Re: [amsat-bb] Powering downconverters

[Paul Yeager <w4ski@xxxxxxxx>]

Steve:

I use a 3731, modified by K5GNA, and operate portable exclusively (but not 
much yet!).

Someone (I think it was K5GNA) told me that the 3731 has an internal linear 
regulator like the 7805.  This would mean you want to supply at least 14 volts.

I built a nicad pack out of 12 cells of unknown pedigree, salvaged from old 
cell phone batteries, but appearing to be in the 800 - 1000 maHr size 
range.  This seems to work well for four hours or so, not far out of line 
with my capacity guess.  The low voltage I'm supplying minimizes the power 
dissipated by the 3731's internal regulator, and therefore heat generated 
by same, which may be why my 3731's LO has always seemed to be about 10 KC low.

Here is another suggestion:  How about three 6 volt gel cells in series?

Good Luck!

Paul W4SKI

At 08:16 PM 7/27/02 -0400, you wrote:

>I am trying to devise a better way to power 2.4 Ghz downconverters for
>AO40 reception during battery-powered portable operation.  110V AC to
>run the wall-warts is not available.
>
>I need to power either a Drake 2880 or Transystems 3731.  Both use
>bias-t's to inject DC power into the feedline.  My DEM preamp is quite
>happy with a 12V supply.
>
>Here are the choices I've come up with:
>
>- Small dc-ac inverter to power wall-wart.  Works (used this for Field
>Day), but it is inefficient  and kills the battery too quickly.
>
>- power off the 12-14V DC runing the rigs.  *may* work (I haven't tried it
>yet), simplest.  Reading the docs on the Drake 2880 and Transystems 3731
>converters, they seem to be happier at 18V.  I assume folks using
>preamp-power supplies built into their radios are doing this.
>
>- Batteries - I'd have to build a large pack of AA's or NiMHs; I don't
>think 2 9V cells in parallel would handle the 180 mA draw.
>
>- DC-DC converter (nominal 12V in 18V out).  Anyone have a schematic?
>
>73 & Thanks in advance,
>
>Steve
>KS1G
>
>-------------------------------------------------------------------------
>Stephan A. Greene     sgreene@patriot.net        ks1g@amsat.org
>-------------------------------------------------------------------------
>
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