How to make a 9 MHz DIPLEXER - placed after the first Mixer

A DIPLEXER's job is to let the wanted 9 MHz signal thru, and shortcut all other signals to 50 Ohm.

Therefore we want a good loss less resonance on the freq. with perfect VSWR,
and all other signals have to see a 50 Ohm shortcut with more than 20 db.

This will minimize harmonic distortion.

The Math is always the easiest part.
Now we must se if it is possible to make it in the real life.

This is a fine result - better than 25 db reflection. Good SWR.

Se the measured results here!

measure-setup with the VNA

FIRST:
Making this filter, I started the GUIDE: MATCH Assistant

Select 50 Ohm as input resistance and 200 Ohm as output resistance.

Low pass High pass
Take the nearest standard Capacitor = 150 pf Take the inductor value = 2.042 uH

Then I combine these two into one, like this:

Then I have this picture of a fine resonance-point.

 

 

 

 

I know that I must have a big capacitor with high Q, so I put on 1 nF Capacitor, MICA 5%
then TUNE the coil to resonance.

Take a look here and see the result.

By using the TUNE-bottom, I find the value of the coil to 315 nH.

As you se - better than 25 db VSWR, FB use for amateur-radio.

 

BACK TO TOP

Try measure the Q:

You will find that bandwidth is about 2,5 MHz
with these components.

 

Q = 9 / 2,5 = 3,6 - not high, but ok.

Measured results:

DIPLEXER Resonance
DIPLEXER ReturnLoss
DIPLEXER Connected to CW-Filter
DIPLEXER Connected to SSB-filter

Setting up the VNA for measuring the DIPLEXER:

Start by setting up your VNA with your bridge:


This is the OPEN-figure

 Start the program: VNA_IO_TCP.EXE (the server)

Start the program:VNADISP02.EXE (the display-program)

Push the CALIBRATE and in RED it says:
MOUNT TRUE ON VNA, AND PRESS CALIBRATE

Just press CALIBRATE, nothing else.

After a while it say:
DISCONNECT DETECTOR (OPEN) AND PRESS CALIBRATE

Now you remove the DDS-connector from the VNA, and press calibrate.

When you se the GREEN Calib OK, you will bee ready for measuring.

1: Connect the DIPLEXER to the DUT-port, and read the resonance. (Device Under Test)

2: Connect the "Load ready for mount", and read the return-loss.

Now you can adjust the coils to get the best result.

This is the way to calibrate the VNA, for mess. return-loss, until the next software-release is ready!