> Thanks very much for this, Brian.
> Can't wait to try it out!
> 73, Jim K9YC
Jim, Rudy Severns, N6LF, is developing a new 24" soil probe. In the
process he discovered that common-mode current on the long cable he runs
to his desktop computer from his older VNA can seriously disturb the
measurements. He used a common-mode choke, but it was inadequate below 3
MHz. I thought of suggesting one of your wideband compound chokes, but I
finally suggested that he just buy a NanoVNA and make isolated
measurements. Rudy will be writing up his new probe for the ARRL Antenna
Book. He will emphasize common-mode issues, which can be insidious.
I'd like to attach a photo of Rudy's new probe, but I gather that's not
possible. Here's a link to a post on the NanoVNA users group that
includes the photo:
https://groups.io/g/nanovna-users/message/26166
Rudy's new probe uses 3/8" aluminum rods spaced 4". Rod length (tip to
crosswire) is 26" and exposed (soil surface to wire) is 2" when fully
inserted. None of these dimensions is critical.
Here's an image of what a poor choke yields. As a test, Rudy wound a
narrowband 1 MHz resonant choke and permittivity rose beyond 110.
http://ham-radio.com/k6sti/badchoke.gif
I'll delete this image in a day or two. I don't want it cluttering my
website.
Brian
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|
