On a sunny day (Sun, 24 Sep 2006 16:50:55 -0400) it happened "Jimmie D"
wrote in
:


"Jan Panteltje" wrote in message
...
On a sunny day (24 Sep 2006 10:03:00 -0700) it happened "Telstar
Electronics"
wrote in
. com:

Jan Panteltje wrote:
At 27MHz 50Ohm this is not critical.

Huh???? Since when is impedance matching at RF frequencies not
important? Then maybe you could tell us at what frequency it is
important... LOL

You really have no experience now have you?
First the little PCBs just form some extra capacitance to ground.
There is no transmission line.
And you may need that anyways, why else solder those caps over your
output transformer.
Second, for a transmission line L and C are important, and L is close
to zero here, and f is very low.
The 'length' of the track is very very short in their design.
You can hardly speak of a transmission line at all at 27MHz.
Not a significant part of the wavelength anyways.
'Transmission line' properly matched only implies no refections
and some known impedance after all.
And where is this 'line'?

You mentioned that calculator, but did you ever use it?
If so what did you enter for the constants?

Obviously you kneel before the SWR gods. You dont have to have a transmision
line to have a matching problem. Matching means to have the output impedance
of a driving stage equal to the input impedance of a driven stage so maximum
power is transfered with minimum distortion. Nothing was said of
transmission lines or SWR.

Oh I am not questioning 'impedance matching', but some points.
1) He refers to that calculator, that also asks for a track length and
load capacitance. In case of distribited loads, and there are of course.
So we need his numbers.

2) The impedance is complex, not simple 'Ohm', and in this case nearly
100% a capacitance, basically the same (leaving out the extra value of the
tape or glue), as between a top and bottom PCB layer, you take the surface
area, and get a capacitance, it is almost a square 'pad' they use (see
pictures) not a stripline! (and so no transmission line with separate
in and outputs either).

So we ask him again: What values did you enter, and what dielectric constant
for the PCB material and 'tape'.

Yes SWR must match but really that is matching of the antenna to the
transmitter, we are here internally, at the most, if there was one!!!!,
we were here in the C of an CLC Pi filter, and impedance matching.
And that is linked to SWR for a known 50 Ohm load in this specific case,
if the antenna is also 50Ohm.
So, any Pi filter in the output could 'match' the 50 Ohm antenna to any
other (higher or lower) transmitter output impedance.
If the input C (the PCB pad cap) changes, the L and output C of the Pi filter
will need to be adjusted.
He does not provide a diagram, but question arises if he HAS a Pi filter
to reduce harmonics.

How ever you slice it, teh few extra Pf from those pads wll make little
difference, maybe he even has a double sided PCB with the same problem
of capacitance to the backplane.
It is all just a way to frabricate as many posts pushing his amp as possible,
right or not makes no difference, it is not some open source project, secret
diagram, just a marketing troll.
No problem with me, but I'd love to hear wha the entered in that calculator,
at least if you recommend something you should have used it once.....

So, now for the next episode of 'the better amp'.
Grin

Sorry it is late, need to get up in a few hours,