Zero Beat Indicator Sampling Audio connection point
- Reply to member johanengdahl,
I got your question about the K6XX zero beat indicator. I have tried to reply multiple times with two different email addresses and received a bounce (account not found or message looks like spam) every time. So, I will reply within the group and hope you see it.
Your question was:
Where on the pcb of sierra did you tap into SA?
I did some experimenting when looking for audio. The Zero Beat Indicator kit came with resistors to put into the line sampling the radio's audio. I initially tried wiring the two resistors in series. I hooked one end to the Zero Beat kit's audio sampling wire and the the other end into the 'SA' point on the Sierra main board which is right behind the volume control.
I experienced the hunting of the PLL circuit mentioned in the instructions which results in some random flashing of the LED. The instructions suggested a second alternative in wiring up for the audio.
In that second case he suggests wiring the resistors in series and using them as a voltage divider circuit. You connect one end of the two series resistors to the side of the volume control coming from the audio amplifier and the other end of the two series resistors to ground. Then run the audio sampling wire to the junction of the two resistors.
So, that is where I finally left things. Look in the photos area of the yahoo group. The last album is 'Zero Beat Indicator (K6XX) in Sierra'. You have to go to the second page of the photo albums (the site only shows 20 albums on a page). In that album there is a picture called 'Audio to Zero Beat Circuit'. That picture shows the two resistors wrapped in heat shrink tubing and connected to the outboard pins of the volume control potentiometer. The audio sampling wire is tapped into the junction between the two resistors.
I can't say that the voltage divider circuit was a huge improvement over the resistors in series. However, the random flashing is not really a big problem. You can easily tell when you are zero beat as the LED flashes in time with the CW audio.
If you need more info. Feel free to contact me.
I hope you enjoy your new enhancement. I really love mine. It has worked extremely well for me.
Richard - K4KRW