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I am in the process of building a SWR meter with VNA-like features. I'd be really interested to hear from fellow hams any input, suggestions, or tips they have regarding this before I go get it mass produces. I'll share the schematic and technical details but I am also looking for feedback just in terms of usability or features or any criticism really

So basically I'm building an Arduino shield where the primary use case is to be a SWR meter with an LCD display (not depicted here as that is a separate shield). But it provides all the functions of a Vector Network Analyzer (VNA) and as such goes well beyond your typical SWR meter.

Because the primary use case here is to act as an inline meter on a transmission line with an existing transmitter its not designed as a typical VNA would be using mixers. The only thing it doesn't have that a VNA would have is a function generator, as it relies on the transmitter to do that, and the directional coupler would be external. However I have designed it in a modular way so not only can the directional coupler be swapped out for one the user prefers or more suited for their setup, but it can also be configured to work more like a traditional VNA as well. With the additional of an additional shield with an in-built low power directional coupler and a sine wave generator it would be possible to also pop on this other shield and effectively have a handheld VNA instead. Being modular there are also several other possibilities for how this device can be configured including as a remote SWR meter so you can have a meter at both the transmitter and the antenna to properly calculate feedline loss, or to understand how the complex impedance of your antenna changes with frequency.

Because of its role as an in-line meter in an existing antenna system it also provides functions a traditional VNA would not, specifically the ability to analyze properties of the transmitter such as accurately determining the true RMS under modulation or precisely determining the frequency the transmitter is transmitting on. Perhaps in the future I may add other features as well either in software of hardware.

Some specifications:

  • Operates 1 MHz to 500 MHz

  • Can measure input signals from -52dBm to 0dBm (adjust external directional coupler and attenuator to handle any power transmitter).

  • Inputs are 50 ohm matched but if building yourself you can switch out different resistors to match different impedances

Note: This is an open-source project and free for anyone else to replicate my work. At some point I may sell kits and/or the printed PCB to people to make it cheaper than needing to pay to get your own PCB printed. So I'd like to make sure if I provide PCBs they have been scrutinized and tested first.

The link to the projects source can be found here for anyone who wants to access the actual files.

https://git.qoto.org/roes/roes-hardware/

Here is a picture of the schematic:

enter image description here

Here is an older picture of the UI in demo mode. The data on the screen is intentionally bogus, and the glitches in the rendering have since been fixed.

enter image description here

This is a four-layer board so you'll have to see the GIT repository if you want to pick apart my layout in detail. But for now I will share the front side and back side so you can at least get a sense of my placement of the chips and my use of shielding.

Front:

enter image description here

Back:

enter image description here

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    $\begingroup$ Hey! While impressive, let's really not double-post this to electronics.SE and here in the exact same shape. I think the electronics design question might really be best off there, maybe you want to ask here specifically about the radio application utility and about UI from a ham perspective. $\endgroup$
    – Marcus Müller
    Sep 8, 2020 at 14:16
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    $\begingroup$ @MarcusMüller Thats fair, the way it is worded is really geared towards the EE side and not the radio usability side here.. I will edit the wording shortly, thanks. $\endgroup$
    – Jeffrey Phillips Freeman
    Sep 8, 2020 at 14:18
  • $\begingroup$ It wouldn't hurt to draw the schematic with lines connecting the components, so the connections can be followed without hunting through the entire page looking for matching labels. $\endgroup$
    – Phil Frost - W8II
    Sep 8, 2020 at 14:18
  • $\begingroup$ @PhilFrost-W8II I'll go ahead and disagree you here, imagine the complexity if the connections were actually executed as lines. $\endgroup$
    – Marcus Müller
    Sep 8, 2020 at 14:19
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    $\begingroup$ I would rather follow some messy lines than hunt over the entire page, not even sure if I've found every matching label. But even better, arrange the components logically on the page so the lines aren't a rat's nest, and use bus lines to consolidate related connections. If you must use a label, at least leave a note to provide some hint about where to look to find the other end(s). Example or a schematic of similar complexity which still manages to be readable: github.com/bitglue/lpsdr/tree/pi_hat/pi_hat $\endgroup$
    – Phil Frost - W8II
    Sep 8, 2020 at 14:29

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I think the problem you will run into is that people will want this to be plug and play. They may not have a directional coupler, or know or feel like to calibrate it and all that other stuff. Even if they do it, they may wonder if they did it right and if the reading will be accurate or not. I think you will need to handle this part in your design and support much greater power handling. Make it a pass-through, one connector on each side and that's it.

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    $\begingroup$ I agree. If I sold this as a completed product it would include a 1500W capable directional coupler and it would be pre-calibrated to use that. so pre-built would effectively be plug-and-play. It is only in the situation of a kit where the user would need to supply their own DC and calibrate it, but if they are working from a kit presumably they are ok with that. $\endgroup$
    – Jeffrey Phillips Freeman
    Oct 22, 2020 at 15:04
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    $\begingroup$ Hello and welcome to ham.stackexchange.com! $\endgroup$
    – rclocher3
    Oct 22, 2020 at 17:52
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    $\begingroup$ If this were intended to be a commercial product the customer probably wouldn't be interested in supplying an Arduino board, downloading and installing the Arduino software, and writing the firmware to the microcontroller either. $\endgroup$
    – rclocher3
    Oct 22, 2020 at 17:57

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