Okay, gang,
Thanks for the advice. I will download the AC6LA info and see if I can improve
my game. :)
This is a learning experience for me, as I haven't gotten into the nitty gritty
of feed line measurements before, and I need to become more familiar with my RF
tools and procedures.
My older MiniVNA -- at least with the Blue VNA software I use with it --
doesn't seem to have the specific calibration procedures that other devices
have. It calibrates "short" on the transmission mode and "open" in the S11
reflection mode. but I'm not finding a 50-ohm calibration setting for the
moment.
I also have a Rigol spectrum analyzer, but my expertise in using it doesn't get
me very far for the moment. It may offer 50/75 ohm calibration. Will have to
check.
Part of this process also involves learning how to prep and install various
coaxial connectors (I was behind the times), so I have been testing
compression, clamp, screw, and crimp connectors, for which I now have suitable
tools.
Interesting: lengths of RG-11 measure exactly the same with three different
connector styles. That's what I was hoping for (and expecting).
I have 2,000 feet of RG-11 quad shield on hand, so I'd like to use it while
actually knowing whether it's working as expected. It seems to be.
Now, to the back yard before it starts snowing for real! I need 102 feet to
reach my inverted-L and 88 feet to reach the tower box for my Death Ray
Hexagonal Beam. It's mounted on the cutest 22-foot tilt-over tower you've ever
seen, but it will have to do until spring when it will move to a 50-foot tower.
By then I hope to have the VNA/coax sweeping techniques down pat.
And for one commenter: I don't have the live sweep in front of me, but as I
recall there were 5 or 6 "sine wave" peaks in the 1-35 MHz VNA sweep, so
perhaps your comments about specific reflections explain "the wiggles" when
sweeping 75-ohm coax.
Regards,
Kirk, NT0Z
My book, "Stealth Amateur Radio," is now available from www.stealthamateur.com
and on the Amazon Kindle (soon)
On Saturday, November 28, 2020, 1:08:38 PM CST, Jim Brown
<jim@audiosystemsgroup.com> wrote:
On 11/28/2020 3:43 AM, Kirk Kleinschmidt via TowerTalk wrote:
> I'm trying to characterize some coaxial cables and various connectors, and
> the results from my two measuring methods aren't reconciling well. My
> understanding of the tools is also less than complete.
First, make sure that your VNA is well calibrated. For cailbration, you
will need standard Open, Short, and 50 ohm parts.
Then, use it to make S11 measurements over the frequency range of
interest. I'd go with 1-50 MHz. Then download a copy of AC6LA's ZPlots
Excel spreadsheet, export your data to it, and follow his instructions
for characterizing the cable.
This will give good results for coax and two wire line of any impedance.
73, Jim K9YC
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|