[time-nuts] Surge Arresters

[David Kirkby]

On 26 November 2012 15:44, Peter G. Viscarola <PeterGV at osr.com> wrote:
> Hi TimeNuts,
>
> What are people using for surge arresters between your GPS receiver and the antenna, at the entrance to your house?

Several years ago there was lightning near my house, which I think
went on the telephone lines, as it destroyed the ADSL modem, and
destroyed the ethernet ports on everything connected to it. Luckily my
instance company paid for this, although it was a battle with their
"computer experts", who clearly got very lost when coming to Sun
workstations, despite me warning the insurers before that these were
not ordinary computers.

I once worked for a defunt company "Belling Lee Intec" who built
Electromagnetic Pulse (EMP) protection systems for customers. 95% were
military, but the BBC were also a big customer. These systems used to
consist of 3 components.

1) Spark gap
2) Voltage dependant resistor
3) Low pass filter.

You could take a similar approach, but with a band-pass filter.

A VDR is not going to be any use at 1.6 GHz, so you could forget that
part. But that method is not going to be foolproof, as a direct hit
would destroy the capacitors in your BPF.

If I was reallly concerned, then I'd look at using an optical
interace. Use a battery to power the GPS antenna, modulate a laser and
detect the RF on a photodiode connected by a metre of so of optical
fibre. Whilst nothing can be considered 100% relieble, an optical
interface is probably the best you can do. One might consider this
OTT, but I don't see any other method can be very certain to work.

Having had the problem with the ADSL modem on the telphone line, I did
promise myself I'd build such an optical interface, which is much easy
at ADSL frequencies. But I never did!

Dave