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Cracked it at last using Nano vna. Analysis shows cut length of 16feet and 6 inches is too long as resonates at 13.198MHz and not my target of 14.175. Reverse maths gives a constant of 218 (resonant frequency of 13.918 X antenna length of 16.5feet. When this is applied to required frequency of 14.175 a wire length of 15 feet and 4 inches results. A cut of 14 inches off the original gave me a perfect swr of 1.1.
Thanks guys for all your answers and help. Have learned a lot about checking swr with my Nano vna especially moving the start and end points just outside the full band (my case 20m) with 11,000 as start and 14.500 as end to see exact point of lowest swr. Extremely useful. Now working qrp with confidence that most of my signal is getting into the air.
72 (or is it 72 for qrp) to you all.

On 7/28/22 8:01 AM, N0YWB wrote:

The formula (feet)=234/MHz for a quarter wavelength is just a rough starting point.
The resonant length is affected by many variables, like conductor diameter and
the placement of nearby conductors within 2 wavelengths, including other antennas and the earth.
It usually comes down to:
measure in place, then take down and adjust length. Repeat.

Or use a tuner at the feedpoint. Small changes in resonant frequency (10%) are easily tuned out with minimal loss. Even with a feedline, and tuner at the radio end, the losses are small.

The formula (feet)=234/MHz for a quarter wavelength is just a rough starting point.

The resonant length is affected by many variables, like conductor diameter and
the placement of nearby conductors within 2 wavelengths, including other antennas and the earth.

It usually comes down to:
measure in place, then take down and adjust length. Repeat.

See the effect of height above earth (roof ground plane) for vertical and horizontal antennas
in figure 1 of chapter 3 of the ARRL antenna book.





--
N0YWB

On 7/27/22 10:25 PM, F1AMM wrote:

Since I switched to nanovna-saver 0.3.10 -win7 the display time of the "console" window remains displayed for 12 seconds. Previously with version 0.3.8 it was only 3 seconds.
It really is a great product.
I don't know anything about Python; I have never done development in Python. From what I understand, Python is an interpreted language well not really that interpreted.
Python*.* I have a multitude of them on my disk:
12723 files
941 directories
537 MB
I think that's a lot. For example I see 28 python38.dll files in directories like _MEI00000

This can be a problem...

Some installers are less than smart, and copy all the files into a new directory each time, add that directory to the path that python searches, and then that longer path gets searched every time something runs.

You really should have just *one* python38.dll for instance.

It is possible to set things up so you have distinct python environments for different applications/uses (for instance, I have an environment for Python 2.7, and for Python 3.8, for testing purposes). But I'm assuming that for NanoVNA-Saver that's not what you're looking for.

I'd go take a look at the PATH environment variable and see if the same directory appears multiple times.

If you would take your existing board and use a sharp knife to remove the excess copper you might get a better result, or at least see what changes occur. Trimming the connector pins back will also help reduce THEIR capacitance, as will using minimum solder on the pins.

Of course matching the dielectric constant/height/width to the connector dimensions is the ideal solution. I would do this before going out and fabbing another batch of boards with the same thin dielectric. Thicker boards lalso have larger features so are proportionately less sensitive to mechanical tolerances. The transmission line calculators are accurate, problems with unexpected results are almost always a result of poor layout rather than calculation errors. Trying to compensate by tweaking dimensions instead of making a better layout will not end well, I have been there.

An S11 of -20dB or better is a good result for a length of microstrip or CPWG line plus two connectors/transitions, although I have seen better than -30dB.
The S21 that you are getting where the S11 is good should be achievable across the band, if you get the match fairly good; much of the loss you are seeing is reflection loss due to mismatch, not dissipative loss.
73, Don N2VGU

Hi

Thanks a lot for your responses.

Jim, I was not aware that Er would potentially drop significantly by frequency. I will check if data exists for Er vs frequency. Thanks.

Donald, good point on the trace width at the connector pins. I have used the recommended footprint from Molex, but I do see the issue that the pad is part of the trace and does not satisfy the trace width that I calculated. Thanks.

I will order a range of test boards with different trace widths and ground gaps to see if I can get closer.

Do any of you have an idea to what a target S11 / S21 should be for such as trace?

br
Christian

Since I switched to nanovna-saver 0.3.10 -win7 the display time of the "console" window remains displayed for 12 seconds. Previously with version 0.3.8 it was only 3 seconds.

