Tubular Bells and VLF interference

Tubular BellsRemember that album from Mike Oldfield? A user on YouTube found out that this album contains a hidden and unintentional CW message.

This was caused by a powerful VLF station located next to the recording studio, which interfered with the recording equipment. Because the signal is very weak nobody ever noticed it — until now.

The video below shows you how to receive VLF signals with nothing else than an antenna plugged into the microphone input of your sound card and SDRSharp to make it visible and audible.

The decoding of the the Tubular Bells signal is shown at 9:54.

(via Reddit)


CW message hidden in song reached FARC prisoners

In 2010 the Colombian army used Morse code hidden in a song to reach soldiers who were kidnapped by FARC guerrillas. It took a while to compose the song in such a way that only people proficient in CW would be able to pick it up from the background music, but eventually they succeeded to compose and send the following message:


A team began experimenting with Morse code using various percussion instruments and a keyboard. They learned that operators skilled in Morse code can often read the signals at a rate of 40 words per minute — but played that fast, the beat would sound like a European Dance track. “We discovered the magic number was 20,” says Portela. “You can fit approximately 20 Morse code words into a piece of music the length of a chorus, and it sounds okay.” The song was called “Better Days”.

Noble Radio NR-4SC: 4 meters for pros

When I first posted about Noble radio, the transceiver was still under development and looked quite different from the final product. Now the radio is for real; time to give the product some more attention.

noble_02The NR-4SC is a simple to use 10 Watt (minimum) 4 Meter SSB/ CW transceiver. The radio operates USB and CW. The NR-4SC uses a single conversion design with an IF frequency of 10.7 MHz. Front end bandpass filters limit out of band signals into the RF Preamp stage.

A double balanced diode ring mixer provides good strong signal handling capability. There are two 8-pole crystal filters following the mixer which are designed for 3.0 kHz and 500 Hz -6 dB bandwidths. The 3 kHz filter allows for good SSB voice fidelity while the 500 Hz filter provides good adjacent channel rejection on CW. Either filter can be selected in both modes.

Two IF amplifier stages and fast attack AGC provide good receiver sensitivity while leveling the audio output on strong signals. AGC action starts at approximately a -120 dBm input signal level. The local oscillator is derived from a DDS/PLL circuit providing a high degree of stability and low noise. A high stability 107.374 MHz reference oscillator is used for all local oscillator generation. The high frequency provides low DDS spurious output. The transceiver offers a 10.7MHz IF out on the back panel for connection to an SDR so it may be used with a PC for a Spectral Display.

Other features of the NR-4SC include RIT (Receiver Incremental Tuning) and SPLIT mode functions as well as a built in Iambic Keyer for CW. The AGC rate has a FAST and SLOW speed to suit operator preference.
GVXE was the first to post some first impressions, and added an extra article later in time about the radio being subjected to strong signals.

Factory specifications:
2) 10 Watt output power
3) Built in Iambic keyer
4) Analog S-meter, not a bargraph.
5) RIT
7) Variable Speed Tuning VST
8) Wide and Narrow filter
9) Fast and Slow selectable AGC
10) Output to key an external Amplifier
11) Can be switched for QSK and Non QSK compatible Amps
12) Simultaneous display of RX and TX frequencies
13) 13.8VDC at 4 Amps TX current
14) 650 mA RX current
15) Built in loudspeaker
16) Audio output .6 Watt
17) 10.7 MHz IF output
18) RX Sensitivity -130 dBm MDS
19) IF rejection greater than 100 dB
20) Blocking dynamic range 107 dB
21) Third Order Dynamic Range = 96db (IP3 = +14 dBm)
22) 2nd Order Dynamic Range 87 dB (IP2 = +44 dBm)
23) TX spurious is better than – 55 dBc which meets CE ETSI EN301 783-1 standards

Website: Noble Radio
Manual (PDF): download

Price in The Netherlands : € 499,00 incl. 21% Dutch VAT.

New SSB/CW dual-band for 4 and 6 meters

Still in beta, but might be interesting for the European market. A company called “Noble Radio” (link) is developing a dual-band SSB/CW transceiver for 4 and 6 meters. Price point unknown at this time.

Noble Radio

Preliminary Technical Specifications

Frequency Coverage
4M: 69.9 MHz to 70.5 MHz
6M: 50.0 MHz to 52.0 MHz

SSB (USB & LSB) and CW

Circuit Type: Down converting design
Dual Conversion: 1st IF: 10.7 MHz 2nd IF: 25 kHz

Sideband elimination using phasing techniques with digitally generated Quadrature carriers and Image Reject Mixers preceded by 15 kHz crystal roofing filters

Ultimate receiver bandwidth set by adjustable SCAF filters (two 8th order filters used. One for High Cut and one for Low cut)

MDS = -130 dbm

Dynamic Range Figures:
Blocking: 110 db
IMD (3rd Order) = 95 db

500 Hz to 4 kHz adjustable with the SCAF filters
Ultimate attenuation of filters are 55db or better

Frequency Coverage:
4M: 69.9 MHz to 70.5 MHz
6M: 50.0 MHz to 52.0 MHz

SSB (USB & LSB) and CW

Output Power:
20 Watts CW or SSB (PEP)

SCAF Filters can be used to tailor SSB Transmit audio.

DDS/PLL synthesizer with 10 Hz minimum step size. Tuning rate is variable depending on the Tuning Knob speed (Variable Speed Tuning – VST)

10 Memories per band