hamguy1 wrote:
hi ham radiogroups, im after the internal power control or alc inside of a
icom725 hf transceiver the radio is doing way to much power for the power
supply, it currently is doing 150 watts it needs to be turned back down to
around 100 watts .thanks in advance david from nsw australia .
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If the current RF power output itself is not a problem ,but the max
current which can be supplied by the power supply unit (presumably
13.8V) I would suggest to put a sealed (car) battery in parallel.

The quoted 150W RF power is highly likely PEP ,so when operating SSB the
average current consumption is possibly half the peak current or less
even with some speech compression .
The battery will happily supply some of the current during peak demand.

Since the battery is permanently 'on the charger ' being in parallel
with the power supply unit , you don't need a deep cycle battery ; a
cheap and cheerful 40 -60Ah sealed car battery will do the job well.
It is essential to put a 25-30 A fuse in series with the battery .

Note : I recommend anybody to use a (sealed) battery and a low power PSU
to feed a transceiver requiring (13.5 -13.8 V-DC) external power.
During rx periods the PSU output could be (automatically) disconnected .
Receiving on battery power alone is often beneficial eg less noise and
mains borne interference. Although the low impedance of the battery
will cause it to 'kill' most external mains borne interference already.

A local ham uses a FT857 with a 110Ah sealed battery, without a mains
fed PSU . When not operating the battery is connected to an automatic
car battery charger ,which is only disconnected during operation.


Frank GM0CSZ / KN6WH