Receiver front end protection?

[6SN7WGTB]

I did search for this but did not find a relevant thread, so by all means point me to one if I missed it.

I will probably be putting up some sort of simple loft aerial to assist me getting a better signal and lower noise to the bench for my restorations of MW/LW/SW radios.

The aerial (which I may pursue on here separately for advice) is likely to be a single wire dropped down to my bench in the house via some sort of balun and coax.

My question here is: do I need some sort of protection with this sort of aerial?

I've seen the attached which appears workable.

Without great knowledge on this subject, my questions are:
(a) Is this necessary with an indoor loop (There are no known Tx nearby)?
(b) It appears not to provide DC protection - is there a need?
(c) Won't the diodes only conduct/protect when there's way too much voltage anyway?

Sorry of this is a bit basic, but I'm only just getting into radio work.

[G6Tanuki]

Don't fret.

An indoor 'loft' antenna is not likely to be troubled by static/lightning [not, that is, unless your house takes a direct lightning-strike, in which case you'll be having lots more issues to worry about than the fate of a few radios].

Indeed, including non-reverse-biased diodes in the signal-path is more likely to be a _cause_ of problems - they will act as mixers and cause all sorts of horrible intermodulation-products. In times-past, inadvertent diodes caused by the 'rusty-bolt effect' in guttering, pipework, fencing, galvanised-iron shed-roofs and similar could be a difficult-to-locate cause of a whole range of annoying 'spurious signals'.

[6SN7WGTB]

Thanks, looks like sound advice.

Apologies attachment now attached!

[G6Tanuki]

Personally, I wouldn't bother with anything like that.

It's jusyt not necessary for an indoor antenna [or, for that matter, a typical outdoor antenna].


I've got a 100-foot longwire at about 30 feet above ground, and have never had any issues with 'protection', and I'm regularly firing a couple of hundred Watts of RF around the place from other experimental antennas.

If you really feel the need, spend less-than-a-fiver on this:

https://www.nevadaradio.co.uk/product/uhf-090/

to fit to your coax. But I'd honestly think you'd be wiser putting that fiver towards a bottle of wine to enjoy at Christmas.

[Radio1950]

Originally Posted by 6SN7WGTB

Without great knowledge on this subject, my questions are:
(a) Is this necessary with an indoor loop (There are no known Tx nearby)?
(b) It appears not to provide DC protection - is there a need?
(c) Won't the diodes only conduct/protect when there's way too much voltage anyway?

Sorry of this is a bit basic, but I'm only just getting into radio work.

My answers

(a) no
(b) no
(c) yes, they will conduct just a little with low voltage.

I agree with Tanuki.
Protection is required sometimes, but not for your situation.
Good luck.
.

[Radio Wrangler]

Also, the full-on protection circuit isn't quite as good as you'd probably assume. GDTs are only good for a limited number of zaps and there is no indication of their ageing. So high voltage transients from nearby thunderstorms use them up if you do have a large external antenna.

I used to design radios for planes. Direct hit to an antenna was not going to leave a useable radio. Planes are expected to take occasional hits to the fuselage which then zap off from somewhere else on the fuselage. Induced currents and voltages are large and must be survived leaving the radio working. All connections not just the antenna get zapped.

So GDTs are nice with low capacitance, but wear out. MOVs can handle fast surges. Tranzorb zeners can take a fair amount of energy, but watch out for the capacitance. In general, effective lightning induced surge protection needs to be done in several layers. The layer nearest the radio needs to be fast and accurately low enough in voltage to protect the set. It won't take a big surge, so a layer further out has to protect the protector... and maybe a beefier on further out to protect that one.

But for a receiver on an indoor antenna, nobody bothers, and nobody has much trouble.

For a direct hit, then all bets are off. The home of the chairman of the G-QRP club (low power radio amateurs) took a direct hit in the nineties. Wiring and plumbing vaporised, all electronics gone. Humans OK. He knew people were going to laugh... his name? Gordon Bennett (and a very decent chap. GP, lived on Whinmoor between Leeds and A1)

David

[ex seismic]

Years ago I worked in the North African desert where we used low dipoles for 5 MHz-ish. If we remembered we disconnected them in sand storms, (lots of static) indeed I have been thrown across a room disconnecting one too late. But we never lost a radio even when left connected. They were Pye commercial SSB radios with a transistor receiver but valve transmitter. So for the UK, do not worry.

Gordon

[lesmw0sec]

Here on the wilds of Anglesey, we get quite a bit of sudden static discharge - not just through lightning, often for no obvious reason or warning. Never had a problem through my various am. radio aerials, although they are disconnected when not in use, apart from the 2 meter rig.
I have however had problems with routers being vapourised from the voltage induced on the telephone line. In the end, I made a unit with a 100 mA fuse in each line, leading to a gas-discharge device. Since then the fuses have blown on a few occasions, but the internet gear has remained un-scathed.

[PJL]

I did some lab testing for system X lightning protection and Zeners were the chosen solution as they fail short circuit very quickly. It involved charging up a string of high voltage capacitors to many kV and discharging into the poor old Zener whilst monitoring with a fast Tek scope.

[Ian - G4JQT]

If your radios need protection, they'll probably have it built in. The main reason to have it is for static protection and local transmitters.

Solid-state front ends are more susceptible than valve sets, but most have a DC path to earth via an inductor so rain/snow static will leak away on an outside antenna.

Unless you have a huge outdoor antenna, don't worry. If you're using a balun (probably an unun) there should be a DC path to earth via one or both of the windings anyway.

Silicon diodes across the antenna input are sometimes used in professional receivers. If my memory serves me I think I remember seeing them across the 50 ohm input of a Racal 1772 receiver - but thay may not have been run-of-the-mill 1N4148s!

[tanveerriaz]

Static shock damages your radio's front end. All radios need protection.