Hello Andy,
09 May 2017
I would like to try the transformer coupling, what turns ratio should
I use please? I will not try and be too clever and impedance match
there as well, i will leave the impedance matching transformer outside
by the loading coil for now, so as not to introduce too many
variables. Should I be OK winding on a stack of three FT-240 ferrite
toroids in 77 material that are in the combiner right now? And
finally, apart from the math to work out if a toroid might saturate at
a given power level, is their an instrument test to see if that is
occurring in real time? Thanks.
Best regards,
Chris 2E0ILY mailto:[email protected]
>> Why not keep it simple, and do it like the Decca transmitters?
>> Forget complicated splitters/combiners with messy deliberate
>> isolation. You are combining identical signals so that sort of design is
>> not required.
>> BEFORE any low pass filters, take each output of each transmitter
>> module to separate identical primary windings on one, normal ferrite
>> transformer core. Use a single secondary to take the combined power
>> off through a low pass filter to your antenna. (But do size the
>> core and turns for the TOTAL power to be generated)
>> As both transmitter modules will be delivering identical outputs,
>> the voltage induced in primary 2 coil from Tx module 1 will be
>> exactly equal to the that delivered to it from Tx module 2 (and
>> vice versa) so with both transmitters operating correctly, the
>> outputs will sum in the secondary. you are adding teh currents
>> delivered by each stage, from an equal voltage delivered by both.
>> You are, to all intents and purposes, connecting the transmitters in
>> parallel to multiply the current delivered in total
>> You can use the combining transformer for impedance matching if
>> wanted - for example the Decca ones have direct drive to the
>> primary windings via a tank circuit and each of the ( In their case
>> three) primary to single-secondary turns ration ratio sets the impedance
>> transformation.
>> Isolating combiners like Wilkinsons only come into their own
>> properly when non-identical signals need to be summed while keeping
>> the two sources isolated. Intermod testing in receivers is a
>> particular case in point, where the two test signals have to be
>> summed without generating their own intermod products caused by the
>> output of one source leaking into the (probably non-linear) output
>> of the other. If that happened, self-generated IMPS that could swamp those
>> being tested-for.
>> Andy G4JNT
>
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Best regards,
Chris mailto:[email protected]
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