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As noted in my previous post, my unscreened NanoVNA seems to perform
marginally better than my screened sample in terms of noise & internal
crosstalk.

As I no longer have access to an anechoic chamber or GTEM cell I did some
relatively crude interference tests in front of and behind the vnas using a
4w 2m/70cm handheld to see what difference screening made. I terminated
both ports on both vnas & left them on default bandwidth and calibration.
Both were set to show logmag for ch0 & ch1.

The screened vna didn't show any sign of signal pickup on either band, so
is definitely the better product. The unscreened one ignored 70cm but did
show a low-level signal at 2m when the handheld was any closer than 7m.
Even 30cm away the signal was still at -40dB. The general noise floor
didn't seem to increase at all.

The only scenario I can think of where this low level of pickup would be a
problem would be in the unlikely event you were trying to adjust a screened
filter while very close to a significant source of rf on the same frequency.

BTW - a correction to my earlier email - the screened vna does have a
screened rear panel.

73

Mike

On Fri, 23 Aug 2019, 23:09 Mike Brown via Groups.Io, <mbmail=
[email protected]> wrote:

Unless I'm doing something stupid (which is entirely possible) or have
been very lucky it may not make very much difference which clone you buy
(as long as it has a battery and the soldering is ok!).

If my recollection is correct, according to Hugen (who we believe is the
developer of this variant of the original 300 MHz NanoVNA) the worst clones
not only have no screening but also the manufacturer tried to make up for
this by using PCB for the rear panel. Apparently the PCB reflects signals
back into the VNA, making things worse rather than better.

I have two NanoVNAs. One came from UK seller sqcase, has 900 MHz 2-trace
firmware and no screening. The rear panel is plastic so I called it a
semi-bad clone. The second was ordered before Hugen made his available on
Alibaba. It came from AliExpress seller Guangyi0016, has 4-trace 900 MHz
firmware, does have screening and a plastic rear panel. Both VNAs came with
batteries.

In theory the lack of screening of the semi-bad clone should mean more
crosstalk between TX and RX channels. I did the following to check:

On both VNAs I terminated ch0 and ch1 with 50 ohm loads and set the
display to show ch1 logmag, scanning from 50 kHz to 900 MHz. As the two
channels are not connected I believe that any signal appearing on ch1
should consist purely of crosstalk and noise.

Below 300 MHz the signal levels are off the screen on both VNAs (so lower
than -70 dB). Surprisingly the unscreened clone has roughly 3 dB less
xtalk/noise between 300 and 400 MHz, although it does have spikes at 300
and 600 MHz. (The spikes seem to vary between VNAs. The ICs are being
pushed beyond specification so spikes seem to be a matter of luck rather
than build quality.) What I'm seeing above 400 MHz is very similar on both
VNAs, with displays showing noise that bounces around a lot but at 900 MHz
is rarely above -50dB.

I also tried placing a metal sheet behind and then in front of the
input/output areas of the unscreened VNA, to see if I could increase the
amount of crosstalk. No effect was apparent.

These simple tests seem to suggest that screening may not be as critical
as we all thought it was. Could the calibration isolation measurement &
subsequent correction be reducing the effect of crosstalk to below the
noise floor?

Mike







-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of GARY GILES
Sent: 22 August 2019 21:30
To: [email protected]
Subject: Re: [nanovna-users] Your NanoVNA version

Hi, new to this group,
I recently purchased a NANO VNA from eBay. Unfortunately it was before
this series on the bad clones....I got a bad one. They showed pictures of
the good ones and sent me a clone. What are the operational differences
between the original and the clone? I can see where the lack of shielding
would pose a problem at higher frequencies, but other than that it seems to
be working correctly.

Tnx de Gary, KF9CM

There's a bunch of different manufacturers making clones.
Seems dangerous to make blanket statements about performance
on the basis of screened (shielded) vs unscreened or black vs white.

Perhaps identifying the seller of the two nanoVNA's being compared
would help make such information useful to others.
But keep in mind that sellers may be sourcing nanoVNA's
built from multiple manufacturers. And that there may be
significant differences among units from a given manufacturer.

