开云体育

Please disregard my previous post. I found the answer.

I'm just learning about the Nano-VNA; I don't actually own one yet. I understand that the source is a square wave, which contains odd-order harmonics. Suppose I want to measure return loss on some device that has a narrow-band response. It has very good return loss at F but very bad return loss at 3*F, 5*F, etc. Does the Nano-VNA somehow filter the reflected signal so that it only responds to F, not 3*F, etc. I.e., does the Nano-VNA processing include something like a digital filter that eliminates the harmonics? Otherwise the return loss response would be corrupted by the harmonics.

(Of course I am assuming that I am operating the Nano-VNA at a low frequency - not operating on the harmonics.)

Hello,

thanks for the information.
But the question is nothing extraordinary and simple:

Suppose you have just tested with the nanovna 2 filters 2 poles 45mhz. They look identical.
If you want a 4 pole filter, how do you plug them in. (They are often serial with the 2 center legs connected to a capacitor to ground)
The question is: You serialize them in the order of the nanovna test or you reverse the direction of the 2nd filter?
or how is the black dot determined if the question is asked differently?

Simple no?

cdt

TenTec had their "Patented Jones Filter" which worked very well. It was more for a variable bandwidth, but some of the techniques may apply here.

Schematic at:

Minor point, but QRM is interference from other stations. QRN is interference from noise.

On my V2Plus4 it needs to be entered in percent. e.g. A velocity factor of 0.73 should be entered as 73.

Hello,

Jim, yes i known that
But i have 5 filters 45R15AZ. No black dot.
My question is:
How after testing then with a nanovna select the 2 betters, and the best combinaison to connect them?

cdt

OK, I'll add a small correction to that last post

...measurement accuracy...the nominal value of an inductor or capacitor is highest at 0+j50 ohms or 0-j50 ohms, respectively.

Just so people don't get their knickers in a twist. ;-)

Regards,
--
VE6WGM

The reason why people make measurements at +/- 90 degrees on the smith chart is because the measurement accuracy using the shunt configuration when trying to measure the nominal value of an inductor or capacitor is highest at 0+j50 ohms.

"Nowhere in the references above does it indicate that measurements are made at a 90 degree reflection coefficient angle which is the 12 o'clock position of the Smith chart. In fact you can see from my graphs (that used your s1p file) that good results are obtained at reflection coefficient angles over a wide range.

I think part of this "90 degree belief" is that the S11 refection coefficient phase is sometimes confused with the phase of the impedance Z. Somehow this leads to the belief that measurements of inductors have to be made at 90 degrees. This subject has been discussed several times in this group. I just noticed that Owen Duffy (who writes technically thorough articles on the NanoVNA and other electronic subjects) just wrote an analysis of the s1p file you posted and it is interesting reading."

--
VE6WGM

Mini-Circuits has TONS of applications literature, and like their products, it's pretty much all top-notch. Look here:



and here:

The black dots connect together in the middle of the pair.

Yet another splitter document. This one is from Mini-Circuits:
RT

On 5/6/22 10:23 AM, Jim Dawdy wrote:

I hooked up my nanoVNA to 100ft of Belden 9913 to measure length and it shows it's about 1 foot. I tried other cables and got the same thing. It worked in the past. The cables are good cables. Could this be a firmware issue?

is velocity factor entered as percent or decimal? I can't remember which it's supposed to be, but that *would* make 100 ft look like 1 ft.

On Thu, May 5, 2022 at 08:34 AM, kosmos wrote:

I've calibrated my NanoVNA-H4 and double checked the calibration with the 3
tips once again as per hexandflex' guide, with the isolation and through,
since I want to measure the coax loss.
So far so good.

Now when I plug in the cable to both S11 and S21, I get some really odd
readings that don't seem to match up with what I'm seeing in guides and
videos. My logmag is all over the place and nowhere near showing a proper
reading.

