Pieter Hoeben said:
Yes, very important! Place it as close to your radio as possible.
But usually using beads is not enough or even the wrong solution. What
they do can be two things:
- dissipate hf by eddy cirrents, but you need special beads with loss
for this!
- make the hf impedance of the cable part after the bead higher so if
<IF!> your radio has a low impedance there, some attenuation will be
done.
Putting beads in series increases the impedance, so the cut-off
frequency will get lower.
A good radio is not so sentitive to its power lines. So i doubt the
usefullness of the beads.
I personally think that your should not only look at the radio's but
go to the source of the problems: the power supply and voltage
regulator. Are they analog or switching?
Also look at the wiring, at loops etc. Are the radio's grounded?
Regards,
Pieter Hoeben
www.hoeben.com
Guess my question was a bit vague.
I have four voltage regulators which supply voltages for 4 radios
respectively. The radios sit very close (about 2 inches) to the
regulators. My aim is to eliminate the noises that appear at the
output of the voltage regulators. The noise amplitudes were getting
very very high ( up to 13.0V peak to peak! ) when 4 radios were keyed
up simultaneously. I am not sure whether it's the RF frequencies that
emitted by antennas cause non-linearity to the voltage regulators and
distorted the output voltage.
The voltages were supplied to the radios through a battery connector.
But the battery connector supply was not tapped directly from the
output pin of the regulator. Regulator voltage would travel through
and PCB trace, go through a banana jack and power supply cable before
reaching battery connector. In order to eliminated the annoying
noises, I have:
-Put ferrite beads at the battery connector supply line. It didn't
seem to be working fine. The regulator circuits were covered by metal
plates which has the common ground as the circuit. The weird thing was
when the plate was shorted to main supply ground, the noise reduced
significantly, from about 13.0V pkpk to 3.5V pkpk. A factor of about
3.7! Nevertheless, this method had to be used along with the ferrite
bead at the battery connector supply line. If the ferrite bead was
removed, noise amplitudes would stay at the same level.
-Put a big cap (4700uF) at the output of the regulator. Not good
though. By observing the noise through oscilloscope, the noise
frequencies were below 100Hz. Hmmmm...noises only appeared when radios
keyed up.
-Wrapped the regulator with aluminium foil. However, noise amplitude
still wouldn't go down.
-Now I'm planning to put two bypass caps 0.1uF and 680nF as close as
possible to the output regulator on the PCB. I doubt whether that
would work.
I really don't have any ideas why this would happen. Ok, I know by
separating the radios some distance away from the regulators would
help to reduce the noise. Any other suggestions other than this?