SWR Problem

[wewill]

My 4170 ran great yesterday. However, today, when I tried to measure a vertical antenna, the SWR stayed constant across the top of the screen. (the Theta curve looked fine.)

I tried different custom calibrations, rebooting the computer and cycling the AIM off and on. But nothing helped.

Next I did another custom calibration on 18 inches of new RG-213 which ran with no error messages. But, when I put a load of 100 Ohms on the end of the coax (expecting an SWR of 2:1) I again got a constant and infinite SWR.

What am I doing wrong?

Thanks for your help.

[Bob]

Your procedure sounds reasonable.

Make sure Zref is set to 50 ohms. Click Setup->Enter Zo Ref if it needs to be changed.

To make sure the hardware is still working, do a standard cal with the loads connected directly to the RF connector. After cal is complete do a scan from 1 to 20 MHz with a step size of 0.2MHz. This should give a Zmag of 50 ohms and SWR = 1.0. If the cal resistor is not 50 ohms, that's ok. The SWR will read Rcal/50.

-- 73/Bob

[wewill]

Hi Bob,

The Zref was the problem. When I went to Setup>Enter Z0 Ref, it read something like 50 + j338136628000000000000000000000. When I set it to 50, everthing worked fine.

Thanks again for the quick and accurate fix.