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:

Xiegu G90 output power versus supply voltage

Someone pointed to me that the Xiegu G90 has inconsistency in Tx power at various power supply voltages.

So, because I am a brave curious ham, I setup a quick test bench with some pieces of hardware laying around at my home lab.

The setup is pretty simple:

The radio is connected to a Proxel 832 NFAR power supply (slightly modified for 16V output) and to the R&S NRP-Z11 power sensor (through a JFW 30db/50WJFW 30db/50W attenuator).

The radio firmware is:

-Main unit: 1.77

-Front Panel: 1.76

The PC software was:  R&S Power Viewer. 

Note: The power sensor is working from 10 MHz so i measured the power from 10 MHz to 30 MHz. Below 10MHz, the results are pretty consistent at various voltages but I cannot hold them as being accurate therefore I removed them from datasheet.

The RF output power was measured from 9V to 16.5V and when i was playing around 9V i noticed a faint sound from inside the radio. The origin was determined to be the relays in the ATU path. Rising the voltage, they will switch around 9.3 V and will keep the contacts untill under 8.7V. Therefore, even the radio is able to work under 9.3V, there are reason not to do that because the voltage drop in SSB or CW will affect the proper function of various relays.

I choose 4 power levels to measure: 1W, 5 W, 10W and 20W. The results are in dbm. You can transform those values into W by using an online dbm to W conversion tool.

The radio was set in CW mode and a straight key was used to put the radio in Tx for the time reading was made.

I also made crude measurements for the Rx current and the Tx current (the last one, just the maximum values).

The voltage was tested against a VC-960 DMM which was then used to measure the current draw.

Here are the results in images. You can download the full test in pdf from the link at the bottom of the post:

9V:

10V:

12.8V:

14.4V:

 

16.5V:

And here are the values in W, courtesy of EA5IYL:

Some conclusions:

-At minimum power set in menu, the radio puts around 1.3W.

-Between 10 and 16.5V, setting the radio to 10W will put very close to 10W.

-When settings are for full power, the radio will put between 10W (10m@10V) to 20W (10m@16.5V) being pretty consistent to 20W from 12.8V to 16.5V.

-There are slight variations at max power when using in normal voltage range (12-14V) between 16-20W but in real life this is neglictible, in my opinion.

Much interesting is how the Rx current is evolving on various bands!

Power attenuator:

Power sensor unit:

You can download the test results in pdf format HERE.

Protecting the ham radio station against lightning and EMP

 Lightning is a natural event with a tremendous destructive power. You have the electric hit and the associated EMP hit; you have to match protection for both.

For many years, Polyphaser set the standard in industry.

Here are some documents to read about lighning and protection against it, those documents are in PDF format and the links are from Polyphaser website. Click on them, download and keep it stored!

-The Lighning Event;

-Significance of Surge Protection for Radios;

-EMP Mitigation - Protection Land Mobile Vehicles from HEMP

-Coaxial Cable Protection

-Equipment Rack Grounding

-Halo Grounds

-Ham Radio Station Protection

-Insulated Support Structures

-Lightning Protection Location

-Tower Mounted Electronics Protection

-Tower Strikes and Solutions

-EMP Mitigation

-Built-in protection... Can You Trust It?

Xiegu G90 Block Diagram and Schematic

Based on work of Bob, W9RAN and some modest contribution from my side, here is the block diagram of the popular Xiegu G90 transceiver.

 

 

THIS PART IS NO LONGER ACTUAL BECAUSE THE FULL SCHEMATICS ARE AVAILABLE

 

And, based on reverse engineering of parts I am interested in, here is the schematic. Attention, it is work in progress!

Last version: September 15, 2021 - minor corrections

I received a very interesting e-mail from Nils, W8IJN. 

Many thanks Nils for the informations:

Adrian,

I've been following your adventures exploring the inner workings of the G90. I've downloaded all the schematic diagrams that you've put together about the radio.

Recently I blew up the two 100 Ohm resistors in the area around the key jack. I sent Radioddity a note and they responded with a schematic of that area. The drawing is included with this email to add to your collection.

The problem came from testing a EFHW antenna with the 49:1 balun sitting a meter from the radio and connected by what turned out to be a faulty cable. The radio wasn't grounded and the key line did not have any RF suppression/chokes on it. I figure the RF got past the RFC and the zener diodes shorted the RF through the 100 Ohm resistors to ground.

I repaired this with parts I had and added 1nf caps on the high/key jack side of the RFCs. We'll see how that works out. Oh, and I grounded the radio and put a clip-on ferrite on the key line.

Stay safe and well, Adrian. We will survive!

73

Nils R. B. Young
W8IJN

There is a small difference between the schematic received from Xiegu and what i found on my board. The supressing capacitors in my radio are between the resistors and inductors while in the picture sent by Xiegu are on the ESD suppressing diodes. This might be from a different revision or even a mistake in my drawing. I will check this soon.

Split one COM port between two software programs

Many times I was facing a complicated problem: using two software programs that need to access the same serial port at the same time. This is the case when a CAT program like Ham Radio Deluxe want to access the radio but, in the same time, I want to use my favorite Log program! 

Usually, this is not possible because the intrinsec properties of a serial UART prevent it to be addressed by two different programs

Usually, commercial products are spicy and, if I can use the money on hardware, this is what I choose to do.

So, I search and search for a proper solution to use my SW without paying too much and I found that it is possible to have a really freeware solution.

And the solution came from ETERLOGIC  and it is named: VSPE - Virtual Serial Ports Emulation.

Unfortunately, this solution is no more freeware! 

Download it, install it.

Create a "New Device". It will made a new virtual serial port and will connect it to the hardware serial port.

Then, this new virtual serial port can be used into the software.

I used it with:

-HAM RADIO DELUXE

-N3FJP Amateur's log

-N3FJP CQ WW DX Contest log

All simultaneously!