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Your balun looks exactly like the ones sold on ebay now for listening. These are 1:9 with a core of unknown properties.
You have to make a decision, you could make a resonant halfwave endfed or a random length non resonant endfed.
Your wire length is almost correct, but the balun needs to be 1:49. You need a SWR meter to prune the wire to length, after that you don’t need a tuner and you may work other bands as well (20, 15 and 10).
Random length endfed:
The wire length is wrong, because it is almost resonant on 40 and with a random length piece of wire and a 1:9 balun it should not be. And you will need a tuner.
By choosing the correct length of wire you could work more bands also.
The toroid in the balun is very small and the material is of unknown properties. I recognise the balun, it is being sold on ebay now as a very cheap balun for listening only. I don’t know what kind of transmitter you intend to use, what the power level is an what internal protection of the power stage it has but I would not risk my transmitter on this balun.
But it lends itself for improvement, a new toroid with a 1:49 winding of the right size (a 140-43 will not fit in the housing) may give you a decent balun for a halfwave endfed.
Google for “halfwave endfed” or “EFHW” and you will find lots of information.
Cor – PA4Q
From: QRPLabs@groups.io <QRPLabs@groups.io> On Behalf Of JohnL
i have this balun from an old end fed 1/2 wave antenna that I was using for listening. I cut a new 70ft chunk of speaker wire for transmitting on 40m. I don’t have an antenna tuner and I am just getting started with my first radio. Does this balun look okay to use and it won’t harm the radio? I doesn’t quite look like other 1:9 end fed 1/2 wave baluns that I have been reading about. Here are some picts.
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