An Interesting and True Story About RF Signals

You may have been close to a trucker using a linear amplifier on his CB radio.

The radios were limited to 5 W of Rf output, but boosted to godawful power with the amps and your speaker wires picked up the signal.

Quite common then, and maybe still.

"Wall to wall and treetop tall" it was.

The output of the CB would be at a high frequency, so if it was picked up by the speaker wires, wouldn't it have been at that frequency approx 27-27.5 MHz? It shouldn't have been audible, correct?

It happens, obviously it must be somewhere at the front end of the amps, maybe a sub frequency also.

A quite common occurrence with AM CB radios.

I unknowingly blacked out an entire counties police, fire and ambulance service radios by coupling a 5W CB via an SWR matching unit to the 250ft plant exhaust stack lightning conductor.

I wasn’t the flavour of the month.

As a novelty, I matched my CB radio to my metal patio umbrella and talked from my patio during nice weather.

I used to park my car in the plant workshop on nights. The structural steelwork was every bit as good as the exhaust stack, the result, I’m in trouble with the emergency services again.

What you described may be very well true!

I somehow remember during my younger years I used to hear an am station while sitting on a mountain top back home.... I noticed that this only happened when I placed or lightly grinds my upper with the lower teeth..some of which were filled with amalgam fillings or capped with gold then!

I wanted to ask my buddy if he can also hear the sound I'm hearing But the radio station disappear as soon as I opened my mouth to ask!

Remember the old Gilligan's Island episode where they picked up radio signals from what I believe was fillings.

I like your logic. You're thinking that the CB signal used a diode to modulate the carrier out and the audio was amplified and sent to my speakers. Did I understand correctly?

According to the son of the Guy I bought my house from (30 years ago), he (the son!) erected a huge CB antenna and linear amp on the roof, and could to talk to people 1000's of miles away (people with similar setups, even ones from the USA, when the weather was right!).

He had to take it down after a very windy night, as it made an awful noise that kept the whole family awake!

Its lying still in my roof space......its HUGE!!!

I bet he interfered with other people's radios!!!

Andy, can you post a picture of the antenna ? Is it a beam or a multi element Yagi ?

Was it mounted on a tower or a pole with guy wires ?

I used to have a catalog from a cb radio company on the east part of u.s. that offered these antennas for sale, the catalog was from the 1980's, and even then they were expen$ive.

I never saw it mounted, it was taken down before I bought the house as it vibrated in high winds.

It was one of my trucker buddies on their cb radio. I didn't have a separate linear amplifier like many of my friends do. My radio was peaked and tweaked and had the funnies installed. I had a high end Galaxy and I was running Wilson 5000 twin trucker's.

It's amazing how 150 watts out before the antenna can really get the boost for putting out that skip wave. For example: rolling east just past chiracao summit on i-10, I used to talk to base's just on the other side of Goodyear, Az.

That's making an over 200 mile jump.

I used to do it at night, signals tend to go farther and are clearer when the sun doesn't get in the way.

I imagine I blew out one too many, car speakers, here and there.

Having a son and a cousin in this field. Brought back memories of discussions and tales of their exploits. Having a heated argument with the son 30 years ago about putting a floppy aerial on the corner of the front of our house. Very interesting topic.

I've picked up aviation band transmissions on my FM car radio with analog tuning. The frequencies are pretty close, Navigation frequencies are 108 - 117 MHz, Communication frequencies are 118 - 136 MHz.

I am thinking of UFO signal.

When I lived in NYC used to get a local taxi dispatcher on and off.

If you were in Chicago, I wouldn't be surprised if it was the same thibg!

Could've been a taxi dispatch radio, but it wasn't close to a taxi garage, so I'm not sure. Thanks for giving your thoughts.

As an aside;

Competition is fierce among dedicated ham radio enthusiasts.

If you have ever wondered why airline electronics rules are so strict;

any of the devices mentioned below can be powered from a 12V portable battery.

I had a similar issue in college. A kid moved into the dorm with a 500 watt linear amp with a really filthy signal. He was using CB to talk skip wave to half way across the country and his signal would pop out on all the stereo systems in the dorm when he transmitted. If you were playing a magnetic tape recording, his signal would overwrite the tape with his transmissions.

Couldn't get action through the dorm or FCC, so we put a pin through his coax cable at the antenna, blew his amp and then repaired it for him with a limiting resistor in the power supply. Mischief managed.

My brother once live about 100 yards from am AM radio station broadcast tower.

He had an electric coffee pot (unplugged) in his garage. The heating element picked up and amplified whatever was being broadcast at the time. It was clearly audible when things were quiet.

I knew a guy could get TV reception in his coffee pot....

Cheap,poorly designed linear amplifiers bleed all over the frequency band.

It is very hard to get power out on a AM signal without bleed over.

It requires some serious and expensive electronics,like in a commercial radio station.

The FCC cannot remotely tell exactly how much power you put out of your CB radio,because it varies with antenna design,and they really don't care.

(Well,they probably could if they wanted to,but they don't bother as long as the bandwidth is in spec)

What really chaps their cheeks is bleed over outside of the assigned channel.

Which is why most linears are a running violation.

Truckers use a phased array,that directs the output to front and rear and concentrates the power in the forward/backward directions.

This gives them more range on the interstate highways.

You probably crossed paths with a sloppy linear signal from a trucker,and when you were "off beam" it stopped.

That's what I was thinking. Thanks for the explanation. GA to you!