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Building S-A-A-2 from scratch for external test set configuration (like "Option 011") - specialized/difficult parts required?


David Feldman 2020/06/14 07:20

I am interested in using an altered version of the S-A-A-2 PC board design/artwork, with an alteration to delete the built in bridge, and instead provide source output, reference input, reflect input and through input connections as four SMA connectors.

The purpose of this would be to permit other types of test sets (similar in concept to the HP/Agilent "option 011" - delete test set.) The benefit of this kind of interface is to allow additional test configurations that cannot be well supported currently due to damage limits in the bridge circuit (such as RF/microwave power amplifiers).

Before I expend additional time in this direction, I'm concerned about sourcing component parts (in US, probably from US distributors) for the PC board - are there any parts (other than the bridge-related circuitry which would be omitted) that I should focus on to avoid a show-stopper problem?

Thank you,

Dave

OwO 2020/06/14 22:35

There is also a much simplified design you can look at, under the name
v2lite_1 in the same repo, but without a display and si5351 (so minimum
frequency is 140MHz). It has two channels (and adding another one is
easy) using IAM-81008 mixers.

The hardest parts to source are the ADF4350 and AD8342, they are quite
expensive from the usual distributors. The other parts are available
from most distributors and LCSC.

On 14/06/2020 22:20, David Feldman via groups.io wrote:

ok1vaw 2020/06/15 14:46

Could you place a link, where the schematic could be found to better
understand the hadware limits of the V2?

Dne 14.06.2020 v 16:35 Gabriel Tenma White napsal(a):

Wouter van Gulik 2020/06/15 23:54

It is in this groups files. See
https://groups.io/g/NanoVNAV2/files/User%20Manuals,%20How2,%20Examples/Gabriel%20v2_2%20schematic.pdf

HTH,

wouter

David Feldman 2020/06/30 08:25

Continuing parts gathering for "011" type (external bridge) nanovna-v2 homebrew-for-fun project. Adhering very closely to the schematic except for a couple of minor parts substitutions (below) and use of N connectors (now on hand).

One part I'm not certain about - U501 oscillator (driving Si5351) is specified in schematic as only as "3225", which I assume is the package size, not part number. What is the operating frequency (25-27 MHz? other? Software presumably written for a specific frequency, I haven't investigated yet but plan use existing binaries without change.) I assume CMOS output type.

To source parts not already in hand (synthesizers, mixer) from LCSC, had to substitute MXD8641H for MXD8641 which is not in stock; the -H type has 0.1 dB additional insertion loss, higher P0.1dB limit, other parameters seem same (particularly checked isolation.) Also buck regulator AP3419 seems replaced by AP3429 (didn't opt for the AP3429A as no need for self-restart after short circuit event.)

Tks,

Dave

OwO 2020/06/30 23:57

It's a 24MHz oscillator, CMOS output level. I think sinewave TCXOs can
be used too.

On 30/06/2020 23:25, David Feldman via groups.io wrote:

Siegfried Jackstien 2020/06/30 16:27

maybe an xnclh24.000thja0p0 or similar could be used?? (i use a similar
but 25 megs device for modding lnb)

0.2 ppm is a good number and price is fair (10 bucks) if you want a
PRECISE clock

parts with higher ppm are cheaper (and for antenna tests sure would also
work) ... but if you also wanna use it as test generator a lower ppm
value is maybe a bit better

do you wanna go cheap?? or precise??

greetz sigi dg9bfc

Am 30.06.2020 um 15:25 schrieb David Feldman via groups.io:

David Feldman 2020/06/30 10:20

Thank you - 24 MHz - it is no problem to source this locally. Precision is not mandatory at this stage, I am just doing a personal project for learning and enjoyment. I will provide connection option for external reference.

I will await receive parts from LCSC before proceeding more (I selected Fedex International option on LCSC.) At that point, parts gathering will be complete.

