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RF Breadboarding System

saelig.com

56 pointsChuckMcM17 comments

I thought I'd see something more like this Amateur Radio homebrew proto board I designed a while back:

https://www.pcbway.com/project/shareproject/W7RLF_Proto_Boar...

That is pretty neat!

Pretty cool--it seems very focused on FPGA type RF backends, so stretches a bit what I'd personally call RF breadboarding (compared to actual RF circuits, power dividers, etc).

I feel there's definitely a need for generally making RF equipment more hobby friendly. I've long had the thought to make a modular RF test station, similar to the NI-PXI [1], but you know, not $50k. Similarly at one point I actually starting making prototypes of a simplified, low-frequency clone of the X-Microwave [2] system, which feels more like what I mean by RF breadboard.

[1] https://www.ni.com/en-us/shop/hardware/products/pxi-rf-multi...

[2] https://quanticxmw.com/reference-design-kits/

Do you know of any good source of CAD files or even just schematics for DIY PXI modules out there in the wild wild internet?

This looks interesting, but not particularly well marketed. Probably close to $4K configured to do basic RF work but I found it interesting. I am a bit surprised it doesn't have a basic FPGA + ADC/DAC module that could provide transceiver functions. (it may, it could just be the sparse descriptions)

I have been noodling on the idea of a "modular" amateur radio and this popped up on my research on whether or not there was something out there already doing that.

Maybe not entirely what you're looking for but certainly modular. https://quanticxmw.com/

That is pretty cool.

Kind of clever, but you could probably accomplish most of this with modules from Mini-Circuits:

https://www.minicircuits.com/

Very cool, asking as a layman, what parts would one use to implement hobby level microwave, two way, point to point communication?

Surplus ones from eBay. Buying this stuff new would send most of us to the poorhouse.

ubiquiti gear? https://store.ui.com/collections/operator-airmax-and-ltu

I've also been working up an idea. You can do a lot with a frontend and ADC that can be on a single board and push everything into the digital domain where board to board connectors work better. I want to do a vhf/uhf+ dual slot modular SDR handheld that has first class data support, so no stupid AF modems to get APRS or M17.

Pretty much. There is an interesting protocol for sending IQ data over Ethernet (VITA 49.2) which can be decoded in an FPGA and dumped into a data stream. LVDS pairs work too of course. I've got a 4MSPS ADC which is being driven by an ICE40 FPGA to generate a 1MSPS fully analytic stream. 1MHz of bandwidth isn't really good for WiFi or Bluetooth but you can easily do all of the common modulations in use by amateurs.

How are you thinking you'll structure your frontend? I've been looking at ZIF, maybe the CMX991 or similar.

One thing I've also been investigating is the possibility of pushing the bandwidth way up to 10-20MHz and using a larger FPGA for DSP then conversion to PCIe. An increasing number of smaller SOCs/SOMs are supporting PCIe so that opens up interesting options like a CM4 on the low end or a Jetson Nano on the high end for all manner of shenanigans.

    LNA -> band filter -> mixer -> LPF -> ADC
                            |
                           LO

My current bodged together setup as 40/20/15/10M filters tied to a 4:1 RF switch (mini-circuits).

The "easy" design is the reference design for the AD9863 (they even have layouts you can use) but I wanted to see if I could make it so that the entry level version was very inexpensive and you could add money for more capability.

Nice, that's a good band selection. With the 9863 you could pretty much cover everything without even mixing but you'd be looking at some high end FPGAs and processors

RF electronics, systems and control are normally considered as black arts in the electronics community due to the "distributed" nature of RF signal waves propagation. Most of the RF literatures even by the veteran experts are still working in the obsolete old school framework without regards for the other improvements in the field for example software-defined radio (SDR). For those who want to know modern approach to RF systems design please check these two books by Earl McCune and Huseyin Arslan [1][2].

However something very important is missing from many of these RF books including the books mentioned above. The most important thing is how to reliably and accurately detect, measure and control the impedance of RF signals. This topic is so pertinent that the terminology of "impedance mismatched" is even widely used outside of the RF domains or circles. The mechanism for detecting, measuring and controlling impedance mismatched is relatively unknown outside RF community that are called load-pull and source-pull. Coincidentally these happened to be part of my research study topics about 15 years back and it's a kind of solved problem now even for RF wideband signals that are common in modern RF system set up. Spoiler alert, to do it properly it cannot be done in analog domain but need to done in digital domain. Looking back on why the solution is not popular although it is being openly published is quite a mystery to me personally. Perhaps this what Dijkstra lamenting why his solutions to OS problems were oblivious to most OS implementors was perhaps because he is not from MIT.

The solution is not without its limitation because real-world RF signals have baseband, fundamental and several harmonics and the solution does cover the baseband due to the limitation of direct conversion transceiver being used. But now since companies like AD and TI have managed to manufactured fully digital high frequency ADC/DAC transceiver architecture that the limitation kind of disappeared for good.

[1] Practical Digital Wireless Signal:

https://www.cambridge.org/core/books/practical-digital-wirel...

[2] Wireless Communication Signals: A Laboratory based Approach:

https://www.wiley.com/en-ie/Wireless+Communication+Signals:+...

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