Tag Archives: Interference

iZotope RX6 – A Miracle in restoring Audio

If you still desparately looking for a software to restore your recorded DX audio clips, iZotope’s RX6 offers an alomost perfect solution. While the de-crackling tool automatically removes all of these annoying statics, the near-unbelievable tool “Spectral de-noise” is doing wonders in extracting e.g. formants of speech out of noise, thus greatly enhancing intelligibility.

I did a convincing test with a clip of CKZN, New Foundland’s shortwave station still transmitting on 6.170 kHz with 1 kW; received June 1st, 2017 at around 02:00 UTC. The original recording is heard like this:

It looks like this, when opened in RX6, with spectrogram in the background:


First step was to automatically get rid of most of the static by “de-crackling”. RX6 offers you the chance to see also the garbage, e.g. what has been subtracted from the signal, see screenshot below with a focus on the identified crackles:


After this first step, the audio sounds like this:

Second step is the tool “Spectral D-noise”. Most comfortable is the “adpative mode”, where you see the audio much more clearly than in the original recording:


And that’s the way, it sounds, with 12 dB attenuation of noise (default):

Another mode is the “learning mode”, where you teach the software what it has to consider as noise in the recording, and then clean it up. First, I did it with the strongest value of 40 dB reduction:

Sounds quite artifical – but drop your ear onto the last part, how clean the jingle sounds!

With some right, default is 12 dB, listen here:

This may be reduced to even 6 dB – you have to find the right balance by yourself:

To restore audio of DX MP3 clips, is not where this software is really adressed to. But even for this purpose, it’s strong algorithms perform better than any other device/software, I’ve seen in the last 50 years. And there are a lot more functions to tweak a signal further. Not really cheap, but unique. There’s simply nothing better!


Ham Radio: Intruder Watch, State of the Art. Oder: Bandwacht nach dem Stand der Technik.


HF spectrum is precious. Each user has to obey specific rule – of ITU and his own country. For best communications, there have been assigned exclusive band for different user groups. The amateur radio bands for hams are among them.

“Intruder Watch” is to look out for stations which do have no legitimation to transmit on the frequencies they use. These signals can originate from broadcasters, bad transmitters with their fundamental on a legitimate frequency, broadcast, military (OTHR RADAR!), diplomatic …

Amateur radio with it’s relatively small transmitters and antennas is especially prone to be disturbed by intruders. SDRs, software and a specific workflow (see illustration on top of this page) offer an as easy as complete monitoring of such bands on a 24/7 base at low costs.

This paper shows how that can be done: monitoring and analyzing on a professional level.

Professionelles Monitoring spürt zuverlässig sämtliche Bandeindringlinge in Frequenzbereichen auf, wo diese nicht hingehören. Das ist, sogar auf 24/7-Basis, auch mit Amateurmitteln möglich. Das Werkzeug sind ein SDR, Software und ein spezifischer Arbeitsprozess.

Hier kannst Du das Paper auch auf Deutsch lesen, wie alles funktioniert – Schritt für Schritt.

Active Antennas, Interference by Power Supplies: A Test


If you don’t have much place, an active antenna is a fine alternative. You have to concentrate just on the signal-to-noise ratio, not so much on the S-Meter.

A recent test of some pre-production and (semi-)professional active antennas did not only had stunning results, but also draw my attention to noise coming from the switching power supplies of SDRs.

I did some investigations on both the performance of two active antenna vs. a quad loop of 20 m circumference and the noise coming from switched power supplies vs. two linear regulated power supplies. Read more