Tentec RX-320 – Total USB conversion. No more dongles!

The venerable old RS-232 port is becoming harder to come by in a modern computer. Yes, USB to serial port adapters and dongles kinda sorta work – most of the time, but they are often unreliable, and can introduce their own brand of headaches into the process.

I’ve recently come across a device that can remove the need for dongles and serial cables, and provides for a USB cable that connects not only to the computer, but directly to the radio.

It is a pretty serious modification, and only suitable for the technically advanced who have skills repairing both surface mount and through hole circuits, and have access to a high quality vacuum desoldering gun that is absolutely needed to safely perform the job.

Or – you can send it to me and I’ll perform the mod for you! More on that – later.

In essence, the radio is dismantled, the logic board removed, and the 9 pin serial connector is carefully unsoldered from the circuit board. This is the hardest part of the job – because if you screw up – you can easily do very serious damage to the board.

In addition, the Serial Port transceiver I.C. (U1) is removed. It’s not needed any more – this is now a USB controlled radio!

At first glance, the replacement device looks like a 9 pin connector – but on closer inspection you’ll see a mini USB connector where the pins would normally be. The device is nearly identical in size, and has 9 pins that neatly fit in the same circuit board holes that the serial connector used to occupy. The special USB interface circuitry is embedded inside of the connector body.


Here’s the final result!


Note the vastly superior TNC antenna connector!

Plug in a suitable USB to mini USB cable into the new connector – and to a computer with internet access. The computer should discover the device, and automatically find and install the needed device driver – at least it did for me when tested on a windows XP and a Windows 7 computer. Can’t speak for Vista – but I’d say it’s likely to work well too.

The beauty of this situation is – even though the serial port / RS-232 hardware has been done away with, from a software standpoint – it still looks like a serial port – and that’s exactly what you need since your RX-320 control software is expecting a serial port.

Next, go into the windows device manager, find the new “USB serial port adapter”, and configure it for the serial port you want to use – obviously the same one you told the radio’s software to use.

That’s it!

Why do you want this?

Your computer does not have a serial port and you are sick of dealing with unreliable dongles, and want a cleaner situation.

Perhaps your dongle is making RFI that’s wrecking your reception.

RS-232 is a messy “standard” (take a look at the Wikipedia listing : http://en.wikipedia.org/wiki/RS-232).

The signals can go as high as plus and minus 25 volts! More often than not – it is a lower voltage level, but it is always “bipolar”.

Serial port transceiver circuits – including the one INSIDE the RX-320 incorporate a “DC to DC converter” circuit. This circuit takes +5 volts from the USB port (in the case of a dongle) or from the logic board (in the case of the radio) and using a high frequency conversion process – “pumps up” the voltage in order to create the positive high voltage component of the RS-232 signal.

Another DC to DC converter does the same thing, but creates a negative polarity voltage for the negative component of the RS-232 signal.

These DC to DC converters often have the unfortunate side effect of being very effective noise generators, and can reek havoc with your sensitive Short Wave receiver. Getting rid of all things RS-232 may help to clean up your reception.

One way you can test it: Tune the radio to a station that is being interfered with. Now unplug the serial cable from the radio and move it away. If the noise went away or was reduced, it’s probably coming in via the serial port, and this mod will probably help you.


I am offering my services to those who are interested.

For $125.00 I will:

Test and qualify the radio for proper basic operation using a serial cable.

Provide all parts and labor to modify the radio as described.

I’ll also:

Calibrate the PLL’s master oscillator.

Calibrate the PLL’s two VCO circuits.

Re-test for proper operation.

Provide a new USB to mini-USB cable.

Return shipping (CONUS) is included at no additional charge – elsewhere actual shipping charges apply.

Reasonable phone and email support is also included.

If you can’t make it work, return the unit and I’ll restore it to Tentec’s design refund your $125.00 and return it to you.

This USB conversion process can be implemented to many other radios and devices. Contact me for details.

I can repair your sick RX-320 too!  Free estimates!


I have other modifications available and more in the works.

Sick of the crappy RCA antenna jack?

Interested in turning this rig into a SDR?

Contact me for more information.


73s – Steve



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