Posted by
Guy, K2AV on
Jan 05, 2012; 4:27pm
URL: http://elecraft.85.s1.nabble.com/Horizontal-Delta-Loop-Questions-tp7154769p7155012.html
In an antenna design where one is already committed to a broadband feedline
and a tuner, particularly one that is working, making the antenna
"resonant" may actually WORSEN your results. Efficiency is not hide bound
to "resonance". What most people mean by resonance is a low Z feedpoint
that has no reactive component, and also want to feed it with 50 ohm coax
with no further devices. In other words what they want is SIMPLICITY. I'm
not knocking that at all, but it is NOT the only way to fly. The doublet
with the most gain is something called a double extended zepp, is NOT
resonant, needs a low loss balanced feedline and a tuner to feed it.
Working wire solutions for most gain, best efficiency in a given space is a
tricky science that involves modeling, and RARELY produces resonant
solutions that feed with nothing except 50 ohm coax. In critiquing one
person's work, he had defeated himself by forcing the wires to produce a
no-tuning-device 50 ohm feed. When he dropped that requirement and got
used to the idea of designing for results and matching it to coax
afterward, he very quickly designed something that fit his back yard and
worked well.
In your case what screams at me is "If it ain't broke, don't fix it!" and
"Model it, and see what is going on."
"Resonance" is way, way over-rated.
73, Guy K2AV
On Thu, Jan 5, 2012 at 10:13 AM, Rick McClelland, AA5S
<
[hidden email]>wrote:
> Hi,
>
> I'm a CW operator who dwells in the lower end of the HF bands. My current
> antenna is a 200' horizontal delta loop 40' high, fed with 87' of 450 ohm
> ladder line. This connects to a 4 to 1 balun (common mode choke?) which is
> attached to my Dentron Jr. Monitor tuner via 5' of RG213. Looking at a
> spreadsheet, I see that a full wave loop for 80 meters is 287' and 143.57'
> for 40 meters.
>
> A hypothetical question to the wise ones on this list is would I expect any
> practical improvement in performance of my antenna system (on 40 meters and
> above) by reducing my 200' delta loop to 143.57' and feeding it with 71.78'
> of ladder line so that the sum of the antenna length plus twice the ladder
> line length is 287'? This seems to make theoretical sense since the
> entire system would be resonant at 7mhz and integral multiples thereof.
> However, the performance of my current 200' loop appears to be quite good
> from 80 to 6 meters and my small tuner matches whatever impedance this
> system is presenting to it so I'm hesitant to take a pair of snippers to my
> antenna.
>
> I would like to increase the length of the loop to 287' feet and feed it
> with 71.78' of ladderline but that is another story. Also, would I expect
> to be able to tune any of the these three antennas on 160 meters if I were
> to purchase either a KXAT100 or KAT500 tuner which presumably have a wider
> tuning ranges than the Dentron Jr. Monitor tuner?
>
> Rick McClelland, AA5S
> Fort Collins, CO
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