[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 
is negligible.
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 
 the US!
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:

Hi Tom,
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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