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Help with tuning uBitx v6


Dj Merrill
 

Hi all,
I am trying to fine tune my uBitx v6 w/ 6.1 firmware.  It could be that my understanding is faulty, and I'm hoping for some clarification.

I have two identical Raspberry Pi 4 computers running the same patchlevel of the OS, with the same version of WSJT-X 2.4.0-rc1 software and using FT8 mode.
One of the Raspberry Pis is connected to a Yaesu FT-991A radio using the built-in USB interface.
The other is connected to the uBitx via a Signalink USB interface.

If I have both radios set to the same frequency, and I have FT8 set to Tx 1000 Hz, for example, I am expecting that if I transmit on one system that I should see a signal being received on the other at 1000 Hz if everything is tuned properly.

Is this a correct expectation?

What I am seeing is the Yaesu receives the uBitx signal at 1063 Hz, and the uBitx receives the Yaesu signal at 942 Hz. 
Before I went through the tuning procedure on the uBitx I was seeing the Yaesu receive the uBitx at 1320 Hz, so the tuning process definitely improved the situation, but I would really like to see a closer match.

Is this possible, or am I just being ridiculous?  If it is possible to tweak the uBitx, how do I get it to drop another 63 Hz in frequency?  I'm not understanding what the tuning process actually does behind the curtain, and am hoping to learn.

For reference I am using Ashhar's tuning video at https://www.youtube.com/watch?v=t6LGXhS4_O8

Thank you,
-Dj


Evan Hand
 

Dj,

The FT8 frequency on the µBIKTX is a function of both the Master Calibration and the BFO tuning.  Either can change the displayed frequency on the FT8 software.

The way that I would do the calibration, assuming that you believe the FT-991A is correct, is to follow the process that Ashhar Farhan did in his video, keeping track of the saved calibration and BFO values (the stock software does NOT remember what the last calibrat90n value(s)).  This is the starting point.

Once you have the BFO correct, and the starting point from Ashhar Farhan's video,  then you can go back and tweak the master calibration using your FT8 readings with the understanding that the value that is saved is the correction value for the master clock with 875 counts per hertz.  This means that if your µis off by 10 hertz, you need to adjust the last saved calibration value by + or - 875*Error or 8750 counts.  I would do this by first assuming a positive increase, try it again, and see if that corrected it.  If not, then use the original value -8750.  The two points here are:
1 - keep track of the values you are saving for calibration
2 - the correction is 875*the error in Hertz.

You will be making changes to the Master Calibration value only.  The BFO is corrected to stay aligned with the master calibration.

Hope this helps.
73
Evan
AC9TU


Scott
 

This is amazing, I was about to post a nearly identical question and decided to do some reading first.  Saved opening another thread - good on me.

Unlike you I don't have a second radio to test with but I do have access to pskreporter!   I transmitted a CQ on FT8 on 10.136.600   At this point I'm only really interested in the "600".   I instantly received 13 reports and had a look at what each reported as the RX frequency,

(10.136.xxx)
739
749
862
756
753
764
751
752
751
804
767
750
756

Similar to what DJ was asking, is it solid theory using this smallish sample to assume my uBITX is transmitting about 160hz higher than called for?    Obviously this takes the leap of faith that on average, people are running properly aligned equipment.

Scott

Scott


Dj Merrill
 

Thank you Evan! 
That explanation makes sense, and I was able to tweak the tuning successfully.  Interestingly enough, on my uBitx one increment of tuning (875) results in a 22 Hz difference in FT8.  Nevertheless, I was able to get it very close, so that when the FT-991a transmits set at 1000 Hz, it shows up as 995 Hz on the uBitx, and when I transmit on the uBitx, it shows up as 1004 Hz on the FT-991a.  That's close enough I think!  :-)

Thank you for taking the time to help!

-Dj


Dj Merrill
 

Scott, based on my vast experience (all of it learned today!  :-)  ) I would agree that yours is about 160 Hz high.  Mine started out around 320 Hz high before I went through the tuning procedure, bringing it down to 63 Hz.

After Evan's insight, I am now within 5 Hz, making the assumption that the FT-991a is correctly tuned.

On the positive side the tuning procedure is really easy to do and it should get you in the ballpark to start.  I wrote down the numbers and made a single increment change (875), then checked with FT8, rinse and repeat until I got it where I am happy with it.

-Dj


Evan Hand
 

DJ,

You are welcome, though not sure why 875 adjusted by more than 1Hz. I will have to go back and look at the code again. 

5Hz error is really good in my book. 

73
Evan
AC9TU


Zvi Segal
 

You may use FT8 at TUNE mode.

It transmit constant tone at 1,000Hz if I am not mistaken.


--
Zvika 
4Z1ZV


Dj Merrill
 

Last night I powered down both radios and turned off the 35A power supply that powers them both.  This morning I turned everything back on.   I am working on 28.074 Mhz.  Initially the uBitx was showing 48 Hz high.  I left everything powered on but idle for 10 minutes, and then it was 14 Hz high, and after another 10 minutes it was 3 Hz high.  Another 10 mins shows it to be about 9 Hz low.  Another 10 (40 mins total) and showing 18 Hz low.  After 50 mins, 20 Hz low.  After an hour, 19 Hz low.  70 mins, 22 Hz low. 

