226 pages, comb-bound
©2002 Rod Dinkins
$24.95 list price, QTB price $23.70 ORDER IT NOW!
226 Pages, comb-bound, 8-1/2 x 11
� Rod Dinkins, AC6V
While this book’s title might lead you to think it’s just about DX, it’s really about HF operation, in general. In Chapter 2, for example, Rod talks about equipment specifications. This is all good stuff to know even if you only plan to rag chew once in a while. Here’s an excerpt:
2-1. SENSITIVITY
Sensitivity is the capability of a receiver circuit to detect weak signals and the major factor in receiver sensitivity is the signal-to-noise considerations. Due to the resistance and temperature of various components, receiver noise is inherent in any receiver. In lab measurements, the amount of signal input required to produce a signal to noise ratio of 10 dB is generally used to specify the receiver sensitivity specification.
In modern transceivers, this is typically a few tenths of a microvolt to a few microvolts depending on the input frequency, mode, and bandwidth of the receiver. Another figure of merit used in determining sensitivity is the noise floor, which is another way to express the receiver noise. Typical values are �€“130 dBm to �€“140 dBm depending on the mode, filtering and preamplifiers used.
However atmospheric and man-made noise enters into the real environment so that the minimum required sensitivity is something quite different than the lab measurement. On the lower bands the noise can be quite heavy, an S-Meter reading of S7 of noise is not uncommon. So even though the receiver has excellent sensitivity, it is unusable in the presence of atmospheric and man-made noise. Using well-designed DSP units and low noise antennas (beverages and loops) are necessary, particularly on the lower bands. Increased sensitivity is gained at the expense of dynamic range, the latter being of greater importance in today�€™s crowed bands and the noise, both atmospheric and person-made noise.
Discerning weak signals generally requires a signal to noise ratio of 10 dB. The noise is a combination of atmospheric noise, receiver noise and circuit design. Note that many CW operators can typically copy code at a signal to noise ratio of almost 0 dB perhaps accounting for the superiority of CW over phone under minimal signal conditions.
2-2. DYNAMIC RANGE
Dynamic range is expressed in dB where the lower limit is the smallest discernable signal (receiver noise floor) and the upper limit is the point where intermodulation products become noticeable. It is an important specification as it gives a figure of merit for evaluating the strong signal handling characteristics of a receiver. Values of 103 dB are typical. The use of front-end attenuation and an AIP circuit can help reduce the effects of intermodulation. The receiver noise floor can be affected by receivers using synthesized tuning schemes. This has improved considerably with the new transceiver designs.
Chapter 4 is all about propagation. Again, this is stuff that all HF operators need to know whether you’re hot to work Pitcairn Island or Pitcairn, PA. Here’s another excerpt:
4-1. SOLAR FLUX , A INDEX , K INDEX
Propagation is tied to the number of sunspots on the surface of the sun, since the areas around sunspots emit large amounts of ionizing radiation – extreme ultraviolet radiation. Increased sunspots correlate closely with better worldwide radio propagation. When there are more sunspots, the sun emits radiation that charges particles in the earth’s ionosphere. Radio waves bounce off of (refract from) these charged particles, and the denser these clouds of ions, the better the HF propagation. The sunspot numbers are calculated by counting the spots on the visible solar surface and also by measuring their area.
Listening to WWV or checking propagation web sites will give the latest solar-terrestrial indices. It includes the 10.7cm solar flux index, Boulder A index and the Boulder K index. Solar Flux at 10.7cm is essentially a measurement of the thermal radiation of the sun, and contributes nothing to the ionization process. Solar flux is measured at several points on the earth, for example one is an observatory in Penticton, British Columbia using an antenna pointed toward the sun connected to a receiver tuned to 2.8 GHz, which is at a wavelength of 10.7 cm. The 12-month running average of 10.7cm solar flux correlates very well with the 12-month running average of the sunspot number �€“ called the smoothed sunspot number and abbreviated SSN. The higher the smoothed SFI number, the better. Typical daily SFI values have ranged from 67 (Jan 1997) to 370 (Jan 1991).
Other solar activity of concern to HF operators are solar flares and coronal holes, which can emit energetic protons and X-rays and cause a significant increase in the solar wind speed. Energetic protons can cause polar cap absorption events (PCAs). X-rays can cause blackouts on the daylight side of the Earth due to increased absorption in the D region. And a significant increase in solar wind speed can result in geomagnetic storms that generally depress MUFs.
