A 135' end fed half wave should be resonant somewhere in the vicinity of
the 80 meter band (3.5 MHz). The exact resonance will depend on height
above ground and the proximity of structures, among other things.
But there is another thing going on. An end fed half wave has a high
impedance at the feed point, in the thousands of ohms. If you want to use
one directly in a 50 ohm system without an antenna tuner, a 49:1
transformer (balun) is typically used. A 9:1 transformer brings down the
impedance to a point that a typical antenna tuner can handle, but it won't
present anything close to a 1:1 SWR to a 50 ohm device like the NanoVNA or
a ham radio rig.
Bottom line: your NanoVNA is probably accurately representing what is going
on with that antenna. It's not broken.
On Wed, Sep 9, 2020 at 10:25 PM Bob Albert via groups.io <bob91343=
[email protected]> wrote:
First decide the frequency range of interest. Then program it either as
start and stop, or center and span. Then set up for Smith chart and SWR
display.
The Smith chart will plot the impedance of the antenna. The marker, which
is controlled by the rocker switch, can be moved to any frequency point and
the resultant impedance will be displayed. If the impedance is anywhere
near 50 Ohms you will see the SWR at all frequencies in the range.
Antennas are complex devices and characterizing them is partly art and
partly science. Most people think in terms of 50 Ohms as a standard, and
the Smith chart is set up for that. If your antenna impedance is much
different from 50 Ohms, say by a factor of three or more, it won't work
well with a 50 Ohm system. The alternative is either to change the antenna
to bring it closer to 50 Ohms or transform its impedance to something near
that value.
Random wire antennas may do well enough for receiving but for transmitting
it's a different story. A transmitter will not perform properly if its
load is far from its design value. There are losses when mismatch is great,
and these sometimes can cause problems such as arcing or favoring undesired
frequencies.
There is, of course, no substitute for a good understanding of the
principles. There are many books on the subject, and not all of them are
good. Just because it's been printed and bound, don't assume it's correct.
I am a great fan of resonant antennas, and they have worked well for me.
I routinely plot SWR across the appropriate band for each antenna and thus
see if anything has changed much. I almost never use an 'antenna tuner'.
Bob K6DDX
On Wednesday, September 9, 2020, 07:00:10 PM PDT, Darrell Carothers <
rescuemedic1@...> wrote:
Doubting the accuracy of my NanoVNA H4. Is there a way for a non
electronics minded person to verify the accuracy of my H4? I am a beginner
with the NanoVNA. I have calibrated the unit per recommendations. After
calibration the open, short and load show where they should be.
I have used the helpful recommendations from members in this group. I am
trying to analyze a random wire antenna that shows no resonant areas. I
have a lot of noise and do not hear a lot of stations. I did make one
contact last weekend, my only QSO, from Arlington Texas to Jinks OK on
7.280.00 LSB.
Thoughts, suggestions, solutions?
The antenna is a random wire 9:1, 135¡¯ element, 35¡¯ counterpoise, about
40¡¯ up in the tops of trees with leaves. Line was placed with a drone. I
would like to learn to use the NanoVNA in and out for my benefit.
Thanks
Darrell
Sent from my over-rated IPhone 7 Plus. Any Mis-spellings or grammar
errors are due to my IPhone auto correct feature.
Shirley Dulcey KE1L