Friday, June 17, 2022

WSJT-X FreqCal & Waterfall Flattening

Simple method using WSJT-X to do frequency calibration of an Icom IC-7300 (or any rig with a reference adjustment), and waterfall flattening.

Frequency Calibration

I got the idea from this post https://groups.io/g/icom705/message/532

Let the radio warm up for a couple hours or so in a room at average operating temperature. Mine is on 24/7 since I leave it running overnight on 160m FT8, or 6m MSK144 to spot meteor scatter stations, so there is no warming up and cooling down :-)

WSJT-X has a FreqCal mode - the manual covers how run a calibration cycle which will work with any radio by configuring WSJT-X to do an internal adjustment compensating for the radio, or it can also be used to align the radio it self - easy if it offers a reference adjustment via a menu option.

If in range of WWV or WWVH, or another (highly) accurate time standard broadcast, edit the FreqCal frequencies (Settings > Frequencies) to use only those you can receive.

Switch to FreqCal (Mode menu) and select one of the time standard frequencies from the frequency/band drop down.

WSJT-X sets the radio to USB mode and 1500 Hz below the carrier frequency, it then measures tone or heterodyne and displays the frequency.

If your radio has a frequency reference adjustment such an the Icom IC-7300 (Menu > Set > Function > REF Adjust) adjust it until you are close as possible to 1500 Hz in fMeas column or 0.0 in DF column.

WSJT-X FreqCal

Here I was able to get very close using WWV on 10 MHz, I see about the same DF on WWV at at 5 and 15 MHz. It will drift slightly with changes in room temp which you can see by repeating the measurement.

If the radio doesn't have a user setting for frequency reference, execute a WSJT-X frequency calibration cycle per the manual with the Measure box checked (this writes the fmt.all file in logs directory). I found I had to let it run for at least two or three cycles. Edit fmt.all and remove any lines with a * at the end, then run solve for calibration.

The latter may be more accurate, WSJT-X will apply the offset needed internally, but I didn't like it showing this offset subtracted/added to the WSJT-X frequency display (blame OCD) and it only applies to WSJT-X when it is running.

More words about FreqCal by AG6EE at WSJT-X Calibration.

Waterfall Flattening

A good guide by KA1GT - https://bobatkins.com/radio/wsjtx_wide_graph.html - while orientated for EME use the steps can be followed to optimize your waterfall.

After running through all that this is what my waterfall looks like

WSJT-X waterfall Ref Spec

The one signal at 1090 Hz is -17 dB on a quiet 6m band.