HF spectrum monitoring using a PC-based scanning receiver

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HF spectrum monitoring using a PC-based scanning
receiver

• M.R. Hyde
• IPS Radio and Space Services

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Abstract

• Real-time HF spectrum monitoring using scanning
  receivers has traditionally required expensive
  radio equipment with a hardware computer
  interface, dedicated logging equipment, and
  custom software. These diverse components can
  require considerable expertise to integrate into
  a working system sufficiently reliable to deploy
  at remote sites. This presentation describes a
  simple, relatively low-cost setup using one of
  the new PC based scanning receivers. The system
  consists only of a PC with installed receiver
  card, and an antenna. There is a freely available
  form of interpreted BASIC programming language
  for these receivers, which includes commands to
  control receiver functions. Commands are also
  available to control data logging and produce
  simple on-screen graphics. This small
  instruction-set language makes monitoring
  acquisition and control program development quick
  and easy, even for novice or non-programmers.
  Given a stable mains power supply, the system is
  sufficiently reliable to operate unattended for
  many months. Some HF spectrum data from scans
  acquired during field trials on a range of
  antennas are presented. A near-real-time
  short-wave fadeout monitoring application is also
  discussed and some sample field data presented.

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HF channel occupancy monitoring

• The scanning receiver used in these trials is a
  WinRadio model WR-1550. We are using the internal
  version, which occupies a single ISA-bus card
  slot. An external (serial interface) version is
  also available. IPS is primarily concerned with
  radio propagation in the HF spectrum, so the
  trials were limited to a 2 - 20 MHz frequency
  range, although the receiver has a very wide RF
  bandwidth extending to 1.5 GHz. A newer series is
  now available from WinRadio, the WR-G303/313,
  which is restricted in maximum frequency to the
  HF range, but has greater flexibility and
  functionality than the 1550 series.
  Internal/external configurations for this newer
  series are PCI-card/USB-bus format respectively.
• The HF spectra below show channel occupancy in
  the 2-20 MHz region. At present, the logging
  program is set up to maintain a continuous record
  of all scans and a separate record of the most
  recent 24 hours of data at half-hourly intervals.
  In a projected service application, the 24-hour
  record can be accessed half-hourly and used to
  update a running plot of near-real-time channel
  usage, to be displayed on the IPS public website.
  
• The present program scans the range 2-20 MHz in 5
  kHz steps (3600 steps/scan), taking an average
  of each 50 steps, making 72 data points per scan.
  The minimum time the receiver must sit on each
  frequency is 100 mS, so a scan takes 6 - 7
  minutes to complete. At the end of each spectrum
  sweep, loops in the program perform some other
  measurement functions including the short-wave
  fadeout monitoring also discussed below.
• The program was written in the dedicated RBasic
  programming language. This language includes
  commands to access most user-functions of the
  receiver, access to the PC system clock, and the
  ability to create, delete and append text files
  for logging receiver settings and output level.

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Fig. 1 WinRadio Application control panel
Fig. 2 Screenshot of IPS HF Monitor program
running
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Fig. 3 Camden 60m horizontal longwire antenna
Fig. 4 Camden 27 MHz whip antenna
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Fig. 5 Wagga Wagga discone antenna
Figures 3 to 5 show typical HF spectra over 24
hours recorded at two locations on a variety of
antennas. Camden is located on the urban fringe
of Sydney and would be expected to experience
relatively dense local radio traffic and man-made
noise. The horizontal longwire antenna (Fig. 3)
is more sensitive to high-angle, short to medium
distance signals arriving by ionospheric
propagation. The response of this antenna
reflects local ionospheric conditions. There is a
reasonably strong diurnal pattern, with increased
signal density during local night hours. This is
especially true at lower HF frequencies, which
are less attenuated by absorption in the lower
ionosphere at night. The effect of the dawn
terminator can be seen around 18-20UT, with F2
region maximum useable frequency (MUF) reaching a
minimum pre-dawn, some atmospheric mixing
occurring post-dawn, before absorption increases
again on the day-side The vertical whip antenna
(Fig. 4) should be more sensitive to low angle
long distance signals, but in this case the
antenna is designed for a band somewhat higher
than 2-20 MHz. Probably much of the received
signal is local groundwave, which is relatively
constant over the day. A vertically polarised
antenna is more sensitive to man-made noise, and
a horizontally polarised antenna less sensitive
to groundwave. The discone antenna (Fig. 5) is
also vertically polarised, and has an essentially
flat broadband response above its resonant
frequency. In this case it was located in a
radio-quiet rural area. Again there is a strong
diurnal pattern to the response. The exclusion of
low HF frequencies during local night is a
function of both antenna response and local noise
conditions. Formation and dissipation of the
daytime D and E regions can be clearly identified
by absorption in the lower HF spectrum.
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Fig. 6 Single sweep Camden longwire antenna
Fig. 7 Single sweep Camden 27MHz whip antenna
Figures 6 to 8 show single sweeps of the 2-20 MHz
band, taken at selected times from the same data
as presented in Figures 3 to 5. The longwire
antenna at Camden has a significantly better
low-frequency performance than the others due to
its physical size. Regular peaks in the response
at higher frequencies may be resonances on the
wire. The 27 MHz whip shows low sensitivity in
general at these frequencies. Much of the
received signal is probably of local origin. The
discone antenna has low sensitivity below its
resonant frequency. This sweep was taken near
local dawn, when fOF2 would be at a minimum.
Hence acquisition of distant signals would be
limited. The figure emphasizes the very low radio
noise environment.
Fig. 8 Single sweep Wagga Wagga discone antenna
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Shortwave fadeout monitoring

