Novel use of ESP32 modules to 'see' microwave Wi-Fi signals

Florian Euchner is a student at the University of Stuttgart in Germany and he recently put up a video on his YouTube channel detailing his recent radio experiments. In it, he shows how by using a matrix of low-cost ESP32 modules, he was able to measure the delay and amplitude of some microwave WiFi signals and with some very clever software, he was able to display this on a screen. In a way, his method allows users to 'see' where radio signals at 2.4 GHz are coming from.

In the screenshot above, the direct Wi-Fi signal from a phone can be seen as well as a reflection on the left is from a metal screen.

What was really impressive was the ability to 'see' radio waves through something that is probably a wall made from plasterboard. As long as radio signals can pass through then they can be 'seen'.

Another interesting aspect of the experiment was how the radiation pattern from an antenna was 'visible'.

The video can be seen below...

Link...

1) Florian's website... https://jeija.net/

talkSPORT in the UK to close 7 AM transmitters on the Medium Wave band

It was recently announced that OFCOM, the UK regulator has given permission to talkSPORT to close down 7 of its 18 AM transmitters on the Medium Wave band. It is claimed that the move will reduce its national AM radio coverage from 92% to 88.9% of the UK adult population. 

The reasons given by talkSPORT for these changes include declining listenership to its AM service as people turn to alternative platforms, considered against the ongoing viability of each transmitter site.

The transmitter sites talkSPORT will close are...

1053 kHz - Stockton (Durham/North Yorkshire)(1kw), Southwick/Brighton (West Sussex)(2kw), Rusthall (Tunbridge Wells)(4kw)

1071 kHz - Clipstone (Nottinghamshire)(1kw)

1089 kHz - Lisnagarvey (nr Belfast)(13kw)

1107 kHz - Duxhurst (Surrey)(1kw), Lydd (Kent)(2kw)

As can be seen from the list above, the stations are relatively low power for an AM transmitter with levels of about 1 to 4 kw. The highest power transmitter is the 13kW output from Lisnagarvey near Belfast.

The remaining 11 transmitters will continue to transmit on 1053, 1071, 1089 & 1107 kHz. Some of these run in the region of 80 to 130 kilowatts so it's likely that most listeners in the UK won't notice any difference when the seven listed transmitters above are turned off.

A timeline for the closures wasn't given but it seems likely that it will be done after an appropriate warning to listeners.

The trend of closing down AM transmitters continues as more and more people opt to listen to radio stations via FM and DAB or online by using Smartspeakers or phone apps.

New DAB+ trials to commence in Ireland - 2025

Back in March of 2021, the Irish state broadcaster RTÉ announced that their DAB digital radio service was ceasing. More details in my previous post HERE

It has just been announced that a new DAB+ trial will commence in the east of Ireland in the late Spring of 2025. This time, the trial is being conducted by a company called Foothold Communications under a ComReg DAB+ trial license. 

In the press release, Stephen Foley, Managing Director of Foothold Communications said... “Today marks a major milestone in Irish broadcasting as we work alongside ComReg to develop DAB+ services. With 80% of radio listening happening in vehicles, and all cars sold in Ireland since 2021 equipped with DAB+ as standard, the time is right to expand and enhance this technology to reach a wider audience. We appreciate the opportunity to roll out this critical DAB+ service, which aligns with Ireland’s Broadcasting Services Strategy. This trial will showcase the immense potential of digital audio broadcasting for both listeners and broadcasters.” 

According to their website, the licence from COMREG for the DAB+ trial will operate for 1 year from the April 2025. They go on to state... "It is intended that user feedback along with in depth analysis, will give useful user experience and technical information to aid in the process of future licensing of DAB+ in Ireland."

Analysis... The coverage area is shown on the map above and the black dots show the associated 6 transmission sites with high power assignments. A 20kw transmitter in Three Rock will cover Dublin, along with a number of 8kw and 10kw sites, giving coverage along the east coast.

This area covers the capital Dublin and the surrounding counties with an estimated population of about 2-million people.

It's a surprise to me to see the re-appearance of DAB radio in Ireland and it'll be interesting to see what the interest will be like. I think most people thought the DAB wouldn't reappear for a very long time.

For a lot of people, they no longer listen to actual radios but get the programmes instead via smart speakers and apps. Why go to the trouble of tuning into DAB+ when you can just stream the service online instead.

On the other hand, a lot of new cars in Ireland have DAB+ in their entertainment systems and it's no great effort to do a scan and find the new signals. There are a lot of stores which are common to both the UK and Ireland and DAB radios often appear in Ireland even though there were no signals.

