Hi Chris, MMmm well is is and it isnt :-)) the classic Wikinson I know has
two quarter wave sections of (I think) 1.5*Zo transmission line with a 2*Zo
resistor across. Of course a quarter wave of coax at 136 or 475kHz is not
practical. So the way round this is to increase the "lumped inductance" of
the coax with ferrite loading (dropping the velocity factor considerably).
The result is a higher impedance in the coax, and the impedance at the
common end becomes greater than 50ohms so the transformer is necessary to
bring the terminal impedance back to 50 ohms again. (I am not completely
happy with my explanation because the previous delay-line coax I have played
with Zo=1kohm had the ferrite under the braid).This is an interesting
design, but unlike the pure "lumped circuit" design you were using it does
not need large input capacitors, which Markus indicates may be affecting the
tune of the individual PAs. The filter provide isolation I dont think the
pure sine-wave is that important. After all your Wilkinson inputs are
Pi-section low-pass filters, and they are causing the problem we think.The
filter format is more important, "T" which is inductor input.
Of course the "lumped component" line.....the Pi format could be directly
replaced with a T format. It would (I think) require two 82uH coils in
series (not coupled) with one capacitor at the junction, rather than a
separate "T" LP-filter (without doing the calculation I am not sure of the
cap value it may be half what you are currently using on the Pi-section). I
think this might meet Markus's criterion.
Transmission line Wilkinson combiners are used as module combiners on most
of the cellular base station PAs but at these frequencies the transmission
line is strip-line.
As Andy when we mentioned this today, at LF you can really just use a
transformer as the old Decca PA decks do.
Alan
G3NYK
----- Original Message -----
From: "Clemens Paul" <[email protected]>
To: <[email protected]>
Sent: Sunday, April 09, 2017 7:13 PM
Subject: RE: LF: Wilkinson combiners
Hi Chris,
Alan: The ferrites I was on about are the ones in the W1VD combiner,
which i believe is NOT a Wilkinson type. The one at
http://www.w1vd.com/137-500-500WCombiner.pdf
Jay's design is in fact a Wilkinson type,namely a broadband design.
A good tutorial on broadband Wilkinson dividers/combiners can be found
here:
http://www.minicircuits.com/app/AN10-006.pdf
T1 is made as classical Faraday transformer,for T2 Jay uses transmisssion
line sections
loaded with ferrites while Minicircuits uses toroids for both transformers
for their low power combiners.
I am using two very
big wire wound ceramic resistors of 50 Ohm each in series for "R"
which look very very similar to those Steve VE7SL is using in the
photo he publishes on this page.
You might check this resistors with you AIM and see how much undesirable
reactance they show
on your operating band(s).
73
Clemens
DL4RAJ
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Chris Wilson
Sent: Friday, April 07, 2017 12:29 PM
To: Markus Vester
Subject: Re: LF: Wilkinson combiners
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