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Have built a magnetic antenna for the 80meter band as shown on my homepage .
As the antenna has an excellen high Q (bandwidth aro 9kHz) it shows a sharp dip in S11 return loss.
To integrate the analyzer I removed the battery, supplied 5V through USB and bridged the ON/OFF switch
set in OFF position with an external relais contact.
Found out that the 5V have to be present before switching to ON or closing the relais contacts, otherwise
the unit won*t start at all. It then draws about 110mA of supply current. (An empty batterie would increase
the current to beyond 700mA, that's why I removed the battery)

The instrument setting is fix and saved to SAVE0, so it starts always with this setting.
See the picture.

Anyone having good advices or ideas for this application, or already done something similar?

Great would be an extended marker feature to direct display the frequency of the dip in S11.
--
Arno DK3SS

Hi Arno,
a good idea! In My EU1KY analyzer I have implemented a function to automatically search the frequency with the best SWR, or the minimal S11.
For the makers of the nanoVNA software this is no problem.
A good improvement.
Best regards,
73, Wolfgang, DH1AKF

Hi Arno,

I visited your page. Very nice construction on the mag loop. I see 20 to 30 dB return loss, between the VNA on the web page and the new unit in the photo. Quite well done. I have a few questions.

Do you switch the VNA out during transmit? I assume your loop is used in the Tx mode? How do you protect the VNA input? What power are you running? Are you using a relay to switch around the VNA for protection?

Finally, the radiation R of the loop vs. its loss. Curious about the mag loop antenna efficiency.

On your question... any ideas for an application. I saw a cute photo that Larry Goga sent me. He posts on this forum. He took one of the classic antenna tuners and I assume did a photo shop mod of the front panel. He removed the cross needle forward and reverse power indicators and replaced that meter movement with a VNA in the S11 mode. So in essence the old SWR meter indicator could now be afforded a VNA display. Auto tuning the S11 marker to the lowest point in the SWR curve would be a nice firmware update.

Thanks! 73' Alan W4AMV

Hi Alan,

yes I use a SPDT relais to switch either the TX to the loop, or the VNA to the loop an the TX is offline in this case. When the relais gets
its 12V DC, this is the source supply for the VNA as well (regulates down to 5V with a 7805 regulator ic. It can be seen in the bloc diagram as well.
Typical TX-power ist the full 100W.
With some efforts in EMI suppression the unit withstands the fieldstrength, not running wild. I could tune under full power.

Have put a lot of effort in reduction of any avoidable losses, thus the high Q ist the benefit.
The use of extreme low loss capacitors helps a lot (the 300pF comes from China with outstanding performence)
(the 3600pF capacitor is made in Germany with glimmer dielectric).


Have testet the loop in several QSOs around Europe as listet in my homepage and found it*s a good working antenna anyway. The theory of calculating effciency
gives no more than 1%, but my testing brought up a reasonable performence anyway.
Many hams uses dipoles or W3DZZ-antennas with our european narrow spaces and in most cases these wires are hung up much too low,
thus loosing a lot of efficieny either. So it makes sense to compare what comes out in reality.

With the gamma-match I use, it is no problem to achieve over 30dB return loss.

I used some good old test equipment to develop this antenna, a vector voltmeter ZPV from Rohde&Schwarz and as Network Analyzer a hp8713B,
the foto with the green CRT ist taken from it..

Some extra features like remote control via WiFi to tune up or down the resonance freuency,or switching on and off the nanoVNA with the antenna
relais are implemented right now, some more ideas I still have aren*t yet.
A lot of fun for a retired engineer!

I relize a lot of reads of my homepage since I posted this topic. May be I have to make an english version of it in near future.

best 73s

Hi Wolfgang,
the search for freqency with best SWR and printing it on the display or via I2C to an external LCD would be great to have.
As I'm not a maker of software for the nanooVNA or the used STM32F072C-MCU I've to wait for someone doing it.

best 73s de DK3SS Arno

Hi all,
a special use case of this analyzer would be an automatic antenna tuner for magnetic loops.
The software had to read the operating frequency, and to calculate, if more ore less capacitor is necessary.
A good and easy to handle task for the programmers!
best 73, Wolfgang, DH1AKF

