Re: LF: Wilkinson combiners - More

[Andy Talbot <andy.g4jnt@gmail.com>]

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

On 10 April 2017 at 19:20, Clemens Paul <cpaul@gmx.net> wrote:

Hi Chris,

I've found additional info on the broadband Wilkinson combiner on my hard disk,
which I believe stems from an old ANZAC data book.
The info refers to T2 and there are two ways of how it can be made.
Type 1 corresponds to the design shown in the mini circuits application note
with the bridging resistor on the 100Ohm side of the transformer
and type 2 is exactly the design which Jay is using with the bridging resistor on the
25Ohm side.
Beside the pictorial view schematics and equivalent circuits are shown for better understanding.

73
Clemens
DL4RAJ


>-----Original Message-----
>From: owner-rsgb_lf_group@blacksheep.org
>[mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Chris Wilson
>Sent: Monday, April 10, 2017 12:47 PM
>To: Markus Vester
>Subject: Re: LF: Wilkinson combiners
>
>Hello Clemens, Markus, 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,
>
>> either method should work: two separate T-type lowpass filters
>> after each PA will reflect the harmonics before they reach the
>> narrowband combiner. Or build Jay's broadband combiner, which will
>> pass on the harmonics to the T-lowpass instead of shunting
>them to ground.
>
>> Best 73,
>> Markus (DF6NM)
>
>
>
>--
>Best regards,
> Chris                            mailto:dead_fets@gmail.com
>
>