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From: usenet@ucbvax.BERKELEY.EDU (USENET News Administration)
Newsgroups: sci.electronics
Subject: Re: Boosting output of a little walkie-talkie
Message-ID: <38070@ucbvax.BERKELEY.EDU>
Date: 9 Aug 90 23:04:31 GMT
References: <90080614412836@masnet.uucp>
Reply-To: hull@janus.Berkeley.EDUIn article <90080614412836@masnet.uucp> peter.saulesleja@f630.n250.z1.fidonet.org (peter saulesleja) writes:
Organization: University of California at Berkeley
Lines: 37

> > No. Unless you find a very high current op amp, you can't
> > supply enough
> > current (remember it is power we're talking about here)
> > to get 3-4 Watts.
> 
>Why high current?  There is very little current travelling through 
>the antenna, so you'd require a higher voltage, wouldnt you?  After 
>all, P=VI...  And air is a very good insulator.   A high current would 
>be impossible, at reasonable  (below 1,000,000 Volts) voltages.
> 
>
>                            -=Peter Saulesleja=-
>
>
>--- Opus-CBCS 1.13
> * Origin: Nowhere(833-2814) "I hate origin lines!" (1:250/630.0)
From: hull@janus.Berkeley.EDU (Christopher Hull)
Path: janus.Berkeley.EDU!hull

An antenna is hooked up so that it looks like a short circuit at D.C. and
is usually 75-300 ohms at the RF frequency.  You need both higher voltage
and higher current to put out large amounts of power.  Tranformers can be
used to convert a high voltage and low current to a high current and low
voltage or vice-versa.  A standard 9v Cell will not delver enough power
to drive more the 100mw for a reasonable amount of time.  Hence, most
powerfull C.B.'s use banks of 8-12 AA cells to derive the necessary 
power output over a sustained time.

Design of a power amp also requires transistors with enough power handling
capability.  The design requieres some knowlidge of electronics beyond 
Ohm's law.

          Chris Hull


hull@Janus.berkeley.edu