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ZR6JDE > TECH 10.01.05 11:47l 73 Lines 3550 Bytes #999 (0) @ WW
BID : 810032ZR6JDE
Read: GUEST
Subj: Re: Lightning protection
Path: DB0FHN<DB0MRW<DB0HOT<DB0ERF<DB0GR<DK0BLN<UA6ADV<ZS6FB<ZS0DLD
Sent: 050110/0829Z @:ZS0DLD.PTA.GAU.ZAF.AF #:56960 [Pretoria] $:810032ZR6JDE
From: ZR6JDE@ZS0DLD.PTA.GAU.ZAF.AF
To : TECH@WW
I have now looked at a commercial installation of especially Television
and FM Radio transmitters, You hardly ever hear or see any of these
suffer "hits" or "strikes" from lightning. I was wondering why?
Is it the perception that these guys have "unlimited" funds? Maybe?
Or is it that they tend to plan their systems far better that we do?
Definitely!
A well known site near my QTH is high on a rocky hill - it is by far the
highest point in the area, furthermore the tower at the site is in excess
of 70 m above the ground level. It is used to distribute FM Radio, public
broadcast TV, and several other commercial repeaters. But it always seem
to be on an running - I live in the area now for 4+ years and have never
seen the TV or Radio signal "out" for more than a few seconds?
They employ the basic priciple of a low loss (less than 10 ohm) path to
earth from the top of the tower to dissapate any Potencial Difference
quickly and effectively to a carpet of copper burried on the rocky hill.
There are also no antennas right at the to of the tower. All installations
start at least 2 m below the top of the tower on different levels.
I realise we don't have all the resources - but a simple earth carpet made
for copper wire with a low-loss path to the top of the tower (again copper
wire) and not neccesarily puting our antennas right at the top of our
tower will probably imitate the commercial installations sufficiently to
safeguard against entry through the rf path into our equipment.
This is no expert opinion but only an observation of something that works
in practice that I intent to "copy" for my own installation for a tower
soon to be erected!
My problem however still remain to protect the AC and Telcom paths to my
equipment. My experience with rather "cheap" telephone surge protectors
are that they are effective proportional to the price yu are prepared to
pay. The highveld region of South Africa is well known as one of the
lightning capitals of the world - I have had numerous times had to call
telkom to com and fix the telephone line after a "strike" while the
equipment in my qth were sucessfully protected by these units that
dissipate the current to the mains earth. I just wonder why the overhead
lines for telephone network can not be "earthed" at every pole? surely the
costs of repairing the network everytime after a lightning strike
eventually adds up to far more than the few bucs to fix a copper strip to
each pole to dissipate any PD -
I have to correct myself on the issue in Southe Africa - It will definite
become very expensive as some sorry pathetic thief will relief all the
pole from this piece of copper just for the sake of stealing it.
Recently I lost a whole lot of electrical appliances through a lightning
strike on the neutral of the electrical network outside our property.
Interesting the UPS's did protect my computer and power supplies to my
radio's without damage whatsoever and even "tripped" the circuit breaker
(Earth leakage) but the damage to the TV, VCR and DVD on the same circuit
was done while the HIFI on the same power point as the TV etc was not
damaged? (the damage was restricted to the AC to AC/DC power supplies of
the equipment and were easily fixed resistors & caps).
I have heard of a device called a "spike-eater" but I doubt if it will
really work? The other problem could be that it gives a false sence of
safety? Does anyone have more info on this?
73's
Hannes
ZR6JDE@ZS0DLD.PTA.GAU.ZAF.AF
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