There is very little information at the moment as to who will be on the platform for the trail and as always, content is king. So far, Radio Nova and Classic Hits Radio have expressed an interest in taking part in the trial.

At least this time, the trial will be on a commercial basis and it will show if there is a demand for a DAB+ service in Ireland.

Links...

1) https://failtedab.ie/

Aircraft Scatter causes interference to radio telescope in Australia

The Murchison Wide-field Array (MWA) is a radio telescope located in a remote part of western Australia and it's made up of 4,096 antennas designed to detect radio waves between 70 and 300 MHz. One of its primary goals is to detect very weak radio signals coming from the reionization when the first stars and galaxies were forming. 

The MWA radio telescope is located inside a 300-kilometre-wide radio quiet zone which is supposed to eliminate all signals from terrestrial sources. This is very important because any signals from a source on Earth would likely be  much stronger than any signals from the cosmos.

It turns out that the 300km wide quiet zone may not be wide enough as the array was still picking up some interference as shown below. The image shows a signal between the frequencies of 181.5–187.5 MHz, and with times between 35 and 50 s.

By analysing the signals, they were able to determine that the interference was from Australian digital TV channel 7 and the signals was being reflected off an airplane traveling at 38,400 feet (11.7 kilometres) in altitude and at a velocity of 792 kilometres per hour.

A recent study has found that aircraft are present above the horizon line at the site at least 13% of the time, establishing a lower limit on the data potentially lost to reflected interference from aircraft.

It is now hoped that this type of new interference can now be modelled and be subtracted from the final data from the observations.

A highly detailed account of how they found the interference can be found HERE

Comment... I found the above news item of interest for a number of reasons. There are similar but smaller VHF radio astronomy telescopes scattered across Europe as part of the LOFAR network and these must surely suffer from similar interference considering the higher density of aircraft over Europe and the extensive DAB radio network.

It's also a reminder that the VHF bands are certainly not 'line of sight'. There are multiple propagation modes that allow signals to be heard even briefly over many hundreds of kms.

Irish VHF beacons off-air for the foreseeable future

For the last few years, the EI1KNH, EI0SIX and EI4RF beacons have been operating from a site to the south of Dublin with an excellent take off to the east towards the UK. Now due to a change of ownership of the site, the radio beacons will be turned off on Saturday 15th February 2025.

The EI4RF beacon on the 70 MHz band (4m) will be the first to re-locate and it is hoped that a site will be available in the same general area. All going well, it will be operational for the start of the Sporadic-E season in May. It is hoped that EI0SIX operating on 50 MHz (6m) will be added soon after.

Getting the EI1KNH 40 MHz and 60 MHz beacon back on air will take longer. The change of location will likely require a change of callsign and this must be applied for. Hardware considerations at the new site should mean that the 60 MHz (5m) beacon will appear first but the 40 MHz (8m) beacon may be more problematic.

As soon as there are any more developments, I'll post them on the blog.

A look back at the Long Wave band in 1991...

In a recent video on his popular Oxford Shortwave Log YouTube channel, Clint, M0OXF lamented on how few stations are now listed in the 2025 edition of the World Radio TV Handbook. 

I have embedded the video at the bottom of this post.

Just by chance, I came across the 1991 edition of the same publication today and I had a look at the Long Wave section.

As might be expected, there were no shortage of stations back then in Europe and in Asia.

The list for Europe, Africa, the Near & Middle East is shown above and below..

As was common with long wave stations of the day, power levels up in the hundreds of kilowatts were pretty common.

The other region of the world where Long Wave was used was the eastern part of the then USSR and Mongolia. The first section is shown above with the second part below...

This was of course a time when broadcasting on the Long Wave, Medium Wave and Short  Wave bands was a source of information and entertainment in a pre-Internet World.

The video below from Clint shows the current state of the Long Wave band in 2025...

Ongoing WSPR tests on the 144 MHz band in Australia - Dec 2024 & Jan 2025

While the WSPR beacon mode is very common on the HF bands, it seems to have been largely ignored worldwide by the VHF community. 

The exception however is in Australia where there is a very active group of radio amateurs sending and receiving WSPR signals on the 50 MHz and 144 MHz bands.

The map above shows some of the typical paths recorded on WSPR on the 144 MHz band in Australia. The longest distances are usually the sea paths across the Great Australian Bight.

John, VK2IJM compiled a list of the longest paths on 144 MHz during the months of December 2024 and January 2025.

