
> *Steps performed:*
>
> 1. Warmed up GPSDO (~24h beforehand).
> 2. Warmed up KX3 until OSC temperature stopped climbing (~1h to reach 34C).
> 3. Performed reference calibration at 50.000MHz (5th harmonic of 10MHz
> square wave output) using the automatic method.
> 4. Placed KX3 in fridge for ~1-1.5 hours and set up heating equipment
> (100W incandescent bulb and makeshift box using baking sheets to keep heat
> in).
> 5. Removed KX3, turned it on and began data collection/storage. I also
> started logging using KX3 Utility. (OSC was ~14C at this point.)
> 6. After ~70min or so, stopped data collection at 52C and turned off bulb.
> 7. Reset reference calibration after allowing cooldown.
> 8. Started fldigi in analysis mode and recorded frequency data for ~15
> minutes.
>
> *Discussion:*
>
> See attached. In short, frequency differences vs. temperature seem to be
> linear up until close to the end of calibration, where the frequency starts
> to go back up. The data collected from fldigi also seems to indicate an
> average frequency shift of 0.04ppm at 10MHz, which IMO is perfectly
> acceptable. (For reference, the specs for the Yaesu FT-817's TCXO claim
> 0.5ppm.)
>
> That said, I did notice--as with others in previous posts to the various
> Elecraft/KX3 lists--that the signal is significantly shifted on 6 meters
> when performing the second reference calibration based on a HF signal (and
> vice versa). However, there doesn't seem to be much of a difference
> regardless of where one calibrates on HF. For me, since I don't do much
> operating on 6 meters, I kept the 10MHz based reference calibration. It
> would be nice if one could set a separate reference frequency for 6m/2m vs.
> HF so that the radio can be right on frequency regardless of where it's
> being used.
>
> Also, I haven't tried transmitting with the new calibration yet, but given
> that I didn't have any problems with the digital modes I commonly use in
> the past, I don't expect any issues now. I did find
>
http://www.bigskyspaces.com/w7gj/KX3HeatSinks.htm before doing this,
> which (a) indicated that there's a newer version of the RF board and (b)
> required board modifications to get the oscillator to be stable enough for
> all but JT65A on 6 meters. I'm not planning on modding my own KX3 in this
> manner, but out of curiosity, is there a RF board newer than revision D (as
> indicated in the schematics document on Elecraft's site)?
>
> Anyway, let me know if you have any questions or if there's anything with
> the methodology I could have done better. Offhand, calculating and setting
> ppm offsets in fldigi might improve the frequency analysis a little bit,
> though I don't know if it'd be by enough to matter much. Not to mention
> doing a temperature compensation with the XG50 again to see how much a
> GPSDO truly adds.
>
> Thanks,
>
> -Mooneer K6AQ
>
>
>
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