Cracking the SA818-V Radio Module

What is the worst part of trying something different you ask? Lack of documentation. But that is what the adventure is all about, right? To learn something. Well this project was all about that.

Over the last few years, there has been a massive influx of Chinese made ham radios. Marketed under different names, the most popular make is Baofeng. These have had a certain amount of criticism surrounding them, mostly around lack of filtering causing interference on adjacent frequencies and ease of purchase by non-licensed individuals.

Most of these radios share the same chip set, the DRA818/SA818. I ordered a two pack of the “modules”, direct from China on eBay. I was actually surprised at how fast the package got to me, considering the delivery was estimated at five to six weeks. It took about three weeks for them to get here.

The manual for these devices can be found here. The package itself only came with the two radio modules, a business card and no documentation. The devices have eighteen solder tabs on them, which thankfully are clearly labeled. Below is a detail of what they all are.

Myself and Jesse (KC0UCQ) searched out how to setup the serial connection to program the devices. Obviously, we need to set a frequency for transmit and receive at the very least. To set it up, I wired the jumpers to the appropriate pins and connected them to my USB to the TTL converter board. I purchased the board off of amazon and it can be found here.

The USB to the TTL board comes with six different pin outs:

• 5 VDC
• GND
• TX
• RX
• GND
• 3.3 VDC

I wired up the TTL to the radio module as follows:

• Red wire: +5V to pad 8
• Green wire: Tx to pad 16
• White wire: Rx to pad 17
• Black wire: GND to pad 9

The converter was connected to a Raspberry Pi 3B+, running the latest Raspberry Pi OS (Linux). To get this ball rolling, we needed to find out what the converter is identified as on the system by doing “dmesg | grep tty”:

This identified the appropriate port for the device as “ttyUSB0” for using the serial.

Now by rights, this should have worked. We should have been able to access the device through any number of serial programs. We poured through the documentation found in the programing manual. We had the settings right, 9600 baud, 8 bit data, no parity, and a stop bit of 1, but it would just not work. Jesse then found this program, which someone had wrote to program the modules directly, instead of trying to feel your way through the serial connection. But, it still would would not connect.

We were about to give up, it was around 0200, and then in a last ditch effort Jesse came across this archived web post from W0ANM, which changed everything. Of course, the module has a built in power switch, why wouldn’t it?! But, that was not something we had been thinking about, nor had anything we read suggested that it needed to be wired up. The blog had a diagram, which matched what we had done, but it had the added “power switch” wired.

So, I quickly dug through my thousands of random electronic parts. I managed to locate a 10K resistor and wired it from the 5 VDC line to the power switch pad (6). I flipped on the power and we gave it a shot.

Everything changed, it connected, and victory was had! So the config file was edited to what we needed:

Then we wrote it to the module:

Well, most people would call it a night, as it was now around 0300. I should mention as well, when Jesse is helping me with these projects, he is hundreds of miles away. We use a VPN, screen sharing and our EchoLink nodes (which I will write about at some point) to work on these projects. He is the true master when it comes to much of this.

We decided we would test the fruits of our labor. So, on came the soldering iron once again. I started wiring the module to a breakout/hat board that will be placed onto the Pi eventually. I sliced up a stereo cable, and wired the ground line and PTT to the radio module. For the purpose of testing, I had to manually connect the PTT (push to talk) line to the ground. I then wired up a small antenna to board.

I recorded a simple .wav file of my voice, and transferred to to the Pi using Cyberduck using SFTP (SSH File Transfer Protocol). Using a USB sound card plugged into the Pi, and my hand ready to do close the PTT circuit, we commenced the test. It worked, my voice came over at 146.550 MHz, just as planned.

I finished soldering the HAT and placed it on the Pi.

To sum this one up, it was an adventure to say the least. Sometimes solutions for issues come when you are most disheartened. When we could not get the serial to work, it really seemed like the end. But, the solution came through when Jesse found that archived post.

I have a few ideas of what I am going to use this board for. Possible applications are portable EchoLink nodes, APRS beacons, or who knows what else. I do need to figure out how to filter the output, so the signal is not so “dirty.” The module also appears to get quiet warm fast when transmitting, so some type of cooling will be needed for it.