Mike wrote: "As noted in my previous post, my unscreened NanoVNA
seems to perform marginally better than my screened sample in terms of
noise & internal crosstalk." That previous post would be this one, in case
anybody is trying to follow along:
/g/nanovna-users/message/1297

Are there issues beyond "noise and internal crosstalk" that we should consider?

All that said, Mike's tests do help us know what's going on.
The more actual tests between instruments the better.

Jerry, KE7ER

Hi Jerry

If you re-read my first message (which was included below the text of my
second email and is still present at the end if this one) you'll see I
acknowledged that I may have been lucky in the VNAs I received. No blanket
assertions made, other than it 'may' not matter which you receive.

You'll note that I did identify both sellers. If I was buying another I'd
definitely order from Hugen's friend's Alibaba store in preference.

I fully accept all my tests are rough & ready, with a tiny sample size. It
would be great if someone with better test facilities and/or different
clones could do some comparative testing too.

73

Mike

On Sun, 25 Aug 2019, 16:37 Jerry Gaffke via Groups.Io, <jgaffke=
[email protected]> wrote:

There's a bunch of different manufacturers making clones.
Seems dangerous to make blanket statements about performance
on the basis of screened (shielded) vs unscreened or black vs white.

Perhaps identifying the seller of the two nanoVNA's being compared
would help make such information useful to others.
But keep in mind that sellers may be sourcing nanoVNA's
built from multiple manufacturers. And that there may be
significant differences among units from a given manufacturer.

Mike wrote: "As noted in my previous post, my unscreened NanoVNA
seems to perform marginally better than my screened sample in terms of
noise & internal crosstalk." That previous post would be this one, in
case
anybody is trying to follow along:
/g/nanovna-users/message/1297

Are there issues beyond "noise and internal crosstalk" that we should
consider?

All that said, Mike's tests do help us know what's going on.
The more actual tests between instruments the better.

Jerry, KE7ER


On Sun, Aug 25, 2019 at 05:30 AM, Mike Brown wrote:

As noted in my previous post, my unscreened NanoVNA seems to perform
marginally better than my screened sample in terms of noise & internal
crosstalk.

As I no longer have access to an anechoic chamber or GTEM cell I did some
relatively crude interference tests in front of and behind the vnas

using a

4w 2m/70cm handheld to see what difference screening made. I terminated
both ports on both vnas & left them on default bandwidth and calibration.
Both were set to show logmag for ch0 & ch1.

The screened vna didn't show any sign of signal pickup on either band, so
is definitely the better product. The unscreened one ignored 70cm but did
show a low-level signal at 2m when the handheld was any closer than 7m.
Even 30cm away the signal was still at -40dB. The general noise floor
didn't seem to increase at all.

The only scenario I can think of where this low level of pickup would be

a

problem would be in the unlikely event you were trying to adjust a

screened

filter while very close to a significant source of rf on the same

frequency.

BTW - a correction to my earlier email - the screened vna does have a
screened rear panel.

73

Mike

On Fri, 23 Aug 2019, 23:09 Mike Brown via Groups.Io, <mbmail=
[email protected]> wrote:

Unless I'm doing something stupid (which is entirely possible) or have
been very lucky it may not make very much difference which clone you

buy

(as long as it has a battery and the soldering is ok!).

If my recollection is correct, according to Hugen (who we believe is

the

developer of this variant of the original 300 MHz NanoVNA) the worst
clones
not only have no screening but also the manufacturer tried to make up

for

this by using PCB for the rear panel. Apparently the PCB reflects

signals

back into the VNA, making things worse rather than better.

I have two NanoVNAs. One came from UK seller sqcase, has 900 MHz

2-trace

firmware and no screening. The rear panel is plastic so I called it a
semi-bad clone. The second was ordered before Hugen made his available

on

Alibaba. It came from AliExpress seller Guangyi0016, has 4-trace 900

MHz

firmware, does have screening and a plastic rear panel. Both VNAs came
with
batteries.

In theory the lack of screening of the semi-bad clone should mean more
crosstalk between TX and RX channels. I did the following to check:

On both VNAs I terminated ch0 and ch1 with 50 ohm loads and set the
display to show ch1 logmag, scanning from 50 kHz to 900 MHz. As the two
channels are not connected I believe that any signal appearing on ch1
should consist purely of crosstalk and noise.

