Measurements:

To pick up the signals I’ll follow the instructions on the SB-650 user and assembly guide.

BFO:

The BFO signal is picked at the IF board placing a 220pF cap on point A of the picture.

The signal at this point in the radio, before the 220pF cap has 5.12 Vpp with a bias of around 2V, this will be removed by the cap.

After the said cap the signal has 4.84Vpp with almost no bias.

This signal will be enough for the circuit, but I’ll place some kind of protection before feeding it into the logic circuits.

HFO:

This signal is picked up in the band pass circuit after making a cut on one of the tracks and placing a 51Ohm resistor (I placed 2 100Ohm in parallel.)

The challenge here is the signal amplitude of around 1 to 2 Vpp. This changes with the band and is somewhat tunable. But I want to make this as adaptable as possible to various configurations that may appear on other radios.

LMO/VFO:

Picked up on the band pass board where the connector wire of the LMO attaches.

Signal here is also bellow 2 Vpp so it will need to be amplified…

Heathkit SB and HW series frequency meter and CAT signaler – BelkaDog Labs