[TowerTalk] UL listed protector for ladder line

[john at kk9a.com]

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 at gmail.com> 
Sent: Monday, June 16, 2025 1:25 AM
To: john at kk9a.com
Cc: towertalk at 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 at kk9a.com <mailto:john at 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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