Before putting my recently completed homebrew single conversion 20m mono-bander on the air, I borrowed another radio to listen to the transmission and make sure everything was OK. It turns out, it definitely wasn't and all I could hear on the receiving radio was a high-pitched squeal. I'm hoping it's a simple matter of tuning the BFO on transmit to place the audio correctly in the crystal filter passband (I can pick up stations fine on receive), but it could be something else of course.
Which brings me to the question. Are there time-honoured ways to test the quality of a transmitted SSB signal before putting it on-air? Obviously, having another radio is the easiest way: transmit into a dummy load with a small pig-tail on the receiving rig. But, what if you don't have another radio or a spectrum analyzer with a RBW fine enough to see the sidebands properly (I have a TinySA, but it's hard to see the sidebands)? Are there methods available for those with more basic tools: signal generator and oscilloscope? Happy to accept all methods (including additional receiving radio).