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What's new with uBITX V5. #1 - Changed IF frequency

What's new with uBITX V5 #1 - Changed IF frequency

UBITX Version 5 with improved  filter for spur has recently been released. I always appreciate Ashhar Farhan, who always makes great work.

Information on uBITX Version 5 can be found on the link below. and you can download to sourcecode with schematic
https://github.com/afarhan/ubitx_v5

uBitx v5 Changes
https://groups.io/g/BITX20/wiki/uBitx-v5-Changes.



I reviewed the schematic and source code of uBITX Version 5 and modified the CEC Firmware source code. I am reviewing the circuit and trying to post what is found while modifying the firmware.
I am looking for someone who can help me test the firmware.

1.changed IF frequency.
It has been changed to reduce spur.
It seems to have been changed so as not to be affected by the oscillation circuit of Raduino.

Left : uBITX v3, v4, Right : uBITX v5

Both the crystal and the capacitor used in the filter have been changed.

Below is the Ruduno Schematic. You can see a 25Mhz crystal to operate the Si5351 (Red square), And there is a 16Mhz crystal in the Arduino nano itself, which is built into the Raduino.



This is the most important part of modifying the firmware, so let's take a closer look.

2. IF filter operation in V3, V4
Below is an example of operation in V3. (Same for both reception and transmission except CW)

This is an example when receiving 14Mhz. Approximate frequency flow.




The antenna receives a lot of radio waves. We will leave only 14.000Mhz and remove all others.
Our uBITX has a nice filter that only passes 45Mhz and removes the rest. So we are going to change 14Mhz to 45Mhz.

To make 14Mhz to 45Mhz we know we need to put 31Mhz or 59Mhz in A.
(when A is 31Mhz, output 31 + 14 = 45, 31-14 = 17.
 when A is 59Mhz, output 59 + 14 = 73, 59 - 14 = 45 )

Anyway, we will try to create 59Mhz in A.

14Mhz has been changed to 45Mhz. (59 - 14 = 45Mhz)
After passing the 45Mhz filter, all frequencies are removed and only 45Mhz remain.
(We know that 45Mhz was originally 14Mhz)

Here we can find the formula below.
A : 45Mhz + Target Frequency or 45Mhz - Target Frequency, right?


Below is the part to set the frequency of 4.3 source code.



I want to select only some of the signals that pass through the 45Mhz filter to be converted to audio signal.
A very sharp filter is required.

The filter shown below, consisting of a 12Mhz crystal, is a very sharp filter that only passes about 3Khz.




To pass the signal through this filter we have to change the 45Mhz to 12Mhz again.

B : 45  - 12 = 33,
    45 + 12 = 57

(when B is 33Mhz, output 33 + 45 = 78, 33 - 45 = -12  (LSB)
 when B is 57Mhz, output 54 + 45 = 98, 57 - 45 = 12   (USB)



uBITX 4 source code



uBITX V3 source code

The codes for V4 and V3 are different, but they are similar. SECOND_OSC_USB and SECOND_OSC_LSB already applied a usbCarrier (12Mhz) value, so they look a little different.


3. IF filter operation in V5




I could not find the 45 Mhz filter part changed on the V5 circuit. Only the IF filter has been changed from 12Mhz to 11.059Mhz.
However, the V5 source code shows that the frequency is increased by 5khz when mixing frequencies to pass 45Mhz.


I do not quite understand why. It seems that uBITX V5 should be purchased and measured by an instrument. I think that if the 45Mhz filter has not changed, this part should be kept, but it is not accurate because I have not tried V5 yet.

I need help from someone with V5. I would like to offer two firmware and check the difference in the reception ratio of the two firmware.

I modified this part as follows. I respect the original author's intentions.
modified the 45Mhz filter section to pass 45005000 like Farhan as below.

If anyone can test this, I would like to test a few passes through 45Mhz.



Below are SetFrequency codes in CEC Firmware. The CEC firmware uses ATT and IF Shift functions, so some code is added, but the frequency setting method is similar.



The code is different, but the clock oscillation frequency is expected to be the same as the V5 code.

56064200 + 0 (without att, ifshift ...) - 11059200 (usbCarrier (USB)) + f = 45005000 + f
V5 Code : firstIF (45005000) + f

The same operation as the source code of the original author is performed.


4.conclusion
In the next post I will explain the LPF and other parts.
I'm talking again, but I need help from a user with V5. Please contact me and we will send you a compiled .HEX file for testing purposes.

I am seriously thinking about converting the unassembled V4 board to V5.





Below is an video of the firmware test that supports V5.


Thanks for reading

Ian KD8CEC

Comments

  1. I see a birdy on my v3 at 7.078.500 very weak... and 14.075.500 aprox. Are these the birdies your dealing with ?

    ReplyDelete

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