I notice that the FT-857D's current consumption is a maximum of 22
amps, but I'm guessing that this is when transmitting with maximum
power on HF, correct? For operating on VHF and UHF, would my Astron 20
amp power supply suffice? I can always upgrade power supplies later,
if necessary, when I upgrade my license, but I'd like to think that,
if I buy the FT-857D now, I won't also have to buy another power
supply right away.
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That 22 Amperes max is highly likely for more than 100 Watts RF PEP
(Peak Envelope Power) You rarely need that peak current ; the average
current being approx 8 Amperes on transmit (even with audio compression)
If you are worried that your PSU can't handle brief excursions above 20
Amperes , causing your PSU (perhaps) to shut down or the supply voltage
to drop (when your unit has a voltage fold back facility) ,you can
simply put a (sealed )12 v lead acid battery with a capacity of say 10
Amperes*Hours (AH) parallel to the PSU. The battery will then take care
of the peak current.
With a battery of say 18AH (golf trolley variety) your power supply
unit (PSU) won't need a capacity higher than 8-10 Amperes since the
battery will supply the higher current.
On receive the current will be approx 2 Amperes ,with the PSU having
sufficient excess capacity to charge the battery .

Frank GM0CSZ / KN6WH