Hi
I used the following approach with my mag loops.
Capacitor is driven by a stepper motor controlled remotely (Arduino + Nrf24l01 module)
When I decide to have a QSO session, I first run a calibration.
I move automatically from begin to end of the relevant band by small steps and each time measure the resonance frequ (S11 dip)
At the end I get an x,y table where x are the resonance frequencies, and y the corresponding stepper positions.
I then compute the table to obtain the function stepper pos= f(frequency) (Polynomial interpolation)
All above is carried out automatically (Python script running on a headless Raspberry PI including a Web Interface)
In this way I can move very fast within the band without having to tune each time.
(frequency is read via CAT interface and stepper is then moved to the new position)
Currently developing a solution for the Ciro Mazzoni loop which is driven by a linear piston.
Positioning of the piston will be done by means of a fix rotary encoder (600 counts/360°) driven by a small 3d printed rack.....
Will soon share some pictures!
73 de HB9IIU

This is how I am driving the Mag loop

Following up on this thread 6 months later. Does anyone know if there has been any firmware development performed on a function to track the lowest SWR for the nanoVNA?

John - W3JED

I'm not sure exactly what you want, but my NanoVNA H4 can find the minimum
value for SWR or s11, whichever is selected. Choose "Marker" > "Search" >
"Minimum" and then "Search Left" or "Search Right."

I did this with my 4 band (40-20-15-10 meters) vertical antenna. I chose
5.0 to 30.0 MHz as the range. I was impressed. The display matches what my
RigExpert AA-600 displays. The routine I listed above would go right to the
dips. I found that my antenna also has minor dips around 9 and 25 MHz.

73, Zack W9SZ


On Thu, Jun 18, 2020 at 8:37 PM John Dusek <johndusek3@...> wrote:

Following up on this thread 6 months later. Does anyone know if there has
been any firmware development performed on a function to track the lowest
SWR for the nanoVNA?

John - W3JED

<>
Virus-free.
www.avast.com
<>
<#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>

Hi Zack -

What I am trying to do is tune a magnetic loop antenna and have the nanoVNA actively track the single lowest
SWR across the range as I tune the loop antenna, that would continuously show me where the antenna is currently tuned as I adjust it towards the frequency I want.

Does the Search Left/Search Right function actively keep rescanning for lowest dips, or is a single scan manually executed each time?

John

That's a good question! I was using it on a fixed antenna, that wasn't
being adjusted. I'll play around with it and see if it follows something
that is being tuned.

73, Zack W9SZ

On Sat, Jun 20, 2020 at 3:00 PM John Dusek <johndusek3@...> wrote:

Hi Zack -

What I am trying to do is tune a magnetic loop antenna and have the
nanoVNA actively track the single lowest
SWR across the range as I tune the loop antenna, that would continuously
show me where the antenna is currently tuned as I adjust it towards the
frequency I want.

Does the Search Left/Search Right function actively keep rescanning for
lowest dips, or is a single scan manually executed each time?

John




-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of Zack Widup
Sent: Friday, June 19, 2020 8:31 AM
To: [email protected]
Subject: Re: [nanovna-users] Integration of a nanoVNA unit into an antenna
system as indicator of resonance frequency

I'm not sure exactly what you want, but my NanoVNA H4 can find the minimum
value for SWR or s11, whichever is selected. Choose "Marker" > "Search" >
"Minimum" and then "Search Left" or "Search Right."

I did this with my 4 band (40-20-15-10 meters) vertical antenna. I chose
5.0 to 30.0 MHz as the range. I was impressed. The display matches what my
RigExpert AA-600 displays. The routine I listed above would go right to the
dips. I found that my antenna also has minor dips around 9 and 25 MHz.

73, Zack W9SZ


On Thu, Jun 18, 2020 at 8:37 PM John Dusek <johndusek3@...> wrote:

Following up on this thread 6 months later. Does anyone know if there
has been any firmware development performed on a function to track the
lowest SWR for the nanoVNA?

John - W3JED

<

Virus-free.
www.avast.com
<

<#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>

<>
Virus-free.
www.avast.com
<>
<#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>

I found a solution to my initial need.

The NanoVNA Saver software dynamically displays exactly what I was looking for - the current lowest SWR for the continuously swept range ("S11 Min VSWR").

This will allow me to tune my (yet to be delivered) magnetic loop antenna to the frequency I desire by watching the S11 Min VSWR value until it matches or is close to the frequency I want to transmit on my radio.

Now if I could only have that dynamic Min VSWR value displayed in its own small pop-up window for screen real estate reasons :-) , but don't look a gift-horse in the mouth, the NanoVNA Saver software is incredible in its features and really makes the device much more usable.