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SWR trace always showing 1:1 as flat line at bottom of screen

nanovnagroup@...
 

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.
Oristo
 

he 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.
1) be sure that the TRACE selected for SWR is using CHANNEL CH0
2) in SCALE, select whatever REFERENCE POSITION that you like
eg 1 x1
3) select an appropriate SCALE->SCALE/DIV
e.g. .2 x1 for 100 Ohm termination if calibrated for 50 Ohms
nanovnagroup@...
 

I am no longer in front of the device, but I am pretty sure there was CH0 preceding all 3 of the active trace readouts (RL, SWR and Smith).
Is there anything else that could have prevented the SWR trace to be non active?

Thanks for the input.
Kevin B
 

I've had that a few times too. I've never been able to figure out why but recalibration seems to always get it going again. Not much help other than I've had that too. I only need the 3 calibration steps but I want to say I've noticed it at least once when I don't complete all the calibration steps. Not everytime though.
nanovnagroup@...
 

I noticed that sometimes after doing a cal without a reset there where sometimes inconsistencies after I verified that each Smith chart indication was in the correct position for each of the SOL cal caps, so I had to do it over. But even so the SWR trace remained flat-lined.
Bill Smotrilla <smopho@...>
 

You may need to use a smaller freq sweep range and select only the bands you want to sweep individually. The device only has 100 data points of resolution and a full 30Mhz sweep could easily miss the SWR dips with only 100 data points.
nanovnagroup@...
 

On Tue, Feb 18, 2020 at 09:27 AM, Bill Smotrilla wrote:
You may need to use a smaller freq sweep range and select only the bands you
want to sweep individually. The device only has 100 data points of resolution
and a full 30Mhz sweep could easily miss the SWR dips with only 100 data
points.
Not sure I am understanding you correctly, but the SWR trace remained flat at the bottom of the screen all the time, there where no dips or peaks of any sort being shown, which is what I would have expected to see, as in fact I know that this multi-band antenna that was being tested has overall quite high SWR across all the ham bands, and that was one of the main reasons that my friend purchased the NanoVNA as he was hoping to make some sense out of the antenna's resonant points, or if there even where any. After the initial 2-35Mhz sweep I switched to a narrower band scan limited to only from 2-10MHz and recalibrated, but the SWR trace was still only flat at the bottom of the screen and the readout was showing 1:1 across the board. I am aware of the 101 data point limitation, but still even with the wider 2-35Mhz initial sweep it should have shown a resolution of about 325Khz which I would think would be more than enough to at least show a good part of the overall varying SWR at the antenna in relation the the frequency sweep.

Another theory I had at the time I was playing with the device is that somehow the "signal" going to the SWR trace is too low, and its trace is just somewhere hidden further down on the screen because the scaling is too high, or something to that effect. But I was not sure how to change the scale only for the SWR trace as the other two traces (Ret-Loss, and Smith) seemed to be working fine.
RetroDude <k0crx@...>
 

I have not had a flat line problem, but, my NanoVNA displays SWR values that are consistently much lower than shown on any of my outboard bridges.
Oristo
 

I was not sure how to change the scale only for the SWR trace as the other two
traces (Ret-Loss, and Smith) seemed to be working fine
CHANNEL, SCALE and FORMAT menus apply only to the most recently selected TRACE
Ed Humphries
 

Mine also. VNASaver is somewhat more in line with other tools. I''ve been wondering why, too.

Cheers, Ed -KT4ED

On 2/18/2020 4:46 PM, RetroDude wrote:
NanoVNA displays SWR values that are consistently much lower than shown on any of my outboard bridges.
Edwin Michal
 

-same problem-solution return nano -2nd nano reads 1;1.19 with dips=another return, The dips are at the right freq. but read 1: 1.09
Clyde Spencer
 

Are you sure you had the proper port selected for the SWR trace? S21 not
S11?
*Clyde K. Spencer*

On Tue, Feb 18, 2020 at 3:11 AM <nanovnagroup@...> wrote:

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.
aleks07111971@...
 

I asked a friend to solder me a test load of VSWR 1.5 and now, before measuring, I always check the correctness of the settings and calibration, if something is wrong, it is always and clearly visible!
Edwin Michal
 

after careful calibration the swr seems to be reading correctly with high
values on the edges

On Wed, Aug 19, 2020 at 9:59 AM ekmichal82 via groups.io <ekmichal82=
gmail.com@groups.io> wrote:

-same problem-solution return nano -2nd nano reads 1;1.19 with
dips=another return, The dips are at the right freq. but read 1: 1.09

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