I had acquired a used but like new 590SG, with the intention of using it portable from the wall tent. I found the radio liked to drift from around 30Hz low to 10Hz high depending on ambient temperature. This was not going to cut it in the tent with temps being all over the place when camping, so I ordered the SO-3 TCXO. I would recommend anyone who is thinking about installing one of these to do it. It is about as easy as it gets without being plug in. Yes, you need some soldering skill, but a little research of technique and some practice and anyone should be able to successfully complete this. This is the TCXO and box it came in. The TCXO and provided adjustment tool. Put the radio on its top and remove the bottom cover. The yellow square below indicates the area of interest for the installation. Unplug the connector noted by the red square. Remove the indicated screw. NOTE: A #1 Phillips is needed for this. Remove the board from the radio. The connector