Hello Clemens, Alan, Graham and all who replied re my combiner questions,
Some great and patiently presented info here, thanks a bunch for
explaining it so well and in such detail. I now have a much better
grasp of how the wide and narrow band ones work and why a narrow band
combiner might work best with pre filtered outputs sent to its input.
I will build the W1VD design as I already have ferrites to do this,
before buying hard to get (in the UK) and costly big iron cores for
building a second W1VD LPF bank. If the W1VD combiner is not suitable
I may well buy 3 more iron cores and build a second LPF. I will also
try some low inductance resistors instead of the wire wounds, and look
at the wire wounds with my AIM analyzer. Thanks agin everyone. Off to
mow the lawn or I won't get a lift to and from the pub tonight ;)
> 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
--
Best regards,
Chris mailto:[email protected]
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