By resonant, I was referring to 1/2 wavelength dipole. I stated that a half
wavelength dipole will have a nicer pattern than using a W7FG ladder line
dipole across multiple bands. A half wave dipole pattern has two lobes and two
nulls, perhaps the nulls are -5dB. If you were to use a 100 foot long dipole
on 28MHz, beside the antenna having a very high feed point impedance, the
pattern would have a number of deep nulls, perhaps -15dB. The pattern and the
impedance of this 100 ft dipole would change dramatically, depending on
frequency. A fan dipole or the loaded dipole that K9YC suggested would have a
consistent pattern with no deep nulls and ~50 ohm impedance on the designed
bands. It would work well with the listed protection devices.
John KK9A
From: Ken WA8JXM <wa8jxm@gmail.com>
Sent: Monday, June 16, 2025 1:25 AM
To: john@kk9a.com
Cc: towertalk@contesting.com
Subject: Re: [TowerTalk] UL listed protector for ladder line
Resonance does not really change antenna performance. Feedline performance,
transmitter matching, yes. Antenna performance, no.You would have trouble
convincing me that a double extended zepp (!.28 wavelengths long), with more
than 3 dbd gain over a dipole performs worse than a dipole
Most AM broadcast antennas are not resonant. The most powerful AM broadcast
station ever in the U.S. originally operated with a 831' vertical , about 0.6
wavelength. It was later reduced to 747' and then 736', all non resonant
frequencies.
Ken WA8JXM
On Sun, Jun 15, 2025 at 9:36 PM <john@kk9a.com <mailto:john@kk9a.com> > wrote:
Besides it being easier to find a certified protector for 50 ohm coax, a
resonant dipole or a fan dipole fed with coax will have a nicer pattern and
perform better than the W7FG dipole with ladder line on non-resonant
frequencies.
John KK9A
Jim Brown K9YC wrote:
And, as noted, they won't work for your chosen antenna, for the reasons
noted. You should probably pursue one or more of the options for
antennas that are relatively well matched to coax on their operating
frequencies.
73, Jim K9YC
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