http://www.dsprelated.com/showmessage/58085/1.php

Interesting. Best not to listen to AM talk radio anyway. Usually, with my FoMoCo Zenith 1949 Mercury radio, I get absolutely no static no matter where I go. It's a typical Zenith, supreme in every way. This radio should be called the miracle radio or something. It has little filter chokes and condensers everywhere. It also has superb audio. When I drive under some REALLY high voltage wires on some REALLY HUGE towers, though, I get a deep hum that has more bass than my Crosley Super 11 (1117). I guess it helps that I have a 5 foot antenna on my car. It really is a "whip" antenna.

When I lower the antenna, I get less hum, that is.

Thomas

Wow... that's saying something compared to AM radios these days.. what's the circuit design secret for pure no static sound??

Peter,
Its called FM radio. Been around for years. It was actually produced as a replacement for AM radio, and has done quite well. Don't think we need to re-invent the wheel, and besides that there are very few AM stations broadcasting worthwhile material these days, and primarily because of the competition from FM. Then of course there are the sun spots to contend with. Some years are good, and AM radio listeners are overwhelmed with crystal clear reception from distant stations, then bragging 'bout their re-build and the great performance of their mundane five and dime set.
As we meander unwillingly into the 21st century, lets remember that AM radio served its purpose, and was a modern marvel of the 20th century, but like Model T's
has been replaced by newer fuel injected marvels (integrated circuits) with complete receivers, AM and FM, on a single 20 pin chip barely visible to the human eye. I love rebuilding these old timers, and marvel at the engineering that went into their design, fine tuning their apparatus, polishing their elaborate wood cabinets, thinking of the yesteryears of providing the ultimate in entertainment, news boxing matches to name just a few. The PC, cell phone, garage door opener, wireless networking, RFID, home entertainment centers are all contributors to the cluttered AM spectrum, and the list goes on. Those noisy overhead power lines provide the power I'm using right now, and my radio is off. Silence is golden!!!!!

marv

:Wow... that's saying something compared to AM radios these days.. what's the circuit design secret for pure no static sound??
:

Someone's feeling happy to-day. AM radio sucks to-day, but I rather liked it when it used to have all sorts of old music all over the dial. The constant murmer of stations across the country coming in at the dead spots gave me this feeling of this living mass or something. When listening to music, crashes of lightning added to the thrill of the storm.

At any rate, here's an auto AM radio that sounds terriffic, and is static free, too. This radio actually makes music sound great on AM (like most old radios do). There will be slight static if steel ignition wires are used. I prefer steel, though, because it gives me a better spark. If out in the middle of nowhere, you'll get a rushing sound even with resistor wires. This is due to static in the wheels, among other things. I never did fill my wheels with anti-static powder. Oh well.

http://www.nostalgiaair.org/PagesByModel/442/M0025442.pdf

Note: my radio is the one with octal and 7 pin tubes. It doesn't have loktals, though both types were available. A great improvement in power and lack of current drain can be had by gutting an 0Z4 and replacing the innards with 600 volt diodes. Then insert this in the 6X5 socket (same pin out). ...More power, less filament drain.

T.

And by the way Peter, I went to the sight you recommended, and put in my 2 cents worth about contaminated insulators causing a buzz and other nonsense unrelated to DSP.

marv

:http://www.dsprelated.com/showmessage/58085/1.php

The person who started that thread said the problem was a 60-Hz "buzz," not hum.

High-voltage transmission lines will generate static -- that can be worsened by dirty insulators or sharp edges in the hardware that support the conductors, e.g. nuts and bolts. The field strength at those sharp points can be high enough to cause discharge. The discharge will have all kinds of frequencies in it, but will be modulated by the 60-Hz. You're really not picking up the pure 60 or 120 Hz (which would be a hum, not a buzz).

A new transmission line may generate a lot of static because the hardware edges are sharp. As time goes on, those edges and points become less sharp, so the static is reduced.

I don't think a pure 60-Hz signal would be picked up by a standard AM radio unless it somehow jumped straight into the radio's audio section. This, I suppose, could happen if the field strength was strong enough.

I think that the hum that my radio picks up (it's a real hum, not a buzz) is from induction or capacitance or something. The wires that cause this have extremely high voltages in them.

Anyway, if the reply has anything to do with what I wrote, I was just adding my two cents worth. I know that the guy was originally talking about buzz. What I was saying is that my car radio doesn't ever pick up buzz or static (except in thunder storms or slight static when I use steel ignition wires). Only on rare occasion does it pick up a deep booming hum, and it's only when I drive under super high voltage wires. My radio is amazing. It even fairs well under bridges. It obviously gets quieter, but the AVC works overtime to pull in the signal anyway. In clear open spaces it is just jam packed with stations even in the day. The thing I like the most about this radio is that it has push-pull output. I got it for only $10. These two keep me from getting the original 1951 Chevrolet radio, which has a single 6V6 for the output, and often costs over $200.

T.

I hadn't thought of the possible capacitive or inductive coupling between the power line and the radio.

I wonder if your hum comes in through the antenna somehow or if it excites the car's body and then jumps into the radio's audio section.

Whatever it is, I worry that it'll give me a brain tumor or something. The problem isn't as pronounced when I lower my five foot antenna to two feet.

T.