I did it.
Tantalum 20 mF 2 pieces per 3.3 volt bus.

Dear Alexander,

Your post is on its own, so I am not sure if there has been any discussion anywhere about your mod, or you have just done it, on spec.

It looks (relatively) simple to do and I am sure there might be several other areas where additional psu smoothing could be useful. I believe the screen (especially the 4” one) creates quite a psu ripple and some decoupling on the screen board is worthwhile. I am ordering a strip of tantalums after I send this post.

Steve L

i added 470uf direct on the lcd connector (anything above 220uf ... with
220 i still had some ripple ... 367 was clean so i took next bigger
value ... 470uf) ... can bbe seen best with an open port ... should be a
nice smooth circle

maybe tantalum does a better filter job but i took what i had flying
around here on the bench :-)

a bigger cap and a series resistor towards lcd would be even better i
guess (did not try that yet)

if you (while running) unplug lcd and reconnect ... the noise is gone
(lcd shows complete white and does not show "usb mode text"after
reconnect) ... the now clean sweep clearly shows that the currents
change (depending what the lcd does display) is what makes that circle noisy

means ... the 3v3 rail is dirty caused by the lcd currents change when
showing "usb mode text" (the picture update is not synced to scanning
update)

additional cap on the 3v3 rail cleans it up somewhat ... add some avg if
you need cleaner sweeps (or even bigger caps or the above idea with rc
filtering??)

greetz sigi dg9bfc

ps i lay the caps flat on the pcb next to the lcd connector and added
short jumper wires

Am 30.12.2020 um 18:29 schrieb Stephen Laurence:

> Dear Alexander,
>
> Your post is on its own, so I am not sure if there has been any discussion anywhere about your mod, or you have just done it, on spec.
>
> It looks (relatively) simple to do and I am sure there might be several other areas where additional psu smoothing could be useful. I believe the screen (especially the 4” one) creates quite a psu ripple and some decoupling on the screen board is worthwhile. I am ordering a strip of tantalums after I send this post.
>
> Steve L
>
>
>
>
>

I am doing it here.
https://vrtp.ru/index.php?showtopic=32010&st=750

I have just come across your message.
However, where you “are doing it” is in Russian, which only a minority of us are familiar with.

Is it possible to post your progressive mods in English on this site? I think quite a few ofus would be interested.

Steve L

Who are you writing to?

Mike

------------------------------------------------------------------------
*From:* Stephen Laurence [mailto:Gaslaurence@gmail.com]
*Sent:* Tuesday, 23 February 2021, 7:49 pm
*Subject:* [NanoVNAV2] Upgrade v2 for stable operation.

> I have just come across your message.
> However, where you “are doing it” is in Russian, which only a minority of us are familiar with.
>
> Is it possible to post your progressive mods in English on this site? I think quite a few ofus would be interested.
>
> Steve L
>
>

Sorry, I assumed I was replying to the group in general and the sender, in particular, of a message in December, referring to a site which looked interesting but entirely in Russian.

The string, it seems, has been lost and I will have to finish this to look for the original post. The screenshots were of the v2 board with various capacitors strung around the board, which seemed to reduce the noise on scans, especially phase.

Steve L

To further the information, the original sender was:-
Aleksander Shalygin on 31 December.

He pointed to a Russian chat site with this link:-
https://vrtp.ru/index.php?showtopic=32010&st=750

I cannot copy it “in blue” on my old Ipad. I must try to get Google translate on it.

He also posted another message with a couple of screenshots of tantalum caps hung on the board.

It all looked as if performance could be improved by a few extra smoothing caps on the 3.3v line. I presume this removes residual line noise, rather than prevent leakage to port 2.

Steve L

its all about adding a few caps on the 3v3 rail

the current of the lcd lets the voltage "wiggle" a bit

caps lower noise on that rail

smith chart is less noisy (scratchy ... criss/crossing)

dg9bfc sigi


Am 23.02.2021 um 21:12 schrieb Stephen Laurence:

> To further the information, the original sender was:-
> Aleksander Shalygin on 31 December.
>
> He pointed to a Russian chat site with this link:-
> https://vrtp.ru/index.php?showtopic=32010&st=750
>
> I cannot copy it “in blue” on my old Ipad. I must try to get Google translate on it.
>
> He also posted another message with a couple of screenshots of tantalum caps hung on the board.
>
> It all looked as if performance could be improved by a few extra smoothing caps on the 3.3v line. I presume this removes residual line noise, rather than prevent leakage to port 2.
>
> Steve L
>
>
>
>
>

See V2mod_imped..... PDF in Files section for a simpler solution using 4" display

Cheers

Gary,

So I looked at the PDF document in the Files section and ran what I believe is the same test, turned off all but the Smith Chart, left it Uncalibrated, Freq from 1 to 3000 MHz, but I see pretty much smooth lines on the trace. I trust that this means that I won't gain anything if I add the 470 uf capacitor.


--
Mike, W0IH

Hi Mike,

It looks fine to me. Perhaps the V2N is already modified?
Mine was an original board with 2.8" display and a 4" display added retrospectively.

Cheers
Gary