Hard hack - Embedding a SDR in FT-991A - Need RF designers review

Hello there, QRZers! o/

I'm working on a personal project to embed a SDR inside a FT-991A.
This project is a hard hack on something that it was already being done. Check the vanilla instructions in https://c.rf01.co:8443/q/pat-70-ft-991a.pdf .
I don't like the idea of drilling a hole in my radio's chassis. And I thought... What about if the radio had a SDR INSIDE it, and exported through its USB port, without hanging or extra wires, ports, etc.? THAT would be slick.

After a full sunday brainstorming the idea, reading datasheets and using the radio schematic as a source for inspiration, I have come out with the schematic in https://c.rf01.co:8443/q/panadapter.pdf .

So, this is obviously designed by someone without a degree in Electrical Engineering, and I have used the Radio's schematic as a source of inspiration for the decoupling and stuff.

The part that I actually designed was the "Signal Control Board", where I have a AND port to bias a transistor which will actuate a solid-state analog switch, which will connect or not the RF signal from the radio's IF tap to the Buffer Board & SDR.

Since this is going to be installed in a RF-harsh environment (inside a 100W transceiver, though not on the same board as the RF PA unit) AND, to make things worse, where the RF quietness is highly critical (this is actually close to the tuner stage), I was wanting to check with you guys:

1. Is the Q1 & U2A in Signal control board correctly designed? I'm under the impression that I should have used a PNP here instead;
2. Does the decoupling look sufficient?
3. Any shielding suggestion/recommendation, etc.?
4. In the original project, the PAT-70 IF input uses just a as-short-as-possible standard wire. What about using a co-ax?
5. Any other ideas?

Appreciate your awesomeness ;-)

73s de PY2RAF.

 

Your drawing don't show how you are coupling to the IF. Or if it does I missed it. Looks like direct coupling. That will most likely Not work.

I think that was one problem people had doing the mod.

If Not done correctly, It kills the IF signal, Lowers it a bunch.

Good Luck.

 

Hi Don! o/

This is documented here: http://huprf.com/huprf/wp-content/uploads/2016/03/PAT-V2-description.pdf

It is the PAT-70 board.

 

OK cool.

That is Version 2 and should work. Unlike V1 that was different.

Have Fun. Nice project.

 

Okay, here it comes, Rev C -

I was not entirely convinced that the transistor was actually well designed (well, it was NOT) but in the end, it was entirely disposable - The gate output is enough to flip the switch. Removed it.

New PDF: https://c.rf01.co:8443/q/panadapter-rev-c.pdf

73s

- RF

 

Okay, here comes Revision D!

Instead of reinventing the wheel, I reused OE2DOR's AWESOME and NEAT design and embedded my new logic over there.

First Panadapter (PAT) design screenshots:
Back: https://c.rf01.co:8443/q/ft-991a-pat-back-d.png
Front: https://c.rf01.co:8443/q/ft-991a-pat-front-d.png
Schematic: https://c.rf01.co:8443/q/ft-991a-pat-d.pdf

The entire project connection overview:
https://c.rf01.co:8443/q/panadapter-rev-d.pdf

Comments, suggestions and most important, design flaws comments are welcome! ;-D

73s de PY2RAF.

 

And here it is.... Revision E!

Changelog:

- Now sports a RF switch (PE4259) instead of a regular Analog switch (was: SN74LVC1G66);
* Also contains its resistors as per reference design;
- Changed voltage from 5V to 3.3V to Switch and AND port;
- SDR output will be grounded by default when switch is in default state (RF 2 port) port
- Updated list of contributors in Silk Screen.

Files:

PCB Back: https://c.rf01.co:8443/q/ft-991a-pat-back-e.png
PCB Front: https://c.rf01.co:8443/q/ft-991a-pat-front-e.png
Schematic: https://c.rf01.co:8443/q/ft-991a-pat-e.pdf
Overview: https://c.rf01.co:8443/q/panadapter-rev-e.pdf

Appreciate your comment, review, criticism and suggestions!

73s de PY2RAF.

"given enough eyeballs, all bugs are shallow"
- Linus Torvalds

 

Eagle Board and Schematics at https://github.com/rfrht/FT991A-PAT

73s de PY2RAF.

 

Reaching the 6th iteration, it is.... Revision F!

Changelog:

* Added 1 nF capacitors in RF lines in PE4529 (except RF2, goes with a 470 pF to GND)
* Got rid of the VCC via which was crossing the RF line (argh)
* Finally got the courage to change a bit the board layout and escape from the thin strip that I was working previously.
* And another THANK YOU to Gordon AD5GG for his invaluable feedback

Files:

PCB Back: https://c.rf01.co:8443/q/ft-991a-pat-back-f.png
PCB Front: https://c.rf01.co:8443/q/ft-991a-pat-front-f.png
Schematic: https://c.rf01.co:8443/q/ft-991a-pat-f.pdf
Overview: https://c.rf01.co:8443/q/panadapter-rev-f.pdf
Eagle Schematic and board: https://github.com/rfrht/FT991A-PAT

Appreciate your comment, review, criticism and suggestions!

73s de PY2RAF.

 

Things are getting final, with a few refinements (and bug hunting). Revision G.

Changelog:

* Removed a forgotten 1 nF capacitor
* Implemented RF chokes in DC IN lines, as per Gordon AD5GG suggestion.

Files:

PCB Back: https://c.rf01.co:8443/q/ft-991a-pat-back-g.png
PCB Front: https://c.rf01.co:8443/q/ft-991a-pat-front-g.png
Schematic: https://c.rf01.co:8443/q/ft-991a-pat-g.pdf
Overview: https://c.rf01.co:8443/q/panadapter-rev-g.pdf
Eagle Schematic, board and other details: https://github.com/rfrht/FT991A-PAT

Appreciate your comment, review, criticism and suggestions!

73s de PY2RAF. \o \o