开云体育

Roger,

Thanks for confirming my suspicion...I guess this also implies that the WSPR spot counts/pattern might also be different between the two configurations, since the shield/chassis would be playing a slightly different role in the two cases (?).

Bruce

Bruce,

Your plots will be different because the common mode current (and therefore feedline radiation) will be different. Your friend is using a transformer as a voltage balun. With a good current balun the difference would not be so great because equal current would be going into each leg and reversing the connections would not make that much difference.

Roger

(forgot to attach these two SWR plots to the previous post)

A ham friend has an unusual indoor antenna that he uses with a Zachtek WSPR transmitter. He gets lots of spots from the 200mW transmitter (>500 unique band/spotter combinations in 24 hours), and the beauty of the Zachtek is its tolerance of essentially any antenna load (from nothing attached to fully shorted). His antenna is effectively an off center fed dipole, where the two wire legs wrap around the inside bedroom walls, and are of random/different lengths..i.e .just whatever would fit onto the four walls. The two dipole legs are connected to a simple 6:4 turn ratio transformer (approx. 2:25:1 impedance ratio), with the primary side of the transformer attached to a 4 ft coax feedline line to the Zachtek transmitter.

I decided to make some measurements of the SWR with the nanoVNA attached to this "creative" antenna setup. The nanoVNA was OSL-calibrated, followed by attaching the antenna feedline to collect data in nanovnasaver software. After collecting the data, I decided to reverse the two dipole legs connected to the transformer secondary, just to make sure I was getting reproducible data. What confused me were significant differences in the SWR/return loss/Smith charts for the two configurations. I am wondering if this simply reflects how non-balanced the dipole is, such that the coax feedline shield (about 4 ft long) from the transformer plays a different role in each of the two configurations. While making the measurements the nanoVNA was dangling hands free while connected to the USB port on my laptop...so the coax shield side would be the same in both cases...and the only electrical difference was in reversing the dipole legs (of differing lengths) connected to the transformer secondary.

Nico,

After reviewing the data sheet that you posted earlier I see that Linx does offer customer support for this antenna. They state that they can supply PCB layout files and recommend matching network components. Since they are the designers of the antenna I suggest that you contact them and have them review your layout and see if they have any testing and matching network suggestions for you. Let us know how it works out for you with this project.

Roger

This is what it looks like when I reset the calibration.

Can you send an uncalibrated image?

I confirmed that short/open/load standards are measuring as they should at the terminals on the pcb board.

I bought the unit from R&L on Oct. 31, 2024.

I did an ohm reading between blocking capacitor on the circuit side CH0 port terminal and ground, as described in this blog post (), and my reading was 10.3k ohms. According to the blog post this is what the reading should be and possibly my MXD8641 is not blown.

If you buy from RANDL, we can provide you with after-sales service.
But since we have discontinued the SAA2N for a long time, RANDL may not have the stock to replace it for you.
This is usually caused by a damaged RF switch on port1, if you can you can try to replace it yourself, model number MXD8641.

The make up is one thing were the clones come in is the software and firmware that you cant make work or upgrade.
________________________________
From: [email protected] <[email protected]> on behalf of Siegfried Jackstien via groups.io <siegfried.jackstien@...>
Sent: Sunday, March 16, 2025 6:29 PM
To: [email protected] <[email protected]>
Subject: Re: [nanovna-users] Erratic traces with SAA2N

they claim ALL (except their own) as clones ...

but they are all "brothers and sisters", cousins .. ... etc etc

they all are made quite similar in circuit design

dg9bfc sigi

Am 15.03.2025 um 11:33 schrieb K3IY via groups.io:

I got an email response from NanoRFE support with some concerning information. They suggested that the hardware version of my SAA2N "is a clone" and many users have reported issues with it. I was puzzled because I did my research (or at least I thought I did), and all sources online said there's enough bad clones out there and if you're in the US avoid this by buying from R&L electronics. NanoRFE support pointed me to their website which has a listed of suppliers selling clones. To my surprise R&L electronics is on that list and they're noted to "keep selling clones despite not being asked to by the original developers". If this is indeed true I am very disappointed in R&L and will be giving them a call to discuss a possible resolution.

they claim ALL (except their own) as clones ...

but they are all "brothers and sisters", cousins ..? ... etc etc

they all are made quite similar in circuit design

dg9bfc sigi

Am 15.03.2025 um 11:33 schrieb K3IY via groups.io:

maybe the case is pressing on the touch screen? ... or the screen cable is not well fitted

did you try to connect it to pc (example nanovna app)??

dg9bfc sigi

Am 16.03.2025 um 23:31 schrieb Taracait via groups.io:

Sorry, it is indeed -H; but not '4'

I'll try with differeny connection - thanks!

Battery is fine, 3.7VDC; checked at the unit PCB.

And the screen is lighting up (white), so power isw not the problem

If I get you correctly, that is the "skin" current that gets radiated from
the antenna as pure RF ? If so, that remaining common mode current is
reflected back at the source and then "recombine" at the connector to be
read as "raised noise" or reflected power ? Can I see it this way ?

RF energy that is intended to be radiated from the antenna all reduces as
fields inside the coax. Fields between:

1) The inner surface of the outer shield, and

2) The outer surface of the center conductor.

The internal fields carry the RF power.

What is referred to as the common mode current travels on the outside
surface of the outer shield.

If I'm still correct, then the 2-3 turns around the ferrite will "trap"
this third wire current and give me a more accurate reading ?

