Improves uBITX receive performance by CEC Firmware V1.07 (include example of the ATT feature)

Improves uBITX receive performance by CEC Firmware V1.07 
(include example of the ATT feature)

This document is for uBITX users and students.

Version 1.07 firmware can be downloaded from the link below.

http://www.hamskey.com/2018/04/cat-support-ubitx-firmware-cec-version.html

I implemented IF-Shift while creating Version 1.01.
The idea of implementing IF-Shift started with a suggestion from a friend with a great idea.



As you all know, IF-Shift is used for ambient noise.
For a description of IF-Shift, see the link below.
http://www.hamskey.com/2018/03/test-and-explain-for-if-shift-function.html

I received good ratings from amateur radio friends from all over the world.


I'm not talking about IF-Shift right now.
This is because it is possible to improve the reception performance and implement the RF Gain Control for Receive (ATT) in the same way as IF-Shift.

uBITX has two filters using crystals.
(two red square)


Anyone thinks that 12Mhz will be much sharper?

I returned the VNA to test the receiver performance of uBITX and brought my favorite equipment.


12Mhz filter part.
I respect the developer who created uBITX.
I was able to remove noise by shifting the signal to one side as it passed through this filter.




The video below is a test image of IF-Shift when releasing Version 1.06. You can see that the signal passes through the above filter only.

Anyway, when I did the above IF-Shift experiment, I experimented on 45Mhz.
That's what I'm talking about today.
It's a 45Mhz filter.
(It is the image which made the bandwidth more than three times wider than the above figure.)


1. The curve is smooth.
2. The peak point is near 45Mhz.
 (Version 1.061, which retained the original source code and method, is slightly lower than 45Mhz.)

I have created a function that can shift when passing through that filter.



in the code above, increase the frequency before passing through the filter, and then pass it down.
In the case of LSB, the frequency decreases by Clock 1.

And I saved the Adjust value in eeprom so that it is always available.




-------------------- TEST ------------------------------

The reason I brought the above old equipment was to do the following tests.
The reason why I use the instrument in this post is because the reception ratio is quite subjective, so I need to confirm it more objectively.
In the following post I will improve receive without instruments.
I will post this article and write soon.

1.Upload the original firmware.

2.Connect uBITX to the instrument.

  (RF and AF)

3.Because the instrument does not support SSB, it generates a signal below 1Khz.

 

0.04332v was measured at -95.0 dbm input.

4.Upload Version1.07 firmware to uBITX.

The measurement results from the instrument are the same as when the original firmware was uploaded.

5.Now I enter the ATT menu to reduce the RF Gain (for Receive).

Default Value is 0

Turn the dial to increase the ATT value.
Originally, as the ATT value increases, the reception tone should decrease but it will increase. This is lucky for you. Because your uBITX can get better.

The maximum increase was about 80 to 100.
at 80, a maximum of 0.07020 was measured.

This is probably the situation below.
(Below I have added a value to the graph to help you understand it.
The values are exaggerated for understanding. Please use it for reference only.)

[before IF Tune Applied]

Your uBITX is ready for the best performance.
'I am annoying to use uBITX so I always have to turn 80 on the ATT menu!' -> It is a wrong idea. The ATT function applies only to receive. If you save the Tune value as shown below, your SSB transmmit performance may be slightly improved.
(In CW mode, only receive performance is improved)


Then run uBITX Manager.
(IF Tune is supported from Version 1.02)

Check 'Enabled IF1 Calibration Value'
Then enter 80 in the IF1 (45Mhz) Calibration field.

(Firmware Version 1.071 will add the option to use IF-Tune and ATT in the opposite direction.  For people using modified filters or using DIY uBITX)

Write to uBITX.
(If you are using uBITX Manager for the first time, please refer to the article on uBITX Manager in other articles of my blog.)

Reboot uBITX.
Calibration values are applied so you can feel that reception is improved no matter what frequency you are going to.

Now let's see if the ATT function works properly.

Enter ATT Menu


Try increasing the ATT value.
As the ATT value increases, the reception ratio decreases.
ATT value 0 is the best receive condition.



 When ATT value exceeds 200, almost no signal is heard.
 

This is probably the situation below.
(Below I have added a value to the graph to help you understand it.
The values are exaggerated for understanding. Please use it for reference only.)


[After IF Tune Applied]

Added comment
If you have done this in the LSB, it may not have a big effect when you enter USB mode.
If you subtract 30 from the measured value at LSB, both LSB and USB will be satisfied.
But I do not recommend this method. 
because At the 1.7x beta is over, I will make sure that I get the best performance on both LSB and USB.

If you have followed this method, just enter the measured value from the LSB. Updating Version 1.71 may have increased USB reception performance.

This is the experiment I've done so far.

Using this function, John (VK2ETA) created AGC.
When I apply S.Meter in my firmware I am going to apply John's code.
Thanks to John for discussing this feature.