the most I have seen for HF is the Racal 10
module 1Kw HF amp and , 16 in a ' tree ' uhf wide
band system , using 4:1 combiners
73-G,.
--------------------------------------------------
From: "Alan
Melia" <
[email protected]>
Sent: Saturday, April 08, 2017 9:30
PM
To: <
[email protected]>
Subject: Re: LF: Wilkinson
combiners
> John this is a common misconception, these PAs produce
something close to a
> sinewave not an RF square wave. I am not sure of
Chris's design but Class E
> generally has a THD of about 7%.
> See
Prof. Nat Sokal's original QST article. They are however sensitive to
>
load reactance changes.
>
> There is another way of combining 2
Class E stages that was devised By Johan
> Bodin, but again I am not sure
it applies to this design.
>
> Alan
> G3NYK
>
>
----- Original Message -----
> From: "John Fisher"
<
[email protected]>
> To:
<
[email protected]>
> Cc:
<
[email protected]>
> Sent: Saturday, April 08, 2017 6:58
PM
> Subject: Re: LF: Wilkinson combiners
>
>
>
> Hi Chris,
>
> To me, it doesn't sound like a good idea to
combine two switching square
> wave signals together...Might be okay if
they were synchronized...Better to
> filter them into sine waves first
and then combine them...More expensive for
> double the number of iron
powder toroids though...
>
> Jay is combining them ahead of the
filter...That type of combiner must work
> okay that way.
>
> Cheers,
> John VA3VVV
>
>
>
--------------------------------------------
> On Sat, 4/8/17, Chris
Wilson <
[email protected]> wrote:
>
> Subject: Re: LF:
Wilkinson combiners
> To: "Markus Vester"
<
[email protected]>
> Received: Saturday, April 8, 2017,
12:42 PM
>
> 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:
[email protected]>
>
>
>
>
