HF SDR-IQ for Shortwave Radiogram

Introduction

Several years ago I received a Shortwave Radiogram broadcast (Ref.1) using the RTL-SDR and 125MHz up-converter (Ref.2). It has been 4 years so I thought I would try again. As I mentioned in previous posts, I am using an HF loop antenna due to it’s ease of setup and noise rejection & directionality, since I am right next to a power line.

Equipment Layout

Fig.1 Equipment Setup

Figure 1 shows the equipment setup. I received SWradiogram Program 411 on August 2nd at 2300UTC on 9455KHz. I pre-tuned the HF Loop antenna to that frequency. In order to study the transmission, I received the signal using the SDR-IQ receiver with Spectravue software. I captured the whole program video/audio using Camtasia and as well recorded the audio using the Spectravue record feature. Afterwards I played back the .wav/.m4a files with Audacity and sent the audio via VBcable to Fldigi.

Transmission Schedule

Fig.2 SWRadiogram Transmission Schedule
Fig.3 VOACAP Propagation Path WRMI to VE3PKC

Figure 2 shows the transmission schedule taken from the Shortwave Radiogram web site (Ref.1) There are two transmitters, WRMI in Miami Florida and WINB in Red Lion Pennsylvania. Various transmitter powers and antennas are used depending on time & target areas. Figure 3 shows a propagation forecast for August 2nd between WRMI and my location. I used dipoles at 60m/20m and 10KW AM as parameters. This is very conservative since the transmit power is probably much greater with antenna gain as well. 30m propagation at 2300UTC is 80%.

Reception Details

Fig.4 Spectravue Reception at 9445KHz AM
Fig.5 FLDIGI Decoding MFSK32
Fig.6 MFSK Decoding MFSK64

Figure 4 shows the Spectravue receive screen. Noise level was around -125dB and the carrier with QSB from -90dB to -115dB. The transmission starts with a voice announcement and then switches to text at MFSK32, then pictures are sent at MFSK64 and finally transmission finishes with text at MFSK32. MFSK32 bandwidth is approx. 1250-1750Hz as in Figure 5. MFSK64 bandwidth is approx. 1000 to 2000Hz as in Figure 6.

Reception Results

Barbados Snake
Sunset Cayo Costa State Park Florida
Tower Bridge England
Fig.7a Pictures Sent MFSK64
Nocturnal Butterflies Santa Cruz California
Raindrop in Scotland
Wild Berries Buffalo New York
Fig.7b Pictures Sent MFSK64
Black Oystercatcher California
UK Red Arrow Aerobatics Team
San Jose Improv Comedy San Jose California
Fig.7c Pictures Sent MFSK64
Street 1930 by Gosta Adrian-Nillson
Fig.7d Pictures Sent MFSK64

Figures 7a/d show the pictures sent using MFSK54. As was mentioned previously there was some QSB, so on some pictures there is granularity. On Fldigi the SNR varied from approx. -5 to +10dB. I studied MFSK extensively in my HF eBook and found that you could have error free transmission with negative SNR (Ref.2).

Fig.8 YouTube Video HF SDR-IQ for Shortwave Radiogram

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YouTube Channel
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References

#1. – “Shortwave Radiogram”
https://swradiogram.net/

#2. -“RTL-SDR for Shortwave Radiogram”
https://jeremyclark.ca/wp/telecom/rtl-sdr-for-shortwave-radiogram/

#3. – “VOACAP HF Prediction Program”
https://www.voacap.com/

By Jeremy Clark

Jeremy Clark is a Senior Telecommunications Engineer and Advanced Amateur Radio Operator VE3PKC. He is the author of E-Books on Telecommunications, Navigation & Electronics.