I realize this hardware is not made for this and results will be poor but I want to give it a shot anyway. New user of the H4 version. Looking to get some idea of signal strength of some local FM and TV stations. I tried setting the start and stop freq for the FM band and looking at logmag of S21 and got nothing - just an almost flat line near the bottom of the screen. Thinking I am missing a few settings. I have searched and read some but haven't found a complete list of settings needed. If I need to do this as some smaller freq bands I could do that.

It really is the wrong hardware for that. Get a TinySA. I have one of the
original TinySA's plus a TinySA Ultra (which goes up to at least 10 GHz). I
got my NanoVNA and both TinySA's from R & L Electronics. Fast shipping.

Zack W9SZ

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On Mon, Dec 2, 2024 at 8:11 AM jskinner58 via groups.io <jskinner58=
sbcglobal.net@groups.io> wrote:

I realize this hardware is not made for this and results will be poor but
I want to give it a shot anyway. New user of the H4 version. Looking to
get some idea of signal strength of some local FM and TV stations. I tried
setting the start and stop freq for the FM band and looking at logmag of
S21 and got nothing - just an almost flat line near the bottom of the
screen. Thinking I am missing a few settings. I have searched and read
some but haven't found a complete list of settings needed. If I need to do
this as some smaller freq bands I could do that.

This is exactly the response I was thinking I might avoid by stating I was aware of limitations. If I really need a SA I will borrow one from work. Interested in what this hardware can do.

Clever idea - the RBW is a few kHz, and it’s not particularly sensitive (i.e. somewhere between -10 and 0 dBm is S21 of 0). Noise floor is around -80 dB (on S21 log mag), so you’d need -60 dBm into the receiver to see anything.
I’m not sure a TV or FM station would have that much power in a 5 kHz BW. TV is spread over 5-6 MHz. Say an EIRP of 1 MW at 100 MHz 10 km away = +90 dBm -32.44 - 40 - 20 = about 0dBm, and the RBW is about -30dB of the signal BW. So you would see that. But 10 km is pretty close (which is why nobody in Pasadena needs a TV antenna - a paper clip in the antenna connector is plenty). And 100 MHz is the middle of the FM band, where EIRPs aren’t 1 MW, like they are for TV.

I note that when I was running two NanoVNAs back to back with a SMA T (to try making full 4 parameter measurements at one time), you could see the other NanoVNA sweep across the receiver occasionally (a big spike in apparent S21), if they were both sweeping.

A few years ago, I have tried to use my VNA-H as a spectrum analyzer. For sure there are many design ands hardware caveats dealing to limited relevant results. However, below are some interesting results that I have got. Sorry parts of comments on pictures are in french. Port 2 is used as input with 0 dBm max level

Large span measurements on a SINGLE signal source (CW) are possible, but results about relative levels are false. The reason is the amplitude-frequency response provided by the VNA is driven by the calibration corrections values (THRU). Here is the same signal (50 MHz) displayed on an Ultra SA and the NanoVNA-H. There is a difference of 23 dB on the harmonic 2 part.

01 and 02 pictures

Small span measurements provide confusing results for several reasons : low IF values (here 12,5 kHz) dealing to a false product (mirroring), and also spectrum aliasing according to span range value. Here is the same 10 MHz CW signal displayed on the NanoVNA-H with changing only the span range ! Totally unusable ...

03 and 04 pictures

The only relevant measurements that I got is in using the NanoVNA-H as a "modulation analyzer" for AM and FM (narrow bandwidth). Span range value is 10 kHz in order to avoid the previous artifacts.

- AM : relative sideband level measurement : AM rate 30% (picture 05), AM rate 100% (picture 06)

- FM : Bessel Null method (first zero) : AF=1 kHz, deviation = +/- 2,5 kHz, no null (picture 07) AF=1 kHz, deviation = +/- 2,4 kHz, perfect null (picture 08)

Comparing the previous results to a real modulation analyzer (Racal Dana) proved to be relevant.

Jean-Roger

There may be a way to use the NaoVNA as a spectrum analyzer, but I don't
think you can get an absolute measurement of the signal strengths like you
can with the TinySA. You can get relative measurements, comparing the
strengths of two signals. But I would not trust it to indicate a desired
value like "+6 dBm" with accuracy.

73, Zack W9SZ

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On Mon, Dec 2, 2024 at 9:40 AM Jim Lux via groups.io <jimlux=
earthlink.net@groups.io> wrote:

Clever idea - the RBW is a few kHz, and it’s not particularly sensitive
(i.e. somewhere between -10 and 0 dBm is S21 of 0). Noise floor is around
-80 dB (on S21 log mag), so you’d need -60 dBm into the receiver to see
anything.
I’m not sure a TV or FM station would have that much power in a 5 kHz BW.
TV is spread over 5-6 MHz. Say an EIRP of 1 MW at 100 MHz 10 km away = +90
dBm -32.44 - 40 - 20 = about 0dBm, and the RBW is about -30dB of the signal
BW. So you would see that. But 10 km is pretty close (which is why nobody
in Pasadena needs a TV antenna - a paper clip in the antenna connector is
plenty). And 100 MHz is the middle of the FM band, where EIRPs aren’t 1 MW,
like they are for TV.

