[jrblasde]

Just confirmed that you are correct. It’s the function generator. I connected the signal output probe to one of the inputs on my oscilloscope, and I do not have control over amplitude or DC offset. I’ll have to open it up later tonight. Fingers crossed that it’s not a total loss, but at least it was a dirt cheap oscilloscope!

Rookie mistakes were definitely made. I had started out using a capacitor (as the instructions do indicate), but it kept falling out of the alligator clip on my probe and I grew frustrated. I figured what the heck, I’ve got the radio connected to an isolation transformer. But I failed to consider the DC voltage I might introduce to my signal generator.

[462ron]

Oh that sucks. It’s something easily overlooked. Hopefully it’s nothing more than a resistor!

Ron

[jrblasde]

After a couple of days worth of troubleshooting my signal generator, I gave up. The oscilloscope still worked fine, so I used it to trace the signal on its own circuit board. I checked the signal generator output, the resistors and capacitors, the op amp, etc. but no signs of a signal. I traced everything back to the DSP IC and gave up at that. I ended up buying an identical oscilloscope with arbitrary waveform generator on Amazon. It’s a Hantek DSO2D15. For the price, it is surprisingly feature rich. The oscilloscope is rated for signals up to 150 MHz, and the signal generator can produce an arbitrary waveform (including AM and FM modulated waves) at frequencies up to 25 MHz. This enables me to produce AM and FM IF signals for alignment. For FM RF signals I can use one of those automobile Bluetooth-to-radio transmitters.

I shopped around quite a bit. I know people online tend to harshly review the Hantek equipment (bug prone, tend to lock up, etc.) but that hasn’t been my own experience. Anyway, I looked at Rigol, Siglent, and others. I couldn’t find a model with built in signal generation below the $500 price point. Even when browsing dedicated signal generators, I was easily looking at spending $300 on one of the frontline models. For me, the Hantek was a no-brainer. I couldn’t justify the higher prices for a unit I use on perhaps five projects a year. The new unit should arrive on Monday, and I can reattempt alignment with a capacitor connected to the signal generator output this time!