[TowerTalk] Par Electronics - End-fed 1/2 wl antennas

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

Hi Tom,

W8JI wrote:

>My point is they can tell you anything they like in the
advertisement but make no mistake about it, the coax is the
counterpoise in that antenna.

        I'm sure that is true, but the current must be quite
low.  This is probably summarized by AA5TB (not Par) here:

The idea is to convert the very high impedance of the antenna (usually 
around 5k ohms in real life) down to the relatively low impedance (50 ohms) 
of the transmission line. Now it should be known that if the antenna was 
infinitely thin, in outer space, and was exactly resonant no energy could 
be coupled into this antenna using this method (this is what the physicists 
will tell you). If things were perfect you would have to couple into the 
antenna just slightly in from the very end of the antenna. In other words, 
move the feed point from the very end to a foot or two from the end. This 
would mean that the antenna would be on one side and a very short return 
wire would be on the other side. This would present a small amount of 
capacitive coupling from one side of the circuit to the other and RF 
current would flow. "Luckily", things are never perfect and this situation 
almost always exists anyway. Therefore, a small return wire may be 
necessary although there is usually enough stray capacitance from one side 
of the circuit to the other to satisfy this requirement without any 
additional return wires.

http://www.qsl.net/aa5tb/efha.html

>My point is they can tell you anything they like in the
advertisement but make no mistake about it, the coax is the
counterpoise in that antenna.

        True, but I don't feel Par's advertising is misleading.
They simply say it performs, which IMHO is absolutely true.

>What I refer to in power limits is getting away with the
feedline being part of the radiating system. At 5 watts, you
probably won't get RF warts on your fingers if the cable is
the wrong length. At a kilowatt, you could have some serious
RF burns.

        Again, Par claims their monoband versions work with a
conservative 100W and user reports appear to support that.
I can only speak personally for the dual band version which
I have never used with more than 15W (versus its rated 25W
continuous) from my K2.  This is a very reputable company
in my opinion, making a product that works very well for
its intended use (portable, easy-to-erect and easy-to-feed
vertical dipoles).  Dale Parfitt W4OP gives great response
via E-mail and supports his products (unsolicited, he sent
me an extra bit of heat-shrink and an extra 40m resonating
wire when I had a minor problem tuning my EF-20/40).  If
you poke around on his website, I think you'll also see he
is not a CB'er.  ;-)

http://www.parelectronics.com/index.html

                                        73,  Bill W4ZV

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