Measuring Pi networks and tuned inputs for amps

[mike]

This device is fantastic for "pre-tuning" when constructing an amp for HF. For G-G amps terminate the cathode/plate with the expected/desired resistance and drive the I/O
of the amp with the 4170. BUT, when you get in the ballpark and see a big dip in return loss and theta crosses at the center frequency/band of interest, insert a 50 ohm 3 or 6 db pad inline to really see the effect of "Q" on the Pi in/out network as you vary C and L and refine your values. I've used the 259B as a quick "backup" to verify readings. I am a newbie 4170 user and the hb amp is still on the bench, but I thought it was worth mentioning the effect of the pad.

If this approach if out of line, please comment!

Mike, K4EAR

[w0qe]

Mike,

Your post is definitely NOT out line. However I do not understand how the addition of a 3dB or 6dB pad in series with the AIM4170 shows anything better. Inserting loss drives all impedances towards the characteristic impedance of the loss device (50 ohms in this case). A 3dB pad will map all impedances into a 3:1 SWR circle while a 6dB pad will map all impedances into 1.67:1 SWR circle. Don't be afraid to post here as there is always something new to be learned by all of us.

73, Larry, W0QE

[w0qe]

Mike,

Hope I didn't run you away. Would you please explain why you added the 3dB or 6dB pad and what was easier to see with the pads inserted. There is no reason to be concerned about posting something that makes sense or not. Does anyone else know what Mike was referring to?

73, Larry, W0QE