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Readers: if you haven’t checked out the SWLing chat room, I would encourage you to do so! There’s almost always someone there and, many evenings, readers share reception reports in real time. Click here to check out the chat room.
SWLing Post contributor, Richard Langley, is not only a dedicated shortwave DXer, but he’s also on the faculty of the Department of Geodesy and Geomatics Engineering at the University of New Brunswick. Additionally, Richard coordinates Innovation: a regular GPS World feature that discusses advances in GPS technology and its applications.
The latest Innovation feature is absolutely fascinating in that it highlights the potential for AM broadcast band HD radio signals (IBOC) to be an effective navigation aid. Richard’s introduction to this article takes us back to the time of Reginald Fessenden:
THE YEAR WAS 1906. On Christmas Eve of that year, Canadian inventor Reginald Fessenden carried out the first amplitude modulation (AM) radio broadcast of voice and music. He used a high-speed alternator capable of rotating at up to 20,000 revolutions per minute (rpm). Connected to an antenna circuit, it generated a continuous wave with a radio frequency equal to the product of the rotation speed and the number of magnetic rotor poles it had. With 360 poles, radio waves of up to about 100 kHz could be generated. However, Fessenden typically used a speed of 10,000 rpm to produce 60 kHz signals. By inserting a water-cooled microphone in the high-power antenna circuit, he amplitude-modulated the transmitted signal. On that Christmas Eve, he played phonograph records, spoke and played the violin with radio operators being amazed at what they heard.
Fessenden had earlier worked with spark-gap transmitters, as these were standard at the time for the transmission of Morse code, or telegraphy, the wireless communication method already in use. But they couldn’t generate a continuous wave and couldn’t produce satisfactory AM signals. But as telegraphy was the chief means of communication, they remained in use for many years along with high-powered alternators and the Poulsen arc transmitter, which could also generate continuous waves.
After a 2005-13 hiatus, I have rediscovered a childhood hobby and your reviews have helped me find my way to the post-Sony portable shortwave radio markets.
First, I obtained my “childhood dream” radio (Sony ICF 2001D), because at the time I made these recordings I was still in school and 1300 DM would have equaled over 1 year of pocket money, so a Supertech SR16HN had to do. I thought I got some fine results with this Sangean-Siemens re-branded receiver then, using a CB half-length antenna, a random wire, and much endurance.
The Supertech SR16HN (photo: Radiomuseum.com)
I kept regular logs throughout the years, wrote to 50 international and pirate stations for QSL and compiled this cassette.
A few years before I got that trusty SR16HN, however, I recorded a few number stations (such as G3, Four Note Rising Scale etc) with an ordinary radio cassette recorder, and in 1991 I put them onto this tape as well. The other recordings are done with the same radio placed right in front of the SR 16HN.
Feel free to make use of these recordings. Most of it are the well-known international state-owned shortwave stations of the past; plus European pirates; plus number stations; and at the end, a few (off-topic) local Am and FM stations interval signals.
As I said, this collection I made shortly after the Wende/reunification period, when all former-GDR state broadcasters changed their names, sometimes more than once.
Please continue your good work on the blogs! Weather permitting I am often outside cycling and always have the tiny Sony ICF 100 with me (which I call my then-student’s dream radio of the later 90ies).
Cassette Side 1
Frank’s original hand-written notes. Click to enlarge.
Wow! Frank, what a treat to listen to all these station IDs!
I had forgotten how many interval signals have changed over time and how many, of course, have disappeared. This tape represents a flood of nostalgia for me.
I should add, too, that I’ve enjoyed hearing so many IDs in German. It’s funny, but we all get hooked on listening to language programming from our native or second languages. It makes me realize just how many broadcasters used to have German language services.
Again, many thanks, Frank, for taking the time to digitize these recordings and scan your original hand-written notes. This stuff is invaluable, in my book!
BBC director general, Tony Hall, said the corporation will become an “open BBC for the internet age”.
While Hall was quick to add that funding cuts would equate to “the loss or reduction of some services” he also highlighted several efforts that would include shortwave and mediumwave broadcasts, including:
“Significant investment” in the BBC World Service, including a daily news programme for North Korea and more broadcasts to Russia, India and the Middle East
A news service for Ethiopia and Eritrea on medium wave and short wave
Of course, we can expect more cuts to BBC World Service shortwave broadcasting over the next ten years even if it wasn’t specifically mentioned in Hall’s speech. If we’re lucky, the BBC will continue to broadcast into those parts of the world that still rely on shortwave. Specifically mentioning North Korea, Ethiopia and Eritrea appears to be a nod in that direction.