It really is a great product.

I don't know anything about Python; I have never done development in Python. From what I understand, Python is an interpreted language well not really that interpreted.

Python*.* I have a multitude of them on my disk:
12723 files
941 directories
537 MB

I think that's a lot. For example I see 28 python38.dll files in directories like _MEI00000
--
F1AMM (Fran?ois)

I think the startup delay has a lot to do with what version of windows you
are using.
Mine used to start up fast like that, 3sec or so - but after the latest
Saver update, which happened to coincide with a win10 update, mine takes
forever to start up, but then operates fine. I didn't make other startup
config changes, so it's not likely that in my case. I haven't yet tried to
investigate the delay, since I can just leave it up after starting it.
Stan

On Wed, Jul 27, 2022 at 7:31 PM Charlie N2MHS via groups.io <ucfargis1=
[email protected]> wrote:

Mine starts goes to DOS window and then windows window in under 3
seconds.Add some laser oil to your dilithium crystals.....or how much stuff
is in your process table

On Wednesday, July 27, 2022 at 09:59:22 PM EDT, Glen Jenkins WB4KTF <
wb4ktf@...> wrote:

I had not waited long enough, it did take a while and did pop up and run
successfully.
Thanks to all who replied.
-----
Glen Jenkins, WB4KTF, Austin, TX

Sounds like you have a lot of overhead background running, or slow/low resources, or both. Mine launches within a few seconds of the DOS terminal.

Stephen W9SK

Mine starts goes to DOS window and then windows window in under 3 seconds.Add some laser oil to your dilithium crystals.....or how much stuff is in your process table

I had not waited long enough, it did take a while and did pop up and run successfully.
Thanks to all who replied.
-----
Glen Jenkins, WB4KTF, Austin, TX

On 7/27/22 5:25 PM, Donald S Brant Jr wrote:

At a glance I noticed the wide traces at the connector pins, which are excess capacitance. Unless there is a compelling reason to do otherwise I tend to select a dielectric material whose 50Ω width is slightly larger than the connector pins and component pads I plan on using. It is only necessary to use thin boards such as you are using for very high frequency (>20+GHz perhaps), work, to avoid resonances and radiation. 0.8mm board (or thicker) might be more appropriate.

As I recall, 50 ohms on 1 ounce copper on an 0.031" board with epsilon=2.5 as microstripline was 0.1" wide. There's countless calculators out there. If you pick the board correctly, a 4 pin SMA solders on very nicely. (the gap between corner pin and center pin is about 1 mm, which is close to 0.039")

I also like to pull the solder mask away from the RF traces ideally 2 line widths wide, again to avoid excess capacitance; solder mask has a higher dielectric constant than air. This excess capacitance is particularly problematic in the gaps between RF line and ground of your .
I like to chamfer the corners of the transmission lines and leave a small gap at the connector pin, again to avoid excess capacitance.
Finally, many board houses charge per hole drilled ("hits") and if so, you can drastically reduce the number of vias to a single line on each side of the RF line, with a cluster of vias, or better yet, wraparound grounds (could be copper foil added at assembly), for the connector grounds.
Best regards, Don Brant.

ONLY if you test that coupon at 2,400,000,000 Hz!
Testing with the typical C Meter won't do it!?? The usual standard is 1000 Hz.

The Er changes with frequency when you get in the MHz.and up.?? Kent

Copper-clad steel and woven copper (with a plastic covering or not) are other good choices for antenna wire. People have even used aluminum electric fence wire and horse fence wire with some success.
73, Don N2VGU

At a glance I noticed the wide traces at the connector pins, which are excess capacitance. Unless there is a compelling reason to do otherwise I tend to select a dielectric material whose 50Ω width is slightly larger than the connector pins and component pads I plan on using. It is only necessary to use thin boards such as you are using for very high frequency (>20+GHz perhaps), work, to avoid resonances and radiation. 0.8mm board (or thicker) might be more appropriate.

I also like to pull the solder mask away from the RF traces ideally 2 line widths wide, again to avoid excess capacitance; solder mask has a higher dielectric constant than air. This excess capacitance is particularly problematic in the gaps between RF line and ground of your .

