Hello Jerry,
Sunday, August 16, 2020
Yes, when I measured using RG-58 test coax the results were very
different from measuring with LDF4-50 coax, That's the influence of
the coax itself. I want to see just the antenna at the shack end, not
the antenna and coax. Given enough length of poor coax I believe you
could see a good impedance match measuring without reference to the
antenna as the coax would swamp the reading, pretty much whatever the
antenna was like. So, how to do the O S L at a none coaxial
connection point remains the question? :)
Best regards,
Chris mailto:chris@...
JGvgi> I think Chris had it right, assuming he wants to measure his antenna
JGvgi> and does not want to measure the effect of adding all that coax and the balun
JGvgi> into the mix:
Now, my set up is transceiver - short LM400 flex pigtail to outside
shack window, 100 feet LDF4-50 coax, short LM400 pigtail around
rotator at the top of the tower, balun, antenna itself. The balun
(actually a choke in reality, toroid wound with a single length of
coax), has two 5mm stainless stud terminals with butterfly nuts. How do I do a O S L
on them, will just leaving them open shorting with heavy gauge bare
copper wire, and putting a 50 Ohm metal film precision resistor across
them be OK for up to 30MHz?
JGvgi> Doing the O-S-L calibration "at the same point where your transceiver will be connected"
JGvgi> is also correct, but you will then be measuring the reflection coefficient
JGvgi> of the entire system consisting of the antenna, balun, and the 100 feet of coax.
JGvgi> That will be a much different reading.
JGvgi> Jerry, KE7ER
JGvgi> On Sun, Aug 16, 2020 at 07:23 AM, Brian wrote:
The O-S-L should be done at the same point where your transceiver will be
connected - so, assuming you have a short (`12 inch) test jumper connected to
Port 0 on the NanoVNA - you would calibrate with your O, S and L at the end of
this test jumper - which then attaches to the same point where you intend on
connecting your radio. Done this way, the Nano VNA will test your balun/choke,
cable and antenna as a whole....
Brian - KI8KY
JGvgi>
