Get me FT8 DXCC!

 Too good not to stole it and post it here!!!

9A/YO3HJV/P

 I planned to work HF/portable from Dubrovnik when coming back from Austria but, unfortunately, the change of pandemic rules for entering the country was subbject to a last minute change thus I replanned my trip.

I ended on the Lake Balaton, in Hungary and I spent my birthday there with my wife and my daughter, on a very nice villa with a beautifull view and a balcony that was the perfect spot for my HF portable setup.

I had with me the little Xiegu G90 with some portable HF antennas from which the MP-1 was the "hero".

I managed to work in 20m band some YO stations from Bucharest, Constanta, Timisoara and Brasov and from Bulgaria and on the West side, Finland, Germany and UK.

It was nice but I am a little sad I could not reach Dubrovnik!

Xiegu G90 MCU and DB9 reference

## Board revision: V2.0.7 GAI03 

## LCD Display: KD018QQTBN009-RT 

 Link to manufacturer: http://en.tft-tft.com/product/detail?id=19 

### uC pinouts and signals

 

FRONT PANEL UNIT
STM32F103RCT6 - LQFP64
Pin no	Pin name	Description
51	PC10	USART_3_Rx 3.5mm PC_RING
52	PC11	USART_3_Tx 3.5mm PC_TIP
42	PA9	USART_1_Tx to MAIN DB9_2
43	PA10	USART_1_Rx from MAIN DB9_3
MAIN UNIT
STM32F429ZGT6 - LQFP144
Pin no	Pin name	Description
96	PC6	USART_6_Tx to Front Panel DB9_3
97	PC7	USART_6_Rx from Front Panel DB9_2

DB9 connector between MAIN UNIT and FRONT PANEL

Pin	Description
1	9V after POWER ON from PWR Board LM2940-9.0 LDO
2	USART From PANEL to MAIN UNIT
3	USART From MAIN UNIT to PANEL
4	Vcc (13.8V) on stand by /POWER COMMAND/ 3V3 on POWER ON
5	GND

Xiegu G90 power supply section

 Here is the schematic for the power supply section on the PA Board of the Xiegu G90 transceiver.

The board is marked "G90-BASEBD-V2.0.7-GAI01" and contain:

-Power supply section with EMI filter, reverse voltage protection, electronic power switch, linear regulators for 9V (LM2940-9.0) and 5V (LM7805).

-Tx drivers

-Tx PARF

-Dir/Ref RF power bridge

-Band filters

-Antenna Matching Unit (ATU).

Here is the schematic for the power supply section (for high resolution click on image then right click and "save as"):

NOTE: There is an error in the diagram; will be corrected soon. The voltage divider R3/R4 is connected to the main V+ and not to the 9V rail.

Most probably, there is an error in the resistor values, the resistive divider most probably is connected to the ADC input of the main MCU for Battery voltage indicator.  Thanks Jake G1YFF for this pertinent observation!

You can download the schematic as pdf HERE.

Xiegu G90 replacing 5V LDO with SMPS

Owners of Xiegu G90 knows the radio can get pretty hot just on receiving.

Looking inside the radio, on the lower board are two linear regulators.

One is a LM2940T which lower the power supply voltage down to 10 9V followed by a LM7805 which power all the logic circuits in the radio. So, there is a significant current through it.

The LM7805 is one of the worst linear regulators ever...

The thermal protection and short circuit are bad jokes. I never saw one to work!

Also they work hot and often need some sort of current limiter before.
Overall, bad choice from Xiegu.

I had some sort of DC/DC converters in my boxes and one of them in particular work pretty well and, BEING A BRAVE HAM, I thought, why not replace that piece of shit with one I already have?

The D-Sun DC/DC Buck converter is based on MP1584, a compact monolithic high frequency SMPS. In my particular case, the switching frequency is 1.5 MHz which can be conveniently filtered. Also, a major advantage is the overshoot protection which is essential when using it to power sensitive circuits.

The board have common negative ground so everything is OK from electrical perspective.

I test the dimensions and the little board almost fit into the slit of the PCB so I removed the LM7805. The removal was more like an extirpation as I removed it without lifting the lower PCB...

I used a little piece of sandpaper to fit the board, and i scratched a little bit the Ground around the SMPS board to add some capacitors.

After soldering the ground and before connecting the positive wires, I set my lab power supply to 10V and set the output of the SMPS precisely to 5V (actually, 5.002V, HI HI).

One concern was the conducted RFI from the converter so I added some capacitors to filter whatever ripple and noise the regulator is making; 150 nF, 1.5 nF and 150 pF on each side of the board.

Under the board I placed a piece of Kapton tape, just to be sure...

The photos are pretty self explanatory about how the things were done.

After this mod, the radio is much, much cooler; I will replace the LM2940 too, but I didn't find another SMPS. The other one will be place under this one.

Also, a nice result was that the current in Rx mode dropped from abt 650 mA to 520 mA. Probably will go further down with the LM2940 replaced.

I did a quick check in bands and no noise from the SMPS was found.

LATER EDIT.

I got another SMPS and I got into the radio one more time to change the 2940 too.

So, there are now two SMPS, first one is under the PCB and the second one is above the first. Here are the pictures:

The Rx current present now a significat drop.

With ATU:

Without ATU: