[TowerTalk] UL listed protector for ladder line

[Jim Brown]

On 6/13/2025 4:22 PM, Martin A. Flynn wrote:
> The more I look at this, I'm leaning towards a recommendation of 
> scrapping the dipole and going to a 125' long wire and weatherproof / 
> outdoor tuner

For most configurations, it needs a counterpoise, and building could be 
a good option. But antennas like this are generally poor at rejecting 
noise, and most buildings are noisy.

What bands do you want to operate? Could your rig a fan dipole? Antennas 
that are near resonance at frequencies of interest can be effectively 
choked at the feedpoint, offering at least a bit of noise rejection.

There are some very effective symmetrically loaded dipole designs for 
two bands with the second band being the second harmonic of the first, 
and that dipole can be one element of the fan. I've used that to cover 
160 and 80 with the loaded dipole, 40 and fifteen with the 40M dipole in 
a two-element fan. For CQP (California QSO Party) county expeditions, 
our club (NCCC) has built and loaned both wire and aluminum versions of 
the loaded design for 20 and 40M. I did the electrical design, W6GJB did 
the mechanical design and built them. Depending on mounting height and 
ground conductivity, both designs provide a pretty good match to 50 or 
75 ohm coax. SWR bandwidth of the un-loaded band is comparable to a half 
wave dipole, while bandwidth on the loaded band is reduced by about 
half. For the 40-20 combo, you want to tweak the design for the primary 
operating mode.

These are NOT traps - their self resonance is well above the higher 
band. Unlike trap antennas, the radiation efficiency of these loaded 
antennas is comparable to an un-loaded half-wave.

Single-band elements of a fan are generally usable on the third 
harmonic, but the loaded elements are not.

While there are a few multiband versions of the loaded designs 
advertised in QST, they're much more complex to design and SWR bandwidth 
suffers as the number of loading coils increases.

73, Jim K9YC