The UPS is huge noise generator – or it should I say, it was!
In picture below, on the left hand side this is the noise generated by the UPS when running, on the right hand side UPS is inside a very simple metal mesh cage built from the stuff from the attic in half an hour. Receiver antenna was 34cm away from the UPS case and SDR was set to listen from DC to 10MHz (note the scale in the picture, I’m using HamItUp converter with 125MHz base frequency). I consider this test to be successfull 🙂
This is my second metal mesh I have built and based on the test I will cover all my computers, peripherals and other with similar cage during the next field day at my remote site.
While waiting my trip to my remote site I started to plan a new RF shielding and interference protection. After all I’m going to replace 99% of the computer HW I have at my remote site and it is known fact that computers are the worst noise generator one can have.
The new system is built using the latest version of Intel’s NUC computer and RaspberryPi 4th gen. The NUC is well protected by default but of course it will cause a lot of noise to VLF and HF bands, but the worst is the RPi.
Next step is to level down the interference SDR HW causes, for that I needed to measure the base interference of all the RTL-SDR dongles I’m gonna use and also the RSPdx.
I’ve had a great experience how to level down RF noice by wrapping cheap power supplies with metal mesh, so I’ll continue with that idea with the computers and external devices that are going to be installed to the remote site.
Measuring the BASE interference
As with the power supplies, I used Airspy Mini as a receiver and HamItUp up-converter so that I can have measurement from the DC to 10MHz. Software used was SpectrumSpy and during the measurement the antenna was kept in place and all the devices under measurement were placed inside the antenna loop one by one.
“Under the Loop” went:
NooElec SDR “Mini” – without it’s cheap plastic case (removed for cooling) NooElec SDR “NESDR SMArt – Original metal case intact NooElec SDR “Nano three” – Original metal case intact RSPlay’s RSPdx – Original metal case intact
RaspberryPi 4 – Aluminum cooling grid installed, but no RF shield External USB 3 HDD – Samsung 2TB 2,5″ HDD with plastic case External USB 3 SSD – Kingston 256GB 2,5″ SSD with aluminum case External USB 3 SSD – Samsung 256GB 2,5″ SSD with aluminum case
Yes, I need to have metal mesh especially around RPi and external HDD’s, but it would not be that bad idea to have a metal mesh also around RTL-SDR dongles and even the RSPdx too as they seem to be quite noisy ones too.
Measurements were done so close to the device as possible – do note, that noise levels went dramatically down when I moved the antenna loop 20cm away from the device, so the metal mesh does not have to be a “military” grade EMP protection 🙂
1: Open USB 3 cable, no connected device 2: Open USB 3 cable, no connected device, cable wrapped around the loop 3: External 2,5″ HDD, plastic case, Drive software eject 4: External 2,5″ HDD, plastic case, Drive connected, spinning up and active 5: External 2,5″ SSD, aluminum case, Drive connected and active, model Kingston 6: External 2,5″ SSD, aluminum case, Drive connected and active, model Samsung 7: External 2,5″ SSD, aluminum case, Drive software eject, model Kingston 8: External 2,5″ SSD, aluminum case, Drive software eject, model Samsung 9: RPi 4 max load shutting down to standby 10: RPi 4 from bootup to running, no load 11: RPi 4 from standby to power cutoff 12: RSPdx 10M mode, max USB bandwith in use 13: RSPdx UNO started device active (Play) 14: RSPdx UNO device not active (stopped) uno closed 15: RSPdx UNO started, SDR activation 16: RSPdx plugged in, no UNO running 17: 1st Gen. NooElec dongle no plastic case 18: 2nd Gen. NooElec Dongle no plastic case 19: 3rd Gen. NooElec Dongle original metal case 20: 4th Gen. NooElec Dongle original metal case
And the bonus measurement – The UPS
I need to install an UPS (Uninterrupted power supply) to my remote site as I need to have better protection against lightning, power grid interference and mains power loss. The internet connection is via 4G broadband radio modem, so I am able to connect to the remote site as long as there is still power on the operators radio tower and in my UPS battery.
UPS devices are terrible noise generators. What they do is that they rectify the mains 220v AC to DC, store spare power to battery for later use and for devices. To be able to react to the power line fluctuation, un-clean power grid electricity and total power loss in few milliseconds the UPS devices usually re-create the output to consumption devices using AC–>DC–>AC conversion. To achieve this these UPS are generally powerfull DC to AC inverters – and inverter is huge noise generator what comes to the VLF, HF bands. Usually the switching power system used in cheap inverters works around 100KHz up to 600KHz switch frequency. If you live near an solar plant you know what kind of interference an inverter can spread around if not well insulated and RF protected.
My UPS is a cheap Eaton model 3S 550 with plastic case – absolutely great device for uninterrupted power and noise! 🙂
So, how noisy the UPS is, lets find out! Loop next to the UPS and …
Well, yes – maybe I need to first protect the UPS and then go with the rest 🙂
The bottom part of the picture above is when the small loop antenna was 1 meter away from the UPS. I then slowly moved the loop closer to the UPS and the upper part of the picture is where the loop rest against the UPS case.
