Shortwave Radio Diversity Reception
Shortwave radio diversity reception provides a way to combine several fluctuating signals and get a solid result. It provided the foundation for most radio news received in America for years.
During World War II, most countries around the world relied on Britain’s shortwave radio broadcasts for the latest news from Europe. In the days before transatlantic audio cables or satellites, distant news traveled fastest by radio. Networks in the America’s, Australia, New Zealand and elsewhere re-broadcast shortwave radio news domestically.
Getting reliable, good quality audio programs over shortwave is always a challenge because of fading. As signals bounce off the ionosphere, they split over multiple paths. Often they fade and flutter, sometimes significantly, as the nature of the layers change with time. Here are several examples of shortwave signals fading, so you know what it sounds like. Skywave radio signals are subject to complex patterns of travel and interference.
Eventually, domestic networks found a clever way to get better audio from these distant signals.
[…]Diversity reception works like this. Instead of one signal, you monitor several signals at once and blend them together. Harold Beverage and RCA pioneered work on shortwave radio diversity reception in 1920’s. Commercial solutions arrived by 1933. Typically, you would use three receivers with three different antennas, spaced 1,000 feet apart. When antennas are widely spaced, signals arrive with different fading. Just combine the signals and let the strongest signal dominate. As long as the fading is not correlated across all three antennas, improvement can be significant.
Diversity reception can be achieved in several ways. The most popular – spatial diversity – is described above. Other methods include frequency diversity – mixing together the same program received on several different channels.[…]
Many thanks to SWLing Post contributor, Richard Cuff, for sharing this column from The Athens News. I’m sure many of us relate to Dennis E. Powell (note this is only an excerpt):
If you lose power at just the right time, it can enrichen your life
This is being written last Monday night.
Several hours after the storms of earlier in the day passed, the sun shining, the birds singing, and all apparently right with the world, the electricity went out. Because there is no cellular telephone service in my part of the county, this necessitated a drive much of the way to Athens to register a report with the power company. The power company’s outage report line is the first entry in my cellular phonebook.
[…]The evening was (and as I write this, is) cool, with a bit of wind passing through the open windows, so there was no panic, as there is when the power disappears in the dead of winter or in the 100-degree summer – both of which I have experienced. But there was no fire to build, no need to think of a reason to drive to town for a few hours in some place air-conditioned.
Instead, I remembered that just a few days ago I had pushed the battery-charge button on one of a couple shortwave radios I have around here, this one a decade-old C. Crane CC Radio SW. It has a big speaker and a pleasant sound, though it’s not the sort of radio you get to dig faint signals out of the mud. It is just right for such an evening as this. So I brought it to the living room, extended its built-in antenna, and fired it up.
Shortwave radio is like Forest Gump’s mama’s box of chocolates, and that’s part of its appeal. Poking around the dial I find some Ohio shortwave amateurs putting on a bit of a panel show, passing the mic metaphorically from one to another. Because they are shortwave amateurs, all they talk about was their shortwave equipment.
The power is out all over the neighborhood, so there is not a single static scratch, no 60-Hz whine of interference. And the ionosphere seems stable, no fading in and out of signals.
Heading up the dial, I find a station in accented but easily understood English. I have to listen for a while before I learn that I am listening to Radio Romania International. That broadcast ended, so I retune and find a cranky man and a cranky woman who are discussing how awful things are and how the only thing you can count on is gold.
Moving along, I find an impassioned man with a deep Southern accent. He, too, is discussing how awful things are – and how they soon will be especially awful for those who put their trust in gold or other things of this world.
There is a broadcast from somewhere – from the accents I’d guess the Caribbean or Africa – that features a man and woman talking spiritedly and sweetly about English idioms.
Now I’m listening to the Argentine national shortwave service, which had a talk program in English though they’ve switched to Argentine music.
[…]I do hope the power comes back. Just not tonight. Tomorrow, maybe. Or the next day.
(Note: Just as I set this to email itself eventually to the Athens NEWS, minutes after I was done writing, the power came back on. And it really was a little disappointing.)
Many thank to SWLing Post reader, Stefano Mollo–a licensed Australian broadcaster–who shares the following news:
I have started test transmissions from Perth, Western Australia, on 5,045 kHz, at 75 watts (300 PEP).
For the time being, I am using the same audio of my other station–77.4 MHz FM–which you can also find and stream online here: www.77400.fm
My test transmission are on the air from about 7:00 pm to about 10:00 pm every evening, local Perth WA time (11:00 – 14:00 UTC).
Please direct listener reports and any enquiries to firstname.lastname@example.org.
Thank you for sharing your news, Stefano!
Post readers: While 300 watts PEP is a modest broadcast signal, no doubt many in Australia, Oceania and Asia will be able to log Stefano’s station when conditions are favorable. During band openings, his signal might travel quite a distance.
Let’s help Stefano by contacting him with detailed listener reports!
Hi there, subscribers to the Oxford Shortwave Log YouTube channel and regular readers of this excellent website will be aware that I have been using a Bonito Boni whip E-field wideband antenna for a couple of months now. You may have seen my previous post here, detailing some excellent initial DX results achieved with the Boni Whip. What makes this antenna so compelling for a DXer such as myself is simply that it’s so light and compact; I can literally take it anywhere. Currently it lives in a small flight case (see above & below) on the back seat of my car, with either my Sony ICF-SW55 or Eton Satellit, a home-brew battery pack (that literally cost pence) and some peripheral bits and pieces; spare batteries, cables etc. I think it’s probably already clear that if you consider the Boni Whip’s performance as a function of portability and price, it’s out there on its own – I’m not aware of another antenna that can match it. Of course, there are H-field antennas, such as the excellent Wellbrook active loops that will effectively reject QRM, if that’s an issue for the user, but at a significant cost delta.
Since my last posting, I have continued to use the Boni Whip regularly on my DXpeditions and upload the reception videos to my YouTube channel. I have been nothing but totally impressed with this antenna, to the point that I’ve actually been surprised by the signals I’ve caught and recorded with it. Recent catches include a number of low-power stations from Brazil, including Radio Bandeirantes – Sao Paolo, Radio Voz Missionaria – Camboriu (on the 49 and 31 metre broadcast bands) and Radio Aparecida. Some of these signals are incredibly difficult to hear in Europe at all, let alone well and yet the ultra-compact Boni-Whip running off AA batteries, coupled to the (equally brilliant) Eton Satellit managed it with aplomb. Other catches include Zambia NBC Radio 1 – Lusaka and a signal from Bangladesh Betar that sounded as if the transmitter was 5 miles down the road!
All-in-all, I’m extremely satisfied with the performance of the Bonito Boni Whip and highly recommend it to those DXers requiring a high-performance, compact antenna, for use at home in electrically quiet environments or on any DXpedition. You certainly won’t be disappointed.
Please find embedded reception videos below and text links that will take you to the Oxford Shortwave Log YouTube channel. Thanks for reading/watching/listening and I wish you all great DX.
Clint Gouveia is the author of this post and a regular contributor to the SWLing Post. Clint actively publishes videos of his shortwave radio excursions on his YouTube channel: Oxford Shortwave Log. Clint is based in Oxfordshire, England.