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 <[email protected]> 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 > _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
