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Good day. I'm fairly new to both amateur radio and this marvelous device, the NanoVNA H4 v4.3 sold by Seesii on Amazon.ca
I find tuning my many inverted V antennas using a manual tuner extremely effective using this Nanovna -- set to s11 on 3 parameters for logmag, Smith and SWR traces.

My question is: for some tuning, I often show a very low SWR (<1:1.05) with a logmag reading of -15 or thereabouts, and another tune showing about the same SWR but a logmag of -40, -50 or even -90 dB. The logmag trace sometimes appearing as a very steep and deep notch, often at or in the SWR trace and other times just a shallow dip. The Smith typically shows a fairly consistent 50 ohms plus or minus 1 or 2 at tuned resonance. Is this a representation of reflected loss and VSWR being shown real time side by side? Is it better to have a logmag reading of -90 dB let's say, as well as a very low SWR -- vs very low SWR and a "higher" logmag of -20dB for instance?

I sincerely hope I'm expressing myself sensibly...
--
- Dave
-VA7WNW-

On Sun, Jul 17, 2022 at 01:17 PM, <cariboome@...> wrote:

My question is: for some tuning, I often show a very low SWR (<1:1.05) with a
logmag reading of -15 or thereabouts, and another tune showing about the same
SWR but a logmag of -40, -50 or even -90 dB. The logmag trace sometimes
appearing as a very steep and deep notch, often at or in the SWR trace and
other times just a shallow dip. The Smith typically shows a fairly consistent
50 ohms plus or minus 1 or 2 at tuned resonance. Is this a representation of
reflected loss and VSWR being shown real time side by side? Is it better to
have a logmag reading of -90 dB let's say, as well as a very low SWR -- vs
very low SWR and a "higher" logmag of -20dB for instance?

Yes side-by-side as you put it.. The NanoVNA is calculating all the parameters (SWR, Return Loss (logmag format) and impedance (R, X) from the same scanned measurements. If your return loss is 14 dB you have a VSWR of about 1.5 which is fine for most purposes. If your SWR is higher than this modern solid state transmitters tend to cut back on their power output. A VSWR of 1.1 is a RL of 26 dB and that is excellent. Here is a link to a table of VSWR vs Return Loss. It also shows the reflected and through power. You should also be aware that Return Loss is a positive number but many publications use a negative sign which is not correct but done anyway. Yes confusing but the way it is...



Roger

Yes side-by-side as you put it. The NanoVNA is calculating all the parameters (SWR,
Return Loss (logmag format) and impedance (R, X) from the same scanned measurements.

Hello

I saw and verified that we can recalculate all the parameters from S11. Can you explain to me :
- What is the native measurement performed at the bridge level
- What is the first parameter produced by the nanoVNA from this native measurement
--
Fran?ois

-----Message d'origine-----

De la part de Roger Need via

Envoyé : dimanche 17 juillet 2022 22:33

My quick notes about used foumulas in NanoVNA

For reference a LogMag reading of -14dB is the same as a VSWR of 1.5:1.
Any logmag reading less than -14dB is better and better. If you get a
logmag reading of -20dB then you are in very good shape. Several external
things can change the resulting logmag such as ground conductivity, height
of the horizontal leg of the antenna above ground, or proximity of the
vertical part of the antenna to nearby objects, and the number of ground
radials.

There is one telltale measurement that can point to the difference. Masure
the feed point impedance. The closer the impedance is to 50 ohms the lower,
the more negative, the LogMag reading. The impedance will be impacted by
the number of radials and ground conductivity.

The logmag is the return loss in dB. EXAMPLE if the forward power is 100
watts, +30dBw, and the reflected power is +10dB, 1 watt, then the return
loss, i.e logmag, will be -20dB.

Hope this helps,



*Clyde K. Spencer*

Hi Clyde,

Reading your message, may I correct your example?
I.m.o. +30 dbW -> 1000 Watt and +10dB*W* -> 10 Watt

-Kees, PE0CWK

Op 18-7-2022 om 14:53 schreef Clyde Spencer:

Thank you all. I've attached images of some early readings made with the NanoVNA as I explored. It's an extremely valuable tool. I'm pleased to confirm I am using it correctly. The traces I was getting looked, to my ignorant eyes, too good to be true! But it is true: my first two attempts at antenna making are wildly successful!

--
-VA7WNW-

Thanks, you are right. My fingers were writing in dbW but my mind was
working with dBm.

Thanks,
*Clyde K. Spencer*



On Mon, Jul 18, 2022 at 9:58 AM PE0CWK via groups.io <pe0cwk=
[email protected]> wrote:

Hi Clyde,

Reading your message, may I correct your example?
I.m.o. +30 dbW -> 1000 Watt and +10dB*W* -> 10 Watt

-Kees, PE0CWK

Op 18-7-2022 om 14:53 schreef Clyde Spencer:

For reference a LogMag reading of -14dB is the same as a VSWR of 1.5:1.
Any logmag reading less than -14dB is better and better. If you get a
logmag reading of -20dB then you are in very good shape. Several external
things can change the resulting logmag such as ground conductivity,

height

of the horizontal leg of the antenna above ground, or proximity of the
vertical part of the antenna to nearby objects, and the number of ground
radials.

There is one telltale measurement that can point to the difference.

Masure

the feed point impedance. The closer the impedance is to 50 ohms the

lower,

the more negative, the LogMag reading. The impedance will be impacted by
the number of radials and ground conductivity.

The logmag is the return loss in dB. EXAMPLE if the forward power is 100
watts, +30dBw, and the reflected power is +10dB, 1 watt, then the return
loss, i.e logmag, will be -20dB.

Hope this helps,



*Clyde K. Spencer*



On Sun, Jul 17, 2022 at 4:17 PM<cariboome@...> wrote:

Good day. I'm fairly new to both amateur radio and this marvelous

device,

the NanoVNA H4 v4.3 sold by Seesii on Amazon.ca
I find tuning my many inverted V antennas using a manual tuner extremely
effective using this Nanovna -- set to s11 on 3 parameters for logmag,
Smith and SWR traces.

My question is: for some tuning, I often show a very low SWR (<1:1.05)
with a logmag reading of -15 or thereabouts, and another tune showing

about

the same SWR but a logmag of -40, -50 or even -90 dB. The logmag trace
sometimes appearing as a very steep and deep notch, often at or in the

SWR

trace and other times just a shallow dip. The Smith typically shows a
fairly consistent 50 ohms plus or minus 1 or 2 at tuned resonance. Is

this

a representation of reflected loss and VSWR being shown real time side

by

side? Is it better to have a logmag reading of -90 dB let's say, as

well as

a very low SWR -- vs very low SWR and a "higher" logmag of -20dB for
instance?

I sincerely hope I'm expressing myself sensibly...
--
- Dave
-VA7WNW-