开云体育

For those wishing to wind their own baluns or even use/test commercial ones, the following may be of interest:

Performance of balun with/without center-tap

Fundamentals of rf transformers, includes various tests of such

Test configurations and circuits for testing baluns

Kind regards

Ed G8FAX

Hello Jim,

I already have small cores, but I am not convinced it was the right
material. but I will also try to rewind 1015 transformer, another DIY
project;-)
I like to test always few 'roads'...
By the way, it needs to be a unbalanced to balanced transformer, so on the
balanced side a centre tap.


Op ma 25 jul. 2022 om 21:31 schreef Jim Lux <jimlux@...>:

You'll not be rewinding that transformer. The assembly is 6 mm (1/4") on
a side, and it is "not user serviceable", in that the winding is probably
bonded to the core, the core is bonded into the tiny plastic package, etc.
And then, you don't know how many turns on each side. or the wire gauge
(other than "very small" - it's probably AWG40 or smaller)

The pictures of the transfomers look doable, I am sure I will need my
magnifying glass (say 4mm core).

I saw a few RF transformers of MCL:

Might but these also. Beside my own DIY.

You'd have a tough time beating the <$4 each that MiniCircuits wants for

something like an ADT1-6T.

Agree. But still, I want to have some fun also;-)

All the best,

Victor

Also remember that a 1/4-wavelength radiator over a "perfect" image plane
(a.k.a. "ground" plane) is not 50-ohms but more like 36 ohms. So, even at
resonance, defined by +jX = - jX, the SWR will not be 1:1.

Dave - W?LEV

On Mon, Jul 25, 2022 at 7:54 PM Greg Giglio <coffeeguy2@...>
wrote:

Generally, look for where the most pronounced ‘dip’ is relative to the
frequency you’re tuning for. It should be close to what you’re looking
for. If the lowest SWR is at a lower frequency than expected, shorten the
wire. If it’s at a higher frequency, lengthen the wire.

73 de KN7GIG

"Silence is golden. Duct tape is silver."

On Jul 25, 2022, at 14:33, DOUGLAS SEWELL via groups.io <douglassewell=

[email protected]> wrote:

?Using formula 234/freq for a 1/4 wave vertical with 4 radials I was

building gave me a wire length of 16 feet 6 and 1/8 inches. Nano vna gave
swr of 2.3 (too high for my qrp station) so tried to find out whether to
shorten or lengthen wire. How can I use the nano vna to help with the
direction to go. eventually lengthened by 6 inches which brought swr down
to 1.3.

As a newbe to short wave radio tx/rx and to nano vna can anyone help

with an easy to follow method to use my nano vna for wire adjustment
direction. Thanks but difficult just now after suffering 2 strokes so hence
the need for help here.

Thanks and 73 to all who read this.
Doug MM7DSA

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


--
Dave - W?LEV

Don't look at just SWR!! Look at the complex impedance R +/- jX. Look at
the sign of the complex term, the +/-jX. If it is negative, it is
capacitive and needs lengthening. If it is positive, it is inductive and
requires shortening.

Dave - W?LEV

On Mon, Jul 25, 2022 at 6:33 PM DOUGLAS SEWELL via groups.io <douglassewell=
[email protected]> wrote:

Using formula 234/freq for a 1/4 wave vertical with 4 radials I was
building gave me a wire length of 16 feet 6 and 1/8 inches. Nano vna gave
swr of 2.3 (too high for my qrp station) so tried to find out whether to
shorten or lengthen wire. How can I use the nano vna to help with the
direction to go. eventually lengthened by 6 inches which brought swr down
to 1.3.
As a newbe to short wave radio tx/rx and to nano vna can anyone help with
an easy to follow method to use my nano vna for wire adjustment direction.
Thanks but difficult just now after suffering 2 strokes so hence the need
for help here.
Thanks and 73 to all who read this.
Doug MM7DSA

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


--
Dave - W?LEV

On 7/25/22 11:23 AM, DOUGLAS SEWELL via groups.io wrote:

Using formula 234/freq for a 1/4 wave vertical with 4 radials I was building gave me a wire length of 16 feet 6 and 1/8 inches. Nano vna gave swr of 2.3 (too high for my qrp station) so tried to find out whether to shorten or lengthen wire. How can I use the nano vna to help with the direction to go. eventually lengthened by 6 inches which brought swr down to 1.3.
As a newbe to short wave radio tx/rx and to nano vna can anyone help with an easy to follow method to use my nano vna for wire adjustment direction. Thanks but difficult just now after suffering 2 strokes so hence the need for help here.
Thanks and 73 to all who read this.

