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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.

On Wed, Jan 8, 2020 at 03:22 PM, Brian wrote:

" .. I am not yet convinced that series inductance of the capacitor leads explains why I measure 26pF more at 28MHz. .."
=========================================
Even with a perfect fixture the capacitive reactance of a capacitor will decrease as the frequency across its plates increases. Therefore, the measured value is going to change in inverse to the frequency and not remain the same. How accurately the NanoVNA, or any other VNA, can measure the change will depend on the test fixture you use and how accurately you calibrate out its effects.

- Herb

A RF measuring instrument works much better withouta built-in QRM source!

The power inverter, microcontroller, USB and display are already RF sources.
BlueTooth should energize only between sweeps.

Thanks all for the comments. I am not yet convinced that series inductance of the capacitor leads explains why I measure 26pF more at 28MHz. The 100pF was connected with minimal lead length so I wouldn't expect 60 to 80 nH stray inductance.
I agree that at low frequencies it measures the same as my LC meter.
I think Dave Eckhardt is correct and the answer to the original question is that the test fixture must be pretty rigid and stable even at 30MHz. At 300MHz you need something really good to accurately measure components. Ideally matched to 50 ohms all the way to the component.
Thanks Brian.

On Tue, 7 Jan 2020 at 22:17, John Ackermann N8UR <jra@...> wrote:

Gary, just a guess (I'm not a VNA designer) but it might be because it's
easier to design and characterize an "absolute" (open or short) with
nominally infinite impedance than something that needs to match some
arbitrary value. And how would you choose the arbitrary values?
Different users have different requirements.

I think, but am not sure, that using arbitrary values also would prevent
any pretense at corrected measurements beyond those arbitrary values.
When your limits are infinity, nothing stands in your way. :-)

73,
John

You can certainly perform a calibration with arbitrary values - all the
electronic calibration units do this - they can't generate anywhere near
perfect opens and shorts using electronic switches.

Best accuracy occurs when the standards are as different as possible. In
principle, you could calibrate with 1.0, 1.0001 and 1.00002 ohms. But such
a calibration would be very unstable. The open and short have the greatest
phase difference that it is possible to make.

They are also the easiest to characterise, as you can determine their
properties from physical measurements and EM simulation, whereas you can't
do that with resistors or capacitors.

You can also calibrate with three shorts or three opens if you want. I have
done it with 3 shorts myself, but it not suitable for use over a wide range
of frequencies. If you look at the attached PDF, of a 110 GHz Keysight
85059A calibration and verification kit, you will see the opens and loads
are only rated for use to 50 GHz. Between 50 and 110 GHz, you use multiple
shorts. There are 4 different ones in the kit.

Dave

On Wed, 8 Jan 2020 at 22:32, <reuterr@...> wrote:

Hello Dave,

I agree to your statement, if the RF Test Kit is used for an university
course.

73, Rudi DL5FA

I personally don't think they will last long in the hands of a ham trying
to learn, or demonstrate it to others.

I rather suspect that sooner or later someone will produce something
similar with SMA connectors, and then nobody in their right mind would buy
a U.FL connector version.

Dave

Hello Dave,

I agree to your statement, if the RF Test Kit is used for an university course.

73, Rudi DL5FA

On Wed, 8 Jan 2020 at 21:45, n5kzw <n5kzw@...> wrote:

That tool looks like it would take all of 5 minutes to make. - Ed

Yes, but it does not solve the problem that a completely inappropriate
connector is used.

I also ordered from Alibaba via a message on hugens store, and paid via Paypal on 12/30/19. I received today 1/8/20 via DHL. Well packaged, VERY nice unit (much better than the junk one I received from fleabay!), with the new PCB and software. Goes to 1.5g. Of course the package had 2 shorts, 1 load and no open for the calibration parts, but I can live with that since I already have an open I can use.

I'm no expert. but it's very clear right out of the box this unit is much better than the previous unit I got (which was the no "ch0" text on the front unit). Off to read/learn me up on this thing. ;-)

--
Regards,
Chris

On Wed, Jan 8, 2020 at 11:33 AM, <entilleser@...> wrote:

I have a relatively new ASUS Chromebook, with the latest Chrome version, and the experimental-web-platform-features enabled. The Web Client is working for me.
==================================================================

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. If you are able to connect off-line using the android application then your ASUS Chromebook would be the first reported to do so.

- Herb