Cable Loss Gone in 675?

[mark6sf]

I use my AIM4170 often in testing antennas I build and put up and it has helped me greatly in understanding how antennas work.

I noticed the Cable Loss info for open or shorted cables is no longer shown as a parameter on the right side of 675. I used this function regularly to test cables.

Was it removed because of some problem with the measurement? Is there another way to get this information?

A second question. Is there any need to run calibration when you install a new software release? I assume not because if it was that would imply that all of the custom calibrations would also have to be redone and that would be a major headache.


Regards,
Mark
N6SF

[Bob]

Hi Mark,

Cable loss is displayed when the Return Loss plot is enabled. It's under Setup->Plot Parameters.

Of course, the cable loss is only valid when the cable is open or shorted.

--73/Bob

[w0qe]

Plotting the return loss vs frequency for all but the shortest cables shows a varying return loss with an increasing trend. These variations in the return loss are both correct and proper even though we know that the matched line loss does not have this variation. Just draw a line through the center of the return loss variations and that will be very close to the correct value. I struggled with this concept a while ago but my big HP VNAalso showed the exact same phenomenon. To really understand what is going on, download the free LT Spice from Linear Technology which has both lossless and lossy transmission line models. It will show what is going on with all the voltages and currents.

Larry, W0QE

[mark6sf]

Happy to hear it was just my operator error. I hadn't realized it was connected to the Return Loss parameter.

Thanks also to Larry for his comments. I had noticed the variations and wondered about them. Still it gave me an indication if the cable was in the ballpark of its expected loss.

I would like to suggest it would be nice to add a pulldown list of velocity factors for common cable types. I'm always looking them up to make sure my memory is correct. I realize this factor can vary somewhat based on manufacturer but if it could be edited then each user could set it up for his needs.


Thanks Again,
Mark
N6SF

[Bob]

Hi Mark,

For information like cable data, it's easy to add custom tables and charts to the present Help or Application files. These are plain html files like web pages. The AIM program doesn't pay any attention to the content, just the file name. When you click on the Help or Application file name, the program opens your web browser to display the page.

Therefore, you can add text or pictures to the Help files to customize them. For example, a large table of cable data can be scanned from a handbook or captured from a manufacturer's web page and then copied to the same folder where the Help file is located. By adding a little bit of html code to the Help file, this chart can be recalled.

Small amounts of data can just be typed in using any text editor, even Notepad is adequate.

-- Bob