Treetop Circuits

Technical Notes

A collection of articles about radios and other assorted electronics.

SSB Adapters Explained
A brief explanation of why SSB adapters are used.
SB-390 Hints
This is a compendium of hints, caveats, and observations, mostly from owners of the SB-390. I'll update it periodically. May 15, 2013.
Automatic Volume Control Problem in PD3
A problem has been found in the automatic volume control (AVC) circuit. It occurs only on units # 17 through # 47, and affects the AVC action when in SSB mode. The fix can be left out indefinitely without causing damage. However, if you wish to experiment with the circuit, you will probably want to put it in before proceeding. January 31, 2010.
AVC Fix for early SB-51 and SB-75 Boards
With early units, a “dead” period sometimes occurs when switching from AM to CW/SSB if there is a strong signal present. There is a period of silence lasting perhaps a second, then normal operation resumes. The fix can be left out indefinitely without causing damage. May 13, 2011
Connecting an R-388/51J Receiver with a KWM-2 Transceiver
Having a second receiver connected allows you to work “split” – that is, you can transmit on one frequency and monitor another. November 12, 2009.
Lead-Free Solder
There is a world-wide trend towards lead-free electronics. Treetop Circuits uses lead-free solder and has found there are minor differences between this and traditional solder. December 28, 2009.
Adding a Crystal Controlled BFO to an R-390A
Pete Williams, VK3IZ, added an R-390 to his R-390A. But he wanted a crystal controlled BFO as well. Here's how he added the feature, and kept the look and feel of the receiver. February 2014.