Run the SWR vs frequency plot. Shortening moves the frequency ( at the minimum ) higher.

For a ground plane vertical, all the elements have an effect on resonant frequency and the depth of the SWR.

The length of the vertical and the radials all mostly affect the reactive part; where the reactance crosses zero is defined as resonance.

The "droop angle" mostly sets the "resistance" at resonance. A dipole (1/4 wave radials essentially straight down) has a resistance of around 70 ohms. If the radials point straight out (90 degrees) then the resistance is closer to a monopole over ground (35 ohms). Of course, changing the angle also changes the reactance.


This is where a VNA is fun.. you can build a model, hook it up, and change them both to see what happens.

I've had a lot of fun just building a dipole out of a stiff wire (e.g. AWG 12 bare wire) for something like 200 MHz. You bring the feed line up a support (like a stick or mic stand) with a RF toroid or two as a balun.

What I usually do is cut the wire long, then fold it back to shorten it.
But you can also do things like just make 90 degree bends (like a Moxon).

Bonjour Francois:

To your first point, your expanded expression in the seventh paragraph for gamma in terms of A,B, and Zo is mathematically correct.

But I will say it is not a form I have ever seen used, and while correct, I find, for my purposes, not particularly useful.

As far as the basic question on the fifth paragraph of your post, the question indeed is answered in the attachment. (For your convenience, I attach the link to Pilloud’s description, written en Francaise)

Typical steps in finding S11 from impedances follow below. But note finding S11 is typically one step along the way towards calculating VSWR and Reflection Coefficient.

General steps are:

1. Measure Zs = Rs + Zs.
Zs will be a vector in the form a + jb

2. Calculate ABS Zs = I Zs |
In terms of SQRT (Rs*Rs + Xs*Xs)

3. Calculate Impedance Phase
Angle Zs = arctan (Xs/Rs)

4. Note Zo

5. Calculate Gamma = (Zs-Zo)/(Zs +Zo)
in vector form using the Excel complex division feature, or by hand is so inclined.

6. The resultant vector will indeed also be in the form Gamma= a + jb

7. Gamma vector will have magnitude rho and Gamma angle, often called Theta, when converted to polar form using the same technique you used with impedance, above.

9. Note Gamma and S11 are the same, and are sometimes referred to as the Reflection Coefficient, a complex quantity, usually discussed in terms of rho and Theta.

8. Once all this is in hand, you can calculate
VSWR = ( 1+ Mag Gamma)/(1-Mag Gamma)

8 As noted above, Mag Gamma is referred to as rho, so VSWR = (1+rho)/(1-rho)

9. You can calculate Return Loss (RL)
using RL = -20 log(rho) in terms of dB.

You will find in this site various Excel-based programs that will allow you to derive Z from S11 and S21, as well as starting with Zs in the form Rs and Xs to derive Gamma and all the other parameters of interest.

My iPhone probably has means to express Gamma, rho, Theta in symbols but I’ve not yet found the appropriate app.

Study Pilloud. You have no excuse! It’s written in French





Ed McCann
AG6CX

Jim is 100% right!

Not worth "redoing" it, possibly not even possible. Not to say that when you are done you need to "weld" your wire to the soldering pad (SMD) in a way that will not get disconnected when you attempt to solder to your PCB :)

In the real spirit of DIY, I'd get a bit larger ferrite cores, a it thicker wire (AWG36 probably) and experiment with the ferrite material used, number of turns, geometry of windings, measure across the frequency range, and after a week of having fun go to Mouser and by a factory made one :)

Generally, look for where the most pronounced ‘dip’ is relative to the frequency you’re tuning for. It should be close to what you’re looking for. If the lowest SWR is at a lower frequency than expected, shorten the wire. If it’s at a higher frequency, lengthen the wire.

73 de KN7GIG

"Silence is golden. Duct tape is silver."

You'll not be rewinding that transformer. The assembly is 6 mm (1/4") on a side, and it is "not user serviceable", in that the winding is probably bonded to the core, the core is bonded into the tiny plastic package, etc. And then, you don't know how many turns on each side. or the wire gauge (other than "very small" - it's probably AWG40 or smaller)

I'd just buy a transformer with what you need. Or use it at 1.5:1 - if you're hooking it up to a VNA, it doesn't really matter, because you would be calibrating out the turns ratio in any case.

or buy some cores in a more practical size and wind your own. You'll need to make sure you get the right mix, and deal with the whole wire size, number of turns, how to put the windings on so the capacitance is well controlled. You'd have a tough time beating the <$4 each that MiniCircuits wants for something like an ADT1-6T.

