"K7ITM" wrote in message
...
On Jan 31, 3:19 pm, "Suzy" not@valid wrote:


"K7ITM" wrote in message
...
See earlier posting in this thread. See various Avago ap notes, such
...


Much too theoretical for me!

OK, here's non-theoretical, practical.

Get a piece of FR4 PC board material, copper-clad both sides, 50mm
wide by 110mm long (neither of these is very critical, but should be
at least that long) by 1.6 mm thick. One side will remain all copper
clad, as a ground plane. On the other side, fabricate at a minimum
three traces, as follows. To make it easier to describe, assume you
are looking at the board with the 110mm dimension horizontal and the
50mm dimension vertical.
Trace 1: the through-line. It will run the length of the board
(110mm), centered between the two sides. It will be as close as you
can make it to 2.9mm wide, uniform width from board edge to board
edge.
Trace 2: It will also be as close as you can make it to 2.9mm wide
for its whole length. The following is the center-line of the trace.
Start at the top edge of the board, 9mm from the left side. Go down
to 9.0mm above the center-line of the through-line trace (Trace 1).
Turn toward the right edge of the board and follow parallel to trace
1, staying 9.0mm center-to-center. Thus there should be a gap of
6.1mm between the two traces. Go a distance of 92mm. Turn toward the
top of the board, and extend the trace all the way to the top.
Trace 3: It will be the mirror-image of trace 2, same 2.9mm width.
It will start 9mm from the left side at the BOTTOM edge, go up till
its centerline is 9.0mm from trace 1, follow trace 1 to the right for
92mm, and then return to the bottom edge of the board.

Mount an edge-mount BNC connector to each end of trace 1, shell to the
ground plane and center pin to the trace. Failing that, do something
equivalent with coax or connectors...if you trimmed the end of a piece
of coax so the braid connected to the back side of the board and a
very tiny stub of exposed center conductor could be soldered to the
end of trace 1, that should be OK.

You'll need two 50 ohm load resistors. 1/4 watt is plenty. Since 50
ohms is not a common value, you may wish to use two 100 ohm resistors
in parallel for each of these 50 ohm guys. Solder one of them so it
connects with vanishingly short leads between the RIGHT end of trace 2
(at the top of the board) to the back-side copper immediately opposite
that point. The resistor(s) will be soldered to points immediately
opposite each other, front and back side. Solder the other 50 ohm
resistor between the LEFT end of trace 3 (at the bottom edge of the
board) and the back side of the board. Those are the termination
resistors, and they are the ones you would adjust to get the best null
when feeding power through trace 1 to a good 50 ohm termination.

Now you'll need two detector diodes (maybe Owen can help out here; I'd
use some surface mount schottkys, but...) and two small ceramic
capacitors. 100pF would be a good value, but it's not critical. All
leads should be so short you have trouble seeing that there's any lead
there at all. Solder one lead of a capacitor to the LEFT end of trace
2 (at the top of the board), and one lead of the other capacitor to
the RIGHT end of trace 3 (at the bottom of the board). Those are the
ends without resistors. On the back of the board immediately behind
where you soldered the capacitors, solder the ANODE of a diode, one
for trace 2 and one for trace 3. Arrange things so that the free lead
of the capacitor and the free lead of the diode (the cathode) come
together off the edge of the board. OK, I lied: leave enough lead to
solder another part to, there.

Now get or make a couple small RF chokes, about 100 nanohenries. The
inductance isn't critical. The way I'd do it is to wind some magnet
wire onto a small machine screw. For example, try about ten turns on
a 4mm screw. The wire diameter should be roughly 1/2 to 3/4 the screw
thread pitch. You can then unscrew the screw and if you're careful
with it, the inductor will be reasonably self-supporting. Next,
you'll install these two and a couple more capacitors. Small ceramic
capacitors, say something in the range from 100pF to 1000pF, should do
nicely. With the board turned over so the back is now facing you,
solder one side of a capacitor just a bit in-board from where you
soldered the diode anode for trace 2. Do the same for trace 3. Now
connect an RF choke (inductor) between the diode-capacitor junction
and the free lead of the new capacitor.

You can make things a bit more robust if you mount some sort of
terminal or pad on the back to solder this last junction to. One very
cheap but effective way to do it is to cut out some squares of PC
board material, maybe 5mm on a side, and glue them down to the large
board wherever you want an electrically floating terminal.

Just about done now! Just connect a wire from each of those last
capacitors (where wired to the inductors of course) to the + terminals
of the two 1.0mA meters, and return the meter - terminals to the board
back sides. Provide a case as you see fit, though it's usable without
a case; just be careful of the parts hanging off it.

After you build it, we can lead you through calibrating it, assuming
the earlier descriptions here weren't clear enough.

And I trust several lurkers will proof-read this and find all my
mistakes and places where I wrote LEFT when I meant RIGHT, etc. Oh,
and the meter connected to trace 2 will measure the power from left to
right in the original orientation; and the meter connected to trace 3
w2ill measure power from right to left.

Cheers,
Tom

At last! And with my new Bird dummy load nearly here I should be away at
last!