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Might appear to be slightly off topic, but I hope it's not :)

Lets assume we have ideal/lossless "everything" from end to end. Source (TX)
is pure 50 Ohm, the same with coax 100 Ohm, antena 25 Ohm. Over simplified,
but will get us going. Reflections everywhere (TX to coax, coax to antenna).

Now, I put antenna tuner between TX and coax (or coax and antenna), make
transition from 50 to whatever impedance coax is now presenting (coax length,
transformed 25 ohm from antenna, ...), get SWR 1:1.

Does it now mean that SWR is 1:1 at the antenna end as well?

Asked differently, if SWR is low at one end, does it mean it's low on the
other end as well (again, lossless components used!)

Hi,

I Ham friend of mine ordered a NavoVNA and he asked me to come over and
help him understand how to check the SWR of his antennas. I am not yet very
familiar with all the operational procedures of the NanoVNA except for what
I could gathered here by reading other posts. But can't seem to remember a
similar issue being brought up and a quick search did not help either. Plus
I still need to order mine, but have not made up my mind between the v3.4
and the 4H, etc, so didn't have any experience at all playing with this
device until now.

What I did first was set the start and stop frequencies (in this case
2-35MHz), then proceeded to make a calibration which included a reset and
then seemed to go well on all three steps, as the markers for open, short
and 50ohm where all showing in the correct position on the smith chart
after the calibration was completed and saved. Afterwards I tried with a
narrower frequency range (2-10MHz) then calibrated again, but the results
where still the same as described bellow.

After connecting the antenna to CH-0 both the Smith chart and return loss
traces seemed to be showing useful indications, but the trace corresponding
to the SWR was always shown completely flat at the bottom of the screen and
the readout for that trace was in fact showing 1:1 as well along the whole
trace. This happened even when the Smith chart clearly was showing a
reading of an impedance that was quite different than 50 ohms, plus
capacitance or inductance. Besides it would be impossible for a single
antenna to have 1:1 on the whole frequency range. Just as a test I
connected a dummy load instead of the antenna and then the return loss
trace would also be flat, and the smith chart would show the marker very
close to where 50ohms would be expected to be.

So my question would be if I am missing to set up something else in order
to be able to make the SWR trace work. I tried disabling all other traces
but that did not solve anything either. Also not being yet very familiar
with practical use of the device, I found that the Scale setting was a bit
confusing as it only has the numbers and then a +1 field. Would this be
used to define the per division dB value of the vertical scale markings?

Thank you in advance for any pointers.

You can match/measure the feed point of your antenna by using an _electrical_
half wavelength or multiples thereof, between the tuner/analyzer and the
antenna.

The wire may be non-resonate without your home brew matching network,but with the network it has to be.??? To be an efficient radiator, you haveto resonate.???? Kent WA5VJB

On Sunday, August 16, 2020, 1:34:08 PM CDT, David Eckhardt <davearea51a@...> wrote:
How many hams actually match *at the feedpoint* to a 50-ohm coaxial line?
I'll bet very few.? At VHF and UHF, yes, at the antenna match is practical
and usually accomplished, but not at HF.

That's why I use open wire feeders where SWR losses are *far* less than in
coaxial cable and the feedline is not stressed even with SWR at full
power.? And......I use a single set of wires for 630 through 6-meters with
that system with home brew matching network.

Antennas do not require being resonant to do a good job of radiating.? My
system is not resonant (± jX = 0.00, the definition of resonance) in any of
the HF ham bands, but it does very well, both in practice and in the 4NEC2
model.? It's lowest 1/2-wavelength resonant frequency is 950 kHz, the lower
1/3 of the AM BC band.? I seriously doubt I'd do any better with resonant
dipoles for all the individual bands.

Dave - W?LEV

On Sun, Aug 16, 2020 at 6:07 PM Chris Wilson <chris@...> wrote:

Hello David,

? Sunday, August 16, 2020

? Without? knowing what impedance the antenna itself presents, how do I
? know the best way to match it to the coax impedance?


Best regards,
? Chris? ? ? mailto:chris@...


DE> What's important is the load the antenna plus feedline present to our
DE> modern transceivers.? So, why the concern for 'at the antenna'
DE> measurements?? Sure, its nice to know, but the coax contributes it's
own
DE> impedance transforming properties.? If you must, make the measurement
at
DE> the shack end of the feedline, and use a tool such as SimSmith to take
out
DE> the impact of the coaxial line.

DE> Again, what is important is the load presented to the transmitter, not
DE> necessarily what the antenna impedance is at the feedpoint.? One must
STILL
DE> consider the transmission line between the transmitter and the antenna
DE> feedpoint to obtain this result.

DE> Dave - W?LEV

DE> On Sun, Aug 16, 2020 at 5:31 PM Jerry Gaffke via groups.io <jgaffke=
[email protected]>> wrote:

Roger wrote:

? You can clearly see that the two plots are nearly identical.

What kind of coax?
I bet it isn't RG174.
I have seen significant differences when checking out an HF antenna over
100 feet of RG8X.

I have a 20M dipole with a current balun attached to it which for this

test I consider to be the "feedpoint" of the antenna.

Not totally clear which side of the balun you consider to be the

feedpoint

of the antenna
I assume this means you leave the balun attached to the antenna, and

only

calibrate out the coax.

Jerry, KE7ER


On Sun, Aug 16, 2020 at 09:47 AM, Roger Need wrote:

I have a 20M dipole with a current balun attached to it which for this

test I

consider to be the "feedpoint" of the antenna. 55 feet of coax runs

back

to

the shack. First measurement with NanoVNA Saver was made at the

feedpoint and

stored as an s1p file. The coax was then "calibrated out" and a second

Saver

measurement made back in the shack. The first s1p file was then loaded

and a

comparison was made. You can clearly see that the two plots are nearly
identical.

Roger

Does anyone have a suggestion for a soft, clamshell style, padded storage case
that'll fit a NanoVNA-H4 with enough extra room for typical accessories?

I’ve searched for hours and so far come up empty handed...

Does anyone have a suggestion for a soft, clamshell style, padded storage case that'll fit a NanoVNA-H4 with enough extra room for typical accessories? It needs to have a separate inner zippered compartment to store the calibration fittings and coax jumpers so they won’t rattle around and rub on the NanoVNA's screen.

I've seen multimeter storage cases which are close, but they're either way too big or lack a zippered internal storage compartment. A portable hard drive case might work also, but again, every one I've encountered lacks an internal zippered storage compartment.

Ideally being able to buy from Amazon or eBay would be best.

Thanks in advance,

John
AA7US