A few turns through the toroid will not "trap" RF energy on the outer
surface of the shield, but it will prevent energy from the antenna inducing
current on the outer surface of the shield. As such, your coax will become
isolated from the assembly. Of course, there will be no effect on fields
internal to the coax. There will be a small amount of "trapping" due to
losses in the ferrite. Some ferrites are designed specifically for loss.

In the last test I did, I had wrapped one ferrite at each end of the cable
for 2 turns. When I put my hands on coax, I could see that I got almost no
" hand touching" effect on the VNA. Well, I want to thank you for this
advice because it really helped me.

Your result is just what we were striving for. There is little or no
interaction between the assembly/antenna and the outer surface of the
shield. Excellent!

Now, here are the inductors and capacitors I bought.

Wurth Electronics 0603 RF inductor designer's ket


RF and microwave 0603 capacitor kit


Excellent!

As for all the previous test I made in the last few days, each and every
time I tried to add a matching inductor and/or capacitor, it did not
helped. My measurement got to the other side of the spectrum. This leads me
to think that as exactly as you pointed out, my measurement accuracy is
distorted.

With a few turns through your toroids at each end of the coax, the impact
of the matching network may become more observable and not disturbed by
grabbing the coax.

I'll make some other testing with my smaller ferrite with 3 turns instead
of 2 as close as I can to the insertion point and get back to you with some
results.

I don't know much I can thank you enough for all the time you take helping
me out. It is truly appreciated.

Just glad to help and apply what I've learned over some 60+ years to help
others.

Dave - W?LEV


On Sun, Mar 16, 2025 at 6:17?PM Nico via groups.io <nicolassimard=
[email protected]> wrote:

@Roger And @Dave,

If I get you correctly, that is the "skin" current that gets radiated from
the antenna as pure RF ? If so, that remaining common mode current is
reflected back at the source and then "recombine" at the connector to be
read as "raised noise" or reflected power ? Can I see it this way ?

If I'm still correct, then the 2-3 turns around the ferrite will "trap"
this third wire current and give me a more accurate reading ?

In the last test I did, I had wrapped one ferrite at each end of the cable
for 2 turns. When I put my hands on coax, I could see that I got almost no
" hand touching" effect on the VNA. Well, I want to thank you for this
advice because it really helped me.

Now, here are the inductors and capacitors I bought.

Wurth Electronics 0603 RF inductor designer's ket



RF and microwave 0603 capacitor kit



As for all the previous test I made in the last few days, each and every
time I tried to add a matching inductor and/or capacitor, it did not
helped. My measurement got to the other side of the spectrum. This leads me
to think that as exactly as you pointed out, my measurement accuracy is
distorted.

I'll make some other testing with my smaller ferrite with 3 turns instead
of 2 as close as I can to the insertion point and get back to you with some
results.

I don't know much I can thank you enough for all the time you take helping
me out. It is truly appreciated.

Nic

--

*Dave - W?LEV*


--
Dave - W?LEV

@Roger And @Dave,

If I get you correctly, that is the "skin" current that gets radiated from the antenna as pure RF ? If so, that remaining common mode current is reflected back at the source and then "recombine" at the connector to be read as "raised noise" or reflected power ? Can I see it this way ?

If I'm still correct, then the 2-3 turns around the ferrite will "trap" this third wire current and give me a more accurate reading ?

In the last test I did, I had wrapped one ferrite at each end of the cable for 2 turns. When I put my hands on coax, I could see that I got almost no " hand touching" effect on the VNA. Well, I want to thank you for this advice because it really helped me.

Now, here are the inductors and capacitors I bought.

Wurth Electronics 0603 RF inductor designer's ket


RF and microwave 0603 capacitor kit


As for all the previous test I made in the last few days, each and every time I tried to add a matching inductor and/or capacitor, it did not helped. My measurement got to the other side of the spectrum. This leads me to think that as exactly as you pointed out, my measurement accuracy is distorted.

I'll make some other testing with my smaller ferrite with 3 turns instead of 2 as close as I can to the insertion point and get back to you with some results.

I don't know much I can thank you enough for all the time you take helping me out. It is truly appreciated.

Nic

This will download the updated S-parameter plotting program:



I was surprised to discover that the final Touchstone 1.1 file specification provides for multiple, real-valued reference impedances. The plotting program will handle these files.

The maximum reference impedance is 9999 ohms. This seems reasonable given VNA accuracy limitations for high impedances. Some interesting devices are beyond this limit (e.g., 27k ohms for Collins mechanical filters). Shunt capacitance can go to 9999 pF.

The program is not intended to replace NanoVNA-Saver or NanoVNA-App. It provides a convenient way to display all S-parameters, including S12 and S22, and to use the full set for reference impedance renormalization. It handles a different reference impedance for each port, with or without shunt capacitance. No need to build a special, impedance-matching test fixture to measure a filter with nonstandard, unequal impedances. The program provides the stray-cancelling Y21 series-through impedance measurement as well as the usual S21 and S11 series and shunt methods.

Brian

Thanks Brian,
That link worked OK
73,
Geoff

I seem to have gotten everything working. The plots show a 280 kHz Murata ceramic filter with an 82 pF load on its output. The dB and group delay curves are similar to those published by Murata for a 230 kHz filter.

I spent a lot of time looking for bugs when I noticed that S12 > 1 for some capacitive loads. I finally found two references that explained how this was possible for a passive device for a complex port reference impedance. It does not indicate a violation of conservation of energy as it would for a real reference impedance. I am using pseudo-wave analysis instead of the older power-wave analysis. They yield identical results for real reference impedances, but only pseudo-wave can handle complex impedances.

I'm going to spend some time checking for bugs as I changed a lot of code. I'll post a message when the new version is available.

Brian