Re: End Fed antennas w/ uBITX #ubitx
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Yes you may infer some things and guess and sometimes the type of the transformer. You can grossly guess also the material chemistry of the core. Suppose you have an unknown transformer and you read 50uH at the SO239 and 450uH between the antenna terminals. The ratio is 9:1, 50uH at the SO239 indicates the lowest frequency is around 160m and the core cannot be made of powdered iron. Most likely is ferrite. If you find that there is no dc short at the SO239 and you find around 50uH across the pin of the SO239 and one of the terminal and between the outer of the SO239 and the other terminal you have a 1:1 balun, i.e. a choke which will be fine for all the HF.
Now an annedocte. A friend of mine bought for 80 euro from a Ham, a monoband wire antenna with a black box but found difficult to tune. He didn't want to open the black box as he was afraid of breaking it, he paid a lot for it! Well, the inner of the SO239 was not shorted so I excluded it was a 9:1 transformer, I thought the black box contained a 1:1 choke, I mean a quite expensive one. But then I asked to measure the inductance between the inner of the SO239 and the wire and between the outer of the SO239 and the clamp. In both cases it was 0uH!!!..... He paid 80 euro for 20 meters of ordinary unipolar wire and an empty black box!!!!
Il 30/lug/2018 20:33, "John Smith via Groups.Io" <firstname.lastname@example.org> ha scritto:
The inductance meter reads 97uH to antenna, and 38uH to ground. The first one I bought that looks like this model and is a 1:1 balun has shielded cable to the toroid and shrink wrapped magnet wire wrapped around it, and looks professional. The inductance readings on the 1:1 balun are 49 and 53uH. This 9:1 unun looks like the typical knock off crap made in the back of a Shenzhen market stall with white shmoo hiding the lies. Are these inductance readings something you expected to see, or way off?