I live near the Helsinki airport and can spot planes arriving from the west fairly easily through my window. What I never noticed before is how many planes are arriving during the weekend.
Starting from 06:00 and happening every few hours or so, there’s a whole ballet of planes landing and taking of, way more than I anticipated.
That also means the airband is very active, so that keeps me busy listening to it.
After playing a bit with my HackRF, I managed to receive some stuff.
Every day or so, balloons called “radiosondes” are launched, and I can actually receive those.
The payload you see below contains position data, battery status, altitude, and a bunch of other stuff.
If you’re curious about receiving those, there is a website tracking those, their TX frequency and all the data.
Airband is used by planes to communicate with the ground. Given I live near the Helsinki airport, I’m in a prime location to receive those properly.
For instance, here is small compilation of recordings:
Do note listening to airband might be illegal in some countries, for instance, Germany or North Korea. Always check your local laws (though unenforceable).
Just yesterday, I received my HackRF PortaPack. The HackRF is basically an SDR, or Software-Defined Radio, that allows you to plug it to a computer and have a nice spectrum view of everything (amongst other things).
While the PortaPack integrates its own screen, battery and everything, I find it more convenient to connect it to my computer and use it that way. I can record more easily, have a larger view thanks to my monitor, etc, etc.
First thing I did was to update the firmware. Luckily, it’s really easy to do so, I just had to download the latest version of Mayhem, put it on a micro-SD card, use the internal flash tool, and done, all up-to-date.
Now, a lot of sellers will try to give you some SDR software to use with the HackRF: don’t listen to them. Instead, try SDR++, a Free and Open-Source SDR software, with built-in support for the HackRF. Added bonus: it’s even in the Fedora repositories! As a side note, you might need to add your user to the dialout group before starting to use it.
Once you have SDR++ installed, just head to the top right, in the “Source” section, in the scrolling menu select “HackRF”, and right below, select your HackRF (there should only be one).
Right below, I can recommend setting both the “LNA gain” and “VGA gain” to something like 16, it’ll make sure you can actually hear anything.
Other settings I can recommend tweaking a bit are within the “Display” section, near the bottom on the right. Do note those settings are my own preference:
Those settings basically reproduce the WebSDR look and feel that I’m used to (for instance, from the Twente WebSDR).
Now time to listen! To make things better, I can also recommend playing with the “Squelch” option. You might need to tweak this differently based on which frequency you want to listen to.
In any case, have fun listening to whatever you can find!
Last Thursday, while being at the radio club OH2K, I built a Pixie radio kit V3 (generously given to me by one of the regulars).
The Pixie radio is a low-power (about 0.4W when we measured), morse only radio that can only operate in the 7MHz (or 40 meters) band. Its main appeal is that you can build it from anywhere from €2 to €5, which makes it a really easy option to get.
The finished thing looks like this:
Given it was my first time building such a thing, it took me around two hours to build. It took that long because I mistook some components for others, and had to de-solder them.
Another issue I ran into was when using it at home. This board takes between 9V and 12V of power, so naturally, I fed it using my switchable power supply.
That’s where the first error came in, this introduced so much noise I thought the board broke during the transport from the club to my place.
Luckily, lazily soldering a wired barrel jack connector to a 9V battery solved the issue, and at night, I can hear really, really faint morse code in the background.
I’ve tried transmitting a bit, but so far, no response yet. I think it’s going to be hard getting anything out of that thing given my conditions aren’t close to ideal either (densely populated area).
I’ve also ordered a V4 board on AliExpress to see if it’s any better (but given the simplicity of the board, I doubt it). In any case, it’ll make for good soldering practice.
While listening to a WebSDR yesterday, I managed to catch a numbers station transmitting a message.
This was recorded at around 19:03:00 UTC, on 7317.0kHz
Looking around, this station seems to be named E11 “Oblique” and is apparently one of the most active. It is operated by an unknown agency, broadcasting from Warsaw.
I didn’t manage to record the whole message, but a good part is there, you can hear a group of numbers being started using the word “ATTENTION”, repeated multiple times.
From the documentation available on Priyom, this is the second part of the message, the first part being a three-digit ID, the word “oblique”, then a count, all of this happening over the course of around three minutes.
The full transcription of what I got (this may contain some errors):
ATTENTION 67438 67438 67860 67860 04039 04039 69177 69177 63054 63054 46049 46049 02736 02736 94777 94777 36055 36055 73069 73069 20594 20594 96622 96622 83251 83251 12182 12182 51324 51324 51379 51379 59126 59126 61168 61168 03718 03718 28981 28981 77820 77820 66222 66222 41823 41823 62573 62573 19825 19825 58059 58059 57872 57872 80128 80128 50473 50473 20071 20071 01721 01721 32356 32356 88691 88691 54694 54694 77204 77204 28423 28423 98119 98119 02337 02337 ATTENTION 67438 67860 04039 69177 63054 46049 02736 94777 36055 73069 20594 96622 83251 12182 51324 51379 59126 61168 03718 28981 77820 66222 41823 62573 19825 58059 57872 80128 50473 20071 01721 32356 88691 54694 77204 28423 98119 02337 OUT
The message, of course, ending at the “OUT”.
Someone out there probably has a better recording (with the full thing), well hopefully. That was just an interesting thing I wanted to share.
A friend sent me a link to an interesting blog post talking about making an Open-Source DMR radio using a LimeSDR board and GNU Radio.
Digital Mobile Radio (DMR) is a mobile radio standard created by ETSI, which is very popular within the amateur radio community. […]
A very basic DMR modem (receiver and transmitter), capable of voice calls, that could emulate a subscriber radio using a SDR transceiver as the radio interface is described in this page.
While this modem is just a proof-of-concept interpretation of the DMR standard with no real use-case, there exists at least one open source project which proposes to create an open source DMR transceiver.
You can see the full blog post over there: https://qradiolink.org/open-source-DMR-transceiver-implementation.html
On April 13th 2025, I managed to receive some odd signals on 14.090.00 which sounded just like packets of information being sent.
What’s weird is that I only heard this one this particular frequency twice, on the 13th and a day prior.
Here is a recording of those:
Currently, I’m using a Kenwood TS-430S with a homemade wire listening antenna.
I should receive a better antenna very soon, so maybe this frequency is allocated for something I am not aware of yet.
Location: Vantaa, Finland
Date and time: 2024/12/08 11:45 (local time UTC+2) – 09:45 (UTC)
Frequency: 15290kHz
SINPO: 2/5
Equipment: Tecsun PL-680 + wire antenna
Content Heard:
Unsure, asked a friend and only words they could understand were “Tokyo 23”.
Notes: I cannot speak Japanese, sadly. Lots of static and interruptions.
Contact: NHK WORLD-JAPAN | Contact Us
Card received:
