[Boatanchors] Antenna Question...

[mac]

Brian,

I've been running end fed wires at all power levels and multiple  
frequencies for years with excellent results.

My current setup is a 130 ft. wire in an inverted "L"configuration,  
vertical (actual sloping) feed end aprox. 40' long and a 90' flat  
top.  The total length (130') is essentially a half wavelength on  
75/80M and as such exhibits a high impedance at the end feed-point  
(something around 2500 ohms) and only a simple "L" network is required  
to match a 50 ohm feed line.  Because of the high impedance at the end  
feed-point (hence low ground currents and low ground losses)  only a  
minimal ground system is required, i.e., a couple of stakes and a few  
short radials. Works out the same when used on 40, 20 and 10M (i.e.,  
even harmonics of the lowest frequency).

Because of the high impedance (see above) high RF voltages will be  
encountered at the feed-point, something around 2KV at legal PEP  
levels and the components in the matching network (particularly the  
variable capacitor) must be selected to accommodate this.  I have my  
"L" network matching system mounted in a little hutch out in the  
middle of the back yard and I tune it remotely with a reversible drive  
motor and change bands with remotely controlled relays. In previous  
locations I have also brought the feed-point into the shack and  
encountered no problems.  Bringing "RF into the shack" can be tricky,  
though and your RG-8  feed out to the antenna ground and end feed- 
point sounds like a good idea to try.  I would use both ground stakes  
and a few short radials, see above.  With short runs of RG-8 your  
tuner and the coaxial line will be seeing high voltages, see above.  
The RG-8 should be OK for 100W but you could run into trouble with  
your tuner depending on the circuit and power rating.

Good luck.

Dennis D.  W7QHO
Glendale, CA

******************
On Mar 30, 2013, at 1:48 PM, Bry Carling wrote:

> Brains trust I need your advice.
>
> I have three possible scenarios for an end-fed antenna for my station.
> I had tried a 102 foot dipole with 450 ohm line feeding it - with  
> very little success.
>
> The FT857D / LDG tuner combo doesn't like it, not even on 80m. It  
> will work fairly well on a
> few bands but not many. I think I can do better changing this to an  
> end-fed 120 foot wire. Yes
> it bends around a bit but the main run of about 80 feet is pretty  
> straight - a partly inverted vee
> shape and peaks at 25 feet high, with the ends down around 8 feet  
> high and bent at 90
> degrees.
>
> I have a ground rod outside the window. I can put another one about  
> 12 or 15 feet away
> from the window, run some RG8U, and feed it from there.  I would  
> like to run 100 watts and
> be able to work ALL bands from 160m - 6m which this tuner is capable  
> of doing with the right
> piece(s)  of wire. Is my wire too long? Too short? Is my wire too  
> bent?
> Will one of my feeding methods work better than the other two?
>
> So here are my three possibilities.
> 1) Just end feed the wire straight off the tuner in the shack. (ths  
> is an indoor only tuner)
> 2) End feed it against a ground rod outside
> 3) End-feed it against a counterpoise outside.
>
> Note that for 2 and 3, I would use a short run of coax from the  
> tuner to the base of the
> antenna getting it out there with less RF In the shack.,
> My rigs seem to not like any RF in the shack!
>
> Pictures of each scenario are here:
> 1 -
> http://af4k.com/ENDFED1.jpg
> 2 -
> http://af4k.com/ENDFED2.jpg
> 3 -
> http://af4k.com/ENDFED3.jpg
>
> I would really appreciate any of you guys making some comments on  
> what you think will work
> the best.
>
> 73 de AF4K - Bry
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