[MRCA] Antenna "protection?"

[Rob Flory]

A broadband un-un is a good way to keep your vertical at DC ground
potential.

RF'



On Mon, May 26, 2014 at 4:40 PM, W2HX <w2hx at w2hx.com> wrote:

> Ok, Thanks Gene, et al  for the info and explanation. Looks like I’ll look
> out for polyphaser/AD unit.
>
>
>
> 73 Eugene W2HX
>
>
>
> *From:* Gene Smar [mailto:ersmar at verizon.net]
> *Sent:* Saturday, May 24, 2014 5:04 PM
> *To:* W2HX; mrca at mailman.qth.net
> *Subject:* Re: [MRCA] Antenna "protection?"
>
>
>
> Eugene:
>
>      You are correct - this device (the P model at least) is a spark gap
> that is intended for use with twisted-pair telco drop wires into a customer
> premises.  It won't fire until the voltage at the terminals reaches about
> 5000 VDC, depending on atmospheric humidity, at the time of the lightning
> strike.  If your tuner is made with QRO components then this device might
> not cause damage to the tuner.  However, if your tuner is an automatic
> tuner, even QRO, I would hesitate to rely on this device to protect the
> innards.
>
>      It won't bleed off static electricity during approaching thunder
> storms.  Static is bled off in many Ham surge arresters with either a high
> resistance or inductance shunting the antenna terminals to ground, as is
> done with Polyphaser or Alpha Delta equipment.  If you're worried about
> static build up, you can try shunting across the antenna feed point to
> ground a 100 k Ohm resistor of some high power rating or a wound-wire
> inductance that presents a high impedance at the lowest operating freq of
> the antenna element.  (At higher antenna freqs the impedance only
> increases.)
>
>      Tying two or more together, presumably in parallel, won't help,
> either.  Invariably only on of the parallel gaps is likely to fire during a
> strike, effectively shunting the other devices and preventing them from
> firing.
>
> 73 de
> Gene Smar  AD3F
>
> On 5/24/2014 4:25 PM, W2HX wrote:
>
> Ok, first – I know this is a fraught topic. Big topic. Volumes have been
> written. I have a basic question.  Today at a hamfest, I picked up this
> little terminal block (see picture below). It is basically a spark gap
> terminal block. As you can see the studs on the bottom are intended to be
> bolted to a grounded block.  Then the terminals have a gap between a fixed
> washer and a finger that connects to the grounded block.  The model is
> Marconi 1648P and the manual says the following:
>
>
>
> “provide protection in a range of 5,000 volts DC and approximately 10KV
> or less on a surge front of 5KV/msec.”
>
>
>
> My intention is to use between a vertical antenna I am planning and the
> antenna coupler that will be sitting at the base of this antenna.  What I
> started to think about is whether this might be of any use in protecting
> the antenna coupler and anything else down stream from it.  I was also
> thinking that if the antenna produces 5000V during normal use (perhaps
> depending on how the impedance works out for a given working frequency),
> this could actually hamper its performance.
>
>
>
> If it would help, I guess I could tie more than one of these terminals
> together before going to the antenna to give more gap area.  Now, I know
> that a direct lightning hit will simply melt everything. But would this
> terminal block add any beneficial protection for other kinds of atmospheric
> activity? The whole thing cost a few bucks so I don’t mind throwing it out
> if it has no value. Thanks!
>
>
>
>
>
> A link to the datasheet
>
>
> http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CCYQFjAA&url=http%3A%2F%2Fwww.emersonnetworkpower.com%2Fdocumentation%2Fen-us%2Fproducts%2Foutsideplant%2Fensys_terminalblocks%2Fdocuments%2Fospds-061900_3-6-pair-blocks.pdf&ei=G_2AU-zeB-jjsASt0IHgDA&usg=AFQjCNE9KIIGnMdho1mx8WVMjmPDB36vzg&bvm=bv.67720277,d.cWc&cad=rja
>
>
>
>
>
> 73 Eugene W2HX
>
>
>
>
>
>
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