Pricing is not for the faint of heart–at time of posting, prices ranged from $395 to $23,000 US. Each radio is beautifully presented, with a full description, and carries a one year restoration warranty. For an additional $95, many models can be modified with an AUX in audio jack.
While these radios are well outside my meager vintage radio budget, I must say that I’ve thoroughly enjoyed looking at the photos and reading the descriptions.
The lighter shaded side of the AM carrier indicates a lower sideband sync lock. (Click to enlarge)
A few days ago, I tuned to 9,420 kHz and found a relatively strong signal from the Avlis transmitter site of the Voice of Greece. The broadcast was quite clear until a heterodyne (het) tone popped up out of nowhere.
I checked the spectrum display of my Excalibur to find two steady carriers located about .5 kHz off each side of VOG’s AM carrier. I assume this may have been a faint digital signal centered on the same frequency as VOG.
The noise was annoying, but SDRs (and many tabletop radios) have tools to help mitigate this type of noise.
The het tone was originating from both sidebands of the VOG AM carrier (see spectrum display above). I had planned to use my notch filter to eliminate the noise, but I had two carriers to notch out and only one notch filter.
Synchronous detection to the rescue…
The simple solution was to eliminate one of the carriers using my SDR’s synchronous detector which can lock to either the upper or lower sideband. In this case, it didn’t make any difference which sideband I locked to because both had similar audio fidelity and were otherwise noise free. In the end, I locked to the lower sideband, thus eliminating the het in the upper sideband.
Next, I enabled my notch filter and moved its frequency to cover the annoying het carrier in the lower sideband; I kept the notch filter width as narrow as I could to preserve VOG’s audio fidelity. You can see the notch filter location and width in the spectrum display above (the notch filter is the thin yellow line).
I should note here that the great thing about using an SDR–or tabletop receiver with a spectrum display–is that you can see where the noise is. I was using my WinRadio Excalibur, but pretty much any SDR in my shack could have handled this task.
The results? No het tone and I was able to preserve the great audio fidelity from the Voice of Greece broadcast!
Here’s a 3.5 hour recording I made after cleaning up the signal. I believe at one point in the recording, I switched off the notch filter to demonstrate how loud the het tone was:
Many thanks to SWLing Post contributor, Moshe, who writes:
About 2 weeks ago, a very good friend called me and exclaimed, “you just have to see this radio…I’m keeping it for you!”–so, I drove to his aunt’s house and saw this beauty.
After hauling the radio to my place, I started to check it out, to see what would be needed for restoration; it was working, with bad contacts, poor frequency response and low output.
I took hi-res pictures of this radio, some during restoration. Now the radio sounds great. It has been recapped, a couple of bad resistors and bad wires replaced, contacts have been cleaned, and some good cleaning for the chassis as well.
As I wanted to keep the original appearance of the chassis, I kept the original filter capacitors on board, but disconnected them from the circuit, added terminal strips and new capacitors from underneath.
The radio uses an EF85 tube as the RF stage. With the addition of a grounding connection and random wire antenna, it’s very sensitive on shortwave.
About the Ben-Gal Duet-Stereo:
It was made in Israel by Ben-Gal, a label inside shows it was made at 12th of December, 1965.
It is a console model with record player. As the model name suggests, the amplifier and record player are stereo (though the tuner is not…).
The radio has longwave (marked in meters), mediumwave (marked in meters) and 3 shortwave bands (with megacycle and meter band marks).
The shortwave bands overlaps with each other, so cover is continuous:
SW3 2.3MHz to 6MHz,
SW2 5.5MHz to 15.5MHz,
and SW1 14.5MHz to 23MHz.
Many thanks, Moshe, for sharing photos and this description of this beautiful Ben-Gal Duet-Stereo. I bet the audio fidelity is amazing. My father has a 1960’s console–with a similar configuration–made by Admiral, though it was limited to mediumwave and FM reception. Some day, I will try to restore it to its former glory!
Thanks for the inspiration, Moshe!
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