bob@elroy.UUCP (02/26/87)
I want to run some 120vac equipment (TV, VCR, stereo) in my vehicle. I want to go the inverter approach (2 or more marine batteries feeding an inverter); I need some input on a good unit. The ones by Tripp-Lite put out square waves, whose RF radiation screws up TV reception. Has anyone had any experience with the Heart Interface units? I could also use some hints on installing such a system. I was wondering how the mobile amateur radio people handle 120vac input requirements (or is everything 12v). I would think a home stereo + inverter would give better fidelity $ for $, at the expense of some inconvenience. Bob
ron@brl-sem.UUCP (02/26/87)
In article <3235@elroy.UUCP>, bob@elroy.UUCP (Bob Yen) writes: > an inverter); I need some input on a good unit. The ones by Tripp-Lite > put out square waves, whose RF radiation screws up TV reception. > I was wondering how the mobile amateur radio people handle 120vac > input requirements (or is everything 12v). I would think a home > stereo + inverter would give better fidelity $ for $, at the > expense of some inconvenience. > Well these days everything is transistorized so even if you have a fixed transceiver chances are that that wall plug is connected to a power supply that puts out low voltage DC. Back in the (good?) old days, when tubes were popular there were several methods of getting the high voltage necessary. The cheapest probably was the vibrator. Popular in old dash board car radios as well. The vibrator turned the DC into a rather crude (yes square wave) AC, which could then be run through a transformer. Mobile transmitting equipment was sometimes equipped with a "dynamotor," essentially a 12V DC motor with an AC generator on it. This of course made sine waves but was big and clunky and since it had moving parts was more prone to failure. Enter the marvel transistor: They hadn't quite managed to make transistor power amplifiers yet, but they were able to make transistor multivibrators. This (as you've descrived) is the square wave generator that is the heart of the inverter. The way to avoid the emmissions, lots of filtering. Even traditional SCR dimmer circuits put out a lot of noise that would be intollerable without a filter on the output. However, artifacts of the T-power were still present, in that you could here in the signal the frequency of the vibrator which used to change pitch with fluctuations in the voltage of the car electrical system. (Of course, even DC rigs often pick up whine from the cars alternator). I suspect if you really wanted to you could modify a cheap intverter to be much less annoying with a few RF chokes. By the way, the output filters on even the best Theatrical Dimmers (where you need to keen the buzz out of the sound system) are pretty simple. Just a few turns of the output wire around a toroid core on it's way to the connector. -Ron
davet@vaxwaller.UUCP (02/27/87)
The original poster requested information on inverters so
that conventional home audio equipment could be used in
the car. Sure, this can be done but I don't think it
would really be cheaper or work as well. Audio amplifiers
designed to provide high power levels in automobiles
already include inverters in their design. Just grabbing
any old inverter and grafting it into a car with a home
amplifier would take a lot of effort to work out all the
problems (size of components and mounting, noise or square
waves, etc.). And, home type FM receivers are simply not
going to work as well as automobile types.
Dave Triplett
--
Dave Triplett (415) 939-2400 x2087
Varian Instruments 2700 Mitchell Dr. Walnut Creek, Ca. 94598
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