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Bryan,
The lab I worked at had spectrum analyzers and receivers that cost more than my first house. To protect the equipment our laboratory manager purchased a set of HP 11867A limiters ( I'm guessing you could buy 5 or 6 nanoVNA's for what he paid for one of those). I believe the limiter was just a couple of well matched, low capacitance, fast switching diodes packaged in a Type N adapter. It turned out that the limiters were a waste of money for our application because diodes are non-linear devices and sometimes would mix with the signal we were measuring and generate phantom signals. For tuning an antenna that extra noise might not be a concern, but for compliance testing it was a deal breaker. We eventually ordered some Type N adapter RF fuse holders that had less than a dB of loss up to 1.5 GHz. The holders had fusible links that could be replaced in-house without having to send the equipment out for expensive front end repairs. I was the beneficiary of their use more times than I care to admit.

Never tried either solution with our network analyzers as I certainly would have been fired on the spot for attempting to use an HP8753 VNA in the scenario you are envisioning. Makes you wonder what kind of front end protection expensive antenna analyzers use.

Yeah, Reg - Python is the future....!

Actually, Python is close to becoming the #1 programming language - educators, engineers and scientists have all created extensions.
Talk to forum member Rune about Python.

Also from today's news, Microsoft has a YouTube series for beginners:


From the article:
"A new video series, titled 'Python for Beginners', hosted by Microsoft Senior Program Manager, Christopher Harrison, and Business Development Manager at AI Gaming, Susan Ibach, has been launched by the firm. Comprising of a total of 44 videos, this series - as indicated by the name - isn't an in-depth study of Python, but rather, it just provides a foundation for the programming language. The course material is noted to be quick and concise, in order to encourage learners to start specifically looking into the areas that interest them as soon as possible."

Cheers,
Larry

Folks,

Thanks for all the comments. I notice that the diagram provided by erik does not indicate any protection. Thanks for that diagram. The 50 ohm bridge mentioned above does provide some help but only a small amount. ESD events are often in the thousands of volts so even a few dB of attenuation is not enough. I have previously blown up a VNAs input switch when I touched an antenna connected to the VNA in my workshop so this is a real concern for me. Yes, it was repairable. I got to learn a lot about soldering very tiny surface mount components in that case.

Back-to-back zener diodes are available for this very purpose with very low capacitance (0.06 pf) for example the PGB010603 made by Littlefuse. I have attached a data sheet for others to consider. The spec sheet says it is good up to about 9 kv for a contact discharge and about 15 kv for an air discharge. Furthermore, the response time is under 1 ns which is about 1 cycle at 900 MHz. I suggest the mixer in the nanovna won't handle a typical ESD event without some help. I purchased some of these devices for about $0.50 each so they are not a big investment. Please be careful interpreting the data sheet. You might conclude these diodes don't help, but they have in my case.

I hope that when we do an open calibration any stray capacitance such as 0.06 pf is measured and removed. 0.06 pf at 900 MHz is a reactance of about 2950 ohms which should not have a major impact on most measurements anyway.

I hope folks find this information useful.

--
Bryan, WA5VAH

On Fri, 20 Sep 2019 at 16:18, Reginald Beardsley via Groups.Io <pulaskite=
[email protected]> wrote:

Dave and Ohan,
I'm rather tempted to load Mecrisp on the nanoVNA and try my hand at
serious work in forth for the first time in almost 40 years.

Have Fun!
Reg

The problem with forth is that nobody else is likely to want or be able to
contribute. There are many languages that have niche areas - Lisp, Haskell
etc. But the number of people knowledgeable in these languages is a small
proportion of the people able to write software.

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

Thanks for posting that detailed test report...fascinating to see what the ultimate ceiling might be. I recall reading that the mixer chip alone has an upper spec. limit of 500 MHz, so the fact that we can get ANYTHING >1 GHz is impressive.