I note that when I was running two NanoVNAs back to back with a SMA T (to
try making full 4 parameter measurements at one time), you could see the
other NanoVNA sweep across the receiver occasionally (a big spike in
apparent S21), if they were both sweeping.

On Dec 2, 2024, at 06:11, jskinner58@... wrote:

I realize this hardware is not made for this and results will be poor

but I want to give it a shot anyway. New user of the H4 version. Looking
to get some idea of signal strength of some local FM and TV stations. I
tried setting the start and stop freq for the FM band and looking at logmag
of S21 and got nothing - just an almost flat line near the bottom of the
screen. Thinking I am missing a few settings. I have searched and read
some but haven't found a complete list of settings needed. If I need to do
this as some smaller freq bands I could do that.

Again...... The proper instrument to use for the stated purpose is a
spectrum analyzer, not a VNA!

Spend the small amount of $$ and get yourself a TingSA.

Dave - WØLEV

On Tue, Dec 3, 2024 at 4:45 PM Zack Widup via groups.io <w9sz.zack=
gmail.com@groups.io> wrote:

There may be a way to use the NaoVNA as a spectrum analyzer, but I don't
think you can get an absolute measurement of the signal strengths like you
can with the TinySA. You can get relative measurements, comparing the
strengths of two signals. But I would not trust it to indicate a desired
value like "+6 dBm" with accuracy.

73, Zack W9SZ

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On Mon, Dec 2, 2024 at 9:40 AM Jim Lux via groups.io <jimlux=
earthlink.net@groups.io> wrote:

Clever idea - the RBW is a few kHz, and it’s not particularly sensitive
(i.e. somewhere between -10 and 0 dBm is S21 of 0). Noise floor is

around

-80 dB (on S21 log mag), so you’d need -60 dBm into the receiver to see
anything.
I’m not sure a TV or FM station would have that much power in a 5 kHz BW.
TV is spread over 5-6 MHz. Say an EIRP of 1 MW at 100 MHz 10 km away =

+90

dBm -32.44 - 40 - 20 = about 0dBm, and the RBW is about -30dB of the

signal

BW. So you would see that. But 10 km is pretty close (which is why

nobody

in Pasadena needs a TV antenna - a paper clip in the antenna connector is
plenty). And 100 MHz is the middle of the FM band, where EIRPs aren’t 1

MW,

like they are for TV.

I note that when I was running two NanoVNAs back to back with a SMA T (to
try making full 4 parameter measurements at one time), you could see the
other NanoVNA sweep across the receiver occasionally (a big spike in
apparent S21), if they were both sweeping.

On Dec 2, 2024, at 06:11, jskinner58@... wrote:

I realize this hardware is not made for this and results will be poor

but I want to give it a shot anyway. New user of the H4 version.

Looking

to get some idea of signal strength of some local FM and TV stations. I
tried setting the start and stop freq for the FM band and looking at

logmag

of S21 and got nothing - just an almost flat line near the bottom of the
screen. Thinking I am missing a few settings. I have searched and read
some but haven't found a complete list of settings needed. If I need to

do

this as some smaller freq bands I could do that.

--

*Dave - WØLEV*


--
Dave - WØLEV

You have more patience than I do with the ongoing answers to the question you did not ask. (Sheesh guys, he has said several times he is aware !

The NanoVNA is not able to make accurate, repeatable level measurements on the S21 port for any signals other than CW. The reason for this is all power from the signal being measured must fit inside one of the "bins" in order for the value to be correct.

FM broadcast signals in the US occupy 150 kHz. If, during the measurement, all 150 kHz of the signal just happen to fall inside one of the "bins" then that particular power measurement can be accurate. This is why CW can be measured and FM/AM/TV cannot.

When the signal spreads beyond one bin then you would see multiple signals with varying amplitudes that are different with each VNA sweep.

On the other hand, level measurements of CW signals are stable, and as accurate as your calibration allows. Measurements of CW signals down to about -80 dBm are accurate and repeatable.

Warren Allgyer - WA8TOD

Figured out the problem without the VNA. Turned out I have a 50kW FM station a bit less than 5 miles away overloading my tuner. An FM band trap solved the problem. In a forum for the tuner someone suggested doing a scan with it set to cable rather than over the air channels which included the FM band and they were able to see the FM strong station - a case of hardware not really made for the job but doing it well enough to see the issue.

On an unrelated side note, if u get the tiny SA, get the 4" version. It will do TX IMD tests....IE: 2 tone...and measure IMD3-5-7 etc. It will also display local AM / FM broadcast stations here in town.