Electronics > RF, Microwave, Ham Radio

Correctly calculating impedance of a biconical antenna and impedance matching

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T3sl4co1l:
It's a stub whether you want it or not :)

Specifically, it's a double-open stub, so, half-wave multiples are relevant.

But it's also ferrite loaded, so it should be well terminated, and grounding one side or the other will be fine. Which of course suggests the unbal side.

Probably, the balance is slightly better with it floating, but as that puts some voltage on the tube, it will also affect the radiation pattern or feedline current a bit. (Probably negligibly.)

Tim

dazz1:

--- Quote from: T3sl4co1l on June 16, 2024, 03:45:14 pm ---It's a stub whether you want it or not :)

Specifically, it's a double-open stub, so, half-wave multiples are relevant.

But it's also ferrite loaded, so it should be well terminated, and grounding one side or the other will be fine. Which of course suggests the unbal side.

Probably, the balance is slightly better with it floating, but as that puts some voltage on the tube, it will also affect the radiation pattern or feedline current a bit. (Probably negligibly.)

Tim

--- End quote ---

Prior to making the balun assembly I did some testing specifically to look at effects of a steel tube.  Originally I planned using plastic or phenolic tube, but too difficult and too expensive to source.  I just happen to have some 22mm OD steel tube on hand.  Experimental results showed the steel had no effect, grounded or floating.

I still have options.  The 3D prints are designed to fit over a 22mm OD tube, regardless of the ID bore,  so I can change the tube for any other material with the same 22mm OD.  Leaving the tube floating significantly reduces the coupling with the balun/coax. So yes it is still a tuned stub, but lightly coupled. 

The bi-conic antennae are still prototypes. I can still make changes if I find problems with further testing.

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