• In the event of a large (M-class and above) solar
  X-ray flare, high energy photon deposition in the
  D-layer results in increased absorption of HF
  radio waves. This effect only occurs in the
  sunlit sector, is greatest where the sun is
  overhead, and progressively affects higher HF
  frequencies with increasing X-ray intensity.
• The IPS HF monitor aims to observe such events
  when they occur locally, in terms of ionospheric
  response. At the completion of each spectrum
  scan, the WinRadio HF Monitor is programmed to
  scan a number of discreet frequencies at the
  lower end of the HF spectrum. The frequencies are
  chosen locally and ideally should have a constant
  signal strength from a distant source. If there
  is a large flare during local daylight hours, the
  response of the monitored frequencies should
  track the progression of a shortwave fadeout
  event.
• The following sequence of figures show one such
  event captured by the Camden HF monitor during an
  X-ray flare originating from a recent
  particularly active solar region (AR808). This
  flare peaked briefly at the X1.1 level at 0300UT
  on September 9 2005, when the sun was close to
  maximum zenith over Camden.

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Fig. 9 GOES12 satellite plot of solar X-ray flux.
Only one flare in this sequence occurred with the
sun overhead E. Australia
Fig. 10 WinRadio SWF Monitor plot. X-ray
intensity peaked briefly at 0300UT. SWF evident
about this time.
Fig. 11a IPS Camden 5d ionogram for 09 Sep, 0239UT
Fig. 11b IPS Camden 5d ionogram 0254UT
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Fig. 11c IPS Camden 5d ionogram 0259UT
Fig. 11d IPS Camden 5d ionogram 0304UT
Fig. 11 shows a sequence of ionograms from the
IPS 5d ionosonde co-located at Camden NSW with
the WinRadio HF Monitor, around the time of the
SWF event of 09 Sep 2005. The flare at 03UT on
September 9 (Fig. 9) was impulsive in nature. The
ionograms show, over a relatively short interval,
the disappearance of ionospheric reflection from
lower HF frequencies, extending briefly to all HF
frequencies near peak X-ray flux, and gradual
return to more normal conditions as the flux
decayed. The event was also tracked by the HF
monitor (Fig. 10). The fact that HF Monitor
signals were not greatly reduced by SWF suggests
significant contribution to the received signal
from local and groundwave sources. The antenna in
use at the time was the 27 MHz whip.
Fig. 11e IPS Camden 5d ionogram 0334UT
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Future directions and conclusion

• The WinRadio HF Monitor offers a simple and
  reliable near-real-time indicator of actual HF
  conditions, at relatively low-cost. It requires
  occasional user-intervention due to the nature of
  the application and the Windows operating system.
  Most IPS sites are networked so that remote
  desktop access to the HF Monitor PC is possible,
  allowing control of remote monitors from IPS Head
  Office.
• The main difficulty to this point has been to
  find a suitable antenna. Ideally a vertical,
  broadband, omni directional antenna would be
  used. The discone appears to be a good choice
  but, for a reasonable physical size, is limited
  at the lower end of the spectrum. IPS hopes to
  install vertical monopoles at two sites in the
  near future which, while primarily intended for
  oblique path monitoring, may be available at
  times for omni directional HF monitoring.
• Selection of suitable monitoring sites is also
  important. The instrument clearly performs better
  at radio-quiet locations. The IPS sites at
  Culgoora, in Central NSW, and Learmonth, WA would
  appear to be good choices. However, the eventual
  deployment of the vertical monopoles may dictate
  site selections.
• WinRadio receivers may be adapted to oblique path
  monitoring if found to be compatible with
  transmitting equipment available to IPS for this
  purpose. The newer HF-only versions of the
  receivers may be used to collect quantitative
  data on digital HF broadcast transmissions.
• Further Information
• WinRadio product range and technical information
  www.winradio.com
• RBasic Programming language www.rbasic.com
• IPS products and services www.ips.gov.au
• Acknowledgement
• The contribution towards this project of Stacey
  Osbrough, LaTrobe University IPS vacation
  student during the summer 2003/04 is gratefully
  acknowledged.
• Contact
• Mike Hyde, IPS Radio and Space Services, PO Box
  1386, Haymarket NSW 1240
• mike_at_ips.gov.au