Latest Radio World eBook explores radio broadcast coverage tools and how to get the most out of them
Broadcasters have endless “what if” questions about their radio station’s signal. How would my coverage be affected if I … moved my FM antenna? Changed height? Increased transmitter power? Added a fill-in translator?
This ebook reveals that new software tools and data sets have changed the game when it comes to answering such questions. The book is targeted to FM, AM and shortwave broadcasters both in the U.S. and abroad. We talk to consulting engineers and other experts about the state of propagation analysis.
What tools are available? How do they work? What does a user need to know about contours, population data, mapping and terms like Longley-Rice? What resources are available online? When is it time to use a professional consultant?
This is the 33rd in Radio World’s hugely successful free eBook library. Read it here!
This article originally appeared on the London Shortwave blog.
As many of my readers and followers will already know, these days I mostly enjoy listening to shortwave radio via the outdoor spectrum captures I make in my local park. Although I have built a system that helps me deal with urban radio interference at home, some of the weaker signals still can’t make it through the indoor noise. Since I have a limited amount of time for making outdoor trips, capturing entire portions of the spectrum allows me to record a lot of shortwave signals simultaneously, which I can then explore individually at a later time. However, these trips still need to be carefully planned because the time of the day and the time of the year both affect long-distance signal propagation, and do so differently depending on the frequency range. For example, signals on the 16 meter band are usually at their strongest during the daylight hours, whereas the 31 meter band is at its busiest around sunrise and sunset. Because my current portable recording set-up allows me to capture only 10% (3 MHz) of the shortwave spectrum at any one time, I decided to carry out a systematic exploration of activity on the shortwave bands to help me time my outings so as to capture as many signals as possible during each trip.
Luckily, I didn’t need to make any of my own measurements for this. For over a year, the wide-band WebSDR at the University of Twente has allowed its users to see what the shortwave spectrum has looked like over the past 24 hours in a single image. More recently, however, the creator of the service, Pieter-Tjerk de Boer PA3FWM, has opened up his spectrum image archives, so it is now possible to see the past conditions of the bands on any single day in the last two years. Intrigued by how band activity changes depending on the time of the year, I created a timelapse animation of these images by taking two from each calendar week and lining them up in sequence. With Pieter-Tjerk’s kind permission, I share this animation below.
First, a really fast version to illustrate the broad effects the time of the year has on peak activity times across the bands:
The X axis represents the frequency and the Y axis is the time of day, starting at the top. Conventional wisdom about band behaviour can be easily confirmed by watching this video: the 60m, 49m and 41m bands are mostly active after dark, with the 60m and the 49m bands being generally busier during the winter months. The 31m band is most active around sunset, but carries on all night until a few hours after sunrise. The 25m band is active during sunrise and for a few hours afterwards, and around sunset during the winter months, but carries on all night during the summer. Peak activity on the 22m and 19m bands is also clustered bi-modally around the morning and the evening hours, though somewhat closer to the middle of the day than on the 31m and the 25m bands. The 16m band is mostly active during the daylight hours and the 13m band is quiet throughout the year except for the occasional ham contest.
It almost seems as though someone positioned in the middle of the image’s right edge (corresponding to noon UTC) is shining two flashlight beams on the bands in a V-shaped pattern, and is changing the angle of this pattern depending on the time of the year: wider in the summer and narrower in winter. Here’s a slower version of the animation that shows some finer week-on-week changes:
Thanks to this data being made freely available, visualising and understanding these dynamics will help me schedule my spectrum capture outings in the weeks and months ahead.
(Source: Southgate ARC)
New Scientist magazine reports the US Air Force is working on plans to improve HF radio propagation by releasing ionised gas in the upper atmosphere using a fleet of micro satellites
As well as increasing the range of radio signals, the USAF says it wants to smooth out the effects of solar winds, which can knock out GPS, and also investigate the possibility of blocking communication from enemy satellites.
The story says there are at least two major challenges. One is building a plasma generator small enough to fit on a CubeSat – roughly 10 centimetres cubed. Then there’s the problem of controlling exactly how the plasma will disperse once it is released.
