Re: End Fed antennas w/ uBITX #ubitx
Gordon Gibby <ggibby@...>
Thanks for confirming that idea of how they work. I have one sitting at home that I flat could NOT understand how it works, but the circuit is identical to what we're seeing here --- two coupled coils (it has two different sets with different number of
turns each, making 4 total cols, two transformers) and they are marked for differnt frdquency ranges, and a built in dummy load and a tuningcapacitor (or more, can't remember). I picked it up at a hamfest unsure of what it was but intrigued.
Obviously I didn't realize what it could do, and will try it with a HIGH impedance antenna some time soon and see what happens.......
Will be a very cool demo to give at club meeting if it does work......
From: BITX20@groups.io <BITX20@groups.io> on behalf of ajparent1/KB1GMX <kb1gmx@...>
Sent: Wednesday, August 1, 2018 3:27 PM
Subject: Re: [BITX20] End Fed antennas w/ uBITX
On Wed, Aug 1, 2018 at 11:47 AM, Gordon Gibby wrote:
The article doesn't go through a smith chart explanation of WHY one needs the TUNED circuit, but I would guess it takes out whatever reactance is there.... I have an ANCIENT tuner at home that works EXACTLLY this way & I've never before understood how to use it ---- but now I might be able to get it working with an endfed and amaze and amuse my ARES group!!I wanted to keep that separate.
There are several reasons one is tuned means any parasitic elements like lead lengths, circuit capacitance
are absorbed in the tuning and inductor. The only reason for tuning other than that is it neatly sidesteps the
loss issues with a high Q coil and a typical air variable is also a very high Q device so circuit losses are small.
FYI the old Johnson matchbox and similar were notable for being able to feed any parallel line and flexible
enough to match most anything from a short vertical without loading to a really high impedance like a half wave.
Those that know and understand them pay top prices for a clean one. That and they are often radio art!