[UK-CONTEST] 12v down a long run of cable

[James Thresher]

Thanks for the responses,

In the short term I'll go with the 12v Batteries at the far end of the run, along with a relay so I completely power things down remotely.

At some point I'll build an AC supply, but for the time being the batteries should suffice.

73 James M3YOM

-----Original Message-----
From: uk-contest-bounces at contesting.com [mailto:uk-contest-bounces at contesting.com] On Behalf Of Paul_group
Sent: 06 January 2009 18:16
To: James Thresher; uk-contest at contesting.com
Subject: Re: [UK-CONTEST] 12v down a long run of cable

James Thresher wrote:
> Hi Paul,
> 
> Thanks for the quick response
> 
> I will be powering a LDG DTS-6 Antenna switch and an SG-230 auto tuner
> 
> Loop resistance is 14 ohms
> 
> 73 James M3YOM

Hi James

Even by commoning up all the available pairs go/return you will still be 
sitting at just over 3 Ohms, at your two amps load that gives 6volts 
dropped. From the equipment manuals that's outside of the tolerance of 
both units. You could potentially increase the voltage but then 
regulation becomes a problem.

I guess the peak current is when you are changing bands, tuning etc but 
the rest of the time the current demand will be steady. How about 
running the electronics from a gel rechargeable battery ?

When you are operating the equipment it will work from the battery and 
you can charge the battery down the cat5 as you only need a few hundred 
mA to maintain charge? This would limit the operating time but maybe it 
would be ok for short spells.


Alternatively you can build a two stage power supply that will send say 
24V down the cable.

Common up your pairs to get down to 3.5R then 2A x 3.5R gives 7volts 
dropped. your voltage at the remote end will now swing between 24v at no 
load and 17V at your 2A demand . The second stage of your psu which is 
located at the equipment end works from from your now *unregulated* dc 
supply. It only needs to regulate that to 13.8V which you could do with 
a simple IC voltage regulator.

You might want to investigate using the braid of the coax as a dc return 
as that will be a much lower resistance.(at least it should be if you 
are using good low loss feeder) In fact you could even investigate using 
a DC bias tee and send the dc voltage down the coax.

regards Paul
-- 
73 de Paul GW8IZR IO73TI
http://www.gw8izr.com

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