Re: End Fed antennas w/ uBITX #ubitx

Jerry Gaffke
 

Gordon,

I think just measuring the SWR into the antenna system using a short 5 to 10 foot of coax from matchbox to antenna analyzer 
gives a pretty good indication of where things will start getting lossy, for both loss in the toroid and in a long coax.
The published SWR charts on myantennas.com (and QST review) are a good indication of what you will get,
agree well for frequencies at which the SWR is under 2.0.  With a long piece of coax, the low SWR numbers
remain about the same, the high SWR numbers shoot up considerably. 
That's as I recall, it's been a couple years since I looked hard at that.

You do need some coax between antenna analyzer and the matchbox.
Take it down to a few inches with an electrically isolated analyzer and things get whacky
due to lack of counterpoise.

Jerry, KE7ER


On Fri, Aug 3, 2018 at 07:33 AM, Gordon Gibby wrote:

Jerry --- likely that a simulator would tell you how much and how quickly reactive components add in as you move away from the exact resonant frequency.   It does seem that significant reactive components might increase losses, huh?  (I'm not an expert on that).

 

Any information on how far from resonant you can be before reactance increases signficnat in an end-fed, high impedance antenna, and then next, how that changes toroid losses????   that might be the $64 question.

 

 

On my homebrew off-center-fed balun diplose they "appear" more broadbanded......suggesting that the closer you get to the end, the less the importance of small variations from exact resonant frequency?

 

cheers,

 

gordon

 

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