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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

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?

On Mon, 6 Jan 2020 at 00:42, Birdman <ccarrara@...> wrote:

.On eBay, I have had to BEG companies/sellers to accept a return, have to
pay the return. Shipping, often also a return fee, and I’ve had 5 or 10
instances over the last 15 years or so they just failed to accept a return
even though there add states they accept returns. The only re-course is
bad feedback, which is almost useless.

--
Regards,
Chris

EBay has a disputes procedure which I have used many times. Every time I
have used it, the case has been resolved to my satisfaction, with either

1) Return item at sellers cost for a full refund.
2) Agree a partial refund and keep the item
3) Receive a full refund and keep the item as the seller didn’t want to pay
the return shipping cost.

I have never returned anything I didn’t like. I have changed my mind about
something after paying and requested a refund, and have received it.

On one occasion I paid for something of low value then realised it was not
what I expected. I told the seller to keep the money and not to bother
sending it, which he did. I thought to myself afterwards, he could have at
least returned the carriage fee.

The only serious problem I had with ebay was when I items tracking was
shown as delivered, but it was not. eBay made me jump through endless
hoops, but I did eventually get my money back. The courier company had
closed the item was left in my back porch, but I don’t have a porch in the
back of the house.

I had an amusing incident where I ordered an expensive Agilent VNA
calibration kit and received a little tiger figurine. It was very easy to
prove I had the wrong item as the box it came in had the tracking number.
The box was much too small for the item ordered. I received a refund very
quickly. I later received an email from someone in Wales who had ordered a
helmet and received my calibration kit. There was a mixup at the eBay
global shipping centre

1) Lady ordered the tiger, but received a calendar
2) I ordered the calibration kit, but got her tiger
3) The guy in Wales ordered the helmet but got my calibration kit.

eBay gave us all refunds, but had no interest in allowing me to get the
tiger to the person who ordered it. They said keep it, throw it, or take it
to a charity shop. I eventually managed to find out the buyer, despite
little help from the seller or eBay. The end result was

1) I got the calibration kit free
2) The lady got her tiger and a calendar free
3) The guy in Wales got his money back, but no calendar. He also got a
drink from me as I appreciated his honesty. He could have easily seen it
was valuable and kept it, but he returned it to me.

So overall I have been happy with all eBay outcomes, but sometimes I had to
jump through quite a few hoops.

Dave

--

Dr. David Kirkby,
Kirkby Microwave Ltd,
drkirkby@...

Telephone 01621-680100./ +44 1621 680100

Registered in England & Wales, company number 08914892.
Registered office:
Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United
Kingdom

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.

Aha! There is so "matching" if there is a network involving reactive components,
regardless of the designer's intent for the operating frequency.

Also, if the cable between the DUT's output and the VNA is problem-free, it doesn't
matter which end of that cable gets the attenuator.

Anyway, I, too, suspect that the amplifier is oscillating. A check with a spectrum
analyzer or a wide range tunable receiver should settle that question pretty
quickly.

The wiki at /g/nanovna-users/wiki/jog_switch has a link to OEM multi-directional switch

This is why I reflashed my Acer chromebook with GalliumOS. Since it's a Linux distro, it isn't dependent on talking to the Internet to function. I still have a newer ASUS Chromebook that does everything I want it to (I don't use it for radio), so I didn't reflash that one. The Acer is an older 11" model, but it runs GalliumOS (which is optimized for Chromebooks) just great.

73,
Gwen, NG3P

HI Chris,
The Smith Chart is a plot of the reflection coefficient, gamma. Gamma is a ratio as follows: The voltage across the transmission line due to the reflected wave divided by the voltage across the transmission line due to the incident wave or Vref/Vfwd. AND very important, the phase angle between these voltages at a particular point on the transmission line locates where the point is on the chart. Gamma is a number that can be from 0 to 1.0. The angle can be zero to 360 degrees but is plotted as an angle between 0 and +180 deg or -180 deg (360 degrees around the chart). Now, plotted on the Smith Chart are circles of resistance and reactance that correspond to each possible gamma and its phase angle. When an antenna is connected to the far end of the transmission line and its Z is not equal to the transmission line's characteristic impedance (the SWR is >1) and the energy that is not absorbed by the antenna and radiated, returns as the reflected wave. Going along the transmission line back to the source this reflected wave meets the forward wave with all of the possible phase angles between them. Therefore at each point the impedance is described by the intersection (coordinates) of the resistance and reactance circles. The point is the impedance is changing depending on where you are on the transmission line with respect to where the antenna is. I know this is a lot to try and explain in one paragraph:)
The Rig expert analyzer and others can mathematically rotate around the chart so you can see what the Z is at each point.

The attenuator should be placed at the output of the amplifier, not the
input of the VNA. Output attenuation is a technique used to assure an
amplifier remains stable throughout its gain/bandwidth product or gain
slope and stabilizes the match to the following stage. Of course, this
attenuator will reduce the measured value of S21 by the attenuation
amount. It's purpose is to stablize the amplifier. - maybe a bit like loss
matching.

Dave - W?LEV

--

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

S21 is likely peaked due to the self resonance of the inductor in the
drain/collector.

--

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

I got so curious that I had to test a 10dB attenuator as David Eckhardt suggested even it is late here. The gain went down 10dB which is good I think, nothing changed much. I noticed that S11 is almost normal but noisy below 200-300Mhz, so I quess this is some kind of feedback. BF199 is not made for 200MHz or more. And the attenuator is next to VNA and there is some 30cm of coaxial between that and the amplifier, so it is not so effective taming the circuit.

To
Dana Whitlow. I build this some time ago and now I noticed that there are two capacitors 22pF and 68pF from collector to ground and output is between them. I wish I could remember what coil inductance was.

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

I evolved from Mickey Mouse "tails" to Donald Duck bill:

Looks *much* better! Now, for results?

Oh, I'm lately working at < 10 MHz and am satisfied to get with 10% of
expectations.
I wish nanoVNA worked at < 10 kHz..

Wow! I'd say that S11 is not the only strange thing here.
For example, why is S21 so peaked?

When you say "no matching" does this mean that the input
is applied directly to the base (or gate) and that the output
is taken directly from the collector (or drain), with no tuned
networks or anything like that?

Could you perhaps supply a schematic?

Dana

Looks *much* better! Now, for results?

Dave - W ?LEV

--

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

For flying wires and alligator clips to work, everything must be in the *exact
same position* as when the calibration was done

I evolved from Mickey Mouse "tails" to Donald Duck bill:

Thanks I will.

There are several SMA board edge connectors on Ebay. There are models for 1.6mm and 1mm thicknessess. And of course normal models for soldering into board.

it looks like oscillation. Connect the output of the amplifier to the VNA
through a 6 or 10 dB attenuator and have another look at s11.

Dave - W?LEV

--

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

This is probably not NanoVNA specific.
I made a quick and simple amplifier of leaded BF199 and some passive components. Collector is via a coil I happened to have. There is no matching. Input is calibrated with a 20dB attenuator.
Gain is 23dB but S11 looks strange in a Smith chart. Is this oscillation or just feedback from output.