Re: RF power combiner

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From	Bill Sloman <bill.sloman@ieee.org>
Newsgroups	sci.electronics.design
Subject	Re: RF power combiner
Date	Sat, 25 Oct 2025 14:49:19 +1100
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On 25/10/2025 4:15 am, Jeroen Belleman wrote:
> On 10/24/25 15:17, Phil Hobbs wrote:
>> Jeroen Belleman <jeroen@nospam.please> wrote:
>>> On 10/23/25 22:48, Phil Hobbs wrote:
>>>> On 2025-10-22 04:40, Jeroen Belleman wrote:
>>>>> While musing over a text about transmission line transformers,
>>>>> combiners, splitters and so on, I came up with a power combiner
>>>>> that promises a bandwidth spanning from some kHz well into the
>>>>> GHz domain, with good isolation between input ports, and that
>>>>> does _not_ have a null where its transmission lines are half a
>>>>> wavelength long.
>>>>>
>>>>> I could find no other examples of this arrangement. The usual
>>>>> combiners are wire- or coax- wound transformers, with 3 decade
>>>>> bandwidths in the 100kHz-100MHz ballpark, or Wilkinson things
>>>>> that only begin to work above half a GHz.
>>>>>
>>>>> This design should be able to work from a few kHz up to well
>>>>> into the GHz domain. Anyway, for what it's worth, here it is.
>>>>>
>>>>> Jeroen Belleman
>>>>>
>>>>> =========================
>>>>>
>>>>> Version 4
>>>> <snip>
>>>>
>>>> That is one weird-ass combiner, for sure.� Looks like it has to be made
>>>> out of coax, on account of the switcheroo in the grounds.
>>>>
>>>> I like it!
>>>>
>>>> Cheers
>>>>
>>>> Phil Hobbs
>>>>
>>>
>>> The way I drew it was a bit clumsy. It's neater to arrange it
>>> to have the center conductors cross over instead of the screens.
>>> It should work quite well though, if constructed correctly. I got
>>> 100kHz-9GHz (-3dB) out of a similar thing, with better than 40dB
>>> of isolation between the inputs over almost the full bandwidth.
>>>
>>> It appears I'm 38 years late though. A guy names Edwards, working for
>>> Rockwell, came up with exactly the same thing in 1988! US patent 
>>> 4774481.
>>>
>>> Oh well.
>>>
>>> Jeroen Belleman
>>>
>>
>> The low frequency behavior relies on the unphysical LTspice T-line model,
>> unfortunately.  In spherical-cow land, the two ends are uncoupled, like a
>> perfect transformer with a delay.
>>
>> The combiner model works even better with 2 ps delay lines. ;)
>>
>> Cheers
>>
>> Phil Hobbs
>>
> 
> Of course, I'm aware of that. A practical implementation would
> begin to work at 100kHz, give or take depending on the number
> and type of magnetic toroids you'd slip over the bits of coax.
> 
> The hybrid bridge from which I derived this worked from about
> 30kHz, and that took lots (lots!) of ferrite toroids.

You can wrap quite a lot of RG405 around an RM14 pot core. You might 
have to wrap the copper outer with plumber's Teflon tape to avoid 
shorted turns.

-- 
Bill Sloman, Sydney

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RF power combiner Jeroen Belleman <jeroen@nospam.please> - 2025-10-22 10:40 +0200
  Re: RF power combiner Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2025-10-23 16:48 -0400
    Re: RF power combiner Jeroen Belleman <jeroen@nospam.please> - 2025-10-24 00:39 +0200
      Re: RF power combiner Joe Gwinn <joegwinn@comcast.net> - 2025-10-24 08:51 -0400
        Re: RF power combiner Jeroen Belleman <jeroen@nospam.please> - 2025-10-24 19:21 +0200
        Re: RF power combiner Bill Sloman <bill.sloman@ieee.org> - 2025-10-25 04:22 +1100
      Re: RF power combiner Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2025-10-24 13:17 +0000
        Re: RF power combiner Jeroen Belleman <jeroen@nospam.please> - 2025-10-24 19:15 +0200
          Re: RF power combiner Bill Sloman <bill.sloman@ieee.org> - 2025-10-25 14:49 +1100
        Re: RF power combiner Joe Gwinn <joegwinn@comcast.net> - 2025-10-24 15:33 -0400
        Re: RF power combiner john larkin <jl@glen--canyon.com> - 2025-10-24 12:48 -0700
    Re: RF power combiner Bill Sloman <bill.sloman@ieee.org> - 2025-10-24 18:17 +1100

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