Below 300 MHz the signal levels are off the screen on both VNAs (so

lower

than -70 dB). Surprisingly the unscreened clone has roughly 3 dB less
xtalk/noise between 300 and 400 MHz, although it does have spikes at

300

and 600 MHz. (The spikes seem to vary between VNAs. The ICs are being
pushed beyond specification so spikes seem to be a matter of luck

rather

than build quality.) What I'm seeing above 400 MHz is very similar on

both

VNAs, with displays showing noise that bounces around a lot but at 900

MHz

is rarely above -50dB.

I also tried placing a metal sheet behind and then in front of the
input/output areas of the unscreened VNA, to see if I could increase

the

amount of crosstalk. No effect was apparent.

These simple tests seem to suggest that screening may not be as

critical

as we all thought it was. Could the calibration isolation measurement &
subsequent correction be reducing the effect of crosstalk to below the
noise floor?

Mike

Mike,

Yup, your right, thanks for the corrections. And for the report.
I just wanted to emphasize that it's not so simple to distinguish good from bad,
which seems to be on the minds of many here.
And hit "send" a bit too soon.

Jerry

No problem Jerry. I probably should have made more of the possibility that
there could be some real stinkers out there.

Aside from buying from Hugen there probably isn't a way to be sure of
getting a good one, which is what everyone is struggling with. It's a shame
Hugen doesn't sell via AliExpress or Ebay as buyers seem to have more faith
in those platforms.

73

Mike

I've changed the project name to NanoVNA-H as recommended by edy555, I'm making a new PCB with a better shield, a brand new plastic case is almost finished, and I'll be offering a new version in the web store in about half a month.
In addition, I am sorry for the recent political problems in Hong Kong that may affect the speed of some express delivery.

hugen

the first one i bought on eBay from tztmotor was (as shown) a white one with a salamander logo. it arrived with S, O, L SMA bits. it has no shields, no clamshell case, and no cables. 2-trace 900 MHz firmware. bonus gift: it had a dead short on the USB connector. not something i expected, so i didn't at first notice it both not charging and the USB cable getting really hot. inspected the device carefully with magnification. determined the solder build-up was too much. used Solder-Wick on the USB connector. repaired!

the second one arrived today bought on eBay from elecdesign2015 is (as shown) a black one with no front logo. it arrived with S, O, L SMA bits, SMA barrel (F-F), shields on-board, clear clamshell case, and short SMA M-M cables. 4-trace 900 MHz firmware. no USB connector short (ahem).

so far, so good.

- \0111 -

more information to report: the salamander logo nanovna has a battery with connector.
the black one with shields has a battery with no connector (battery leads soldered directly).

- 1v (base 41) -

Photos of a white salamander nano.

fascinating. here's where my white salamander nano differs from yours ..

Looks like they sent you one that was rotated 90 degrees. ;-)

The only difference I see is that one has the battery leads soldered in place,
not using a connector. Good (more reliable) and bad (slightly harder
to replace the battery).

Jerry

Forgive my ignorance, what is “screening” referring to? Is it the screening markings on the case or shielding on the chips.

Shielding.

Thanks Jerry!

third one arrived today bought on eBay from supermotor009 (Hebron, KY, USA) is (as shown) a black one with no front logo. it arrived with S, O, L SMA bits, SMA barrel (F-F), shields on-board, clear clamshell case, USB cable, and short SMA M-M cables. 4-trace 900 MHz firmware. power switch was in the "ON" position. switched it OFF, and after a few seconds charging, it booted up fine.

of all the ones received so far, this one arrived in the best condition, even though it was shipped in a bubble padded envelope.

the second one received from overseas had a piece popped off the front lip of the clamshell case. free ventilation opening? :-P the second one's shipping carton had clearly sustained crushing force across the top (broadest) surface.

ps: for those keeping track, the second one also had a USB cable and i neglected to mention that in the previous report.
pps: friend of mine will be the beneficiary of this fine newly arrived NanoVNA. :-)