The system used in my measurement is not meant to be high tech absolute value deep level measurement, but a hobby level visualization of the RF interference present in the hobby level devices for remote site operator. Also it should be noted, that the interference of these devices goes dramatically down after some few meter away from the device itself.
In DX hobby the thing is to try to hear very fade signals all around the world, often signals that are even under the base noise of the band. With a good antenna and a good radio one is able to receive the signal of a “flies fart” from Japan, so when put into that perspective a noisy power supply few tens of meters away of the antenna could totally disable your DX station.
As we all know now, the SARS-CoV-2 virus, commonly known as the “Corona virus” is spreading around the world.
As a member of the HAM community and the full supporter of the HAM spirit I feel obligated to do anything I can to both protect my fellow citizens and to help to find the cure for this new virus that has caused the latest pandemic.
I am huge SDR fan and I use very powerful computers in my hobby. Most of the time my system is still idling, one cannot sit 24/7 front of the computer listening, and the automatic system I also use really does not need full CPU&GPU to do it’s magic.
Folding@home team has released an initial wave of projects simulating potentially druggable protein targets from SARS-CoV-2 (the virus that causes COVID-19) and the related SARS-CoV virus (for which more structural data is available) into full production on Folding@home.
And in the future, if you feel that such CPU donating is something you would like to do, then do not uninstall the Folding@home client from your RIG, while you keep going with your everyday activities, your computer will be working to help find cures for diseases like cancer, ALS, Parkinson’s, Huntington’s, Influenza and many others.
On the other day I was listening SSTV (yes, this is about SSTV 🙂 – again) transmissions and heard familiar sound that should not be there, a Windows USB disconnect-connect-disconnect-connect … … …
My analysis is that the user sending the SSTV picture has some RF leaking to the computer system he/she uses causing Windows to connect and disconnect some USB connected device.
This is a very good reminder about the importance of shielding computer systems from the RF noice generated by the HAM RIG, especially when using high power systems.
I do not know what is the real reason for this, could also be intentional injection of audio to the transmission with low enough frequency that it would not cause problems with the actual SSTV signalling, then again that is not allowed in the SSTV channel so I stick with my analysis about the problems with the sending computer.
While SSTV DX’ng I heard a very familiar melody while listening the transmissions. First I thought I heard wrong, but when this happened again I was sure this was intentional – and I was able to record it too!
I got so excited about SSTV that when I do not use my system to other DX’ng I have it on 24/7 and tuned to 14230KHz and let RX-SSTV to automatically decode and save received SSTV transmission to my Google album.
I’ve been reading about SSTV some time now, but never tried to receive it as the most common bands have been very silent every time I have had time to tune in.
Today was different and I quickly learned that the most common 20m band frequency here in Europe (14230KHz) was packed full with SSTV transmissions. Actually there was so many simultaneous transmission that they overlapped badly, also the secondary frequencies were used to help the situation.
I quickly installed SSTV software and started to experiment with the reception.
With a fast computer, good radio and antenna it was very easy to receive first pictures – just some fine tuning and tweaking was needed for the best picture quality.
Based on the locator ID / Callsign I was able to receive SSTV images from Hungary (Budapest), Italy (Near Milan), Bulgaria (Sofia), Italy (Illasi), Italy (Gorizia), Scotland (Greenock), Hungary (Bekescaba), Russia (Zemetchinskiy rayon) and many others 🙂
And this was just a first try with the SSTV DX’ng!
I just learned, that no more Hi-Resolution pictures are sent from the Russian weather satellite METEOR-M N2-2 using 137MHz frequency as it was struck by a micro-meteorite on Dec 18 2019, causing it to lose control and go offline.
This information is sad as I was so hoping to continue with my experiments with the LRPT decoding later this year when sun light is back with us in the north hemisphere – during winter time Meteor pictures are nothing more than black frames.
There is still the older Meteor-M N2 but the pictures sent by the N2-2 were so much better.
Well, things like this happens when you are in space 🙂
” VVV VVV VVV DE SAQ SAQ SAQ … CQ DE SAQ SAQ SAQ = THIS IS GRIMETON RADIO/SAQ IN A TRANSMISSION USING THE ALEXANDERSON 200 KW ALTERNATOR ON 17.2 KHZ . WE WISH YOU ALL A MERRY CHRISTMAS AND A HAPPY NEW YEAR . = SIGNED : THE WORLD HERITAGE T RIMEION ND THE ALEXANDER-GRIMETON VETERANRADIOS AENNER ASOCIATION FOR QSL INFO PLEAEE READ UR WEBSITE : WWWALEXANDER.N.SE II WWW.ALEXANDER.N.SE = + DE SAQ SAQ SAQ SK ”
(taken directly from the MultiPSK screen – some errors due to interference in reception)
The holiday greetings from the famous Grimeton Radio/SAQ were heard as always beginning with the tuning of the alternator around 7:42 UTC on 24.12.2019.
08:00 UTC started the live keying from the site with the message (above). SINPO of the transmission was great 54445 and was easy to hear with my system. Live keying ended around 08:04 UTC.
Used tech: SRPDuo, PA0RDT MiniWhip connected to Z-input, SDRUno and MultiPSK for the Live CW decoding.