I completed my experiment, and it appears that cooling the transformer by 40
deg C has very little change on the matching transformer.
The 9:1 transformer was terminated with a 560 ohm resistor and swept with the
Nano-VNA and showed almost exactly 75 ohms on 160, 80 and 40m at room
temperature.
The transformer was put in the freezer that is at -20 deg C using my
temperature thermocouple gauge on the Fluke multimeter.
The transformer was swept again after an hour of cooling and the sweep was
virtually identical. No change.
I made a short 2 min video showing the process as I chuck the transformer into
the freezer with the chicken. My wife just shook her head as I explained I am
just doing a very typical Ham radio experiment.
vid here if you want to see my test method: https://youtu.be/CNkSrqG0H1c
73, de steve ve6wz
> On Jan 22, 2020, at 3:07 PM, jimlux <jimlux@earthlink.net> wrote:
>
> On 1/22/20 1:18 PM, VE6WZ_Steve wrote:
>> Thanks Jim!
>> I didn't look at the Fair Rite catalog, but yes…its there on page 8. I am
>> using 73 material Binocular cores.
>> The temp. coefficient for 73 material is .65 % per deg C. My temp change is
>> about 50 deg C, therefore the permeability will change 33 % !!
>> That seems like a decent amount.
>
> Go to page 28, and there's a curve of properties vs temperature. It looks
> like mu is 1500 at -40C and 2100 at 0C (that's at 10kHz, where mu'' (the
> loss) is very low.
>
> The impedance at 10 MHz changes from about 80% at -40 to about 90% at 0 to a
> peak of 100% at 30C.
>
>
>
> https://www.fair-rite.com/73-material-data-sheet/
>
> unfortunately, they don't give you a way to download permeability vs
> temperature.
>
>
>> I am going to do an experiment today.
>> Wind a 9:1 transformer, terminate it with 600 ohm resistor, and sweep with
>> analyzer. Save file. Should be pretty flat at 75 Ohms.
>> Put the transformer in the freezer for an hour or so, take out and
>> remeasure. (I wont cool the resistor) Unfortunately my freezer dose not get
>> to -41 deg C like it does outside, but the results may be telling.
>> Yes I could calculate it based on the catalog info, but that is above my
>> pay-grade.
>> de steve ve6wz
>
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