[TowerTalk] UL listed protector for ladder line

[Jim Lux]

This is why the terminated folded dipole is popular in emergency ops.  It's inefficient - it could be replaced by a 3-6 dB pad in the feedline to any antenna - but it requires no tuner.  In non-amateur applications, running a kilowatt or five isn't a problem.



On Sun, 15 Jun 2025 23:26:41 -0500, Jack Brindle via TowerTalk <towertalk at contesting.com> wrote:

It might be a great idea until the ATU fails. It is mechanical, it will eventually fail, and usually at the worst time. The other problem is that standard coax protectors block DC, which eliminates bias-T connectors. Make sure you get one that doesn’t block DC if you go this way.

The other issue is power. How much you run will determine what you can do. If there is an amplifier, then you need some way for the ATU to break the PTT line to the amp, or it will be hot-switching the RF as it tunes. This will cause short life for both the ATU and the amplifier.

If this is part of an emergency operations center, then you really need resonant antennas for every band you will operate.

Plan for failures, make sure you have redundancies and ways to rapidly repair whatever the failure may be. That also happens to be the recipe for highly-available systems.

73,
Jack, W6FB


> On Jun 15, 2025, at 9:20 PM, Paul Christensen  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"
>
> Performance of the W7FG dipole (aka Dipole-Doublet and CF Zepp) is relative, as shown by Cebik in the PDF attachment. The radiation pattern will be more complex and less predictable than on resonant bands but it will produce gain and nulls in various directions over a resonant dipole -- sometimes to an advantage, sometimes not.
>
> Given the flexibility of running coax to an outside-mounted ATU, then 600-ohm open feeders to the antenna, I find that the benefit of this configuration outweighs its disadvantages when compared to multiple resonant dipoles. With a 136 ft. dipole-doublet, the pattern mostly replicates a resonant dipole on 80m and 40m where I'd rather not have the many lobes and deep nulls that occur when using the antenna on the upper bands.
>
> In this configuration, a certified Z50 surge protector can still be placed on the coax at the outside-mounted ATU, or at the outside point of premises entry, depending on the local code requirement. If at the ATU, the protector's ground stud will require connection to the AC mains bonding point, generally not to exceed 20 ft. in length. The NEC goes into additional detail when it comes to longer bonding lengths. For that reason, placement at the premises entry point is probably easiest, especially if it's close to the AC mains bonding point.
>
> Paul, W9AC
>
>
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