Hello Jon,
As you wish to use the antenna on the higher harmonics as well as 2M, I would suggest you use ferrites to create a Common Mode Choke (CMC) as noted by Roger.
I suspect (but do not know, I am no expert here) that it would be difficult to build a broadband balun to cover your frequency range (x5, x7) at TX power levels.
As for some of the other comments to this thread, I did not say that your antenna would not work without a balun or CMC.
What I said was that without a balun or CMC, the connection of an unbalanced VNA to a balanced dipole would not give correct measurement results of the antenna because the feedline would become part of the antenna measurement as also noted in other responses in this thread.
Your experience when you used a replacement "load" to do your calibration just emphasises how critical it is to do calibrations correctly and to treat your calibration SOLT "standards" with care and respect.
We can measure antennas till the cows come home and hypothesize on the results for twice as long, but we all know that the most unlikely collection of bits and bobs will form some sort of antenna that may, or may not, enable QSOs one way or the other. However a successful QSO is not scientific evidence of a "good" or "bad" antenna.
If it works, great. But do not use this as evidence of optimum antenna performance:-)
The "suck it and see" approach may not quite equate to measured results:-) Just my 2 cents worth.
Cheers...Bob VK2ZRE
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On 1/04/2025 12:25 am, Jon via groups.io wrote:
Bob,
Would you suggest a voltage balun or current balun at antenna feedpoint?
One ham told me that if you use a voltage balun, it can bring down the high
noise I have on 80m.
Regarding the original question, I am tempted to think like Milt. I see a
lot of harmonic resonance in NanoVNA tracings when I set the range high on
purpose. In fact I use them to work higher bands. I am able to work North
America from VU on 12m, using my 80m center-fed dipole mounted at just 5m
height and 100W, with a little bit of touching up with the N7DDC tuner.
That would be the seventh harmonic resonance!
73
Jon, VU2JO
On Mon, Mar 31, 2025 at 6:29?PM Bob Ecclestone VK2ZRE via groups.io
<becclest@...> wrote:
Hello Hobride,
Unfortunately you have not supplied a photo of your test setup.
A dipole is balanced at the feedpoint, your VNA is unbalanced.
I suspect your problem is that you do not have a balun or choke at the
antenna feedpoint to prevent the feeder from affecting the measurement.
I won't make any guess as to why the VSWR appears lowest at 513MHz, but
I do suggest you use a balun or choke at the antenna.
HTH...Bob VK2ZRE
On 31/03/2025 11:25 pm, Milton Engle via groups.io wrote:
You did not indicate the range of your sweep.
Try setting the sweep range to 150MHz to 190MHz, recalibrate
open/short/load, then measure.
I suspect that you will find the lowest VSWR near 171MHz, indicating
that the element lengths are a bit long.
The third harmonic of 171 is 513
Milt
N3LTQ
On Mar 31, 2025, at 03:51, hobride via groups.io <hobride=
[email protected]> wrote:
?Hello everyone,
I have bought a NANO VNA H4 to build simple dipole antennas.
Now I have made a simple dipole antenna for testing. This should be
tuned for 172 MHz. The total length is ~83 cm (2,72 feet), one leg is ~41.5
cm (1,36 feet).
When I now connect this antenna and try to measure it, the result is a
lowest SWR (1.15) at 513 MHz.
Can this be possible? I am not a radio specialist. I am an IT guy.
I have flashed the NANO VNA H4 to the latest firmware (tried DiSlord
and Hugen) and also calibrated it.
Perhaps I need to make further settings after flashing?