Sometimes people ask if a nanoVNA can be hacked to work above 1500MHz.
So I tried. The firmware was modified so it theoretically can go up to 2.1GHz (7/9 overtone mode)
But is it usable with the supplied plastic cables?
Measuring a 2GHz cavity filter the S21 dynamic range is 10dB with a noise of about 5dB so with 1/16 exponential averaging using TAPR VNA PC software you get confirmation the cavity filter is 20MHz wide at 2GHz but due to the long measurement time (about 2 minutes) to get rid of the noise, tuning is impossible.
I could calibrate (1000 points from 0.5MHz till 2.1GHZ but also 101 point in the device) and the difference between S, O and L is visible at the right place of the Smith chart but the noise is at least 10% and sometimes much more and the stability is terrible.
Measuring a 1.9GHz low-pass filter was impossible. Both the S11 and the S21 where basically useless above 1.5GHz, probably due to leakage, unbalance in the bridge and other parasitic capacitances.
To be sure I repeated the tests with semi rigid SMA cables instead of the plastic SMA cables but there was no visible difference.
Further analysis revealed the bridge has still 10dB directivity above 1.5GHz and the S21 dynamic range is still about 30dB but due to leakage, impedance mismatches, bridge imperfections and temperature instability it will be difficult to use this.
Can you tune a 2GHz antenna? Although it is possible to see the L/S/O on the smith chart on the right position it was impossible to determine the input impedance of the 2GHz cavity filter so it may be difficult

I had the same problem and to fix it give the file a shorter name and then upload it.
It then worked for me.
73, Trip

--
"When the people fear the government, there is tyranny. When the government fears the people, there is liberty." ~~ Thomas Jefferson

Hi, Folks,
My whole NanoVNA process started because I went out on eBay looking for an antenna analyzer for ham VHF/UHF use and got my white model because it intrigued me at what was being done at that price point. No prior personal experience with VNAs, although I've been aware of them for years. Big learning curve to get started, but it did almost everything I was looking for once I could see SWR and a Smith Chart. It's been well worth the $60, and I'm getting a VNA education to boot reading here.

I say almost because I would like to be able to get some values to at least compare HT Antenna A to HT Antenna B for gain. To get started, I put a test antenna on CH0 and a reference antenna on CH1. I can tell the CH1 antenna is "seeing" the CH0 antenna because logmag dB values change with/without something on CH0, and I can also see that dB values go up/down as antenna distances change.

What I'm looking for is suggestions on how to do this the right way, or at least a better way. Now I'm using a scanner-type antenna for reference, it's about 30cm/12" away from the test antenna. I'm looking for suggestions on ref antenna type/spacing, and also a calibration protocol to make this choice useful. Nothing really fancy, I just want to get some data so when someone shows up with what they think is an antenna that's cooler that what they (or someone else) already has, I want to have some numbers to avoid a food fight and/or be able to objectively evaluat/comapre the two. Suggestions? Issues?

Appreciate the input...

Ken Buscho
KB6KOB

Rune,

Thanks so much for doing this. Did notice one minor bug. When calibrating out to 1.5 GHz and loading the calibration file in, when starting a sweep it will crash. If only going out to 900 MHz it works fine. Windows 10 system using your provided exe.

Thanks again for all your effort on this.

Jim K.

On Fri, 20 Sep 2019 at 03:04, Reginald Beardsley via Groups.Io <pulaskite=
[email protected]> wrote:

The wikipedia definition of "return loss" is rather absurd. If you have a
*perfect* match and *no* power is reflected, the "return loss" is
infinite. Of course it *is* wikipedia.

I'm not about to try to change the EE community lexicon, but it seems to
me reflected/incident makes a great deal more sense numerically. It also
leads to what I'd expect. "Loss" as a negative quantity when expressed in
dB.

Have Fun!
Reg

What’s the i*nsertion loss* of a 6 dB attenuator? I would have thought it
was 6 dB and not -6 dB.

The same with return loss.

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

Very interesing to read as this my first VNA to have in hand and i want to discover its possibilties with my ARR,PA3BIY and G4DDK 2m LNAs for EME.
I checked a professional cavity BPF (IL=-1.6db) to install after the LNA.
Regards Sid.

