开云体育

Surely I am not the first to do this but I want to crow anyhow.

I have just setup a 6M Yagi in my attic. I am mostly concerned with overall system SWR. I put the VNA at the shack end along with a webcam. What a joy this was to tune. When I did this a few years ago I traveled the stairs way too many times. I also have an 80-10 EFHW that may benefit from this in the fall.

Jim, others may have done this but I haven’t seen their posts. What a great idea!

KI4QCK

Why not tune right at the antenna in the attic using the NanoVNA?

you try everything and nothing works.

This is why being able to have an onsite nanoVNA measure at the antenna may be the only definitive answer.
The nanoVNA does not lie BUT you must ensure ALL the Calibrations are spot on.

I had a case recently where the trace was jumping all around and no matter what I did I could not get a proper reading.
Until I remembered, the THRU path was not calibrated. there are cases when the other port is seeing something, and ensuring the thru (port to port) is calibrated the device will only tell you what it is seeing and if you have NOT calibrated out ALL the extraneous anomalies your measurement will be compromised.

You should not need a THRU or ISOLATION calibration for a pure S11 measurement though it doesn't hurt. Many beginners forget to tap DONE when they are finished with their SOL calibration...

I could but that would require a coax jumper of sufficient length to avoid de-tuning by my body. As is, the jumper goes from the radio to the attic, maybe 30 feet in length. After adjustments are made I simply step away 10 feet and look at my phone.

As I said, my main concern was overall system SWR so as not to cook my radio. If the antenna performs, I am good with it. So far it seems to do OK. Also, this is Alabama in May. The less time spent in a hot attic the better. Thanks.

Use a small common mode choke at the antenna to decouple your body parts
from the measurements.

*Clyde K. Spencer*



On Tue, May 27, 2025 at 4:30?PM Jim K4JDH via groups.io <k4jdh=
[email protected]> wrote:

I could but that would require a coax jumper of sufficient length to avoid
de-tuning by my body. As is, the jumper goes from the radio to the attic,
maybe 30 feet in length. After adjustments are made I simply step away 10
feet and look at my phone.

As I said, my main concern was overall system SWR so as not to cook my
radio. If the antenna performs, I am good with it. So far it seems to do
OK. Also, this is Alabama in May. The less time spent in a hot attic the
better. Thanks.

That is, you need a balun. There has been a lot of talk about baluns here and at other forums.
These stop or attenuate RF in the shack and make VNAs work
I have used Digikey. Mouser and others are good too, ofcourse. These are what Digikey has. The idea is to get a high impedance between antenna and feedline.

Take highest impedance at your frequency and what has large enough diameter for your cable.