[time-nuts] GPS-Attached Equipment Lightning Protection
SAIDJACK at aol.com
SAIDJACK at aol.com
Fri Feb 29 19:07:39 EST 2008
Forgot to mention,
I put that diode and inductor inside my HP GPS Distribution amps
retrofitting all of them, it fits quite well. HP uses a similar inductor (but smaller
current capacity) to feed antenna power into the Antenna, so the effect of this
But caveat-emptor: this only protects the center conductor from voltage
surges. One still needs to properly ground the antenna cable with a massive
ground post to prevent the cable from carrying high voltages to the inside of the
BTW: these voltages can and often are also be generated by antennae falling
into High Voltage power lines. This happens more often than one would think in
Another interesting tidbit: in frost areas (Nordig countries, Canada/Alaska
etc) the freezing ground turns into a very poor conductor, and any grounding
post looses a lot of its current-carrying capacity by becoming high impedance.
In a message dated 2/29/2008 15:40:19 Pacific Standard Time, SAIDJACK writes:
couple of problems with these gas discharge devices: they need a significant
voltage to trip, and usually may only help when the hit is a vicinity hit,
not a direct hit. For direct hits, the goal is to prevent human casualties,
and fires. I don't think any sensitive RF receiver will survive a direct hit
without significant change in performance, or failure. Well, the antenna and
cable would likely be vaporized anyways.
In my experience, putting a low-voltage TVS surge protector such as the
Sision/Panjit 3.0SMCJ24A 3KW diode from RF center to ground (using a 22nH to 33nH
high-power (2-3A) inductor to keep the RF away from the diode) helps protect
receiver inputs against most proximity hits with minimal effect on the RF
This diode will quickly conduct above 24V surges, the Gas tubes need
typically 100's of volts to start conducting.
I used these in a Satellite receiver that was sold in large volumes across
the US after we had a number of receivers returned from the states with active
lightning with input failures. A 33nH inductor and 3KW TVS took care of the
problem. The impedance of the 33nH inductor at 1.574GHz is high (>300 Ohms)
so the transmission loss is << -0.023dB accorcding to AppCad.
In a message dated 2/29/2008 14:51:00 Pacific Standard Time,
tvb at LeapSecond.com writes:
I'd be interested in reports on how well these work for GPS
antennas, both in terms of lightning protection and in terms
of attenuation, tempco, or phase delay.
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