antenna anti static spark gap

[m3vuv]

just wondered if anyone has used a petrol engine spark plug for this application? seems a ready made solution to me,nice porcalain insulator etc.

[bd139]

Wont do a lot to be honest. Anything that can jump a few micrometres is enough to blow a receiver which is way less than the average spark plug gap (0.6-1.8mm). That's not a lot of volts (500-ish). If it's static you want to get rid of, shoving a low inductance 100k resistor across your ATU output (carbon comp will do the job) is good enough. That will keep the DC potential across the feed low and seep off any static.

On mine I don't usually bother with that. The antenna doesn't stay connected and I just short it before I plug it into the radio.

[TheMG]

If it's just static you're worried about, a high value resistor to ground will work fine to bleed off any static charge before it can build up, without adversely affecting antenna performance or tuning.

When it comes to lightning-induced transients, I would use GDTs (gas discharge tubes). They are inexpensive and will provide significantly more repeatable results than an open-air arc gap of any type. They are available in a wide range of different spark-over voltages.

https://www.digikey.ca/products/en/circuit-protection/gas-discharge-tube-arresters-gdt/142?k=GDT

Note that many commercially manufactured antenna tuners are already equipped with these.

You will not get reliable results from a spark plug. The spark-over voltage will vary significantly depending on a large number of variables such as atmospheric pressure, humidity, temperature, corrosion on the spark plug surfaces, any other contamination of the electrodes, etc. The electrodes on a spark plug also have pointed or sharp edges which makes it even more difficult to get repeatable results. Ignition coils in a vehicle can produce a much higher voltage than is necessary to arc across the gap, making several of these variables a non-issue.

GDTs are sealed devices filled with controlled mixture of gases (typically inert) at a controlled pressure, specifically engineered to get the desired spark-over voltage characteristics and repeatability.

Note however that the only surefire way to avoid damage to radio equipment is to physically disconnect antennas during lightning storms and/or when not in use.