Questions about Bob A IF Alignment Series on YouTube

[dtvmcdonald]

Originally Posted by bandersen

You set the contrast control to fix the AGC bias at -4 volts. No need for a battery or external supply.

Tedious? That would be insanely difficult. Rotating the RF gen over about 5-10 MHz, while simultaneously looking at a meter needle swing and translating that into a graph in your mind? While keeping careful note of the response at key frequencies and tweaking coils while doing that?

Get a cheap sweep gen. You can even use the TinySA in sweep mode.

Its actually not difficult. I've done it many times, though using a DC oscilloscope makes it easier to see a curve. The problem with the scope (at DC) is that often you need two probes and two subtracted inputs. I have a pile of Tektronix scopes.

And yes, you need a bias box. You don't for a sweep generator because there are capacitors that filter out the AC so you dont get that acting as AGC. But at DC more or less, those caps are too small.

I used this method for TVs with IFs at about 10 MHz before I got an SDR sweep generator working correctly. Yes, back at the dawn of time there were such sets, and they still work.