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Re: coax loss

 

I am in no way an expert, but if you connect your cable between CH0 and CH1, you will see the loss (or gain) at every frequency. You have to calibrate your VNA fully first .
Re: RF Demo Kit Testing tutorial released

 

On Thu, Jan 9, 2020 at 11:18 AM, <reuterr@...> wrote:

Comparing with your screen shot of *Test field 8* I assume,
that you did not made a *Calibration* with the RF Demo Kit *Test fields
13-15*.
Hello Rudi,

I have made it. I can redo the measurement with the FA5, but as I told you, we tested it with the Rohode&Schwarz with calibrating and the results are comarable.
Re: A strange S11 from a amplifier #circuit #tutorials #general_vna

 

I post this if anyone is interested. 80MHz seems to be quite a lot for this kind of construction and transistor.
I put some aluminium tape on input side parts. Perhaps it made the S11 plot a little cleaner. Below 200-300Mhz the S11 is still not very smooth. (ragged I think is a good word for it.)
I attached schematic and new results from VnaSaver. I took a photo of the amplifier, but the whole thing is so untidy I leave it off.

withshield.png
rfkoe2.pdf
rfkoe2.pdf

coax loss

 

Hi all,how do i measure the loss on a long run of coax using the nanovna,ive about a 60ft run i want to check at hf,cheers .
Re: nanovna that continues to indicate 50 ohms when S11 is open

 

Check all your cal loads to make sure they have the correct impedance.
Re: nanovna that continues to indicate 50 ohms when S11 is open

 

Yes, I have also done a reset before calibration
Re: NanoVNA-Web-Client, problem with Chromebook

 

From hwalker: "The issue with Chromebooks has been that with the latest Chrome update you can connect the NanoVNA with the web based application, but not off-line using the Google Play Store android application."

Ah... Got it. I have not heard good things about the Chromebook implementation of Android apps - slow, buggy, &c...
Re: First PCB pictures of the V2

Brian Ray
 

¡°Crosstalk between microstrips¡± ¡ª one trick used by at least one up-market spectrum analysers is to put small ¡°bridges¡± of ferrite, across the microstrip. These are equivalent to the ferrite beads put onto thin coax and will attenuate signals flowing on the outside of the microstrip. The exact ferrite is not critical providing it has loss at GHz. I have also experienced the problem where a ¡°well-designed¡± amplifier stage becomes unstable when put into a metal box. The eigenvalues of a box with a few holes and one side made from the PCB are difficult to calculate. The overall stability is even more difficult to calculate. (Was said to be impossible by the lecturer in my undergraduate course.) The simple solution - take an old medium wave radio and extract the ferrite rod from the aerial coil. Glue it, or a part of it, to the inside of the box, well clear of the microwave components. These ferrites are very lossy at even VHF, never mind GHz. If I use a metal box for RF screening I always ask myself the question ¡°where does RF energy, radiated by the components and microstrips, ends up?¡±

Brian 5B4AHW

On 9 Jan 2020, at 11:13, Gabriel Tenma White <OwOwOwOwO123@...> wrote:

Tried a TCM1-63AX (had these in stock), it gave really strange S11 graphs and not good directivity. Might investigate it further.

Crosstalk between microstrips or grounded CPW is low in theory, but my experience is it turns to crap as soon as you have nearby metal objects to reflect the radiated signals, or put the board in a metal enclosure. The LCD is mounted right above the PCB so the whole thing forms a nice waveguide for leakage to travel. The remaining bits of leakage seen in the pictures is still due to radiation (maybe not the SMA connectors but shield can leakage) because I can affect it by putting my hand near the board. Past designs didn't achieve good system dynamic range even with shield cans because of the remaining leakage from the SMA connector center pin, so switching to this style of connector (and having the connector footprint in the shield can) was the only way to fix it.

The receiver linearity is important because nonlinearity causes errors that can't be removed by calibration. For example the IAM-81008 mixer has P1dB(in) of -15dBm and IP3(in) of -6dBm, but if you operate at -25dBm (which is 10dB below compression) your third order error power is -6 - (-6 - -25)*3 = -63dBm, which is 38dB below the signal. That's a EVM (error vector magnitude) of 1.25% which is just on the edge of being acceptable. Nonlinearity doesn't just generate harmonics, it also causes amplitude/phase error in the fundamental signal. The rule of thumb is at least 20dB below IP3, and also at least 10dB below P1dB. The way to check for linearity error is to measure a short length of low loss coax (after calibration) and check that it circles the smith chart as expected. I think there was a thread here that showed errors in the current Nano in this setup because of the low IP3 mixer (SA612) used. I'll try the BGA616 for the gain block which has good enough IP3 and P1dB.

I've done FPGA based VNAs before at a different company and I find it much easier to deal with than a microcontroller. All timings are deterministic, and you can coordinate things to happen at cycle accurate times with respect to the reference clock. Spartan 6 starts at $4, so as soon as the required MCU gets close to that price I'd just switch to the FPGA :) Optimal IF frequency is somewhere between 1 to 5 MHz (based on ADF435x noise skirt).

