Idea for enhancement to custom calibration

[wa9zvf]

Custom calibration is an incredible feature but if you are using it eliminate the effects of a feed line to an antenna, you need to do a 3 step calibration (open, short, known resistance). This requires lowering an antenna multiple times to gain access to the end of the feedline and then hoisting it to place, making the calibration, lowering, etc until all three "loads" are run. If you want to test multiple scenarios, for example several different baluns, then you need to repeat the process for each different scenario. The hassle, is raising and lowering the antenna each time. Perhaps the software could be enhanced to allow each portion of the calibration, open, short, known resistance, to be saved independently and recombined to produce the "calibration" file. So, in practice, you could lower antenna, create "open", hoist up and then run the calibration portion for "open", using balun 1 and save the file. Switch to balun 2 and run calibration for "open" and save the file. Etc. Same would be true for short and known resistance.  This would eliminate a lot of hoisting the antenna up and down. You would then select the three files (open, short, known resistance) and run a "function" that would properly combine all three measurements. The burden would be on the user to be careful in terms of naming files and making sure that the proper files were selected to produce the final cal file.

Ray Mikula

WA9ZVF

[jimworth]

I'm not clear on why the far end of the feed line needs to be raised each time the custom calibration test load is changed. It seems to me that you would lower the feed line, disconnect it from the antenna, make the first custom cal measurement (open), short the feed line, make the second measurement, put the known load on the feed line, make the third measurement, reconnect the feed line to the antenna, and raise it back into position. Assuming the feed line is coax, it shouldn't be affected by height or positioning.

73,
Jim AD4J

[wa9zvf]

The feed line in question is ladder line. As a side note, I have found that even coax, laying on the basement floor is somewhat sensitive to a change in position.

Ray Mikula
WA9ZVF

[jimworth]

I certainly understand with ladder line. Even curving it gently well above the ground changes its apparent velocity factor and/or impedance.

Now that I understand why the feed line has to go up and down, I'm still unclear on what could be done in the software to allow you to avoid doing that 3 times for custom cal. Even if you could save each measurement and combine them later, wouldn't you need to take the feed line down to change the load for each of the 3 measurements?

73,
Jim AD4J

[Bob]

Hi Ray,

It is possible to do this sort of operation now by copying and pasting cal data from several files.

1. Mount the short cal load and run up the antenna.
2. Connect balun 1 and start the cal procedure.
3. When the short cal portion is finished, attach balun 2 and then at the prompt for the open ckt load, click continue.
The data that is accumulated will correspond to the short ckt + balun 2. Numerically it's ok and the program won't care.

4. When the "open" ckt cal is finished, click continue and don't worry about the standard resistor not being attached. You will disregard this last data section anyway.
This completes the first cal file with the data for the short ckt.

5. Lower the antenna and attach the open ckt.
6. Repeat this procedure and make a new file for the open ckt data with both balun 1 and balun 2.
7. Repeat again using the standard resistor to make a third cal file with data for both baluns.
8. After all three files are complete, use a text editor to copy and paste the appropriate sections into single cal files. The open and short ckt sections are clearly labeled in each file.

The trick is to keep the data organized. Use comments in the cal data files, use descriptive names for the files and keep notes on paper.

-- 73/Bob

[jimworth]

Ignore my second question above. I now understand that you were talking about changing baluns at the station end of the feed line, so there would be no need to lower the antenna.

Jim AD4J