As you can see, some paths were close to 2800 to 2900 kms.

John, VK2IJM writes... "Many thanks to those that had their rigs turned on and uploaded spots during December and January.

I've collated the 2m results already (see above) and they show a quite amazing summer for troppo downunder. We didn't quite crack 3000km this summer, but the 2850km spot between VK7DC and VK6CPU must be close to a 2-way record. 

The longest spot was from VK6ZE to Leigh VK2KRR. 2m ES were slow in December but picked up in January with several large E storms. The big troppo this summer was across the bight to VK6, where we had days on end with spots to VK3 and VK7 and almost nothing to ZL, which is typical of La Nina years."

It would be nice to see more 144 MHz WSPR activity in places like Europe, USA and Japan.

FOSDEM 2025 in Brussels -- HAMNET, M17 & MESHTASTIC presentations

FOSDEM is a free event for software developers from all over Europe to meet, share ideas and collaborate and it held this year in Brussels on the 1st & 2nd of February 2025.

Out of the 1000+ lectures, a few were radio related...

Saturday - 1st Feb 2025
Using AI hardware accelerators for real-time DSP on embedded devices - NPU, TPU etc,
M17 and OpenRTX: one year later
The AFF3CT framework for building numerical communication chains
HAMNET - Status Update
RF Swift: A Swifty Toolbox for All Wireless Assessments
SDR++, a modular, cross-platform SDR utility
Broadband data transfer over USB for GNU/Linux: 1-2 GHz (L-band) SDR receiver
Meshtastic - off-grid communication for everyone
Yet another new SDR runtime?

Some of these talks have slides available in PDF format and there are links if you want to explore the subject more.

The links to each radio talk can be found here... https://fosdem.org/2025/schedule/track/radio/

Here are three subjects that I found of interest.

1) HAMNET... 

HAMNET is a Highspeed Amateur Radio Multimedia NETwork developed from an experiment into a stable infrastructure, particularly in German-speaking countries. It generally connects unmanned amateur radio stations via microwave links using the IPv4 and BGP protocols and provides a platform for networking amateur radio applications.

The slides for this talk can be found HERE

2) M17...

M17 is an open source protocol for digital radio and its goal is to allow radio amateurs to communicate via digital voice and data. The M17 team are also developing open source hardware in conjunction with this. The net result is to have hardware and software that is designed for the amateur radio community and is not dependant on commercial companies or third parties. In other words, M17 is designed by radio amateurs for radio amateurs.

The slides for this talk are HERE

3) Meshtastic...

Meshtatsc is described as follows... "Meshtastic is an open source, off-grid, decentralized, mesh network built to run on affordable, low-power devices.  It uses Lora-P2P with dedicated radio chips and forms ad-hoc meshes. In HAM mode the encryption is switched off and the ISM airtime restrictions are lifted."

Meshtastic goes beyond the confines of the amateur radio bands and allows anyone with an interest in electronics to experiment on the UHF licence free ISM radio bands like 868 MHz in Europe and 915 MHz in North America. Radio amateurs have the ability to use higher power on bands like 433 MHz.

More links can be found HERE

190km contact on 10 GHz FM from Tennessee to Virginia - 19th Jan 2025

Thanks to Amateur Radio Weekly, I came across a recent contact on the 10 GHz band that took place between the states of Tennessee and Virginia in the United States.

The video shows a successful contact on FM between N4OFA in grid EM86RS and K4LY in grid EM85WB. The distance was about 190kms or 120-miles which on FM over an obstructed path is impressive.

I looked at the path profile and it seems that the most likely mode of propagation was knife edge diffraction over the mountains in between.

It was curious to note the QSB (fading) on the signal as well. Reason? Vegetation moving? Some aircraft scatter?

In the video description, Mike N4OFA writes... "This is a video that amazed both of us, signals were very strong,  I found Doug's beacon where he was portable near his house. A quick touch up with my wonderful tripod and he was hitting S9 with quick QSB.  What kind of propagation is this?  Doug's FM signal sometimes hits S9 on my little FT817nd.  Note:  no elevation on the dish at all,  no rain cells between us.  We did not try CW as there was no need since we could carry on a conversation even on FM."

See video below...

Addendum: Jacob, KG4AUW on Twitter suggested that the path might have been possible by bouncing signals off fire watch towers on the skyline ridge of the mountains.

Over a path of 190kms, it's probably impossible to be sure but there seems to be plenty of reflective metal surfaces there.