Date: Fri, 14 Apr 2017 19:40:56 +0000
From: Manfred Mornhinweg <manfred@ludens.cl>
To: amps@contesting.com
Subject: Re: [Amps] Mobile Amps ?
Mike,
Homebrew, of course! Whenever you need or want something that no company
makes, or something they do make but at an unreasonable price or with
unconvincing quality, then the logical choice is homebrewing it.
You could go the simple route and built several unit amplifiers around
RD100HHF1 MOSFETs, which are easily available at a reasonable cost, and
then join them with a splitter and combiner. Those MOSFETs run directly
from 13.8V. Or you can build a DC-DC converter that raises the car's
voltage to 48V, and use a single high power LDMOSFET. At 600W or so the
cooling would be manageable, while the same LDMOSFET used at a kilowatt
or so becomes hard or even impossible to cool adequately.
Considering that the power available in a typical car is a bit limited
for a big amplifier, this is an ideal case for building a high
efficiency amplifier. Maybe using the same LDMOSFET, but modulating the
DC-DC converter to improve efficiency. This would allow you to get much
more RF output power without exceeding the alternator's capability. You
could run the amplifier in full saturation, which is easy given the high
gain of LDMOSFETs, and use envelope feedback to the DC-DC modulator to
keep things linear.
And if you don't have enough knowledge and experience in homebrewing to
tackle such a project, maybe you can find some other ham locally who
could elmer you?
An intermediate approach is buying kits and ready-built modules from the
web (amplifier blocks, splitters, combiners, low pass filter banks), and
integrating them into a complete unit.
Building you own is certainly more involved than just ordering a
factory-built amplifier, but I can assure you that it's much more
satisfying to operate a station in which as much as possible of the
equipment is homebrew!
Manfred
## assuming he wants an amp that runs on 80-10m, and auto switches
with the xcvr, and using a high eff amplifier, which I have yet to even see,
and then using a modulated DC-DC converter, which I havent seen
either, then adding the usual mess of bandswitched LP filters, etc,
he will be into it for at least $3000.00 canadian, and 3 yrs later, after
blowing stuff up in the process, end up with a working mobile amp.
## As for RFI in the vehicle, you could run some coax from amp in shack,
to the vehicles ant, then stuff 500-600 watts of 20 wpm dashes into
the cars ant, then with eng already running, see if RFI occurs. Then repeat
on every band. If you cant get the RFI sorted out, then dont even start on
any hb SS mobile map...nor any ALS-500, SGC etc, etc.
## In some cases with high power mobile, the RFI, depending on band used,
has actually killed the eng completely...at which point you have no power
steering, nor power brakes...and no acceleration. Some fellow in VE3 land
years
ago ran outa gas, eng died, then he had no brakes, no steering, ended up getting
himself killed in the ensuing accident on the hwy overpass.
## You might want to think this through b4 you proceed. The extra 7 db on TX
might not be worth it.
Jim VE7RF
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|