Here are some screenshots done with my nanoVNA-H4
- One show S21 being 0 dB with cable attached between ports (right after calibration)
- Next shows S2 noise floor with no cable attached between ports (about 70 db or so of range)
- Last one shows 30 feet of RG-58 connected between ports.

Hope these help you to know what to look for...

Roger

On Thu, May 5, 2022 at 08:01 PM, Stan Dye wrote:

An easier way to check coax loss is available on the H4 with most recent
firmware. You connect the coax to only the s11 port, and leave the far end
of the coax open. Then from the menu choose measure / coax. The
measurements will appear at the left of the screen, including a loss
measurement at whatever frequency the cursor is at. So you set the
frequency range to include the frequency of interest, and directly read the
loss at that freq.

The techniques used in the latest firmware to calculate the loss is probably the the "Return Loss Method" of calculating Matched line Loss for a transmission line using an open circuit (or short circuit) line. It is easy to do because you just measure the Return Loss (RL) and divide by two. However it gives an approximation that is poor with low loss lines. A better approximation is obtained if the RL open circuit and RL short circuit measurements are added together and the result divided by 4. An article by Witt explained the rationale behind this method and it is discussed here...


I have attached some measurements done on a 30.75 foot (9.37M) length of Belden RG58 A/U cable. One graph is a plot of Matched Line Loss calculated using RLoc/2, RLsc/2 and using S21 on a NanoVNA-H4. There are large ripples in the RL plots due to the cable impedance not being equal to the reference impedance of 50+j0 ohms. The second graph shows (RLoc+RLsc)/4 and S21 and the two plots are very close. For reference a plot of this cables attenuation from the manufacturer is also attached. The manufacturer data shows 3.53 dB of loss at 50 MHz. for 100 feet which is equal to 1.09 dB for 30.75 feet. This compares well with the 1.16 dB measured using the S21 method

Roger

Yes, I forgot that option. A battery powered receiver tuned to the
frequency of the interference is an indispensable tool in hunting
interference.

Dave - W?LEV

On Fri, May 6, 2022 at 10:01 PM eyelessmisfit <eyelessmisfit@...>
wrote:

Maybe , if you rig an antenna of some kind, directional? But why not use a
radio or a tuned circui with detector or...? 73'sRon W0QVJ
-------- Original message --------From: Karel Gol <karelgol45@...>
Date: 5/6/22 10:56 AM (GMT-07:00) To: [email protected] Subject:
[nanovna-users] QRM searching? Can i use the nanoVNA to search for a QRM
source? As the simple person that i am, i am thinking about connecting an
antenna to S2 and trying to make something of the signal i'm getting. Does
the signal change when i walk around the neighbourhood, or when i point in
a specific direction etc... Is this possible and if so which format setting
should i use?

--
*Dave - W?LEV*
*Just Let Darwin Work*


--
Dave - W?LEV

Maybe , if you rig an antenna of some kind, directional? But why not use a radio or a tuned circui with detector or...??73'sRon W0QVJ

Hi Jim , some information was needed to try to help you.
Which version of firmware are you using now , and are you sure that the setup of the nanovna
in correct to do the TDR measure ? . the same setup used when the nano has measured the length correctly ?
Maurizio IZ1MDJ

I hooked up my nanoVNA to 100ft of Belden 9913 to measure length and it shows it's about 1 foot. I tried other cables and got the same thing. It worked in the past. The cables are good cables. Could this be a firmware issue?

Jim
KQ9I

The task you are describing is far better served by one of the following
options:

1) What you need is a spectrum analyzer, NOT a VNA. The TinySA is quite
affordable and capable for the purpose:

I believe most of the major amateur radio suppliers carry it. If not,
order from the supplier to assure it's genuine and not a clone.

2) Couple an SDR to a laptop running appropriate SW. The SW is free.
Either the AirSpy or SDRPlay are decent SDRs:


I know HRO carries the SDRPlay receivers. These are also quite reasonably
priced.

Dave - W?LEV

--
Dave - W?LEV