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

[Clive Whelan]

James

Use RG8 (213 etc) and feed the DC down the coax with suitable 
decoupling. That's the classic way of powering remote ATUs and works

73


Clive
GW3NJW

Paul_group wrote:
> 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
>