Re: [TowerTalk] Vertcal Dipole

[Bill Tippett <btippett@alum.mit.edu>]

Hi Tom,

I wrote:
>          Par Electronics offers the following series of
> End-Fed 1/2 wave antennas which require NO radial
> and NO tuner.  I've been using the EF-20/40 which
> works very well with direct feed from my QRP rig.
> With the EF-20/40 plus KD1JV's AT Sprint 2, I have a
> complete 20/40 station including transceiver, battery,
> earphones, paddle and antenna (no tuner needed) that
> weighs ~1 lb total.
>
> 
<http://www.universal-radio.com/catalog/hamwire/4456.html>http://www.universal-radio.com/catalog/hamwire/4456.html


W8JI wrote:

>We shouldn't mistake that for a good system. The only reason
you get away with it is you are running QRP, or have a lucky
feedline length.


        Par's monoband End Fedz are rated at "a conservative
100W" although the distributor (Universal Radio) says "a
conservative 200 Watts", so take your pick, but neither is
really QRP IMHO.

http://www.parelectronics.com/end_fedz.htm

Only the dual band 20/40 which I have is rated at less (25 watts
continuous).  It is purely resistive at resonance measured with
an MFJ-259B.  I'm not sure what Dale W4OP is doing inside his
matching network but whatever it is seems to work very well.

>It is impossible to end-feed a half wave antenna without
having equal current entering the feed cable as common point
as the current entering the antenna end. That's what makes
these antennas unpredictable.

        Perhaps there is some capacitive coupling to the coax shield,
but it seems to work equally well with either short runs (a few
feet) or longer runs (~30') in my experience.

        Just 2 weeks ago I used the EF-20/40 while on a camping
trip and it worked very well on both 20 and 40 in the Spartan
Sprint (a QRP to QRP contest).  I was also amazed to even work
several EU stations running 2 Watts on the low end of 40, but
that was surely due to their antenna rather than mine!  If
anyone is looking for a very simple yet effective portable
antenna, I highly recommend the Par End Fedz.  FWIW they also
have some very nice recommendations on eHam:

http://www.eham.net/reviews/detail/3632 (100W mono banders)
http://www.eham.net/reviews/detail/3717 (25W dual bander)

        I never heard of this company until I got involved with
QRP, but the End Fedz monobanders would certainly make a nice
system for anyone operating portable with 100 Watts.  Of course
you could do the same with an LC network but would need a 1/4
wavelength counterpoise.

                                                73,  Bill  W4ZV




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