Preventing electrical spikes

[SteveB]

Had my airnav box a couple of weeks decided to get an aerial mounted on the roof....great coverage 150+ flights..then my box would not work....i sent it back for repair and they kindly fitted a new board..and said the problem could have been caused by an electrical spike or static build up....any advise how i can prevent this, i dont want to be without my box again....the setup i have is as follows

The aerial i have fitted is a Radarama...fitted with RG213 cable....aerial

See link
http://www.rocketradio.co.uk/radarama-base-antenna-for-airnav-radarbox-and-kinetic-avionics-sbs-1-1488-p.asp

[AirNav Support]

Electrical spike would mean your machine got a powersurge and it was passed through to the RadarBox which was connected. In that case you would need a fit surge power connector to your computer so any spikes will be stopped (cost £5-10)

Static build up may be unlikely but if it was I would do the following:

1.) Get an antenna which is designed to limit static build up
2.) Fit a DC Block to stop current getting back to the RadarBox
3.) Add a preamp which had a DC block already

Hope that helps.

[SteveB]

Have a power surge multi connector already fitted....so guess this must have been static from the antea, dont really want to change the antena ive just had it all fitted so guess i need to get a preamp with a dc block.... where abouts does this fit?...anyone got any recomendations?

[Navman]

SteveB

I have an antenna that looks identical to yours and my RB has failed twice due to static build-up on the antenna.

The problem is without doubt static voltage build-up on your antenna.

Take a look at this thread

http://www.airnavsystems.com/forum/index.php?topic=977.30

Since fitting a static bleed device across the antenna coax at the RD end I have had no problems and my RB is working fine.

Jeff

[CoastGuardJon]

Hi Steve, as close to the antenna as possible, to avoid amplifying extraneous noise as well as the desired signals, you could fit one at the back of the box, but the quality of signal would actually be de-graded, because of electrical noise generated within the amp itself.    Most amp specs will show db increase and also a db spec. for the internally generated noise.    On satellite dishes you have an LNA/LNB = Low Noise Amp./Low Noise Block!

[SteveB]

Thanks Guys

So i need to fit one of these?

CA23RW Static Discharge

http://www.radioworld.co.uk/~radio/catalog/ca23rw-diamond-waterproof-static-discharge-protector-p-4002.html

not very technical with all of this....so i would place this in between the box and cable socket?

SteveB

I have an antenna that looks identical to yours and my RB has failed twice due to static build-up on the antenna.

The problem is without doubt static voltage build-up on your antenna.

Take a look at this thread

http://www.airnavsystems.com/forum/index.php?topic=977.30

Since fitting a static bleed device across the antenna coax at the RD end I have had no problems and my RB is working fine.

Jeff

[CoastGuardJon]

Hi Steve,

This does seem rather expensive for what it is, and will not give any protection, until 1,000+ V is reached, it's like a car's spark plug, until a minimum voltage is reached it can't jump the physical gap, unless there is some conductive medium (dust/water etc. which will stop a car plug from firing, if you get the analogy) to assist the path to earth.    The SO239 type (not quite as good as a connector as the N-type) are still obtainable at £2 - £3.    The use of any connector in the co-ax lead will cause some Insertion Loss, as will an extra couple of metres of co-ax.    Just done a quick eBay search and found this

http://cgi.ebay.co.uk/Lightning-Protector-for-WiFi-Antenna-Arrestor-for-Wlan_W0QQitemZ280268104153QQcmdZViewItem?hash=item280268104153&_trkparms=72%3A12%7C39%3A1%7C66%3A2%7C65%3A12%7C240%3A1318&_trksid=p3286.c0.m14

I may just buy a couple of these myself!   - I just did, 3 as I've several outside leads to protect against lightning and need some N-type.   You need to take a heavy cable to an earth spike for these to be effective, but a good earth connection on most SW receivers can help - if you're into that sort of thing.

I will be going for an amp with the DC block, when I take the plunge at Christmas.    The difference an exterior antenna makes over an indoor one cannot be over-emphasised, it will usually make considerably more difference than an amp inserted (simply because an amp will also amplify the background noise as well as the desired signal).

[tarbat]

The difference an exterior antenna makes over an indoor one cannot be over-emphasised, it will usually make considerably more difference than an amp inserted (simply because an amp will also amplify the background noise as well as the desired signal).

Although, a pre-amp with a decent antenna can also make a big difference over the standard antenna, even when not mounted externally.  I replaced my standard antenna in the loft with the Wimo antenna and pre-amp, and have improved coverage by 95%, with the antenna in exactly the same location as the old antenna.

[Navman]

Steve,

Static Discharge Protectors for example the CA23RW is not a DC blocker. It is designed to discharge static to ground when the voltage across the coax reaches 230 volts DC. This is not guaranteed to give protection to very sensitive equipment against static. It is more of a lightning protection device.

My suggestion is to use a CA23RW or similar device with a good solid ground connected to it to capture lightning strikes (not direct hits) followed by a coax tee with a 10K ohm resistor soldered into a plug connected to the tee. The tee then connected to the RadarBox. The 10K resistor across the coax will prevent the static build-up in the first place. I have tested this setup on my antenna on the roof and the 10k resistor does not affect sensitivity.

I have been using this arrangement since last April with my RD permanently connected to the antenna no problems. 

Jeff

[CoastGuardJon]

Hi tarbat, just think how good the performance would be if it was outside!    How do you get the polar diagram?

Hi Jeff, I thought that was what I'd said, or at least tried to!   As I posted above, I don't think you'll find anything less than 1,000v jumping the gap, I used to know how to calculate the voltage to gap, but it's long gone now!    What sort of resistor do you use to bleed - wirewound or carbon?    Used to use an inductor or capacitor across an antenna, to act as a trap to match the frequency, but again can't remember how you calculated values.

[Navman]

Jon,

It says on the side of the CA23RW that the discharge voltage is 230 volts DC so it should offer some protection to the front end of the RadarBox.

Regarding the resistor it must be a carbon type as wirewound resistors are inductive and would be short circuit at 1090 MHz. 

As you say another method would be to connect an inductive trap across the antenna. I have experimented with this and found that 4-turns of enamel copper wire wound on a 4 mm former is about right but due to the high frequency the inductance tuning is influenced by the enclosure. Without the necessary equipment i.e. signal generator and spectrum analyser it was not possible for me to tune it properly.

Finally, I settled for the resistor approach as there was no tuning required and it does the job.

Jeff 

[CoastGuardJon]

Thanks for that Jeff, thinking about it 230v DC is quite a different animal to 230v AC!

[CoastGuardJon]

As a matter of interest, received the arrestors today, they are Diamond Antenna make which is as good as any, and the same as offered by Radioworld - the only difference is that they are (as marked in the eBay pic.) the RP version (discharge voltage 350V DC) not the RW.    When protecting against lightning they are obviously just as effective, but 1/3rd the price!