I'd like to see your coupler design; can you post the title of your paper?
Re: First PCB pictures of the V2

 

The intent is nice but you will not get good calibration using the internal RF switch to do open/short/load/input switching.
Re: nanovna that continues to indicate 50 ohms when S11 is open

 

Did you apply RESET prior to CAL. Sounds like a faulty CAL.
Re: Experimental test fixture

 

Take a measure at 1 MHz. Also, the L value should tend to a larger value as F increases and eventually go parallel resonate on the first loop.
Re: Measuring resonance from coax far end.

 

Hi Pete,

thank you for your interest in this.

My European coax cable type "Aircell 7" is not common in the USA. So it was not listed within SimSmith's coax table.

In my case length measuring was easy. I even used and compared two methods:

1. By normal length measuring of the cable. That - in this case - was easy, as the coax cable was mostly accessible(except some house entering feed through)
laying on the ground in the garden.
2. For comparison - I also did this:
In my shack I had a sample of exactly the same coax from the very roll I had cut the antenna feed cable from.
I determined the length of this sample, too, by normal length measuring.

Then I measured by TDR measurement both lengths again with my AA-600's TDR function using in TDR an assumed VF = 1.
Comparing the length results of the two methods made me find the cable Vf (as well as electrical and mechanical length of my cables).

In SimSmith I used Vf and length as determined above, and I entered these in the simple cable model. The attenuation I did not measure (as I actually should have ), but I used the manufacturer's specs instead.

This was my first such antenne impedance determination from the rig side end in the shack.
The result was satisfactory, but I think, my accuracy could have been improved by exact attenuation
measurement instead of just using manufacturer's specs.

But in principle, that worked quite nicely. Never before was I able to know my vertical 40m endfed dipole's impedance over frequency.
Now I have a good antenna feedpoint .s1p file.

There are no exact endfed data available. In my special case the antenna hangs in a birch tree, that drinks many buckets of water each day.
Further, as indicated in the video, interrupting the stub match for measurement would have changed the total system and would have made
results useless. So the impedance at the dipole end was uncertain, until I did the easy rig end measurement and used SimSmith,
as explained in the video.

My vertical with it's all new stub match adjustment profile used is further described in the attached powerpoint presentation verticals.ppt .
The profile was used for stub length and distance determination by easy adjustment of the two length without any coax cut-and-try over and over again.

73, Hans
DJ7BA




-----Urspr¨¹ngliche Nachricht-----
Von: [email protected] <[email protected]> Im Auftrag von WB2UAQ
Gesendet: Donnerstag, 9. Januar 2020 01:43
An: [email protected]
Betreff: Re: [nanovna-users] Measuring resonance from coax far end.

Hans
Your suggestion would work if you know how long the transmission line is in wavelengths. How can you simply measure the impedance at the shack end and know if the impedance you measured is due to the antenna's impedance or the rotation around constant SWR circle? Another way to look at it is, you measure the Z at the rig end and plot this point on the Smith Chart. Now to find the antenna's Z, you rotate around the chart by the electrical length between the rig end and the antenna (towards the load). Another way to do it is to measure the Z at the rig end and use a program such as TLW (comes with the ARRL Ant Book) to calculate the antennas Z BUT again you need to know the electrical length of the transmission line (or if you know transmission line type and it is in TLW's library of cables, you can enter the physical length). 73, Pete, WB2UAQ

verticals.ppt
verticals.ppt

Re: Experimental test fixture

 

Just for fun, I went on Mouser to look for "high frequency" leaded inductors. The only manufacturer they list for such products is Vishay, who has a model TR021 with inductances from 0.022 uH, tested at 50 MHz, to 1500 uH, tested at 0.25 MHz.
Experimental test fixture

 

In the attached image is a picture of the fixture I rigged up for testing leaded components. The two sma connectors are soldered in to the copper on a piece of single side pcb. The center tine of the fork is ground, a piece of center conductor soldered directly to the copper. For calibration of S11, I have used bits of lead cut off from various projects: a pair of unconnected leads (open), two bits soldered together (short), and a pair of 100 ohm resistors (not wire-wound) soldered in parallel for the load, connected between ch0 and the ground tine.

The Smith chart for a toroid inductor (20 turns on a T50-6), with the Nano calibrated from 5 MHz to 8MHz, shows inductance varying from 1.82 uH at 5MHz to 1.18 uH at 8 MHz.

The nominal inductance for 20 turns on a T50-6, for the 40 meter band (7 MHz, more or less) is 1.70 uH. So, the inductance I am reading on the Nano is consistent with this nominal value. I am new at this, so please correct me if I am misunderstanding.

The Smith chart for a commercial 100uH inductor shows an open circuit. From my reading around this forum, this is consistent with the notion that commercial producers of leaded components are targeting lower frequency applications, and that use of such products at higher frequencies is inadvisable - that is, that at higher frequencies this commercial inductor does, indeed, behave as an open circuit.