Farnell (in UK), Newark, Digikey, Mouser all carry various mfrs of transformers - Murata, Johansen, Coilcraft, and Minicircuits are probably the most likely.

I added a python program to my toolbox that retrieves the S-parameter from NanoVNA-H and stores them either as S-parameter or Z-parameter in touchstone RI (real/imag) format. It would be easy to create also MA (magnitude/angle) format for Z-parameter.



Developed and tested on Linux, but should also work on Windows when you adapt the serial port name.

usage: nanovna_snp.py [-h] [-o [FILE]] [-p [PORT]] [--s2p] [-z]

optional arguments:
-h, --help show this help message and exit
-o [FILE], --out [FILE]
write output to FILE, default = sys.stdout
-p [PORT], --port [PORT]
connect to serial port PORT, default = /dev/ttyACM0
--s2p fetch also s21 parameter in addition to s11
-z, --format_z fetch s11 and calculate R +jX

Using formula 234/freq for a 1/4 wave vertical with 4 radials I was building gave me a wire length of 16 feet 6 and 1/8 inches. Nano vna gave swr of 2.3 (too high for my qrp station) so tried to find out whether to shorten or lengthen wire. How can I use the nano vna to help with the direction to go. eventually lengthened by 6 inches which brought swr down to 1.3.
As a newbe to short wave radio tx/rx and to nano vna can anyone help with an easy to follow method to use my nano vna for wire adjustment direction. Thanks but difficult just now after suffering 2 strokes so hence the need for help here.
Thanks and 73 to all who read this.
Doug MM7DSA

On Mon, Jul 25, 2022 at 07:14 PM, Jim Lux wrote:

So the tools tend to have their own sets of defaults (stored in an .ini or
setup file or equivalent).

`That's what I thought. Looked for a file, but no luck so far.

On 7/25/22 9:39 AM, Nick wrote:

Using nvna-s 0.3.9.
Why idoes nvna-s default to a sweep range of 1M to 100M when I connect to the device?
I have set the cal range to 100k to 50.1M on the device itself.
Where is the nvna-s default sweep range stored?

The NanoVNA doesn't have very good visibility into its internal state, i.e. the sweep range and other parameters. The software can send a sweep command to get the current sweep setup

sweep – sets the start/stop for the next automatic sweep, but you never know when that will happen or when that will be finished and issuing a pause command stops the automatic sweep (per QRP)
- Usage: sweep {start(Hz)} [stop] [points]
- If no inputs, then prints current setup eg: 300000000 500000000 101


but there's other things that are more difficult. So the tools tend to have their own sets of defaults (stored in an .ini or setup file or equivalent). NanoVNA-Saver also can do the nice thing of commanding the NanoVNA to make multiple sweeps over a subset of the range, so you can get 1000 points in a sweep, for instance.

If you have to rewind a transformer then you could just buy a core and completely build it...
Why not just buy a different one that directly fits your needs?!?
73 sigi dg9bfc

Am 25.07.2022 12:01 schrieb Ed G8FAX <ed@...>:

Using nvna-s 0.3.9.

Why does nvna-s default to a sweep range of 1M to 100M when I connect to the device?

I have set the cal range to 100k to 50.1M on the device itself.

Where is the nvna-s default sweep range stored?

I see the link is in his message.

Ed,

Thanks for that link! Do you have a link to the entire work?

Chuck Bland

Fran?ois,

Greek letters are everywhere, in Physics, Maths, Medicine &c. &c. In English there is a fairly uniform pronunciation () (apart from UK/US variation, which is minor.) In French, there seem to be two schools of thought as to how to name Greek letters. offers names close to those used in English, whereas offers different names and pronunciation. Zut alors! [English pronunciation is offered, e.g., at , but don't tell l'Académie!]

If it's any consolation, discovering how an E is pronounced in French is very confusing for a Brit!

? bient?t, 73,

Robin, G8DQX

Mini-circuits T1-1T-X65

Might be a fake, so might other items on ebay!

Kind regards

Ed, G8FAX

On Mon, Jul 25, 2022 at 01:57 AM, F1AMM wrote:

I was disappointed that Excel did not know how to draw a sequence of complex
numbers (a+jb) in the form of a graph. It is necessary to break down the real
part into the imaginary part. So I don't use these functions.

Hi Francois,

It seems you want in EXCEL to separate out the real and imaginary parts of a COMPLEX number.

You could use the functions IMREAL and IMAGINARY to do this.

and then make use of the other functions for working with complex numbers in Excel

There are also other Excel functions useful for working with complex numbers IMABS, IMARGUMENT & IMCONJUGATE

Kind regards

Ed