Hi, i find out that the IP5305 is the same as the IP5303, with one LED less. I can upload the PDF data in English here.

Dave and Ohan,

Thanks. I'm going to try to use the ST-Link V2.0 units I bought so I can gain some experience with using them and the various C development environments. I've got quite a few STM32 discovery boards, "blue pills" etc.

In the past I've used st-flash on *nix to flash Mecrisp forth on to the STM32:



At the moment I can't even remember what hard drive I was using for that work as it was several years ago. The downside of having 2 dozen drives in caddies and swapping drives in a single computer, but a great use for old drives. And a safe way to play with odd ball stuff like Plan 9.

I'm rather tempted to load Mecrisp on the nanoVNA and try my hand at serious work in forth for the first time in almost 40 years.

Have Fun!
Reg

Found a UI bug in latest Sept 18th TDR version firmware from Erik in the filles section:

- select Display -> Transform -> Velocity Factor
- click on the small keyboard image icon at the lower right corner
- display is no longer responsive to touch input and top row of on-screen keyboard partially blanks (attempt to show something?)
- press the Jog switch < or > function and full onscreen keyboard and touch input returns. Jog switch Enter has no effect.

This is repeatable on the velocity screen.

Regards,
Larry

Placing a 20 - 100 ohm resistor has not brought a solution. The IP5303 will not start wiyh the SW1 switch.
Also, as a test with a 6V / 3W light bulb on the load pin 8, it will not start. Here the load must still be sufficient. With pin5 I can start the IP5303, and the light is on, but after the 45sec sleep time, restarting no longer works with the pwr switch. I will have to search for another solution. I am thinking of a larger C3 capacitor, so that when the SW1 is closed, there is a larger charge current for a while. I'm also going to look up more circuits with the IP5303.

Hi Rune

Many thanks; the full path fixes it...

/home/nick/nanovna-saver/full_sweep

but

~/nanovna-saver/full_sweep

does not work.

A few suggestions on the user interface...

- how about removing the plots from the main window and having them open in separate re-sizable windows? That can be saved as .png files?

- how about then moving all the cal stuff onto the main window?

The above motivated to ease the pressure on screen space.

I find I have to run my 17 inch monitor at 1024 x 768 to be comfortable. Perhaps I should get a bigger monitor!

- how about save/load calibration opening "object picker" windows so you can select which cal you want to use from the file system rather than having to remember what you called them?

73
Nick
G3VNC

I can't see anything that tells me what the maximum input is before the device is destroyed.

Inputs appreciably outside power supply limits will be problematic.
ESD was most problematic for CMOS not internally protected.
50 Ohm bridge pretty much protects the active chips;
bridge resistors can of course be damaged
by exceeding power dissipation rating (V*V/R)

Wouldn't a diode introduce capacitance across Ch0 ?
Or inductive lead effects at VHF/UHF and ruin any measurements ?

Having variable amounts of built-in parasitic reactances,
each nanoVNA already needs "calibration".

One other thought.

During a discussion yesterday on this group, measurments were taken as to what the OUTPUT levels were from Ch0.

They were 200mv peak to peak IIRC.

As such, I think I'd want to assume that this would be the maximum level that any of the ports could handle and would want
to account for.

0.6v (600mv) for a basic diode to start clamping sounds a bit risky to me.

If I'm missing something here then I'm willing to learn ;-)

73 de Andy

Thanks Erik.
I read the slides from the link but did not notice mention of another protection method that I've seen using zener diodes.

Referring to the attached image, drawing A is mentioned in the slides.
However, I have also seen the use of back-to-back zener diodes in series as shown in drawing B that I think would provide a higher input range.
Lastly, I wonder how the use of a two-color LED as in drawing C would work, with its higher forward voltage. (and visual indication?)

The original aim of the diode protection was to limit input voltage to 0.6V at the radio's sensitive front-end.
The VNA uses a resistance bridge - how much signal can it tolerate before physical damage or actually modifying what you're trying to measure?

You could use something like a ESD0P4RFL. Will need some space on the board. And it's quite small, but very low capacitance.