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Re: Voltage required for proper radio operation

A guess?
Linear voltage regulators need two things:
(1) sufficient overhead voltage to close the control loop (Vout-Vin)
(2) sufficient output capacitance to keep the loop stable.

There are such things as low-overhead VRs (called "low-dropout voltage") 
but last I checked they needed larger output capacitances to stay 
stable.  So it's a tradeoff of sorts between component 
count/size/cost.  Plus, I imagine that designs are evolutionary rather than 
revolutionary (e.g., if it's been at 9.6V, make improvements but not a 
radical re-design unless a really Really compelling reason exists).

t 11:17 2002-12-31 -0600, Estes Wayne-W10191 wrote:
>N4XEO wrote:
>Most of the radios are rated for 13.8 volts now a days. With the parts
>getting smaller and smaller they just can't run on less than that.
>W9AE replies:
>The VCO, LO, and mixer circuits in ham radios are generally powered by a 
>regulated internal voltage.  Usually 9.6 Volts or less.  It's not obvious 
>to me why a late-model ham transceiver shouldn't have stable frequency 
>when operated at 13.0 Volts.  Maybe some of us are using DC power supplies 
>that have poor load regulation?  Or maybe the DC power cable has too much 
>resistance or poor connections?
>I have used a lawn tractor battery to power my FT-847 at max UHF CW output 
>power, with no noticeable instability of TX Sat VFO frequency.  The lawn 
>tractor battery voltage was approximately 13.0V.  But my 12-gauge DC power 
>cable is only 4 feet long - less than half the length of the original 
>cable set.  And of course the lawn tractor battery voltage doesn't drop 
>when I draw 12 Amps on transmit because it is designed for high current 
>engine starting.
>Wayne Estes W9AE
>Mundelein, IL, USA
>Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
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