Soda Pop noise mod

Colin Evans M1BUU

I wasn't able to source the exact display for my Soda Pop Coaster, but I did find a pin compatible one. Unfortunately I found that my display is very dim, I think the ones supplied with the Soda Pop kits are 'super bright' whereas mine is just normal. I reduced the value of the display supply resistors, which improved the brightness of the display but also increased the self generated noise through the receive chain. I'd had the rig on air for a test QSO before I dropped the resistor values, but I'd not actually tried the rig into an antenna afterwards. I decided to try the rig on air from a friend's shack a little while back and I found the rig was unusable, the display noise was horrendous.

I saw a discussion about the Soda Pop II and the simple circuit added to reduce the display noise, I thought it was worth a try on my Coaster rig.

I cut a pad into the PCB with an xacto knife and used SMD components to make as neat a job as I could. I'm pleased to say that the noise mod seems to have worked very well. I'm planning to take the rig to my friend's shack on Thursday evening to give it shake down on a proper antenna.

73, Colin, M1BUU


Wow! Nicely done, and the enclosure looks great too. Did you use a 2N3904?
& many thanks for the post especially with the close up pictures.

Colin Evans M1BUU

Yes, I used an MMBT3904 SOT23.

Here is the quote from Steven explaining the mod -

"It takes three parts, a NPN transistor (2N3904), a 470 ohm resistor and a 22 ufd cap.

Collector to the + supply, emitter to the mixers and op amp, 470 ohm resistor between collector and base, 22 ufd cap from base to ground.


It looks like the best place to break the + supply to the mixers/opamp would be between CT2 and CT3 on the top of the board as the track goes around X4."