[TowerTalk] surge arrestors or good grounding?

[Jim Brown]

On Wed,8/5/2015 8:06 PM, Grant Saviers wrote:
> I'm wondering what commercial practice is re surge arrestors?
>
> I note the max power ratings for DIN connector arrestors is 250 watts 
> at least at Tessco.  Many are frequency selective. PolyPhasers claim 
> 2500 watts 1.5MHz to UHF.

Change the word "claims" to "rates."  The power rating corresponds to 
the voltage at which the discharge tube inside the arrestor is rated to 
trip. In general, we want the protector to trip at the lowest possible 
voltage above the level of our transmitters. I'm running legal limit on 
HF, so I'm using their highest rated protectors on all the HF antennas 
except 30M.

> With top and bottom tower bonding to a ground rod grid and 125' to 
> tower in a trench with the shack entry plate feedthrough grounded to a 
> 200' perimeter footing Ufer, to center pin arrestors do anything useful?

Lightning is not a DC event, it is an RF event, and there are currents 
induced in virtually every conductor. RF voltage is induced between 
center and shield by current on the shield, the ratio of which is called 
the Transfer Impedance of the shield.  A lightning protector on coax 
shorts the center to the shield, but thanks to wavelength effects and 
that induced current, there can be substantial voltage between center 
and shield several hundred feet away.

> Tower and trench coax is all DIN terminated hardline, so it would make 
> sense to connect to a DIN connector arrestor (if useful), but no such 
> QRO animal seems to exist.

That may be true, but maybe not.  DIN connectors are all the rage for 
UHF systems, so the arrestors that are made with DINs will depend on the 
power levels that are common in those systems. You need to find the 
complete Polyphaser catalog.  Here's a very good dealer for Polyphaser, 
he's a ham, and he likes dealing with hams.

http://wrblock.com/PolyPhaser/PolyPhaser.html

I've standardized on UHF connectors for everything in my station at HF 
and below. I have only a few runs with Ns.  All my hardline has been 
acquired used, some with connectors, some without, so how they are 
connectorized depends on a combination of luck and what connectors I can 
find that fit those lines. All are Ns, most females, so I use N jumpers 
as required. I'm active on 6M, and have Ns on that run, also on a 2M 
Yagi. The VHF-only runs have protectors rated for lower power.

73, Jim K9YC