Custom Calibration

[wa9zvf]

I'm a new 4170D user and am very pleased with the device.

I'm using the custom calibration.  The "cable" consists of 18 inches of RG58 into a DX Engineering 50 ohm 1:1 current balun (choke type) followed by 97 feet of ladder line (300 ohm nominal 270 actual).  I did the custom calibration from 1 to 30 Mhz with spacing of 0.01 Mhz.  Used a 75 ohm carbon comp resistor.  Confirmed the cal data by scanning the 75 ohm resistor.  The swr is as expected and flat.  Z is flat and as expected.   Interestingly, the phase jumps all over the place.  Is extreme variability in phase normal? 

Also, does the custom calibration routine do averaging?  If not, would adding averaging capability improve the calibration?

Ray Mikula, WA9ZVF

[Bob]

Hi Ray,
I'm pleased to hear you like the AIM4170D.
The combination of coax, balun and ladder line is a fairly complex transmission line. That's where the AIM is handy because it shows how a complex system behaves as seen by the transmitter. If it's ok in the ham bands where you operate, then it's ok and the transmitter will be happy. Did you put a 300 ohm resistor at the end of the line?

You may see a difference when the position of the ladder line with respect to ground is changed.
When you connect an antenna, the scan data will get even more complex. The bottom line is, how does it look in the ham bands?

Custom cal doesn't do any additional averaging. The Averaging function is done by the firmware inside the black box. All other calculations are done by the software in the pc.

--73/Bob