'Sorry to hear that it is a myth that antennas can be end fed, as I have
been doing this since my novice days years ago. For the last ten years, I
have been end feeding my 160/80 meter longwire (half wave on 160) with 50
ohm coax, as modern rigs are designed for this (without tuner functions).
Bottom line is that the end of my longwire looks like about 4,000 ohms
impedance at resonance. I simply use an UN-UN to step this down. A 9:1
winding ratio gives an 81:1 impedance ratio, so I get a 1:1 SWR at resonance
without a tuner ( I don't own one ).
If you use a KW Balun sized core, it will handle the power. Also use the
specified number of turns, so that the flux value is the same. With a 9:1
step-up, the voltage is obviously higher, so insulate accordingly. The
larger number of turns also results in more interwinding capacity, so don't
plan on 160 thru 10 meter performance. In this regard, it is wise to use a
the -43 rather than the -61 material, so that the required number of turns
is much less.
The "ground" reference does not have to be extremely low ohms as with a low
impedance feed point. A tuned quarter wave counterpoise would be excellent,
but requires room. I simply attach the shield to the tower or support pipe,
as long as it is well less than a quarter wave high at the highest frequency
of interest. I have used my low 144MHz EME array tower in one case & a 30'
piece of antenna mast pipe in another. Both takeoff points are on high
ground, and the antenna is much higher in its central (highest radiation)
point.
As i said, I have been doing this UN-UN approach for 10 years now. It is my
daily user for regional nets, and works well throughout North America & the
Caribbean. As an alternate DX receive antenna on Top it has provided some
surprising results, particularly at sunrise.
Sorry to be so long-winded,
73 & Best Regards, Brian K8BHZ
Subject: Re: Topband: FEEDING AN END-FED LONGWIRE
> JOSE MATA EA3VY wrote:
>
> > Maybe the end fed antenna is an old myth.
>
>
> Of course that it is a myth that an antenna can be end-fed,
> but that fact does not prevent your antenna to work in some
> other way and serve your needs so well. Your antenna is as
> much center-fed as any "ordinary" dipole. One leg of your
> antenna is what you perceive as an antenna, and the transmission
> line itself, operating in the common mode, provides the other leg.
> That's how it works.
>
>
> 73,
>
> Sinisa YT1NT, VA3TTN
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