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Modification of SI4732-A10 for full HF band reception on UV-K5

 Modification of SI4732-A10 for full HF band reception on UV-K5

I will guide you on applying SI4732-A10, which is mainly used in shortwave radios that support SSB, to UV-K5.   Firmware Version CEC_0.1HF
  1. This version is different from the existing CEC series of UV-K5
  2. This version is a test version for devices in which the FM radio chip BK1080 of the UV-K5 radio has been removed and replaced with SI4732-A10.
  3. Do not upload to your radio if you have not modified the hardware
  4. When the source of UV-K5 CEC version is released (Release 1.0), you will be able to run SI4732-A10 through Makefile options

1. Parts

  1.1 SI4732-A10 * 1

If you search SI4732-A10 on Google, you will find various shortwave receivers. It has been popular with many people for several years due to its pretty good performance.

You can buy it on aliexpress for about $2.xx 

There are several versions of SI4732, but the one that supports SSB is the one with A10. You must purchase SI4732-A10

  1.2 X-tal 32.768Khz  * 1

  1.3 Capacitor 15~35pF * 2 (When purchasing crystal, purchase it in the recommended dosage. Approximately 22pF works in most cases)

  1.4 Capcitor 100uF * 1 (or 50uF ~ 200uF)

  1.5 Registor 10~15K * 1

2.circuit diagram

  The red numbers shown in the circuit diagram below are the pin numbers for the existing BK1080.

In the circuit below, the letters 3 and 4 mean to connect to both numbers 3 and 4

To use FM radio, you must connect a separate antenna. However, even if you only use AMI, you can hear a strong FM signal well. (If you want to improve FM radio performance, you must implement and connect a separate antenna or SPLITTER)

I wrote numbers on the PCB board below.
If you feel the sound is low, connect to POINT.A instead of 3 or 4.

It is difficult to make it in a general PCB form due to lack of space.
I stuck the SI4732-A10 upside down on double-sided tape and soldered the parts.
Before attaching, make sure the lid closes well before connecting.
If you can replace your existing speakers with smaller ones, you can use a regular PCB.


A representative product of SI-4732 is the ATS-20 in the picture below. I created the firmware by referring to the ATS-20's screen interface.

  Number 0 : Long Press -> Enter SI4732-A10 Mode 
  Exit          : Long Press -> Exit SI4732-A10 Mode

  UP / DOWN : Frequency Up or Down (Step)
  Side Button : Frequency 1Mhz Up or Down
  Number 1 : Change Bandwidth (use LSB or USB mode)
  Number 4, Number 7 : BFO Frequency Up/Down,  This function allows adjustment in Hz units in SSB mode.
  Number 2 : AGC ON/Off
  Number 5 : Att Manual Mode (AGC Off) and Att change
  Star (*)     : Step Change  (1 -> 5 -> 10 -> 20 -> 50)
  F (Function): Short Press : change mode AM <-> FM or LSB <-> USB 
                   Long Press : AM/FM   -> LSB/USB or LSB/USB -> AM/FM


6.More Information
 6.1 Using Library source  (my work is below code ported UV-K5, C++ to C and more)

 6.2 Circuit diagram related to FM radio of UV-K5
I did the SI4732 MOD a few months ago. At the time, I didn't have a circuit diagram, so I checked it by scraping the pattern on the board with a cutter knife, and a grateful radio amateur (IU0AZB)sent it to me last night.

If you want to improve reception performance, you can try changing the boxed areas below.
In particular, simply removing all the parts in the red B square will slightly improve reception performance.
A few years ago, I made a receiver with the SI4735, a model similar to the SI4732-A10, and due to the characteristics of the radio chip, I used a transformer to increase the impedance. I experienced a tremendous improvement in reception performance. However, interference waves are also quite strong, so a filter (FMI, AMI) must be used.

The space where we work is small. I hope that the various experiments of amateur radio operators will yield good results.

6.3 TODO : Removing the crystal and two capacitors
We are examining whether three components can be removed by using an external clock (BK4819's reference clock - Checked by IU0AZB)
I experimented a few times, but it didn't work. I suspect an interference problem due to the reset circuit, which is different from the original circuit and is configured as analog, or my experimental environment.
If successful, only SI4732 and two components (C1, R1) are needed.



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