As discussed below, what ever you wish to call it, the antenna that is,
being: a G5RV, a double Zepp, an all band antenna, a center fed dipole
and a few more brand names, the center fed dipole with with a balanced
feed and a suitable balun can be matched on all bands, 160M - 6M with
the tuner in the K3S or the KAT500. There are no magic numbers
regarding lengths.
There are two questions to answer:
(Q) How long should the antenna be?
(A) As long as one has for available space.
(Q) How long should the feed line be?
(A) Long enough to reach from the feed point to the station operating
position.
Now, the length of the wire is relative, being the most one can put up
in the clear. The feedline, be it true open wire of about any impedance
or ~450 window line or 300 ohm transmitting twin lead is all that is
necessary.
Agreed, some combinations of lengths are more difficult to match. If
this occurs, then add some 4 to 6 ft of feed line length, or add 4 to 10
ft to antenna length. Or shorten the feed line length. The point
being, if one can attain a 2:1 match or better it will radiate quite
efficiently. If your amp won't tolerate this, then a bit more attention
to length is required.
The topic of what balun to use is an extensive discussion. Most baluns
are OK, while some are just purely awful. Some may not alone provide
the necessary common mode current rejection. Power rating of baluns are
for a MATCHED condition, to which we most always use them in a highly
unmatched condition. Thus the suggestion is one consider a much higher
power rated balun than one intends to run. My reference to balun usage
and design is https://www.dj0ip.de/balun-stuff/.
The issue of using a balanced feed system is much easier than the "old
ham lore" will stipulate. Just use common sense. It ain't rocket
science folks, nor does it require a Ph.D to make it work and work
quite well, I might add.
Yes, it is very much OK to bring the balanced feed line all the way to
the operating position where it then attaches to the balun of ones
choice. It is not necessary to have the balun outside and bring the
feed point in via a length of coax. If one is going to use open wire
line or balanced line, then don't screw up the system by introducing a
length of coax to go from the station to the balun in the outside
world. There will be an unbelievable amount of high SWR on that coax
{and equal amount of loss} and likely a high amount of common mode
current. Do it correct the first time, enjoy the very favorable
results, and forget about the "old ham lore" for it is not correct!
I've only been doing it this way for some 50+ years.
I sit here today with a very modest station. Then antenna is a 256 ft
center fed wire with 450 ohm window line. The center of the antenna is
50 or so feet and the feed line is what ever it took from a 100 ft roll
to get from the feed point, through the attic eve, drop down through the
ceiling to the operating position. There was about 25 ft of 450 ohm
window line left over. I easily work all modes and frequencies 160M -
6M up to 500 watts from my KPA500 and KAT500. The antenna and feed
line have been in the air and in place for 10+ years and I expect it to
last longer than I do.
Yes, when it rains or snows the SWR goes up, but so what? That is what
the dang tuner is for and it does an excellent job with just the touch
of a button.
If you only have 90 ft for the antenna, that's OK, If you only have 55
ft for the antenna, that's OK. The feed line goes from point A to point
B, whatever that length might be. Shorter lengths of antenna become a
real challenge to get a good match on frequencies lower than the
resonant length but it will work if you can match it. For get about
the charts, the computer modeling, and put up what you can, in a
reasonable fashion, and begin to enjoy ham radio.
73
Bob, K4TAX
On 3/17/2020 2:42 PM, Dave New, N8SBE wrote:
2) A ZS6BKW dipole, which is 92 ft. long, includes a 40 ft. window line
section, and then 75 ft. of coax. I only use it on 30-80M, using the
ATU on my K3S to tune into it:
The ZS6BKW is up about 35-40 ft. (slopes at one end) and doesn't do so
well for DX, but is a killer for NA contests (NAQP, Sweepstakes, MI QSO
party) from the Midwest.
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