"Richard" wrote in message
...
I have an ex AM PMR radio that I wish to use on 144Mhz. I need a PSU
feeding
24V @ about 300mA.

Are switch-mode powers supplies alright or are they too noisy to be used
for
receivers? TIA.


Many years ago I designed a switching power supply for aircraft Nav and Com
VHF radios. The switcher was 100% shielded and line filtered to get the
radio to pass FCC and FAA TSO certification. Even though the Com and Nav
radio's are VHF, they were placed next to an ADF radio (low frequency)
without problems. Testing was performed not only for electro magnetic
emissions, but also for line current emissions, with a line stabilization
network, into the radio from the aircraft power. Even if the switcher is
100% shielded, this will not prevent radiation along the input power line.
You need to consider methods to eliminate pulsed current along the input
power line caused by the switcher. This may be hard to achieve, especially
for high efficiency switchers. A good choke will help, but it will also
introduce additional switching losses. So yes, a switcher can be used; but,
IMHO it must be designed for use in an RF environment.