DIYbanter - View Single Post

gregz

wrote:
On Sun, 17 May 2015 18:10:51 +0000 (UTC),
wrote:

What happened when a taxi's CB could
be heard on my powerless home stereo
speaker (ca 1975)?

If it was a taxi, it was probably not a CB, but a business band radio.
However some of those old business band radios were close to the CB
frequencies.

Except for CB, which is niot used much anymore, the business band radios
are mostly all changed to a higher and narrower band now, and many just
use a cellphone these days.

However, back in the 70's when CB was real popular, and many kids had
them, (often with illegal power boosters), they could be a problem on a
home stereo and other eleectronic devices.

At that time, I loved in a large city and very near a freeway. Many
times I would hear truckers on their CB and a local "kid" with his large
illegal CB amp coming thru my stereo speakers. Even my own car CB radio
with legal power, would come thru my stereo is my car was parked right
outside my house.

There was a simple solution. Replace the standard speaker wires with a
shielded cable. Connect the + (pos) speaker wire to the center wire,
connect the - (neg) wire to the shield. Then ground the shield to an
actual ground, which in my case was a well grounded steel water pipe.

That eliminated 95% of the problem. The freeway truckers were gone, and
the nearby kid was gone too. About the only time there was still a
little "leakage" was when I'd key up my own CB, or someone else would do
the same thing, *right next to my house*.

The speakers themselves are not likely to pick up the signal, it's the
wires that acted as antennas!

THere was a way to also add capacitors across the speaker terminals, but
I never did that. Some of the old 70's popular electronics magazines had
more into about this. Most if not all of those magazines are now online
as PDF files to download.

About the only CB users these days are a few old truckers, so unless you
live right next to a major highway, I doubt CD interference should be a
problem anymore!

I fixed a lady's stereo once with a cap filter on amp output, for local am
radio interference. I don't know what cab would use am cb. You can't hear
fm usually.
Ferrite core would probably work on amp outs.

Greg