On Sun, 24 Sep 2006 21:21:26 GMT, Jan Panteltje
wrote in :

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'.
snip


I see everyone is reverting back to one of the major pitfalls of
single-board amps: soldering high-power devices right to copper-clad
board. My intent was to AVOID this by using solid copper strap, but
it's clear that people are determined to use the cheapest materials
possible. Therefore.....

I'm going to eliminate soldering of the power transistors completely.
They will be 'wired' using 304 stainless CLAMPS secured to the chassis
with teflon standoffs. These clamps will not only provide a much
stronger mechanical connection, but will also, in conjunction with the
gold-plated flags, eliminate ANY possibility of corrosion in damp
(spilled coffee) environments. They will also permit removal of the
transistors without de-soldering, prevent heat damage due to some big
dummy that solders with an arc welder, and help to -dissipate- heat
during normal (and overdriven) operation.

As for cost, the prototype can be cut from a standard beer keg, and in
mass production they will cost only a few cents each.

Now that -this- aspect of the design has been finalized, it's time to
move along.