doc wrote:
> I am combining a pair of eight 2SC2879 KW amps for 160-10M
> and need to acquire a Splitter & a Combiner.
>
> RF Parts www.rfparts.com/combiner.html appears to have the
> splitter and combiner I need.
>
> I will be driving them with a TenTec Jupiter so for a
> Splitter I'll use the COM-2 Input/Output .5 x .5 300W $3.75
>
> The dual 1KW amps will merge power via a Combiner -- COM-6
> Output .5 x 1.2 2800W $6.65
>
> Is the COM-6 adequate or should I use a larger Combiner?
> (I am less concerned about cheap and more about appropriate.)
>
> COM-10 Output* .5 X 2.4 5000W $19.95
> COM-20 Output* 1.0 x 2.4 10,000W $36.95
> *includes 100W termination resistor.
>
> Also, what is the purpose of the terminating resistor for these
> two devices that is not included with the smaller ones?
Maybe they think you won't have a source of 100W resistors with suitably low
inductance(assuming the one they supply is such).
The purpose of the resistor is to absorb any difference between the two
inputs, in so doing it isolates the two amplifiers from each other. This
prevents unwanted effects such as oscillation, or one amp seeing a bad load
if the other one fails. Lead inductance in the resistor means that isolation
will fall at higher frequencies.
The power in the resistor is roughly half the difference between the inputs.
If one amp produces 1000W, the other 900W, then 1850W goes to the antenna
and 50W goes in the resistor. If one amp dies, then 500W goes up the feeder
and 500W goes into the resistor. If the resistor smokes before you notice or
before any protection circuits close things down, the remaining amp might
end up seeing a bad load and be in danger of damage itself. It's laughable
offering a 100W resistor to go with a 10kW combiner.
There's rarely any downside to using a combiner with higher power rating
than is needed.
If you're going to use the amp on SSB, please remember your neighbours, and
don't run more than 800W pep output.
Have fun.
Steve
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