I've been in aviation ground comms pretty much my whole working life,
now about 43 years, and apart from the odd mobile radio just about every
bit of kit runs off regular single phase AC from 100-250 volts 50/60Hz
plus DC at nominally 24 volts, these days often specified as 28 volts in
line with solid state PA device requirements. Pretty much every GATR or
TRACON site that provides a DC supply does so either at -48 volts for
the phone line (and voice switching) systems or 24/28 volts for the
comms radios often deriving the 24 from the 48 volts supply.
I recall some airfield navigations aids, ILS/DME that had a nominal 12
volt backup supply but I think that was only some oddball stuff,
certainly all the equipment I have actually worked on has been 24/28 volt.
Interestingly Icom makes a vehicle radio for air band use 118-137MHz
about 5 watts carrier so around 20 watts pep. This radio is both 13.8
and 28 volts capable. It senses when the supply gets about about 14-15
volt and switches in a buck converter (I guess). Other than small cars
and pick-up trucks most airfield vehicles are also 24 volt.
I think from a ham shack perspective, going to 24 as opposed to 12 volts
should not be a big deal. Two batteries in series instead of one.
Charging in parallel or series as you like. In those same comm site
systems most of the DC supplies are provided by banks of 2 volt cells
all racked together and feeding either a direct DC connection to
equipment or to a UPS. Twice the voltage means half the current with the
added benefit of half the IxR losses in any given cable. Given the
impact of solar energy systems maybe not too long before houses get
built with dedicated battery rooms :)
So far as amateur radio design goes a lot of the top line, for the day,
AC mains powered base station radios have used 24/28 volt final stages,
TS930/940/950, IC781, FT1000. I'm sure their modern equivalents do the
same. Though it does seem that the AC powered base station radio is much
less common these days, I attribute that less to the wishes of the
market and more the costs/demands of testing and certification in our
more risk averse world.
I think it would be a reasonable design goal to have a radio that has
low level 10 watt output from on the base unit, with a plug in 100 watt
12 volts powered PA unit or an equally plug in 100 or 200 watt 24 or 48
volt PA, use of which would necessitate a different supply but could
likely include on board the down converter for the rest of the radio. I
think all of that should be pretty much achievable technically. Not sure
if the market would be smart enough to recognise the benefits though.
Martin, HS0ZED
On 06/11/2019 04:37, lmarion wrote:
The FAA still uses 13.6 volt AM around the world, even the Western
air defense com is same.
The Huge power UPS legacy sytems are part of the same old standard
that won't die.
leroy ab7ce
On 11/4/2019 1:24 PM, Rick Bates (WA6NHC) wrote:
Perhaps since that is the standard voltage for cars, trucks, RVs and
other
vehicles.
Commercial communication base-station equipment has been standardized at
-48 volts(*) for quite a while and actually needs to use a voltage
converter
for the odd-ball +12 V or 120V AC equipment that has to be run.
(*) -48 volts has been the telephone industry standard since Ma Bell
was a
teen-ager!
73 de K2ASP - Phil Kane
Elecraft K2/100 s/n 5402
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