[Waverley ARS] RF fuse

[George Georgevits]

Hi All,

Nice to see such impartial advice on this site. I hope the club gets a
commission!

Perhaps a more balanced approach might have been to include other suppliers
as well (eg. WES Components, Andrews Communications, Jaycar, Dick Smith
etc.)?

On a more serious note, I offer the following comments on the subject, just
to clarify a few myths:

1.	Most lightning damage is caused by surges induced into the antenna from
cloud to cloud strokes, not direct lightning strikes to the antenna.

2.	If you do happen to be unlucky enough to get a direct strike on your
antenna, no amount of arrester protection is going to help you! Arresters
are simply not capable of handling that much energy (the current in a
typical lightning strike peaks at around 20,000 amps, with 10% of strokes
exceeding 200,000 amps). It is easy to see why trees have been known to
explode when struck.

3.	So if we stick to lightning induced surges, gas arrester based protection
devices will clip the surge voltage, but unfortunately they do not act fast
enough to protect semiconductors (eg. as in the front end of your radio).
So, although a gas arrester MAY, under the right conditions, shunt the bulk
of a surge to ground, thus preventing severe damage, a gas arrester will not
operate fast enough to prevent the leading edge of the surge from doing in
the front end of any radio which may happen to be connected to the antenna
during a thunderstorm.

4.	In order for a gas arrester to operate effectively, it requires a
connection to a good PROTECTION earth. This is not the same as a mains
earth. A protection earth consists of a low impedance path to a system of
earth electrodes buried in close proximity to the equipment it is designed
to protect. Consequently, it is not easy or cheap to provide effective surge
protection using arresters.

5.	A much better and well proven approach is to simply disconnect the
antenna except when in use. This can be done using a coax switch for VHF/UHF
equipment, or by using a knife switch for HF gear.

Now I hope I haven't started a storm of ads for antenna switches!

Regards,
George Georgevits
VK2KGG


> -----Original Message-----
> From: members-bounces at vk2bv.org [mailto:members-bounces at vk2bv.org]On
> Behalf Of David Benchoam
> Sent: Friday, 2 June 2006 9:14 AM
> To: Raffy Shammay; Vk2bv
> Subject: RE: [Waverley ARS] RF fuse
>
>
> Hi Guys,
>
> Just wanted to mention that Benelec sells a in line EMP protector for
> lightning protection of radios. It's a Spinner product made in Germany,
> capable of DC-2500MHz
> N socket to N socket bulk head design. The outer of the device needs to
> be well earthed. The voltage of the gas capsule is 90V so max 120W RF,
> however we have capsules capable of upto 2Kw. If you refer to our web
> site we have technical notes on EMP protectors (Under Technical
> Articles) and how they work. Also details of the different versions we
> carry.
>
> Cost of 90V EMP is around $140 plus GST. Keep in mind these are a high
> quality high performance unit. There would be some cheaper solutions
> around.
>
> Regards,
>
> David Benchoam
> Benelec Pty Ltd
>
> Unit 2 / 581-587 Gardeners Rd, Mascot NSW 2020
> PO Box 21, Mascot NSW 1460
> Sydney Australia
> Tel : +61 2 93647000 - Please Note New Numbers
> Dir : +61 2 93647002
> Fax : +61 2 93647099
> Mobile : +61 (0) 418646595
> Email : david at benelec.com.au
> Web : www.benelec.com.au
> Skype : david_benelec
>