Reprogram the Local Oscillator of the SG Lab 13cm transverter

The SG Laboratory 13cm transverter is a popular way to get on 2.4 GHz. Its output of around 2 watts is all you need to work the DX if you’re in an elevated location. 13cm is a noisy microwave band if you’re in the heart of suburbia, or in any major centre anywhere in the world. The 2.4 GHz band is where WiFi started, and most, if not all connected devices have the capability of connecting to the internet of things via this band.

It’s this WiFi noise that discourages many amateur radio operators from dabbling in 13cm.

Recently, amateur operators in Sydney decided to move the calling frequency from 2403.1 MHz to 2301.1 MHz in an effort to get away from the noise generated by WiFi. Moving 100MHz down the band would most certainly improve the possibilities of working more distant stations.

If an SG Laboratory transverter is at the heart of your 13cm station, then it’s possible to extend one of the jumpers used to program the Local Oscillator frequencies of the transverter to the front panel, making it simple to switch between both calling frequencies.

If you don’t mind changing the frequency on your radio then no reprogramming of the transverter is required, but if you’d like to keep the radio on the same IF frequency for both call frequencies, then read on…

There are four jumper selectable local oscillator frequencies in the unit. They range from 1870MHz to 1968 MHz. They’re programmed into non-volatile ram before it leaves the factory. 1870 MHz seems to be the lower limit programmable so let’s do the maths here.

For 2301.1 MHz, subtracting 1870 results in 431.1 MHz

Unfortunately, with the default LO frequencies, we can’t get 2403.1 to work with 1886, 1888 or 1968 MHz. So 2403.1, the current calling frequency minus the required IF frequency of the radio, 431.1 equals the required local oscillator frequency of 1972 MHz.

If we switch jumper 2 on and off, then 1972 MHz needs to be programmed into local oscillator 3.

To do that you’ll need a PC with a terminal emulator. A free program called PuTTY will do the trick. You’ll also need a USB to RS232 TTL Converter Module that runs 3.3V. These are a dime-a-dozen on eBay.

Locate the four header pins for programming on the transverter.  With the transverter turned off, connect TX RX and ground to the TTL converter. You may need to swap TX and RX over, turning the connection into a crossover.

Having checked the Device Manager for any issues, and to identify the com port number, lunch Putty and set the communication parameters to 9600 N 8 1 with no flow control. While you’re there select TERMINAL and make sure Local echo and local line editing are forced on.

Start the putty session and power on the transverter. If everything is connected and working correctly you should a “Press any key for programming” prompt followed by decreasing equals signs and a summary of the current state of the transverter. In this case, it’s local oscillator 4 with an RX and TX frequency of 1968 MHz.

To program Local Oscillator 3 to 1972 MHz, turn the unit off and on again. While you see the diminishing equal signs,  press any key to enter the programming mode.

First, you’ll see the current RX1 frequency followed by a prompt to enter a new frequency. If you do nothing, after about 8 seconds you’ll see the TX prompt.

When you see RX3 enter 1972 and press enter. You’ll soon see a message showing the new 1972 frequency. Do the same for TX3. Leave TX4 to time out and you’ll see the transverter summary to finish off. That’s it, programming done.

To check your handiwork, reboot the unit and enter programming mode again. Sit back and watch the results displayed on the screen and make sure they’re what you expect.

If you find a typo simply restart the programming sequence and change frequency accordingly.

Cable up an external switch across jumper 2 and changing frequency without touching the radio should be as simple as flicking a switch and power cycling the transverter. Super easy to do especially if you’re out portable. If you’re keen to buy a 13cm transverter visit SG Laboratory.