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Yeah, I know. I've designed a lot of preamps optimized for noise figure if
the s-parameter file also includes noise optimization files. Generally, the
input is not a conjugate match when the NF is optimized. This was just to
get me in the ballpark for now. Central States VHF and MUD conferences and
others generally have noise figure testing equipment on hand and the
operator will optimize your preamp for you if is doable. But they have all
been cancelled fro this year, so I'll have to wait till next year unless I
come upon someone with NF equipment (which I don't have myself). Some day
...

That's a good idea on putting the attenuator on the input instead of the
output. Looking at the documents, I see the output is in the range of 0 to
-7 dBm. And like I said, I haven't seen anything about using the NanoVNA
with an active device. Maybe it's lost in the long set of threads of this
reflector, but there were no documents in the "Files" section that I could
find that covered it.

73, Zack W9SZ

On Fri, Jun 19, 2020 at 12:15 AM <david.hostetler@...> wrote:

Optimizing the S11 of a pre amp usually doesn't result in best noise
figures and hence best overall receiver sensitivity. Also having too much
gain in a pre amp may cause overload and intermodulation.distortion in the
receive system. When my job was designing add on VHF pre amps, we aimed for
closer to 12 dB gain.

Also, CH0 has a relatively strong output and connecting directly to the
pre amp input could cause the output to be very high, possibly pushing it
to compression, causing false gain readings and making the bandwidth spread
wider than it really is.

I would put 20 - 30 dB between CH0 and the input and connect the output
directly to CH1.

But this discussion has made me wonder if there is a way to use a VNA for
noise figure optimization.

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Hi David,

Thank you for your answer.

In between, i found the "problem".

The USB port was connected to a battery powered PC.

The NanoVNA's CH0 port was connected to a grounded frequency meter,
powered by the main.

After a main power fail, a fatal overvoltage arrived and the NanoVNA's
USB interface was killed.

Results, no more USB connection; no red line active and no battery
charging possible.

May be, a better USB protection would be required...but for the price...

Regards,

Rudi

PS I ordered a NanoVNA-H4 and i will take it totally disconnected when
not in use...
=====================================

Sorry to hear that. Still a pain, Rudi, but better to destroy a $80 (or whatever) device than a $8000 one!

Cheers,
David
--
SatSignal Software - Quality software for you
Web:
Email: david-taylor@...
Twitter: @gm8arv

Hi David,

Thank you for your answer.

In between, i found the "problem".

The USB port was connected to a battery powered PC.

The NanoVNA's CH0 port was connected to a grounded frequency meter,? powered by the main.

After a main power fail, a fatal overvoltage arrived and the NanoVNA's USB interface was killed.

Results, no more USB connection; no red line active and no battery charging possible.

May be, a better USB protection would be required...but for the price...

Regards,

Rudi

PS I ordered a NanoVNA-H4 and i will take it totally disconnected when not in use...

Have you tried a different USB cable?

Does anyone know of a reasonably priced U.Fl calibration kit?

Thanks,
Mark

Hello Rudi,

The performance of my device was initially very poor. It was one of the early "bad clones" without shields.
The S11 at 900 MHz was in the range of -30 dB, S21 -40 dB.
So i made some modifications.
I added two shields to the RF parts (0.5 mm brass sheet) and a 68 uF / 10 V tantalum capacitor from the 5 V trace to ground (near the TCXO).
I also added 3 100 nF caps to C40, C42 and C44.
Before soldering the shields to the PCB i modified the TX and RX bridges as mentioned above.
Last i soldered C38 - 4.7 uF and TF1 - the SD card holder (below the LIPO pack, unpopulated on my PCB).
I replaced the LIPO by a 2100 mAh (Samsung).
The screenshot You saw are the results of theese modifications when connecting two good SMA 50 Ohm terminators (Teleg?rtner) to the two ports.

Best regards
Bert

Link to the nanorfe store? According to the website it is not open yet:
"The NanoRFE store is planned to open in July 2020 and will have the NanoVNA V2 in stock."


================================================

... and no mention of a big-screen, cased version either.

Guess I'll have longer to wait....

David
--
SatSignal Software - Quality software for you
Web:
Email: david-taylor@...
Twitter: @gm8arv

On Fri, Jun 19, 2020 at 01:07:49AM +0800, Gabriel Tenma White wrote:

Most clones of the V2 now perform ok, but consider buying from the Tindie store/nanorfe if you want to support the original developers (only these two stores remit a percentage of profit to the developers).

Link to the nanorfe store? According to the website it is not open yet:
"The NanoRFE store is planned to open in July 2020 and will have the NanoVNA V2 in stock."

On Fri, Jun 19, 2020 at 10:56 AM, <bert_winkler@...> wrote:

The firmware i use is version 0.9.3.3 beta FAT16/FAT32 SD card by DiSlord.
This combination of hardware and firmware gives good results up to 1.5 GHz.
The S11 up to 1.5 GHz is better than 50 dB.
The S21 up to 1.5 GHz is better than 60 dB.

Hello Bert,
I am using the same firmware version 0.9.3.3.
Congratulation about the good hardware you have.
Mine is not so good.

If you want to show your screenshot in the forum, it is better to convert .BMP to either .jpg or .png format.
See attached screenshot Bert_50D35603.png
73, Rudi DL5FA

Hello Rudi,

Sorry, in my NanoVNA R24 - 91 Ohm.

