In this post you can read about the sensitive SDR receivers SRM-3000 and SRS-3000 and how to intercept mysterious secret transmissions with them. For additional content visit our resources page or subscribe to our newsletter here!

Sensitive SDR receiver based on the DRU-254 digitizer hardware platform

The DRU-254 digitizer board was designed and implemented for building radio receivers. Firstly it contains a 16 bit resolution low-noise Analog-to-Digital Converter (ADC). Secondly it has a low-noise input preamplifier and an input attenuator in front of the ADC. As a result the low-noise preamp provides input sensitivity as low as -111 dBm in SSB reception mode with 2.1 kHz bandwidth and 10 dB SNR. In addition with external preamplifier it could be as low as -122 dB.

Sensitive SDR receiver as long range DRM SDR

To begin with, if you are not a professional radio enthusiast with a vast knowledge of exact broadcasting carrier frequencies, one of the easiest ways to find some DRM radio stations is to just look for its unique spectrum in the HF band. The DRM spectrum is a very typical, noise like, wide band signal. Likewise this is exactly what we did; we simply connected the antenna to our receiver through a 30 MHz low-pass input pre-selection filter. After we started visually looking for DRM radio signals in the spectrum. Suprisingly one of the first signal received turned out to be coming from India. The next one was from South Africa. The SDR receiver seems to be real sensitive if we are able to decode these signals in the middle of Europe.

You can read about how to connect SDR receivers to the Dream DRM decoder software here:

Sensitive SDR receiver for secret transmissions

One of the most interesting signal in the HF spectrum is the UVB-76 Buzzer on 4555KHz. You can read about the mysterious Buzzer here:

As the frequency is well known, you could simply dial it in to the SDR receiver software, and immediately see the transmission on your screen and hear the famous “Buzzer” tone on the speaker with very high Signal-to-Noise Ratio (SNR).

In conclusion there are a lot of mysterious signals in the HF spectrum. As a result the sensitivity of our receiver – especially with an external, low-noise per-amplifier and a good antenna – makes it possible to listen to even the most remote signals.

Sagax Communications – Always on Target

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