I just received the following link to a Forbes article from my buddy Charlie (W4MEC).
If this research turns out to be correct–and time will only tell–it could mean very low solar activity from here on out (let’s hope not!):
(Source: Forbes Magazine via Charlie W4MEC)
The Sun has likely already entered into a new unpredicted long-term phase of its evolution as a hydrogen-burning main sequence star — one characterized by magnetic sputtering indicative of a more quiescent middle-age. Or so say the authors of a new paper submitted to The Astrophysical Journal Letters.
Using observations of other sunlike stars made by NASA ’s Kepler Space Telescope, the team found that the Sun is currently in a special phase of its magnetic evolution.
Heretofore, the Sun was thought to have been just a more slowly rotating version of a normal yellow dwarf (G-spectral type) star. These results offer the first real confirmation that the Sun is in the process of crossing into its magnetic middle age, where its 11-year Sunspot cycles are likely to slowly disappear entirely. That is, from here on out, the Sun is likely to have fewer sunspots than during the first half of its estimated 10 billion year life as a hydrogen-burning star.
“The Sun’s 11-year sunspot cycle is likely to disappear entirely, not just get less pronounced; [since] other stars with similar rotation rates show no sunspot cycles,” Travis Metcalfe, the paper’s lead author and an astronomer at the Space Science Institute in Boulder, Colo., told me.[…]
This morning, before heading out the door, I tuned around the 31 meter broadcast band. I’ve actually been recording 640 kHz of the 31 meter band for almost 24 hours, trying to capitalize on the fact that propagation conditions have been the best I’ve seen in several months. At some point in the future, I’ll load this recording, tune through it and remind myself what’s possible when propagation is favorable! Check out the waterfall screenshot above.
Asian stations had a strong showing on the band in eastern North America this morning.
Here are the stations I logged starting around 12:30 UTC today:
- 9395 WRMI English
- 9410 China National Radio 5 Chinese
- 9420 China National Radio 13 Uyghur
- 9430 FEBC Radio Chinese
- 9440 China Radio International Cambodian
- 9460 China Radio International English
- 9470 UNID (weak)
- 9490 Voice of America Korean
- 9500 China National Radio 1 Chinese
- 9515 China National Radio 2 Chinese
- 9540 China Radio International Chinese
- 9550 Radio Havana Cuba Spanish
- 9570 China Radio International Cantonese
- 9575 All India Radio Tibetan
- 9580 Radio Australia English
- 9600 China Radio International English
- 9620 All India Radio Sindhi
- 9635 Voice of Vietnam 1 Vietnamese
- 9640 Radio Havana Cuba Spanish
- 9645 China Radio International English
- 9650 Radio Sonder Grense Afrikaans (with QRM)
- 9660 Radio Taiwan International Chinese
- 9665 KCBS Pyongyang Korean (weak)
- 9680 Radio Taiwan International Chinese
- 9700 Radio New Zealand International English
- 9710 China National Radio 1 Chinese
- 9720 Reach Beyond Australia (HCJB) Indonesian
- 9730 China Radio International English
- 9735 Radio Taiwan International Indonesian
- 9740 BBC English
- 9750 NHK World Radio Japan (?) Japanese
- 9760 China Radio International English
- 9785 China Radio International Laotian (?)
- 9805 Radio Marti Spanish (w/accompanying Cuban jammer)
- 9820 Radio Habana Cuba Spanish
- 9830 China National Radio 1 Chinese (with RTTY QRM)
- 9835 RTM Sarawak FM Malaysian (very weak)
- 9840 Voice of Vietnam English
- 9845 China National Radio 1 Chinese (weak)
- 9855 China Radio International Chinese
- 9870 AIR New Delhi Hindi
- 9880 KSDA-AWR Guam Korean
- 9920 FEBC Radio Hre
- 9955 WRMI English
- 9980 WWCR English
- 10000 WWV Ft. Collins
That’s 46 signals in a space of 640 kHz–not bad!
I dare say: these excellent band conditions will not last forever.
Make time to play radio today!