After a very pleasing result with the
choke made from coaxial cable on
the antenna feed line followed by grounding I continued doing even more
investigation into noise reduction.
You may need to read Making The
Noise Go Away before starting
here.
With the work that I have already done , my general ¨all
over¨ interference has dropped to a very
low
level ,
but poking around the bands I still find some spurs of noise when
running my
Yaesu FRG-100 from a modified computer power supply.
The power supply recommended for this radio is a conventional
transformer style , but the amperage demand is quite high at 2 amps.
Not having one of those handy I have instead been running my radio off
this PC PSU which I normally use for testing high power UHF two way
radios.
Switch mode supplies can pound out the amps and be reasonably priced
which often makes them an attractive proposition in high current
applications.
When using them for UHF FM mode transceivers they prove to be very
quiet but when using them on shortwave HF radios in the AM mode noise
can be a big problem.
We may not be able to completely eliminate all of the noise from the
power supply , but we can sure give it a good try anyway.
The noise from a power supply like this comes from its switch circuitry
and its oscillators.
The oscillators can wander up and down in frequency usually depending
upon heat effects on the LC circuits and the output wave forms from the
switches are prone to generating harmonics.
This means it is impossible attack this noise by notching out the
particular offending frequency , so all we can do is confine the noise
within
the supply , preventing it from escaping out into our world.
This can be done with RF (radio frequency) chokes on the wires that
enter and exit the PSU.
Chokes like this allow normal electricity to flow but will block
(or absorb) RF energy.
With these
chokes added we should see a reduction in the magnitude of
the major spurs , elimination of minor spurs and a vast reduction of
wide banded hash.