Bert

Hello Rudi,

In hugen79 H4 schematic there ara two versions of the RX input bridge.
From version 4.2
R24 - 91 Ohm
R22, R23 - 51 Ohm
R25 - 11 Ohm
From version 4.2.1
R24 - 56 Ohm
R22, R23 - 240 Ohm
R25 - 49.9 Ohm
In my NanoVNA i use
R24 - 56 Ohm
R22, R23 - 49.9 Ohm
R25 - 11 Ohm
I also tested R22, R23 - 51 Ohm - does not make big difference.
The firmware i use is version 0.9.3.3 beta FAT16/FAT32 SD card by DiSlord. This combination of hardware and firmware gives good results up to 1.5 GHz.
The S11 up to 1.5 GHz is better than 50 dB.
The S21 up to 1.5 GHz is better than 60 dB.

Best regards
Bert

On Fri, 19 Jun 2020 10:00:27 +0200, you wrote:

Hello,

Since this morning, my NanoVNA-H don't accept the USB connection.

I tried on 3 different PCs, no success.

On battery, all is ok but i'm not able to do charging.

I suspect an USB interface failure but i'm not sure...

What can i do ?

Thank you for your help.

Rudi

Why don't you look into the Device Manager.


W.

Hello,

Since this morning, my NanoVNA-H don't accept the USB connection.

I tried on 3 different PCs, no success.

On battery, all is ok but i'm not able to do charging.

I suspect an USB interface failure but i'm not sure...

What can i do ?

Thank you for your help.

Rudi
====================================

Let's hope it's just dust or dirt in the connector, perhaps remove with a brush. Or, the connector may have broken off the board enough to have dropped one connection - physical problem rather than anything more complicated. Tale a look.

Cheers,
David
--
SatSignal Software - Quality software for you
Web:
Email: david-taylor@...
Twitter: @gm8arv

Hello,

Since this morning, my NanoVNA-H don't accept the USB connection.

I tried on 3 different PCs, no success.

On battery, all is ok but i'm not able to do charging.

I suspect an USB interface failure but i'm not sure...

What can i do ?

Thank you for your help.

Rudi

Hello Bert,

There is a schematic from the H4 design version 4.2.1 from 2020-02-13 which is the last version, see:

Unfortunately in the schematic the printed year is 2019, but it is from 2020.

Then the replace list is (SMD size 0603):
- remove R29, R30 and R31
- replace R13 by 0 Ohm
- replace R9 by 200 Ohm
- replace R24 by 56 Ohm
- replace R22, R23 by 51 Ohm
- replace R25 by 51 Ohm
- add a 100 nF capacitor parallel to C40, C42, C44 (SMD 0603)

Additional calibration with the software nanoVNA-saver (version 2.2) with 4 segments (404 points) and average of 4 will bring a few dB better values,
if you calibrate from 50 KHz to 1300 MHz (especially for THROUGH).

73, Rudi DL5FA

Optimizing the S11 of a pre amp usually doesn't result in best noise figures and hence best overall receiver sensitivity. Also having too much gain in a pre amp may cause overload and intermodulation.distortion in the receive system. When my job was designing add on VHF pre amps, we aimed for closer to 12 dB gain.

Also, CH0 has a relatively strong output and connecting directly to the pre amp input could cause the output to be very high, possibly pushing it to compression, causing false gain readings and making the bandwidth spread wider than it really is.

I would put 20 - 30 dB between CH0 and the input and connect the output directly to CH1.

But this discussion has made me wonder if there is a way to use a VNA for noise figure optimization.

Following up on this thread 6 months later. Does anyone know if there has been any firmware development performed on a function to track the lowest SWR for the nanoVNA?

John - W3JED

I hadn't seen much written about using the NanoVNA with VHF preamps. I have
a couple I have never adjusted except "by ear." So I thought I'd give it a
try.

I put a 20 dB attenuator on the output, since the estimated gain for the
two preamps was around 20 dB. I fed the input directly from the port 0 of
the NanoVNA so I could look at s11

My 432 MHz preamp needed some peaking. It wasn't difficult. I got it tuned
so s11 is -45 dB and the gain is about 21 dB. That's as I expected. Not bad
for a 20 year old preamp using an ATF10136.

My 222 MHz preamp uses the same FET and circuit. It did not look so good. I
could only tune the s11 to about -6 dB and the output did not peak anywhere
throughout the tuning range. Gain shows th be about 6.5 dB. There is
definitely something wrong with the preamp. I have also been using it for
20 years. I knew it has gain but it never did seem to have as much as my
144 and 432 MHz preamps. Now I've verified this. I suspect some value
(probably the input tuning inductor) is off.

I can't do anything for noise figure with the NanoVNA but at least I have
the 432 MHz preamp tuned pretty close. I can get the preamps checked and
tuned at a VHF conference next year.

73, Zack W9SZ

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Get the NanoVNA H4 with the 4 inch screen. You will be much happier. I got mine from R&L Electronics.

Sam
W3OHM

P.S. You probably won't touch the MFJ once you have the NanoVNA

Hi Gabriel,



I have bought H4 from eTool Store on Ali.
Pls, what can tell me about it ? Can you?

Just for my curiosity.




Thanks, Milo?


---------- P?vodní e-mail ----------
Od: Gabriel Tenma White <OwOwOwOwO123@...>
Komu: [email protected]
Datum: 18. 6. 2020 19:08:17
P?edmět: Re: [nanovna-users] V2 aliexpress sellers
"A new review posted on an Aliexpress listings reads "The device is
original, which was confirmed by the developer."

I don't remember confirming any device as original. That store used to
get their V2s from shengxun, but switched to selling clones some time
ago. If you really want to be sure you can always PM me before buying.

Most clones of the V2 now perform ok, but consider buying from the
Tindie store/nanorfe if you want to support the original developers
(only these two stores remit a percentage of profit to the developers).




"