BS...... The NANOVNA is well shielded. How many times do we,
collectively, have to remind others that holding onto the VNA while making
measurements is allowing your conductive body to become part of the antenna
and its fields.
READ THE REPLIES, PLEASE. Several of us have made it as clear as we
possibly can that "shielding" or "earthing" IS NOT A SOLUTION!!!! You and
the coax outer surface of the shield are becoming part of the antenna if
means to decouple the coax shield are not taken.
READ THE REPLIES. Several of us have responded in best engineering
practices, not here-say, snake oil, or witchcraft!!!! Read the previous
replies, PLEASE!!!!!!!!!!!!!!!!!!!
Dave - W?LEV
On Mon, Feb 3, 2025 at 6:20?PM Patricio A. Greco via groups.io
<patricio_greco@...> wrote:
Hello: I’m reading this topic since a couple of hour. Its clear that
NanoVNA has a poor shielding. These instruments are very cheap …the good
news is that there are many things to enhance on them. A metallic case
would be a good idea with many grounding points, the problem is the display
it should be outside the RF sections… enhance the design requires more
money so this is . You need first an electrically stable setting prior VNA
calibration. I’ve a NanoVNA and let me tell that you are getting
everything this tool can give. In other posts some people are trying to
measure very low series resistance from an inductor , this is out of
NanoVNA possibilities. I measured the RF generator output and this is
square wave, another source of error in the instrument.
That it does is the limit of his technology.
Regards, Patricio.
On 3 Feb 2025, at 15:04, Roger Need via groups.io <sailtamarack=
[email protected]> wrote:
On Sun, Feb 2, 2025 at 05:06 PM, Coyote wrote:
When using my NanoVNA to adjust length of a 20m hamstick, the readings
kept
changing depending on what the NanoVNA was sitting on (truck hood,
pelican
case, my thigh, or in my hand).
How do I get a reliable reading that I can count on for a properly
adjusted
antenna?
A hamstick is a helically wound whip antenna with an adjustable stinger
for tuning the antenna to a desired frequency. But it is only "one half"
of an antenna system. The other half can be another hamstick (which makes
a dipole) or some type of ground plane or counterpoise. The vehicle body
act as the other half for mobile installations.
What happens if you just connect the coaxial cable and secure the
antenna to a non-metallic structure as some posters have suggested? In
this case the outer surface of the coaxial cable will become the other half
of the antenna and will radiate RF in addition to the hamstick. If you
tune using the stinger you will get a minimum SWR point but if you increase
the length of the cable, touch the cable or VNA with your hand or put the
antenna over something metallic the readings will change.
The proper way to adjust the antenna is to mount it in the way it will
be operated and then adjust the stinger. Be aware that the outer surface
of the shield will still act as part of the antenna system and will radiate
RF. The level of RF will depend on what type of structure the antenna is
mounted over. A metal vehicle body acts as a good ground plane and you
will have less cable radiation than just a trunk lid.
You can get a significant reduction in the cable radiation by using an
RF choke on the coaxial cable like Juan Pablo suggested. You can make your
own or buy one from several vendors.
Roger
--
*Dave - W?LEV*
--
Dave - W?LEV