4" LCD, already received about 2 weeks before (EQV official store "3.95"/4.0" inch 320*480 ST7796S TFT Color LCD Display Module Screen with Touch Panel For Arduino UNO Mega2560 8/16 Bi"), connected by ribbon cable.

https://www.aliexpress.com/item/4000126450233.html

Gyula Molnar 2020/06/30 12:49

Hi Dave,
I'm not sure the LCD is connected properly.
I think SPI needs 14 pins. such as: https://www.aliexpress.com/item/4000946111830.html

73, Gyula HA3HZ

David Feldman 2020/06/30 15:10

Thank you Gyula

Yes, URL indicates parallel port :-( Incorrect type.

SPI port type, with touch now ordered. I think correct display will arrive before LCSC parts (US->US shipping.)

73 Dave WB0GAZ

Gyula Molnar 2020/07/01 00:09

Hi Sigi,
Then I will say that according to the text it is touch screen and in the picture the control IC is missing, so according to the picture this module is not touch screen. Whatever you sell to the trader, whoever installs it, doesn’t.
In other cases, you may notice that they use the same base pcb, just not installing all the components.
That’s why I wrote in an earlier post that it may not be sold at this link as well. Anyone who has given it a try will be happy to give feedback that yes it is indeed touch screen.

73, Gyula HA3HZ

ps.:So for me, the discrepancy between text and image precludes ordering. Once someone has convinced me that this is really touching, I will order from there.

David Feldman 2020/07/18 11:03

Hello Gyula,

Thank you again for kind and helpful inspection of display I ordered first time (parallel port, my mistake.) I then ordered correct type of part (SPI port, Touch, SD connector.)

After LCSC parts for SAA-2 build quickly arrived (everything but AD8342,I obtained mixer easily in US from ADI distributor, AD4350 and SI5351 I have already), finally arrived SPI interface 4" display. New problem! The new display is SPI and has SD Card connector, but has NO TOUCH feature :-( :-( :-(.

Incorrect display part was shipped by error from aliexpress seller (3C Shenzhen) - description was correct, so I think parts error.

Now I have started process with Aliexpress to receive refund, so I can order again for the correct part. I think this will delay start of project for "011" option saa-2 about 8 weeks more. I will have some extra kinds of 4" display of no use for SAA-2 :-(

Also, I find that SP4T switch IC MXD8641 is very small package, about 2mm QFN-type with 0.4mm pitch. I cannot find stencil for this package, and I cannot find substitute with easier package (HMC241, TSSOP16, is obsolete). I received recommendation to use hot air process and pre-tin PCB lands. It will be difficult challenge for hand soldering very small part!

73 Dave WB0GAZ wb0gaz@yahoo.com

David Feldman 2020/08/21 11:39

About 2 months ago (14 June) I proposed develop SAA2 version with external bridge/coupler (new PCB, existing firmware.) I obtained semiconductors and passive parts, and finally obtained 4" SPI ST7796S display with touch feature. I now have original SAA2 (2.8") I can use to verify firmware build/download procedure.

Is there a procedure or resource to help me build saa2/nanovna-v2 firmware from scratch? I will need source code and development system to compile then download. If someone here has successfully compiled/downloaded firmware, would you be able suggest method and location of source code? I wish to verify tool chain procedure with existing (2.8") saa2/nanovna-v2 before I commit PCB layout of external bridge-coupler version.

Project board (for external bridge-coupler version of saa/2nanovna-v2 will duplicate existing saa2/nanovna-v2 design except for omit bridge/coupler, so if board is correct and construction is correct, existing firmware should run OK, but initial testing of board (with temporary firmware modification to toggle control lines) is required because possible layout error.

Thank you!

###

Also - about 4" SPI touch display sourcing trouble:

Try #1 (failed): I ordered by error parallel port version of ST7996S 4" touch display :-(

Try #2 (failed): I ordered ST7796S 4" SPI touch display from aliexpress/3C Shenzhen Store; they shipped wrong version - without touch feature - and would not refund purchase. Aliexpress has only automated system to mediate seller dispute, and in final decision incorrect parts were not refunded. This is valuable lesson in purchase through aliexpress (try verify good seller, 3C Shenzhen Store is not, so there is some risk.)

Try #3 (succeeded):ST7796S 4" SPI touch display module from aliexpress/Ecyberspaces (thank you Gyula for the information!). Ecyberspaces appears to be good seller (very good packaging for safe delivery, confirmed correct type on messaging, and quick delivery to USA.)

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