Message-ID: <5C77C5AC9CE74A7FB3DCE7A77631904C@AGB>
From: "Graham" <g8fzk@g8fzk.fsnet.co.uk>
To: <rsgb_lf_group@blacksheep.org>
References: <1267857963.20170407112913@gmail.com> <15b480ee60e-376e-7ff8@webprd-a14.mail.aol.com> <1294128911.20170408174233@gmail.com>
In-Reply-To: <1294128911.20170408174233@gmail.com>
Date: Sun, 9 Apr 2017 22:14:47 +0100
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Subject: Re: LF: Wilkinson combiners
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Status: O

Significant levels tonight Chris , don't know why  we bothered  with deep 
search :)

73-G


21:05    136 2E0ILY de RA1ADF Op32 -26 dB F:0% in St.Petersburg 1494,9 Hz 
1600 miles

21:05    136 2E0ILY de 9A3KB Op32 928 mi -35 dB F:7%_Ini in Pula 1499,9 Hz 
with 0.1w + Marconi T for TX,  Mini Whip RX
21:05    136 2E0ILY de 2E0ILY Op32 0 mi +10 dB F:6%_Ini in Whitchurch, 
Shropshire 1499.1 Hz with 0.1w + Marconi T for TX,  Mi
21:05    136 2E0ILY de G6AVK Op32 164 mi -14 dB F:5% in Essex, JO01ho 1500.0 
Hz with 0.1w + Marconi T for TX,  Mini Whip RX
21:05    136 2E0ILY de EW6X Op32 1274 mi -27 dB F:1% in KO45kl (2051 km) 
Polotsk + miniwhip 137500.0 Hz

--------------------------------------------------
From: "Chris Wilson" <dead.fets@gmail.com>
Sent: Saturday, April 08, 2017 5:42 PM
To: "Markus Vester" <rsgb_lf_group@blacksheep.org>
Subject: Re: LF: Wilkinson combiners

> Hello Markus,
>
>
> Thanks for the detailed reply, let me see if i have this straight
> though please, sorry if I appear a bit dense, it's probably because I
> am.... :)
>
> Right now I run one voltage mode Class D push pull amp into a T type
> low pass filter. All works great, nice gate and drain wave forms, and
> my Scopematch box shows perfect sinusoidal wave forms for voltage and
> current after the T type filter. Modest output transformer warming,
> each pair of FET's near as damn it cold.
>
> I add another duplicate amp and the Wilkinson combiner. The combiner
> feeds the T type filter. With either one or both amps running the gate
> and drain wave forms go to pot, the FET's run mad hot, as does the
> output transformer (and the power input choke gets hot, too, which it
> doesn't with a single amp straight into the filter).
>
> Are you suggesting I build a duplicate T type filter bank and put a
> filter between each amp and the combiner, with no filter on the output
> of the combiner, just run the antenna co-ax to the matching
> transformer and loading coil which are outside? I can do this, it
> means finding and buying some more big toroids, but it's perfectly
> possible....
>
> Is the W1VD combiner what people call a "broadband" combiner? And if I
> built this instead of the Wilkinson one would I be able to run it in
> front of my single T type filter? Or do I still need a pair of filters
> between it and the two amp's outputs? To remind, the W1VD one is here:
>
> http://www.w1vd.com/137-500-500WCombiner.pdf
>
> Thanks  for  your patience, and thanks Graham for your input too, just
> don't  want to waste time and money building things that are incorrect
> due to my ignorance!
>
>
>
>> Hi Chris,
>
>> the PI-type combiner per se is not the problem. All I was trying to
>> say is that you have to prevent it from short-circuiting the
>> harmonics directly at the output of a (voltage-mode) class-D PA. In
>> that case, I would recommend a T-type low-pass filter between each
>> PA and combiner input, starting with a series inductor rather than a 
>> shunt capacitor.
>
>> Note that the desired harmonic load impedance depends on the type
>> of Class-D PA: Voltage-mode class D with rectangular voltage and
>> sinusoidal current should see a high impedance termination for
>> harmonics, i.e. an inductor or series resonant circuit. On the other
>> hand, current-mode class D designs would have sinusoidal voltage and
>> rectangular current, and require a low-impedance shunt for harmonics.
>
>> Best 73,
>> Markus
>
>
>
>
>
> -- 
> Best regards,
> Chris                            mailto:dead_fets@gmail.com
>
> 

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