Yesterday I made the antenna a bit more weatherproof. Not quite happy with the outcome as the box didn’t fit the way I liked it. It is still a prototype, room for improvement. After a lot of tweaking with the Nanovna I settled with a nice SWR (or Return Loss if you wish, see pictures below).
Previous article of the antenna itself : click here.
Attached the antenna to my balcony on the first floor, 3,5 meter or so above ground. Pulled a coax to the shack and was eager to see the result.
At this moment I have my Ubuntu laptop with Radiosonde_auto_rx connected to the Diamond X50 antenna on the roof. The testsetup with the antenna is my desktopcomputer, RTL v3 stick and RTL Power. Yep, no decoding, just receiving. But I used RTL Power to scan the band and log the values in a file. This morning I compiled the image of the values using Gopow after 12 hours of datalogging.
The command I used :
rtl_power -f 400M:406M:4000 -i 20 -c 25% -g 38 -e 12h data_sonde20200412.csv
So every 20 seconds the band will be scanned, Take 4 kHz wide chunks, Compress 25% , gain set to about 38 dB and this for 12 hours, write all the data in the CSV file.
The image is created with the standard commando :
gopow -i data_sonde20200412.csv
This creates a pretty large image, almost 5 MB in size. You can download the original image if you wish.
I can spot 3 radiosondes. Two are very obvious but the third one was a very faint signal. It was not recorded/decoded on my laptop, too weak I guess.
I took the original image and estimated the frequency to be 405.3 MHz. Every pixel is 2,6 kHz wide, I drew a vertical line and counted pixels (not really, took the measurement tool from Paint.net). The 405 MHz marker is at pixel 1920, the unknown sonde at 2036. Some math : 2036 – 1920 = 116 pixels.
Times 2.6 kHz = 301,6 kHz above 405 MHz, So 405.3 MHz confirmed.
Now the timing, did the same procedure.
The time marker 00:48:05 is at pixel 918, the signal starts at 968 = 50 pixels. Times 19 seconds = 950 seconds. Roughly 16 minutes. So start at 00:48 + 00:16 = 1h04 (23h04 UTC).
The second part, signal ends at pixel 1326, time marker 03:05:09 at 1291 = 35 pixels.
Times 19 seconds = 665 seconds or 11 minutes.
Ends in 03:05 – 00:11 = 2h54 (0h54 UTC).
I now have frequency, starttime and endtime at my location. The search can begin. I took the table from RadioSondy with the data from the last 48 hours. And took only those from 405.3 MHz and unknown frequencies.
![](https://on3jt.byze.be/wp-content/uploads/2020/04/Table.jpg)
My best guess is that it is R1231023 launched in Essen (DE). Not bad for this small antenna, just a few meters above ground.
And finally the pictures and some links 🙂
- RadioSondy 48h data : https://radiosondy.info/sonde_table.php?table=last
- RTL Power manual : http://kmkeen.com/rtl-power/2014-07-27-08-09-20-103.html
- Download RTL Power (Windows) : https://ftp.osmocom.org/binaries/windows/rtl-sdr/
- Gopow : https://github.com/dhogborg/rtl-gopow
- Original bandscan image : Click here (right click to download)