The A Index is an averaged quantitative measure of geomagnetic activity derived from a series of physical measurements.
The Boulder A index in WWV announcements is linear in nature and ranges from 0 to 400, and is the 24-hour A index derived from the eight 3-hour K indices recorded at Boulder, Colorado. The K index is logarithmic in nature and ranges from 0 to 9, and is the result of a 3-hourly magnetometer measurement comparing the current geomagnetic field orientation and intensity to what it would have been under geomagnetically quiet conditions.
Suffice it to say that the geomagnetic activity, solar storms, X-Rays, flares, etc., can have an adverse effect on propagation. The Planetary A index relates to geomagnetic stability. Magnetometers around the world are used to generate a number called the Planetary K index. A one-point change in the K index is quite significant. K index readings below 3 generally mean good stable conditions, and above 3 can mean high absorption of radio waves. Each point change reflects a significant change in conditions. Generally the higher the latitude of the measuring station, the higher the K and A indices reported. This is because the effects of geomagnetic instability tend to concentrate toward the polar regions of the globe.
Oversimplification can be very misleading in the complex field of propagation, but in general for long distance HF, the rule of thumb is the higher the SFI and the lower the A and K indices, the better the conditions on the higher frequencies. The A index should be under 14, and the solar activity low to moderate. If the A-index drops under 7 for a few days in a row and the SFI is up, watch for some really exciting intercontinental conditions.
You can hear the SFI, A and K indices on WWV or WWVH or by calling 303-497-3235. Geophysical alerts are broadcast from WWV at 18 minutes after the hour and from WWVH at 45 minutes after the hour. Both stations operate in the high frequency (HF) portion of the radio spectrum. WWV and WWVH radiate 10,000 W on 5, 10, and 15 MHz. The radiated power is lower on the other frequencies: WWV radiates 2500 W on 2.5 and 20 MHz while WWVH radiates 5000 W on 2.5 MHz and does not broadcast on 20 MHz. Each frequency is broadcast from a separate transmitter. Although each frequency carries the same information, multiple frequencies are used because the quality of HF reception depends on many factors such as location, time of year, time of day, the frequency being used, and atmospheric and ionospheric propagation conditions. The variety of frequencies makes it likely that at least one frequency will be usable at all times.
These values are also available on all DX Packet Clusters (SH/WWV). Also you can find them on numerous pages on the internet, a good one is from WN6K at URL: http://members.cts.com/fort/w/wn6k/
Note that the K index reported on WWV is only updated every 3 hours and the A and SFI values are usually updated once a day at 21 UTC. The A index reported at 21 UTC is calculated from the last eight K index readings in Boulder, so it contains data that is 24 hours old when it is first posted.
For graphs that update every 5 minutes see http://www.sec.noaa.gov/today.html these show short term events long before they show in the WWV report. Also watch the K index graph at NOAA; it often differs from the WWV report, because the web page shows the estimated Kp (planetary K index) rather than just the reading from one site (Boulder) that is reported on WWV.
Classification of K-indices is as follows:
K0 = Inactive K5 = Minor storm
K1 = Very quiet K6 = Major storm
K2 = Quiet K7 = Severe storm
K3 = Unsettled K8 = Very severe storm
K4 = Active K9 = Extremely severe storm
As with the K-index, the higher the A-index, the more unstable propagation becomes. Classification of A-indices is as follows:
A0 – A7 = quiet
A8 – A15 = unsettled
A16 – A29 = active
A30 – A49 = minor storm
A50 – A99 = major storm
A100 – A400 = severe storm
There is, of course, plenty of information specific to DXers. Chapter 5 is all about DX operating procedures, including how to find DX, work pileups, and get awards. Chapter 7 is titled “”DX Secrets”” and has many practical operating tips, such as looking for DX on the 12m and 17m bands because they are generally less busy than 20m or 15m. There are also sections on working contests, QRP Dxing and CW DXing.
One unique feature of this book is that it’s continually being updated. AC6V prints the book on demand and is continually collecting equipment information and operating anecdotes. When you order it, he updates the book, and send you the absolute latest revision. The copy you buy today will be different than the copy your friend bought last year. This approach assures that you get the most up-to-date information available.
This book is really a great value, especially if you’re new to HF operation and DXing, but experienced DXers will find it valuable as well. Click here to see the complete table of contents.
