Electronics > RF, Microwave, Ham Radio

diy 1-1 unun

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A.Z.:
the point is, a metal box will need enough clearance to avoid undesired parasite coupling (same goes for tuners), so it's easier to use a non conductive material box for the balun, instead of making things more complex.

vk4ffab:

--- Quote from: A.Z. on April 15, 2024, 09:42:04 am ---the point is, a metal box will need enough clearance to avoid undesired parasite coupling (same goes for tuners), so it's easier to use a non conductive material box for the balun, instead of making things more complex.

--- End quote ---

Even that, when i think about it, how much separation is enough and how big is the effect? Probably not a lot and the effect is small anyway. Think of a yagi or hex beam. Sure the balun is in a plastic box, but its securely attached to the boom which is made of metal. So 3mm of plastic is some separation, but it is still a capacitor. The bigger reason to use plastic outdoors is that its much easier to seal up and its non corrosive and low cost.

And even then, there is more capacitance in the windings, inherent in coax itself, or twisted pair, that i think a few more pf really wont make much difference. as long as the self resonant frequency it stays above the 30mhz in the OP's case, it should not suffer any performance costs.

That is something the OP can check himself with a VNA.

A.Z.:
think at a classic guanella current balun, some turns of coax wound over a toroidal core; some portion of that coax will have current flowing on the outer surface of the shield... see it ?

I agree that it may be more a "belt and suspenders" approach, but if we can prevent issues, why not ?

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