Several people have responded saying I don't need suppressors at both ends.
I agree that the critical place to put them is at the shack end. My
reasoning for putting another set at the tower is that the cable runs are
long (220') and they'll be direct-buried (no conduit.) If a cable gets
damaged it will be a lot of work to replace it.
Gary points out that a surge could arc through the cable to a metal conduit.
Although there won't be any metal conduit in my installation, each cable
bundle will contain ground wires and most of them have grounded shields as
well. Also, there will be two runs of 1-5/8" heliax buried beside the
control cables. The outer conductor of the heliax is nearly 2" in diameter
and is essentially solid copper. That's got to be a low impedance path to
ground -- probably lower than metal conduit. Seems to me there's a
possibiliy that a surge could arc from a control line to a ground line in
the same cable, to the cable shield, or even to the heliax outer conductor.
I would think the center conductor of the heliax would be particularly
vulnerable, so I'm going to use coaxial suppressors at both ends to protect
the expensive and hard-to-come by heliax.
Flame suit on.
73, Dick WC1M
> -----Original Message-----
> From: Gary Schafer [mailto:garyschafer@comcast.net]
> Sent: Wednesday, September 27, 2006 11:43 AM
> To: wc1m@msn.com; 'Tower'
> Subject: Re: [TowerTalk] homebrew low voltage surge suppressors?
>
> Go to Mouser or anyone else that sells large MOV's. Buy a
> bunch of them. Put one to ground on each control line. That
> is ALL that there is in the Polyphaser rotor protector box.
>
> Keep in mind that the surge energy will be pretty much
> divided among all control lines and coax by the time it gets
> to the shack. So any one line will not be carrying a great
> amount of energy and the MOV's will easily handle it.
>
> If you have only a couple of lines to protect then you need a
> little more sophisticated type unit consisting of a gas tube,
> inductance and MOV. But with multiple lines the full energy
> is divided and no one line carries a great amount of energy.
> Also the long, I assume underground path, of the cables to
> the shack will choke off a great deal of energy.
>
> There is usually not a need for additional protection devices
> at the bottom of the tower, only at the shack entrance at
> your single point ground plate.
> But if you are going to run the lines in metal conduit to the
> shack then it is a good idea to put a set of MOV's at the
> tower base also because you don't want a large difference in
> potential between the lines and the conduit as they may arc
> to the conduit and damage the cables.
>
> The coax is no problem. No protectors needed at the tower
> base just ground the shields at the base and ground the metal
> conduit to the shields if that is what you are using to
> transport the cables to the shack. Again this is done to
> prevent any difference in potential between the cable shield
> and the conduit where it could arc and damage the cable.
>
> 73
> Gary K4FMX
>
>
> > -----Original Message-----
> > From: towertalk-bounces@contesting.com [mailto:towertalk-
> > bounces@contesting.com] On Behalf Of Dick Green WC1M
> > Sent: Wednesday, September 27, 2006 9:36 AM
> > To: Tower
> > Subject: [TowerTalk] homebrew low voltage surge suppressors?
> >
> > My new tower will have three 4-el SteppIRs, three TIC
> rings, a T2X, a
> > stack match and an SO2R switch box. That comes to 96 control wires.
> > Since the tower is over 200 feet from the shack, it's best
> to have a
> > surge suppressor at both ends of each wire. I used Polyphaser RCT
> > surge suppressors for my other tower, but the price has
> about doubled
> > since I did that. I'm looking at close to $3,000 worth of RCT surge
> > suppressors. Besides, the RCT mounting hardware is really
> designed to
> > clamp to a tower leg and I'll be mounting the suppressors on ground
> > panels inside metal NEMA boxes. I've done that before and
> wasn't real
> > happy with the result. Even if I go with the ICE units, which have
> > better mounting, the cost will be quite high.
> >
> > So, I'm wondering if anyone has seen or designed a homebrew low
> > voltage surge suppressor circuit? My understanding is that it takes
> > more than just low voltage MOVs. You need series inductance and/or
> > resistance and a diode.
> > I haven't found anything appropriate on the web. Can
> someone point me
> > to a schematic and/or tell me how they did it?
> >
> > 73, Dick WC1M
> >
> > _______________________________________________
> >
> >
> >
> > _______________________________________________
> > TowerTalk mailing list
> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
>
>
>
>
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