Since the  BC453 was specifically designed for Medium wave, I thought it should perform well on the new 630 meter band.

In fact, it does well on CW and AM but since there is only 7 Khz to the whole band,so many Hams are using digital modes there.

My BC-453 was producing slanted waterfall traces, indicating severe thermal drift over time. This is death to a WSPR-2 session which has a duration of 2 minutes.

If given enough warm-up time , the local oscillator will stabilize satisfactorily, but the BFO had it's own drift charactoristics which made "vertical waterfalls" unachieveable.

Rather than dealing with dualing drifts, I modfied the BFO circuit to use a FET rather than the vacuum tube triode (V7).



BC453_BFO_Stability _modification


Circuit description;


The goal was to make minimal non-destractive changes using as much as the original electronics as possible. The BFO cut-off circuit is unchanged, just the active ocillator device is changed

The BF244 is a 30V RF FET, In order to use it in the original circuit, I protect it with a 24V zener at the junction C15C and R15 in the radio.

All original connections to the triode are disconnected at the BFO coil. The grid leak resistor/cap combo can be removed to provide room for the small FET board.

Ci of the FET circuit is connected to where the Grid leak combo was origianlly.

The FET drain is connected to where V7's plate was connected. DO NOT REMOVE THIS WIRE, but use it to connect to C2 of the FET cicuit.

A blocking cap is used in series with the very tiny coupling cap (C33 from V7 to V6 grid)  to keep the unused triode section from drawing any current..


This modification made it possible to decode WSPR-2 transmissions after the Local oscialltor stabilized.

It seems to work better than a general covergage receiver on Medium wave. I got my first off shore WSPR-2 DX using the BC453!



If you are having similar difficulties as I had using 20th century tech on 21st century emissions, give this mod a try.


73 de Jim , AC2EU