Hi all, as I look through old postings one thing that keeps popping up is poor receive performance and the amount of people that have returned there radar box to have the front end Saw filter replaced. As I stated in my post on 9Db antennas this is a great product but the front end has very poor ESD protection. Due to there tiny size I would doubt that these saw filters would even handle a 50 volt ESD. Wind on a hot dry dusty day will easily cause a static build up of more one hundred times that , may be not in the damp UK ,sorry guys. In my 30 years of aviation radio engineering I have only had 2 problems like this and they were due to direct hits of lightning, but planes get hit every day so its not a common fault with them due to simple protection.
Most high quality Radio's and Aviation equipment have a low impedance (resistance) paths to ground on the antenna input for any DC or a non RF type potential to be shunted to ground, the DC input impedance of the radar box is very high allowing even the slightest ESD to build up and when flash over occurs its to late for the tiny ESD device that Airnav fitted to the later units to do its job. Note ESD in my experience can be a DC , low frequency AC or a pulse (technically AC) nasty stuff and you don't need a storm to get it. Have a look at carrier based planes returning to the deck and see the ESD on the arrester hook as they touch down and Helicopter rotors at night with night vision camera footage and when the plane hit the world trade centre I bet the flash was an ESD. On my unit i have fitted an Inductor to the antenna connector inside the unit.
1.5 turns on a 1/8th drill bit using a wire leg of a 1/4 watt resistor (see photo),it provides a low impedance to any low frequency signal I.E ESD or DC and the inductance is high enough not to interfere with the input tuned circuits of the saw filter. the sensitivity of the unit has not been affected in any way , range is as good as it has always been.
NOTE : THIS WILL VOID YOUR WARRANTY SHOULD YOU DO THIS . YOU MUST ALWAYS USE A GROUNDED TIP SOLDERING IRON AND USE GOOD ESD PRACTISES WHEN SOLDERING. if you have any doubts about anything DON'T do it. This will not stop a direct hit but it will give you massive protection improvement.
If you don't want do this I would suggest that you disconnect your antenna when not in use .
Regards ,Geoff Arnold.
