Lightning, For Your Radio Listening Pleasure

June 1, 2015
Crop from a larger image taken with the new Canon EOS Rebel T6S
RAW image capture mode

  2015 June     Electronics,     Radio


Summer is a great time to listen to weather radio.  Maybe you want to photograph lightning, and you want to know today's chance of thunderstorms. 

We all know you could check the weather on-line, but it's more fun to listen to the radio. 

Unlike the Internet, AM radio gives you those spikes of static that tell you lightning is approaching.  I actually use that "feature" quite often.  Before the wind even starts upturning the leaves, the radio announces the approach of a t-storm.

So I got this Sony Dream Machine, which has an AM/FM tuner.  (It's sort of like this one, but an earlier model.)  And by a strange accident, it tuned in to the NOAA weather station on the first try.  I say "strange" because the weather station is actually pretty faint on AM.  You really have to try to find it.

That led me to try different types of cheap antennas.

Important Caution

You assume all responsibility for anything bad that may occur if you use an extension cord as an antenna.  Don't try to stick anything in the end of the extension cord to "make it work better".   This is not the time to try to make antenna-matching networks or anything else like that. 

Remember, that cord is basically a live wall outlet, unless the breaker is turned off.  Even there, don't put anything in the end of the cord.  You, or somebody else, might forget.

If you're going to do this easy project, do yourself a favor.  Get a pack of outlet safety caps, and use one.

Do not try to use the extension cord antenna in the rain.  And don't use it near water.

A Quick Note

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In This Article

The Radio

Initial Experiments

Easy Antenna

Now Check This Out

Antennas Are Fun


The Radio

Not many people would think of a Sony Dream Machine as a DX (distance) listening radio.  And really, it's not.   If I were looking for a broadcast-band radio that's made today, I'd probably go for one of these instead. Or, maybe I'd get something fancier... 

One good thing about that Sony clock radio, though, is that it's fairly simple inside.  At least mine is;  I don't know about the current-production ones.  There are some IC's, but I didn't see a bunch of surface mount stuff.  It looks repairable, which is important.  Whenever possible, I avoid electronics that are designed as "throwaway".  There is no sense in using up resources to make something that's not fixable, when it's not even necessary to do that.

So, anyway, I started listening to the weather station on this radio.  It was kind of surreal.  The NOAA guy-- that computer-generated voice-- kept saying the same thing for every day.  It was "showers, with a chance of afternoon thunderstorms", right on down the line.

And for several days, that's the weather we had.

Then I stopped listening to the radio, and the weather got better.

Had I somehow bought a radio that was uniquely cursed with the ability to bring bad weather? 

Whatever, man.  I wasn't about to let that stop me.  It was time to figure out a cheap antenna that would make the signal louder and clearer. 

And the weather had to clear up, eventually. 

Initial Experiments

Antennas are complicated.  It's easy to look at some equations in a book and think that's all there is to it.  Thing is, there are a number of variables we don't know and can't really measure.

Sources of RF noise, radio design... even the building's wiring can de-tune a theoretically "perfect" antenna.   So, to some extent, we have to try different stuff and see what works.

A while back I made an antenna tuner with a multi-tapped inductor (cardboard tube and magnet wire).  It has maybe twelve different selectable inductances and a variable capacitor.  (I used a cheapie, but should've used one of these.)

It has a whip antenna, but sometimes I'll put a small loop antenna on there and use it to tune a radio without connecting any wires.

That works OK sometimes, but not for this particular radio.  It's just a matter of how I built the tuner.  There are some inductances and a variable capacitor, but maybe not the right ones for this situation.

Next up was a homemade coil of wire with no particular mind paid to the length.   I dunno;  ten turns?   Eleven?  I used a half-gallon milk carton as the winding form.  Could have sat down and done some math, I suppose, but not today.

That antenna didn't work, no matter what the angle.  I tried a variable capacitor, too.  No luck.  That square antenna was basically a waste of wire.

Then I had an idea.

Easy Antenna

Years ago, I used to have a multi-band radio from the Seventies or maybe the late Sixties.  The reception wasn't great.

One day, I put maybe five or six concentric loops in the extension cord.

Here's why I did that.  Adding a few turns of inductance to the AC power cord can sometimes keep your electronics from getting destroyed in a lightning storm.  (It's not as good as one of these, though... highly recommended.)

Even in the early Twenty-First Century, there is still some question about whether lightning is AC or DC.  One thing is certain:  lightning behaves in some ways like high-frequency AC.  There is not even any question about that.  Lightning protection systems talk about "impedances", which means-- like it or not-- you're dealing with AC.

