protecting a land-based aerial against lightning ? Lowe HF 150

[sarabande]

I have a Lowe HF 150 receiver, which I want to set up at home.

For general use, would a plain long wire about 20m long be OK ? Suspended between insulators of course, and leading to a co-ax downwire..

My concern is about lightning. How do you protect the radio against induced EMF into the aerial please ?


TIA

 

[lenseman]

You can buy "Lightning Arrestors" which go in series with the antenna, get them from any decent Ham radio shop:

http://www.hamradio.co.uk/accessories-general-lightning-arresters-surge-protection-pc-34.php



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[Chalker]

Don't bother with a coax downlead.
You are connecting a 'long wire antenna', coax feeder is irrelevant.
'Long wire antenna' is usually an untuned random length, which is what you have and all you need.
Just extend the wire and take it to the receiver.
Don't forget that an earth will also help. Ground stake, central heating pipe etc. but you may find that mains earth introduces noise rather than helpng to get a clean signal.

 

[William_H]

Lightning strike is a concern on a long aerial. A direct strike while unlikely will probably leave your radio and possibly much of your house or shed in charcoal. However an aerial is also susceptible to current induction from a nearby strike.
This can be led away to avert damage by silicon diodes back to back from aerial terminal to ground. Check to ensure that the capacitance of the didoes does not suck away too much signal. Of course to disconnect and or earth the aerial when you are not using it is or when lightning is around is a good measure.
If you are using just one frequency then a tuned circuit of coil from aerial to ground with a parallel variable capacitor can provide a DC ground at all times which may reduce damage. You can use this to get perfect matching by attaching the aerial to a tap on the coil part way above ground. Try various points on the coil for best signal. While tuning the variable capacitor for best signal. radio will normally be connected tot he top of the coil unless it is designed for 50 ohm coax antenna in which case find the best tap for that take off as well.
As said coax is not the best thing for the lead in. Yes it may screen local interference but 50 ohm coax is made for 50 ohm circuits. The impedance of your antenna will be very variable from 50 ohms to many millions of ohms depending on frequency and length. Coax cable has typically 50 picofarrad per foot (or was that per metre). This capacitance may detune a front end designed for high impedance input. (like a short whip aerial) So open wire is best unless you can find low capacitance screened cable not 50 om coax.
Should you worry about lightning. I don't know. Some places in USA have frequent and fierce lighning storms. Other places like where I am it is rare though occurs occasionally. I have a stout earth wire on my TV aerial pole but i don't know if it has every done anything useful. good luck olewill