So, lightning, is it a problem to any of you guys? I know that it can be. I did find some techniques to resolve risks but not to get rid of the problem 100%. A little copper wire 2 inches above your antenna should be good as a lightning grounding of some sort yes? I just stick with disconnecting the antenna in the first place but what if you are absent from home! Any ideas?
The little wire above the antenna doesn't work. Even a spur streamer has a good kiloampere in it and will vapourize all but a plate of steel.
You can use:
- Spark gaps. This is popular and effective with hams as well as commercial installations. - Gas discharge tubes in line to ground. Also popular with ham and commercial. - Lightning rod 10M from your antenna and much higher... give the lightning something more attractive than your antenna to hit.
BTW the chances of getting struck by lightning is damn near next to none. Not saying it can't happen but for basic LPFM/LPAM, Pirates and so on it's not likely unless you have an antenna at a height well above average objects and well into hundreds of feet above average terrain. Your main goal should be removing static charge buildup if using long wire antennas, large dipoles on shortwave, or non coupled to ground FM antennas (j-poles and 5/8 wave antennas don't have that issue). That alone should set you safe for indirect strikes.
On the other hand.. A real strike, well you're done for. I have seen professional stations taken down from that. You are out of luck. However the chances of that happening is well... have you won the million dollar jackpot yet?
Seriously the lightning you should worry about is charge buildups on aerials. Usually long ones have this issue. As in for FM you almost never have to worry, for AM broadcasting with long longwire antennas for huge dipole antennas used on SW then you should worry. Simple way to fix a buildup of static charge is placing a 10kohm resistor across the antenna terminals. Not necessary for FM obviously. It's also recommended to run a coupling coil to the FM antennas input and ground, a simple RFC so as to cause a short circuit at DC but not at RF.
He means a simple choke. An air core inductor of say, 10uH rated lots of current will work. It will appear a dead short to ground for corona buildup, but look like a high value resistor at FM RF frequencies.
Post by Ozone Express Radio on Mar 13, 2011 22:37:07 GMT -6
I'm kinda with Darklife on this one.
Growing up in the good 'ol TV era, where everyone had an antenna on the roof, or on a tower out in the country, I don't know of anyone who took a direct hit in all those years. I am sure it must have happened somewhere, but it certainly didn't happen with any regularity.
I don't take any chances. If there is any electrostatic activity in the area I apologize to my listeners, (both of them), shut down, disconnect the antenna at the transmitter and also the power. When it passes I power up again.
I don't take any chances. If there is any electrostatic activity in the area I apologize to my listeners, (both of them), shut down, disconnect the antenna at the transmitter and also the power. When it passes I power up again.
I agree there. If a storm is approaching or currently booming, I don't power up either.
I always disconnect my lead at the transmitter anytime I am not using it anyway just as a precaution. I think its good safety practice.
Having a tube RF output compared to solid state seems to be less risky also for large static dumps on the antenna. I know many people who have went through RF transistors during a bad storm. No direct hits, but just close enough that it fried the outputs. Tubes on the other hand seem to be way more forgiving on this. I run a military style 7551 VHF RF tube and it never bats an eye at anything happening along the output. Also because of the low to high impedance coil coupled inputs and high to low coil outputs it also protects a great deal.
Post by computerdoc4751 on Feb 7, 2013 7:52:13 GMT -6
I worked as a field technician servicing Motorola repeater and other transmitter sites in Florida, which is '#1 in lightning strikes in the US. These were sites that were engineered to withstand lightning, and no expenses were spared.. But the truth is when you get hit with 10 million volts at 500,000 amps, nothing man made can withstand it. repair bills for a strike on a tower were always in the thousands.
Being one who lives in an area of frequent thunderstorms especially in the summer months, I also completely shut down my FM operation and disconnect the antenna at the transmitter. I have some experience with RF transistors blowing just as a result of electrostatic conditions. One doesn't need to get hit by lightning to have their transmitter become inoperative.
Tubes on the other hand seem to be way more forgiving on this.
Agreed.
Tubes are a natural "arc discharge tube" and at worst (not worst of worst, though), maybe one turn of wire on the grid is taken out and you have to rebias.
But different areas have different levels of lightning.
Living on the west coast where 85% humidity is a 'dry day', static buildup isn't an issue. Even with local nasty boom-boom-buggers flying around.... there's always one of a zillion 100' cedar trees that'll get nailed before the antenna.
But when I lived in Winnipeg, MB, I learned fear of the cumulonimbus cloud....
So, lightning, is it a problem to any of you guys? I know that it can be. I did find some techniques to resolve risks but not to get rid of the problem 100%. A little copper wire 2 inches above your antenna should be good as a lightning grounding of some sort yes? I just stick with disconnecting the antenna in the first place but what if you are absent from home! Any ideas?
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