I like to chamfer the corners of the transmission lines and leave a small gap at the connector pin, again to avoid excess capacitance.

Finally, many board houses charge per hole drilled ("hits") and if so, you can drastically reduce the number of vias to a single line on each side of the RF line, with a cluster of vias, or better yet, wraparound grounds (could be copper foil added at assembly), for the connector grounds.

Best regards, Don Brant.

Especially the long waiting time is where many users think its not working...
Yes it takes a loooong while :-)
Dg9bfc sigi

Am 28.07.2022 00:05 schrieb Stan Dye <standye@...>:

On 7/27/22 9:18 AM, KENT BRITAIN wrote:

Hi Christian
I do lots of antennas on fiberglass PC Board, and typically the published Er value was measured at 1 kHz,
At 2.4 GHz, Er is going to be in the 3.7-3.8 range.? You can check their spec sheets for Er vs frequency plots, but that data is not commonly provided.

Most people do a test coupon, which is essentially what you're doing.

You have to pay BIG Bucks for PCB material that has little change with frequency.

Rogers Duroid(tm) is an example. It also has low loss at microwave frequencies - the issue is the glass in FR-4. Taconic is another brand. You can get them with epsilon all the way from 2 to 10.

For the record, you have not been able to buy FR-4 for some years.? It contained a Bromide Anti-Flammability compound that was banned by RoHS.??? Yea, lots of similar stuff on the market with slightly different part numbers.

Most fab houses still offer FR4


Note the epsilon they give for the various mfrs (3.2 to 3.92)

whether they are brominated, I don't know - there's lots of materials that can make something fire retardant. I don't know that bromine is as much a concern as lead, which is where RoHS gets to be a big deal.




has more info. Polybrominated biphenyls aren't allowed in RoHS, but that might not be a common problem. There are "FR-4 halogen free" materials too.

Best way to measure the Er at 2.4 GHz, bit out of the range for most Nano's, is to design a patch antenna for 2.4 GHz and see what frequency is really resonates at.? Then back into the calculations for a patch antenna using Er's that give you the actual frequency.?? Kent
On Wednesday, July 27, 2022 at 10:49:19 AM CDT, steiniche@... <steiniche@...> wrote:
Hi
I have a NanoVNA V2 Plus4.
I am trying to validate a PCB 50 ohm transmission line (trace) to be used for 2.4 GHz Wifi.
I am using a 4 layer stack-up (1.6 mm total) with the following configuration:
L1: Signal + ground pour
Prepreg 0.21 mm
L2: Ground
Prepreg 1 mm
L3: Empty
Prepreg 0.21 mm
L4: Ground
Board is FR-4 with Er = 4.6.
I have calculated the trace parameters using Saturn PCB design as a "coplanar wave" with a plane below.
I have attached 6 board files showing the actual board (board_image.jpg), rendered board (board_render.png) and the four layers (board_lx.png) + a screenshot of the calculations from Saturn PCB (calc.png). I use the following connectors from Molex:
I have calibrated the VNA in frequency range 2 GHz to 2.8 GHz with the provided SMA cable connected, see attached cal_load.jpg and cal_thru.jpg, direct_load.png, direct_thru.png
Now I connect the PCB trace and do a S11 and S21 measurement (see s11_s21.jpg). It seems to me that the result is not particularly good (see trace_thru.png and trace_load.png).
Can any of you spot any issues with the measurement method or configuration of the board? Also, if you can provide some realistic target results for such a configuration (two connectors + 82 mm trace) that would be great.
Any help is highly appreciated.
Thanks
br
Christian

Mine goes blank for a short while and then opens ?

The best is Copperweld wire which is a steel wire with heavy copper plating. You get the strength and low cost of steel with the electrical conductivity and corrosion resistance of copper.

SherpaDoug, WA1UWP

I watched the video of how that calculator works and it is a mechanical
nightmare. Yes it surely is a different kind of calculator, but God help
you if for some reason it quit calculating correctly.

Fred - N4CLA

On Wed, Jul 27, 2022 at 5:43 PM Donald S Brant Jr <dsbrantjr@...>
wrote:

Those Curta calculators were the bomb for rally drivers in the '70s, but a
bit rich (they still are) for my budget. The designer came up with the
idea while he was in a WWII concentration camp IIRC.
73, Don N2VGU.