Looks like it takes about an hour for everything to stabilize.

If this is typical behaviour, it seems like it is a good idea to let everything warm up for an hour before doing any tuning. 

I'm assuming the FT-991A is accurate.  It could very well be both radios are off when "cold" and needed to warm up.

-Dj


Evan Hand
 

On Thu, Mar 4, 2021 at 08:51 AM, Zvi Segal wrote:
You may use FT8 at TUNE mode.

It transmit constant tone at 1,000Hz if I am not mistaken.
Zvika,

I thought that the audio tone used was the one you selected so that you would not interfere with another signal.  If that is the case then you can still use the same concept, just note the tone used when activating the tune function.

73
Evan
AC9TU


Dj Merrill
 

Hi Zvika,
The way I am using it is by having two FT8 stations talk and listen to each other using actual messages (CQ), and note the freq difference between them.

The tune function within the software isn't decoded by remote stations, so wouldn't work for what I'm doing.

The tune function would be very useful if someone were using actual test equipment!  :-)

-Dj


Scott
 

DJ/group,

I've been thinking about this a lot before I start messing with settings.   I have this question;

It seems that about 80% or more of FT8 replies to a CQ choose to answer on your called frequency.  Why/how does this line up with my displayed calling freq??

I've gotta be missing something but I would expect stations attempting to contact me on my freq to be offset by my error??

Scott


Dj Merrill
 

Scott, unless I'm misunderstanding how the uBitx v6 is working, the offset we are talking about is really just affecting what is being displayed on the uBITx screen vs what the internal radio is actually using.

For example if I have FT8 set to 1000 Hz, what we should be transmitting on is base frequency + 1000 Hz in FT8. 

If the uBitX radio is 160 Hz higher than what is being displayed on the uBITX screen, the radio inside of the uBitx is actually using (base freq + 160 Hz + 1000 Hz).  The receiving station will see this as 1160 Hz within FT8 assuming their radio is tuned properly. 

They reply on 1160 Hz (base freq + 160 Hz + 1000 Hz).  The uBitx internal radio actually receives it as 1160 Hz but displays it as 1000 Hz due to the offset.

So really what the tuning procedure is doing is simply matching the number on the uBitx screen to the actual frequency being used.

-Dj


Evan Hand
 

Scott,

What is displayed in the WSJT-X software is the relative audio frequency compared to the radio's internal RF frequency.  This means that on either radio's frequency display the transmit and received frequency will be the same.  The difference is when you compare the two audio frequencies as displayed by the other radio.  As an example:

Radio 1 is actually transmitting and receiving on 10.1MHz as the frequency set for the radio with a 1.5KHz audio tone and a received tone of also 1.5KHz
Radio 2 is actually receiving at 10.1005 (a 500Hz error) but its display shows 10.1MHz, the same as Radio 1, with an audio tone of 1KHZ for both TX and RX.
Both will have the transmit and received frequency displayed on the WSJT-X software as the same on that radio.
Radio 1 will have both transmit and receive audio as 1.5KHz
Radio 2 will have both transmit and receive audio as 1KHz
There is a 500Hz error between the two.

The above is assuming you do not have the "keep transmit frequency" set.

There is a mode in the WSJT-X software radio setting to allow for the software to "fake it."  This is a way to allow for audio tones outside of the normal 2.4KHz SSB filters by adjusting the transmitter dial frequency up or down to keep the audio in the SSB filter passband.

To use this method of alignment, you need to see both radio screens or be in communication with the other person to have them tell you what they see.

Hope this helps.
If anyone has feedback on the above, please post to the group so that all of us can learn (especially me).
73
Evan
AC9TU


Dj Merrill
 

Evan, thank you for the clarification vs my oversimplification.  :-)

 

What I should have said was:

If I have FT8 set to 1000 Hz audio tones, on a tuned uBitx we are displaying (base frequency) on the uBitx screen, the uBitx internal radio is transmitting on (base frequency) and FT8 is displaying (base frequency + 1000 Hz audio). 

If the uBitX radio is 160 Hz higher than what is being displayed on the uBITX screen, the radio inside of the uBitx is actually using (base freq + 160 Hz), so what we are actually sending is (base freq + 160 Hz) + the 1000 Hz audio.

The receiving station will see this as 1160 Hz within FT8 assuming their radio is tuned properly (base freq + 160 Hz + 1000 Hz audio).

They reply in FT8 on 1160 Hz (base freq + 160Hz + 1000 Hz audio).  The uBitx internal radio actually receives it as (base freq + 160Hz) but displays on the uBitx screen as (base freq) due to the mistune offset, and thus FT8 shows it as 1000 Hz on your screen.


The way I'm thinking of it is that "tuning" the uBitx using the video link above is simply making the frequency being displayed on the uBitx screen match what the internal radio is actually using.  There might be more to it than that with regards to the internal software, etc.

-Dj