The only adjustment the antenna will affect is L2. Here's an alternative to measuring and averaging the impedance of several antennas: Put a short whip on your signal generator and radiate a signal into the car antenna. Then adjust L2 with the receiver in the car and connected to the antenna as normal but open so you can get at L2. I see no tracking components so the instructions probably just say to peak L2 at some frequency. You can do the rest of the alignment on the bench with the signal generator connected directly to the antenna input. AGC appears to detune the L2 tuned circuit on strong signals. This means you should use a weak signal when adjusting L2. To avoid an in-car adjustment for each radio, readjust L2 on the bench after having set it in the car. Note any difference from the in-car setting and apply it to other radios. This is only an approximate procedure, but it may be good enough.
Rereading your first post, you mention 150 ohms in the Blaupunkt instructions. If the instructions tell you to put 150 ohms in series with the generator, then just do it. Use it for both radios. If a more complicated dummy antenna was really necessary, the instructions would have said so and given a schematic.
Good luck.
Brian
