Using VSWR or Return loss is a practical idea to avoid the dynamic range
issue. Connect a 50 load to both the antenna port and the opposite input.
Connect the NanoVNA to the input port of the duplexer with the NanoVNA set
to S11 with either both or either VSWR or Return loss.the VSWR or Return
loss will increase at the point of the resonance or notch. I use this
method more than the through method. Of course once tuned you can use the
through method to determine the loss at the pass frequency.
I was also thinking about using a low noise broadband amplifier as stated
by W8LM.
*Clyde K. Spencer*
On Thu, Feb 11, 2021 at 11:13 AM Larry Macionski via groups.io <am_fm_radio=
[email protected]> wrote:
55 years as a ham, and years ago, hams made due with what they had and all
they had to tune duplexers was it's transmitter and receiver, a step
attenuator, another 2way radio, Dummy loads and a good VOM. There is a
procedure to do it like hat in an old ARRL Repeater Handbook Circa 1980.
Last January I tuned a old pair of WACO duplexers. with my NanoVNA. All
fine since. Since you have no experience... CHECK the duplexers 1st before
you start screwing around. READ up on everything on repeaters. Go to this
site and download the white paper on "ANTENNA DUPLEXERS".. Print it and
read it twice.
EMR is one of the oldest, most trusted in the business.. The Founder was a
ham and knew his stuff..
A setup to check --NOTE CHECK--- a duplexer.. #1. carefully calibrate
NanoVNA for 3-4 megs around the frequencies of interest. Rough pictorial
but you should get the drift of how to connect.
------------------ ch0
NanoVNA ch1-------------------------
|
|
------------------CAN-------CAN------CAN--------------- |
CAN CAN CAN | |
CAN CAN CAN | |
+-----------
|
|
50 OHM DUMMY LOAD
------------------CAN-------CAN------CAN---------------
CAN CAN CAN
CAN CAN CAN
Set your marker frequencies for repeater input and output frequencies
set display to make 2-3 passes 101 points X3..... as the plot bottoms out,
at -50- -60 dB, the curve will get ragged there. You want the marker to be
in the middle of the ragged area. I have not tried it yet, but I did buy a
$5-10 20dB 0-2Ghz broad band amplifier, to install in the CH0 line to see
if I can "raise" the plot to more accurately adjust the notch. Think of
CH0 as a transmitter and CH1 as a receiver.
I also used this setup to measure SWR at inputs.
Swapping CH0 with the dummy load, will test both sides of the duplexer...
I used VNA saver as you can increase the number of points on a plot to
X8.. all thought the sweep is slower. You can save your plots to a file or
print them out. more practical than the NanoVNA alone.
Larry W8LM
