Scanner discone - connector sparks in the rain

[ASAD]

Currently 3 cables run into my shack from vertical antennas. Two cables are Andrew Heliax - those connectors inside the shack are grounded. According to instructions, I turned the coax at about 4" diameter right underneath the antenna. A radio is connected to one of those cables and does not have problems in rain or thunderstorms.

For the scanner Discone I am using LMR-400 and is not grounded. The same connector sparks in the rain. Good thing scanner was not connected. What are the reasons for the sparks? Does it have to do with grounding, or choke filter at base of antenna (giving the cable a 4" turn)? Should I install lightening arrestor on all 3 cables?

I would appreciate your help.

 

[dave3825]

For the scanner Discone I am using LMR-400 and is not grounded. The same connector sparks in the rain.

Where are you seeing the sparking? Center conductor of the connector?

 

[ASAD]

Where are you seeing the sparking? Center conductor of the connector?

yes. center conductor against the cylinder.

 

[dave3825]

At what rate? Like constant or intermittent?

 

[ASAD]

it sparked once every 3 to 4 seconds.

 

[AI7PM]

Static build up. Are the other antennas DC Ground type? If so, they are bleeding off the static to ground. I've seen this as well in one of my former installations with a vertical.

 

[iMONITOR]

Antenna Static Build-up Before Thunderstorm

 

[iMONITOR]

Be sure to order one with the appropiate coax connectors for your system.




CA-35RS Coaxial Lightning Surge Protector

https://www.amazon.com/Tangxi-Lightning-Protector-0-3000MHz-Connector/dp/B07WXRVBTN/ref=asc_df_B07WXRVBTN/?tag=hyprod-20&linkCode=df0&hvadid=397133308031&hvpos=&hvnetw=g&hvrand=5211984416959265337&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9016806&hvtargid=pla-852730084224&psc=1&tag=&ref=&adgrpid=80571461181&hvpone=&hvptwo=&hvadid=397133308031&hvpos=&hvnetw=g&hvrand=5211984416959265337&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9016806&hvtargid=pla-852730084224

 

[dkcorlfla]

it sparked once every 3 to 4 seconds.

Yikes! That's scary. I recently updated the coax for my Discone to KLMR 400 and used one of these.

I got it from Amazon but they are showing not available, Maybe you can find it or something else that would work. Mount it just out side of the house where the cable comes in and ground it to a 8 foot rod with thick wire.

The PL259/238 connectors might cause a little loss but are easy to work with.

I have heard that grounding like this can improve the received signal but stopping any common mode current that might try to come in on the shield.

 

[mmckenna]

Yeah, this is EXACTLY why we tell people to ground their outdoor antennas. Static build up from the rain/wind will absolutely do this. It's high voltage/low current, but can do some damage.

Looping the coax at the antenna isn't going to help.

Proper grounding will.

 

[prcguy]

Yeah, this is EXACTLY why we tell people to ground their outdoor antennas. Static build up from the rain/wind will absolutely do this. It's high voltage/low current, but can do some damage.

Looping the coax at the antenna isn't going to help.

Proper grounding will.

I had this problem all the time when I lived in Colorado in the mid 70s. Grounding a Discone or other antenna with the main radiator isolated from ground will not help the sparking, there will still be a static buildup across the coax. A receive only gas discharge tube lightning arrestor will help some but it will only fire at some prescribed voltage that might be higher than what will damage the receiver. For HF you simply place a .75 to 1.0 uH choke across the coax connector on the radio but for VHF/UHF maybe a 250k ohm to 1meg ohm chip resistor across the antenna connector might work.

 

[mmckenna]

I had this problem all the time when I lived in Colorado in the mid 70s. Grounding a Discone or other antenna with the main radiator isolated from ground will not help the sparking, there will still be a static buildup across the coax. A receive only gas discharge tube lightning arrestor will help some but it will only fire at some prescribed voltage that might be higher than what will damage the receiver. For HF you simply place a .75 to 1.0 uH choke across the coax connector on the radio but for VHF/UHF maybe a 250k ohm to 1meg ohm chip resistor across the antenna connector might work.

I kind of like DC grounded antennas.

I agree, I should have probably worded my response a bit better. The grounding is there for a reason, and probably would not fix the arcing from static electricity, but would help with nearby lightning.

@ASAD what are the two other antennas that are NOT doing the arcy/sparky thing?

 

[ASAD]

@ASAD what are the two other antennas that are NOT doing the arcy/sparky thing?

Diamond X300NA is connected to Heliax with LMR 400 jumpers. Second Heliax has no antenna yet.
Can you recommend a commercial grade lightning arrester?

 

[Ubbe]

Static builds up from the friction of rain or snow. Most, if not all, receivers have a resistor or coil to ground that will bleed that small current to ground. But if you leave the coax disconnected the voltage have no where to go and the voltage builds up to a level where it will discharge over a gap between outer and center conductor like a spark plug. Keep the coax connected to a receiver or to a load and never leave it disconnected.

/Ubbe

 

[mmckenna]

Diamond X300NA is connected to Heliax with LMR 400 jumpers. Second Heliax has no antenna yet.

OK, that makes sense.

Can you recommend a commercial grade lightning arrester?

Polyphaser.

But as prcguy pointed out, the lightning arrestor on its own isn't going to fix that. Since these are not DC grounded antennas (usually a tapped coil in the base that connects the radiating element to the ground radials or grounded mount), it won't fix the static sparking. Ubbe explained it well. The radio will give it a path. You do ideally want everything well grounded. The radio will get a path through the coax shield back to the lightning arrestor and to ground.
Usually it's recommended to ground the radio chassis if it's a base type radio.
Usually the amateur radio guides will give some good direction on this. ARRL handbook had some good setups last time I looked.

The point I was trying to make in my earlier post was that grounding -is- important, even if you are not in an area that gets a lot of lightning.

 

[Rt169Radio]

Currently 3 cables run into my shack from vertical antennas. Two cables are Andrew Heliax - those connectors inside the shack are grounded. According to instructions, I turned the coax at about 4" diameter right underneath the antenna. A radio is connected to one of those cables and does not have problems in rain or thunderstorms.

For the scanner Discone I am using LMR-400 and is not grounded. The same connector sparks in the rain. Good thing scanner was not connected. What are the reasons for the sparks? Does it have to do with grounding, or choke filter at base of antenna (giving the cable a 4" turn)? Should I install lightening arrestor on all 3 cables?

I would appreciate your help.

Just out of curiosity how is your discone antenna setup? Tower? Side of the house? etc.

I am wondering because I haven't come across anything like this before and now you got me curious just in case I come across this problem with my setup.

 

[ASAD]

Just out of curiosity how is your discone antenna setup? Tower? Side of the house? etc.

I am wondering because I haven't come across anything like this before and now you got me curious just in case I come across this problem with my setup.

The discone is on roof top (2 story house) on a metal conduit about 15 feet. The roof is reinforced concrete. The conduit is bolted to bricks walls.

 

[WA0CBW]

Is the antenna mast connected to a ground rod per code (NEC)?
BB

 

[ASAD]

Is the antenna mast connected to a ground rod per code (NEC)?
BB

No. Another antenna is grounded. NEC is I think a US requirement. The station is not in the US. I am going to do that though. I got my TV and NVR fried. That's why I ended up here.