HF SDR-IQ on 19m VOACAP Prediction

Introduction

It’s been a while since I have monitored the HF bands, so I thought I would do a bit of scanning. In the last several years there has been a tremendous amount of construction near me and the HF noise level has increased quite a bit. I am right next to a power line which may also have some sort of signal carrier. My balcony has been rebuilt several times, so mounting my Buddipole HF antenna is rather risky now. So I used my HF Loop antenna which has several advantages. It is tuneable so you can get rid a lot of the noise as well it is directional. It is very easy to setup (one bungy cord) and take down in less than 1 minute. It is low profile so as not to upset curious neighbours.

Equipment Setup

Fig.1 HF Equipment Setup

Figure 1 shows the HF equipment setup. First I tune the HF Loop antenna to the band I want to listen to. In the case of the 19m band I use a small Sony ICF7600 portable shortwave receiver to do this. I connect the center pin of the PL-259 antenna connector with an alligator clip to the Sony whip antenna. Then I set the frequency to 15.5MHz/USB and tune the loop for maximum noise. I use the SDR-IQ receiver (14bit ADC!!) with Spectravue software.

Transmission Schedule

Fig.2 Spectravue Radio Exterior Espana 15.5MHz
Fig.3 SWL Broadcasts to North America 15500KHz

Tuning the 19m band I immediately noticed an extremely powerful station on 15500KHz as in Figure 2. I used the website “Shortwave Live” (Ref.1) to determine that this was Radio Exterior España with transmitter in Noblejas (south Madrid) as in Figure 3. Carrier peaks were between -50/-60dB and the noise floor was -115dB so a very strong signal indeed. The SDR-IQ bandwidth setting was 11600Hz.

VOACAP Propagtion

Fig.4 VOACAP HF Propagation Prediction

Since the receive signal was so strong, I thought it would be beneficial to study the current VOACAP prediction (Ref.2). I was not sure of transmit power but I used 10KW with simple dipoles on both Tx/Rx ends. This is conservative since I am sure the Tx antenna is some form of directional curtain array with higher power. Local time was approx. 1800 DST = 2400UTC. From the propagation wheel you can see excellent propagation from 2300/0300 on 20m and 2300/0000 on 17m which is what we are seeing. WWV at 15.0MHz was also received with a very strong signal.

Fig.5 HF SDR-IQ on 19m VOACAP Prediction

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References

#1. – “Short Wave Broadcasting Schedules”
https://shortwave.live/

#2. – “VOACAP HF Prediction Software”
https://www.voacap.com/hf/


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.