[Amps] 6kW Coax

[Mike Tubby]

Dave,

Some thoughts:

1. your design really should be a full Wilkinson combiner, the output of 
each LPF should have a 100R across to the output of the other LPF so 
that you have circa 30dB of isolation between the transmitters - 
consider what happens if of half fails

2. you "coax 70-75 ohms" needs to be 70.71 ohms of the system is matched 
to 50R with a decent return loss

3. at the power levels you're aiming for any loss of very important... 
recall that 0.1dB loss is 11% and at your power levels that's a lot of heat

4. if you really do need to use a final combiner made from coax at this 
power level then, as pointed out by others, you're looking for 7/8ths or 
bigger

5. alternatives for your application that are worth considering are:

     a) a six port Gysel combiner (rather than the two three port ones 
you have now)

     b) a further two port Gysel combiner cascaded after your LPFs

     c) a Rat Race combiner which has some advantages:

         * doubles up on the coax (you can use a slightly smaller coax)
         * provides isolation between the two transmitters
         * can be built using 75R coax (lengths 0.25, 0.25, 0.25, 0.75) 
or 50R coax (0.153, 0.153, 0.153, 0.653)

     using 50R coax you might have success with LDF7-50A


Personally, if I was attempting this project I would tend towards the 
KISS approach - you would probably get as much overall transmitter 
output from:

     5 x 2500W FM pallets -> 5-port Gysel -> single LPF

and avoid a significant amount of combining losses and system complexity.


Mike





On 10/03/2012 16:35, David Shapiro wrote:
> Hi Carl,
>
> Yes, it seems so.
>
> I have just fired off a mail to Allied Cable to see what they suggest.
>
> Thanks.
>
> Dave G4ZOW
>
>
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