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Re: Voltage required for proper radio operation

G'day All.

The problem for alot of people seems to be occuring while playing with AO40.
It seems that it is common to run their downconverter from the preamp supply
built into the radio. If you actually measure the voltage supplied up the
cable to the converter ( while under load ) you will find that the FT736 and
the FT847 both are very poorly regulated ( for the preamp supply ). Remember
it is a low current preamp supply not designed to run downconverters. The
current capability quoted in the manuals is very optimistic and most
downconverters are running near the limit quoted by the radio manufaturer.
Most radio's supply 12V up the cable ( who knows what it is by the time it
gets to the converter end of the cable - that depends on cable length and
connections ). Now most of the converters have 12V regulators in them that
need 1.2V extra to allow for regulation. Therefore most converter
electronics powered from the radio are not being supplied with a regulated
supply. As you TX there is a very small voltage drop on the power supplied
to the converter and because its not regulated to the electronics freq
changes in local oscilators etc occur. I fixed this ages ago with a home
brew voltage injector box to supply the converters and all the strange drift
problems went away, I operate both a FT736 and a FT847. The box is a die
cast box with 2 N connectors, a feed thru capacitor for voltage, and
internally a DC blocking cap and an inductor. I may be barking up the wrong
tree here but it solved my problems, your millage may vary.

Cheers Geoff VK3JDG

----- Original Message -----
From: "n4xeo" <n4xeo@bellsouth.net>
To: "Estes Wayne-W10191" <W10191@motorola.com>; <amsat-bb@AMSAT.Org>
Sent: Wednesday, January 01, 2003 8:40 AM
Subject: Re: [amsat-bb] Voltage required for proper radio operation

> At 11:17 AM 12/31/2002 -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
> >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
> >power, with no noticeable instability of TX Sat VFO frequency.  The lawn
> >tractor battery voltage was approximately 13.0V.  But my 12-gauge DC
> >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
> I agree Wayne, but the bottom line is that the specs say 13.8 volts. This
> is what they are saying is needed. Maybe the regulators are being pushed
> the max where they need the higher voltage just to make the 9.6 volts or
> whatever!!!
> Bill N4XEO
> ----
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