The teaching potential is great. I'm having lots of fun for $38. I had
trouble nailing down the swr from my 20 meter dipole tuned to 80 meters
(narrow window) The VNA was the answer. My new IC 7300 only tunes to the
band window and the swr was to high to tune in the window.
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On Mon, Aug 17, 2020 at 10:07 PM Pierre Martel <petem001@...> wrote:
Did not read the whole message , sorry, But I can tell you that as a hammer
it has really poor quality..
One have to ask himself if the job is good for the tool to!
Le lun. 17 ao?t 2020 ¨¤ 19:20, Jim Lux <jimlux@...> a ¨¦crit :
I have one, and it is the greatest thing for HF and VHF since sliced
bread - cheaper than a digital multimeter, plenty of accuracy for most
HF uses (at HF, whether you even bother putting the open on for cal
probably isn't an issue, and the "difference in measurement plane" is
negligible).
The other thing is that I think it is an invaluable teaching tool. EE
professors should be handing them out to their students. You learn a
lot more about "matching" and transmission lines and such from having a
VNA sitting in front of you and just "hooking stuff up".
Put that stub of coax on a T connector and watch it "suck out" the power
at the notch.
For that purpose, running it at 100-200 MHz is probably just about right
- the wavelength is short enough that "resonant things" aren't huge -
the wavelength is long enough that "precision of cal kit phase delays"
isn't an issue.
You can learn all about making microwave measurements, tuning a filter
(does anyone do that these days for new designs?), measurement
uncertainties.
Where I see a problem looming is in applying it to higher frequencies
(2GHz and up), because a) the underlying design and components are being
used at harmonics and well out of their nominal frequency range - it
works, but parts you buy tomorrow may not work the same as parts you buy
today and because b) calibration becomes more critical as wavelengths
get shorter.
There's a whole bunch of cool stuff you could do in an antenna lab with
2.45 GHz antennas, measuring antenna patterns, learning how to do the
measurement at all, the traps for the unwary (reflections from
environment). But a lot of that fun stuff is more "qualitative" than
"quantitative" with a tool like the NanoVNA (or V2 or whatever. So it
would be incumbent on the professor to properly deal with the issues of
calibration, the increased uncertainty, and perhaps, coming up with some
lab exercises where "why good cal kits cost $20k" can be illustrated.
Another thing that would be fun with higher frequencies is making
interdigital filters and couplers on PCBs - send your design out to one
of the fast turnaround cheap protoboard places, hook it up to your VNA
and see if your filter turned out the way you thought it should.
For instance there's a whole lot of cool phased array components (MMICs)
becoming available at low prices for 5 GHz and up. And a cheap VNA
makes working with that kind of thing a lot easier. But I sort of worry
about someone getting frustrated trying to use something like the
NanoVNA (in its current form) to do that.
Maybe there *is* a market for a $500 VNA that does microwave stuff well
(enough). I was willing to pay that for the TenTec TAPR VNA back when
and that's basically a HF only box with a lot of limitations.
ANd there will always be applications where you *need* the high dollar
test set - 26 or 32 GHz has gotten cheaper, but is still a expensive
area to work in. Everything is more expensive - coax is more expensive,
connectors are more expensive, test equipment is more expensive, cal
kits are more expensive. About the only thing that's cheap is the ICs,
because, after all, it doesn't cost much more to make a GaAs amp at 6
GHz as at 30 GHz.