Lightning surges are hindered when they run into an impedance.  (It "impedes" the flow of AC current).  High-frequency gets blocked, while 60 Hz AC can usually go right on through.

Coiled cords may not be perfect, but if lightning is seeking a path to ground, it will tend to go through other stuff that has lower impedance.    (See also this article.)

So, we were talking about reception.  The big breakthrough moment was when I piled the extension cord loops on the radio.  (Hey, it was a coil, and coils have inductance.)  After some adjustment, the stations played much louder, and much clearer.  It was like having an amplifier!

Now Check This Out

You would probably think that an "extension cord antenna" would be no good when there's AC current through the cord.  But my homemade extension-cord-antenna worked great when I used the same extension cord into which the radio was plugged.

Now I want to pause here to remind you of the caution, which I mentioned before.  Do not try to plug anything [but your radio] into the end of the extension cord.  Do not try to jumper the plug holes, or anything like that.   You might fry yourself.   Then, people on the Internet will say that you won a Darwin Award.  That is not an award you want to "win".

So anyway, the antenna doesn't always work well if the radio is also plugged into it.  AC power cords are kind of notorious for acting as antennas:  not for radio reception, but for interference.

With this little Sony radio, the antenna works great when nothing is plugged into the extension cord.

The loops couple inductively to your AM radio's ferrite-core antenna.  That means you don't have to connect any wires to the radio.  In fact, you shouldn't.

The extension cord, when it's plugged in, is basically using your house wiring as a jumbo antenna.   It's a random antenna of unknown size and configuration;  but still an antenna.

Try not to have any battery chargers or fluorescent lights to be on the same branch circuit.  Preferably not even in the same area.  No motors, no high-frequency LED circuits.  Nothing that generates RF interference.  (Quite a few modern devices generate RF pollution.)

I tested the antenna with the extension plugged into the wall, and then not plugged in.  It definitely has to be plugged in to get the maximum effect.   Just don't plug anything into the extension. 

The positioning is kind of tricky.  It won't be the same for every radio.  It won't even be the same every day!   (Someone next-door might be running something noisy.)   That's just how these cheap antennas roll.  Don't expect the performance of a long wire antenna or a dipole with a couple of these, one of these, and some coax;  but the "extension cord antenna" can sometimes improve reception.  Quite a bit.

Extension Cord Antenna

The other end of the extension cord has nothing plugged into it.  Important.
I'll say it again:  Don't plug anything into the end of the extension cord, except one of those safety caps.

In fact, get a pack of these, or these, right now.  Electrical-tape it in place, and you're good to go.

And keep the cord away from water.

Now I just need one of these radios, or perhaps this one.

More Fun

My extension cord antenna didn't have to be the best thing on earth.  It just had to be better than anything that was sitting around nearby.   It's fairly easy to improve it, if it doesn't work that well.

Want better performance?  Try a greater number of turns.  Use a larger radius for the turns.  Move the radio around.  When you get the tuning just right, you'll know it.   The best reception I got was from using a whole extension cord, coiled into loops about a foot in diameter, and propped up so they're above the radio. 

Antenna Version 2

Canon EOS Rebel T6S
ISO 3200

If the parts list for your antenna includes "Jar of Peanut Butter", so much the better.
Get the non-hydrogenated variety.  (There's a reason that goes beyond trans fats.  That's another article, though.)

If you have a place for it, you could have better results with a long-wire antenna.  For AM, though, even a 1/4 wave long-wire has to be pretty long (50 feet or so for the highest AM frequency, and much longer wires as you move down the AM band.)  If that doesn't work for you, try one of these or one of these.  They work great for a large number of AM listening situations.  

Having a variable capacitor in the antenna makes a huge difference.  If you can tune the antenna correctly, it becomes purely resistive.  The inductive reactance and the capacitive reactance cancel each other at that point.   The extension cord antenna doesn't have a tuning capacitor, though.  It's sort of hit-or-miss, but it's fun.  And easy to make.



So there we have it:  the "extension cord antenna" for an AM and SW radio.  It ain't perfect, but it's about the cheapest, easiest solution that's still semi-good.   Does it always work?  No.  Does it sometimes work?  Yes, and it can even work well. 

Just mind the fact that it's basically a live outlet.  Don't forget to put a safety cap in the end of the cord.  Secure it with Super 88 or the equivalent.

Anything you do with this "antenna" is at your own risk, but you knew that.

When I figured this antenna out, I was not aware of anyone else having tried this.  They have, but it was new to me.   Even if the "antenna" doesn't make the stations louder, it will often null out the static and noise.  Again, not always;  but it's worth trying if you do it safely. 

And if you don't like the antenna, the extension cord is still useful for powering toasters, radios, or whatever.

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