IMG_20200108_163719.jpg

Re: First PCB pictures of the V2

[email protected]
 

The power inverter, microcontroller, USB and display are already RF sources.
BlueTooth should energize only between sweeps.
These are not intentional sources, just some weak unintended radiation.
Bluetooth has a *real transmitter* at 2.4 GHz, where the new nano is likely to be used.
Besides slowing down the measurement, the other side of the link does not know when "between sweeps" is.

Marko Cebokli
nanovna that continues to indicate 50 ohms when S11 is open

 

I have a nanovna that continues to indicate 50 ohms when S11 is open. Only if I short-circuit the input will this change. I already calibrated it. But this did not help. Can I do something about this or is it just damaged.
Re: First PCB pictures of the V2

GmailK4KV
 

I can confirm that carbonized foam is quite effective at UHF and above...

73

Glen K4KV

On 1/9/2020 04:57, Slawek wrote:
On Thu, Jan 9, 2020 at 01:13 AM, Gabriel Tenma White wrote:

Crosstalk between microstrips or grounded CPW is low in theory, but my
experience is it turns to crap as soon as you have nearby metal objects to
reflect the radiated signals, or put the board in a metal enclosure. The LCD
is mounted right above the PCB so the whole thing forms a nice waveguide for
leakage to travel.
Hi Gabriel,
I found that simple ESD foam acts as quite good EMI absorber, give it a try and insert some of it between/above the cans.

I've done FPGA based VNAs before at a different company and I find it much
easier to deal with than a microcontroller. All timings are deterministic, and
you can coordinate things to happen at cycle accurate times with respect to
the reference clock. Spartan 6 starts at $4, so as soon as the required MCU
gets close to that price I'd just switch to the FPGA :) Optimal IF frequency
is somewhere between 1 to 5 MHz (based on ADF435x noise skirt).
what type of ADC do you plan to use?
Re: NanoVNA-Web-Client, problem with Chromebook

 

Hi Gwen -

The Acer is an older 11" model, but it runs GalliumOS (which is optimized for
Chromebooks) just great.
Do you use nanovna-saver with GalliumOS?
While you provided the pointer to in an earlier message,
are there URLs you can recommend for hints, tips and tricks to support migration?

Their Wiki looks OK:
but hyperlinks to multiple other pages for substeps imply more opportunities for missteps than with Chrome OS..
Re: RF Demo Kit Testing tutorial released

 

On Thu, Jan 9, 2020 at 09:50 AM, Klaus W?rner wrote:

I've screenshotted the Number 8 and 10 of the new version (serial LC and L):
The capacitive parts at the bottom are good, but the top side isn't it. The
measurement with the professional equipment are similar.
Hello Klaus,

Thank you very much for providing the screen shots.
I have made two measurements with *Test field 8*.

1. In Test field 8 the inductor looks like to have nominal 470 nH.
If you accept a tolerance of +/- 10 % = 423 - 517 nH,
the usable frequency range is measured to 3.4 - 126 MHz.
Above 394 MHz the inductor becomes capacitive.
See nanoVNA-Saver diagram: RF-Demo-Kit_8-470nH_Saver.png

2. A comparable measurement with the semi-professional FA-VA5 and VNWA software.
If you accept a tolerance of +/- 10 % = 423 - 517 nH,
the usable frequency range is measured to 1 - 128 MHz.
Above 375 MHz the inductor becomes capacitive.
See VNWA diagram: RF-Demo-Kit_8-470nH_VNWA-VA5.png

In my understanding both diagrams show *comparable results*.

Comparing with your screen shot of *Test field 8* I assume,
that you did not made a *Calibration* with the RF Demo Kit *Test fields 13-15*.

73, Rudi DL5FA

RF-Demo-Kit_8-470nH_Saver.png
RF-Demo-Kit_8-470nH_VNWA-VA5.png

Re: First PCB pictures of the V2

 

On Thu, Jan 9, 2020 at 01:13 AM, Gabriel Tenma White wrote:


Crosstalk between microstrips or grounded CPW is low in theory, but my
experience is it turns to crap as soon as you have nearby metal objects to
reflect the radiated signals, or put the board in a metal enclosure. The LCD
is mounted right above the PCB so the whole thing forms a nice waveguide for
leakage to travel.
Hi Gabriel,
I found that simple ESD foam acts as quite good EMI absorber, give it a try and insert some of it between/above the cans.

I've done FPGA based VNAs before at a different company and I find it much
easier to deal with than a microcontroller. All timings are deterministic, and
you can coordinate things to happen at cycle accurate times with respect to
the reference clock. Spartan 6 starts at $4, so as soon as the required MCU
gets close to that price I'd just switch to the FPGA :) Optimal IF frequency
is somewhere between 1 to 5 MHz (based on ADF435x noise skirt).
what type of ADC do you plan to use?


--
Regards,

Slawek/SP9BSL
30481 - 30500 of 39696