Direction Finding Method for EW System (ADALM-Pluto SDR)

[Fatih sevimli]

Hello everyone,

I am working on building an electronic warfare (EW) system for a competition using an ADALM-Pluto SDR. As part of this system, I will also need to implement a direction-finding capability.

The signals of interest may be analog or digital, and can be either narrowband or wideband. The system is expected to operate across a wide frequency range, from lower bands such as 433 MHz up to higher bands like 2.4 GHz.

For the direction-finding part, I am trying to decide which method would be more suitable: pseudo-Doppler direction finding or an interferometer-based approach.

For an interferometer system, I understand that I would need multiple SDR channels with very good phase coherence, which seems challenging with ADALM-Pluto SDRs. On the other hand, pseudo-Doppler can work with a single SDR channel by switching between multiple antennas, but I am unsure about its achievable accuracy and limitations, especially across different bandwidths and frequencies.

What are your thoughts on this? Which method would be more practical and reliable in this kind of system? Are there any important trade-offs or implementation challenges I should consider?

Thank you in advance.

[Sweet Thing]

I assume you are familiar with MUSIC?

https://www.researchgate.net/publication/258051205_A_Primer_on_MUSIC_Algorithm_-_A_SRDF_Technique

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[Fatih sevimli]

I have never phase-synchronized two SDRs before, so I am not sure how reliable or successful that approach would be in practice.

Do you think I should focus on single-channel methods such as pseudo-Doppler, which do not require phase synchronization, or would it be worth trying to phase-synchronize multiple ADALM-Pluto SDRs for an interferometer/MUSIC-based approach?

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[Fatih sevimli]

Additionally, the competition will be held on a 1 square kilometer area.

30 Nis 2026 Per 22:41 tarihinde Fatih sevimli <sevimli...@gmail.com> şunu yazdı:

[fasleitung3]

The ADALM-Pluto has some limitations in interferometer applicatios due to packet loss.

For a single ADALM Pluto which has been modified for dual channel operation, we found that coherence between the two channels is lost above 4-5 MHz bandwidth.

Things get worse if there are two separate Plutos. You can phase synchronize two of them using a common antenna and adjust phase offsets by looking for the correlation, but this works only up to about 1.5 MHz bandwidht. At higher bandwidth, you will get occasional packet loss on one or the other destroying the coherence. This is worse compared to the previous scenario and in that case the packet loss occurs, but mostly simultanously at both channels.

So as long as you stay within those bandwidth limits it seems doable. I cannot judge on the pseudo-Doppler as I have no hands on experience with that technique.

Best regards,

Wolfgang

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[Peter East]

The wide frequency range probably needs log periodic antennas and a scanning receiver.
Your simplest option would be a rotating static split. This is a pair of antennas squinted about 30 degrees feeding the two-channel ADALM-Pluto.
Then amplitude comparison looking for equal levels. You may have to do some basic gain tracking calibration.

[Scott Elliott]

Fatiha,

You may want to see how Kracken RF solved the direction finding problem.  They slaved multiple very low-end RTL-SDRs together from a common clock to maintain coherence.  Their software is open source for a starting point.  Kraken's CrowdSupply page has a good table of other examples.  Also Kerberossdr's git page may be of interest.

-scott

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[Adrian]

If you can limit your search for a max frequency of 2 GHz and  5MHz bandwidths drop the Pluto and use an RSP-duo SDR it has two built in coherent receivers and it costs about the same or even less than a Pluto. 

[Fatih sevimli]

Thank you very much for your responses. However, in my country, the only SDR devices readily available are RTL-SDR, ADALM Pluto, USRP, and HackRF. Since USRP is quite expensive, my practical options are limited to ADALM Pluto and HackRF.

I have been considering the pseudo-Doppler direction finding method, as it can be implemented using a single-channel SDR, which makes it attractive for my setup. However, I have some concerns regarding its performance, especially in terms of accuracy and robustness under real-world conditions.

Do you have any experience or insights regarding the performance of the pseudo-Doppler method (e.g., achievable accuracy, sensitivity to noise, or bandwidth limitations)?

Based on your experience, would you recommend pursuing the pseudo-Doppler approach, or would it be more worthwhile to focus on multi-device phase-synchronized methods despite their added complexity?

Any insights or suggestions you could share would be greatly appreciated.

5 Mayıs 2026 Salı tarihinde saat 04:55:03 UTC+3 itibarıyla Adrian şunları yazdı:

[Scott Elliott]

Jon Kraft, the lead applications engineer for Analog devices, has a youtube video of an unofficial do-it-yourself modification to the official Pluto to add a second channel.  That should reduce your switching burden.  There are many other tutorials out there such as here describing external clocks.  

[Scott Elliott]

Jon Kraft als has an interesting tutorial on beamforming rf tracking usign a dual channel pluto

[km...@aol.com]

I don't want to stir everyone up unnecessarily, but watch who you help. Todays friends are tomorrows enemies.  As an old EW engineer (50 years) and a life member of SARA, let me offer the observation that many had wished we had NOT sold scrap metal and aviation gasoline to the Japanese in the late '30's.

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[Doug Leber]

Sir,

I’m not sure why you are making this comment. What’s your point? 

Do you think any of the advice here is not readily available to people with the background to make use of it? Ask Claude or ChatGOT or Gemini…

Check your assumptions, please. Not all English speakers or Europeans  are ‘white hats’. 

Please  keep politics and prejudice outside this venue.

—Doug Leber

PS: By the way,  Turkey has been a member of NATO since 1952.

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[Fatih sevimli]

  I would like to thank everyone who has helped me with this matter. I would also like to mention that I am an electrical and electronics engineering student working on affordable projects for competitions, and I have no commercial or any other ulterior intent behind my questions—they are purely for educational purposes.  

5 Mayıs 2026 Salı tarihinde saat 20:34:26 UTC+3 itibarıyla Doug Leber şunları yazdı:

[Pablo Lewin]

Doug

The original poster said that he wants to build an"  electronic warfare (EW) system"....WARFARE....I had no idea that we at SARA were in business to help anybody (Other than the US armed forces of course)build WARFARE systems...

I think we should keep WARFARE systems outside this venue period.

Take care

Pablo Lewin WA6RSV

[Doug Leber]

Agreed. I'm more concerned about the tone of the response by kemc. No problems with objecting to the content of the thread. EW belongs on a different list.

However, we need to work hard to keep the poison of politics and cultural ignorance out of amateur activities. The author of the post I responded to chose to make reference to aiding and abetting enemies--- that's completely inappropriate for this venue.

--Doug

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