Amateur radio inventions h&made in NZ by Chris Day ZL1CVD

CatTouch - SWR Screen


This information is for firmware version 2.15 & greater

WARNING:
This test turns on the transceiver transmitter.

Pay attention in case a fault condition causes unintended issues

Overview
This screen visualizes the antenna response over a range of frequencies within the currently tuned band
CatTouch SWR measurement includes the internal transmission path, tuner & everything to the antenna.
This provides the most accurate picture of the system's overall SWR, not something an external SWR meter or antenna analyzer can show.
Every transceiver's internal transmission path is slightly different due to component tolerances & factory alignment.

It will also store & display historical SWR data if a SD card is inserted
The procedure begins by asking if the antenna or load is connected & if any amplifier is in bypass mode
If both conditions are met, it asks if the user wants to test the SWR now
If the user chooses to, it plots the current SWR values & displays them on the chart
Historical plot/s are color-coded & a legend indicates date & time of each test
SWR plot screen also shows the VFO frequency & if the internal tuner was turned on or off

How to use this SWR test
If you want to store or view history, insert a compatible SD card
Tune the transceiver to a frequency on the band you wish to test
Turn ON or OFF the internal tuner as required
Make 100% sure the correct antenna or dummy load is connected
Also make sure any connected amplifier is in bypass mode
Select SWR screen & answer the questions about antenna/load & amplifier, pressing NO restarts CatTouch
You are then asked if you want to perform the SWR test now
Next any history on the SD card, for the current band, is plotted
If you chose to test SWR now, it will be tested & plotted on the chart
If an SD card was inserted, the current SWR test will be added to the history file

NOTES:
The lowest FM power level is used to test SWR
During testing, transceiver frequency will change & transmitter will turn on & off
Once testing has completed, the original frequency, mode & power is restored
Trying to test SWR outside an allocated amateur band, will error & CatTouch will restart
Bands are determined by IARU zones which you can change on the CFG screen
CatTouch has no provision for MARS / no frequency limit SWR testing
Once a SWR measurement starts, the only way to stop it is to remove power to CatTouch & Transceiver
Yaesu transceivers report SWR as a value 0~255 & not a ratio of forward & reflected power
There is no magic table that converts Yaesu's value to actual SWR
Different transceivers report different SWR values for the same antenna
If dial frequency changes after SWR test, go to transceiver CW setting & set CW FREQ DISPLAY > DIRECT FREQ
During SWR testing, it may try to transmit on a frequency not allowed by your transceiver, in which case a high SWR will be reported
CatTouch does not control any tuner - internal or external. You must manually set this yourself
SWR data is stored in the CSV file swr.csv which is formatted like this:
# band,F(Hz),SWR(0~255),YYYY-MM-DD,HHMM,RIG
20m,14000000,98,2023-05-08,01:38,FT991A

Date & time is Zulu


Why FM for SWR measurements?
Accurately measuring SWR requires a stable carrier signal and frequency, along with sufficient power.
The carrier bandwidth should be as narrow as possible to minimize interference with other users.
Yaesu transceivers have many modes that can be summarized by:
CW fits all the criteria, but a transceiver can be set up so the CAT TX command won't produce a carrier.
AM takes too long to stabilize, probably due to the way Yaesu uses ALC action to limit AM PA power.
SSB requires external modulation to generate a carrier.
RTTY contains additional frequency components (mark & space tones) that interfere with measurements.
PSK contains additional components like RTTY and varying power levels per frequency component.
FM has a constant amplitude carrier. If not modulated, it is a constant frequency. It requires no additional configuration to TX via CAT.
An often misunderstood fact about FM is that if it is not modulated, its carrier occupies the same bandwidth as CW.

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