Introduction to LF and VLF radio monitoring

(Copyright © Popular Communications Magazine Vol. 16, No.3, November 1997. Reprinted with permission)

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Introduction

As we move towards the fall and winter monitoring seasons, many people will be looking for new challenges for their DX'ing abilities. While many will explore the "traditional" frequencies found in the medium wave, short wave and VHF/UHF ranges, there is an often overlooked group of frequencies that can provide interesting monitoring targets for both the beginner and the experienced listener. These are the "Low Frequencies" which covers from the beginning of the Standard Broadcast Band at 535Khz and extend all the way down the radio spectrum to 9,000 cycles per second ( which is the lower limit for frequency allocation) and beyond ! Indeed many listen to radio frequencies that are only a few hundreds of cycles per second in order to hear fascinating radio signals produced with in nature and the earth itself.

The many types of signals that people can choose to listen to in this low range of frequencies can vary greatly in their nature and purpose. This is not only due to the type of communication work being done, but due in great part to the propagation characteristics of the frequencies being used. For example, the frequencies that are found between 535 kHz to 300 kHz tend to have much the same characteristics as those of the low end of the Broadcast Band. You will find that these frequencies exhibit the same day time ground wave propagation over short distances of roughly 200 miles, then open up at night to much greater distances when the ionosphere enables skywave propagation. This range of frequencies are used primarily by utility stations and navigational beacons, and there are great many low frequency listeners who do specialise in logging these types of stations, finding great DX challenge in searching out weak and distant signals.

For many others the VLF spectrum (30 kHz to 3 kHz) offers many interesting monitoring possibilities due to its unique characteristics. What is found with this range are propagation characteristics that are very different from those of higher frequencies. When transmitted, these frequencies travel in powerful wave fronts that follow a "trough" formed between the earth's ionosphere and its surface. Unlike the higher frequencies, these waves follow the contour of the earth's crust and ocean's surface very closely and actually penetrate to distances below both. This unique characteristic of penetration has been used primarily by the US and other naval powers to maintain constant communication with their submarine fleets when they are operating at depth. These frequencies are also of interest to the Scientific community due to their unique behaviour during various natural phenomena that takes place both on earth and in space. This has lead many to begin to explore the ELF frequencies below 3 kHz, where you can hear such phenomena as "whistlers", which is believed to be the sound of the energy pulse of a lightning bolt following the earth's magnetic field.

The ability of even the most casual listener to be able to monitor the lower radio frequencies has been made easier with the introduction of new communications receivers. Most sets are coming standard equipped with frequency ranges that begin below 500 kHz. While most offer coverage beginning at 100 kHz, many of these sets are able to tune as low as 10,000 cycles or even less, with some claiming to go all the way down to DC ! It is not necessary to purchase one of these new sets to monitor low frequency ranges, as some of the classic tube sets and many early transistor models of the last few decades have low frequency bands available. Even those who currently own a short-wave or band frequency only receiver, may listen in by placing a low frequency converter between their antenna and radio. These converters change low frequency signals into an alternative range (such as 3.510 to 4.0 MHz in the 80 meter ham band) which enables them to be monitored on that existing equipment.

The question then what is to be found there for the casual listener ? The first thing that is encountered by most people who tune in to the low frequencies are the slow and repetitive letter codes of their local airports and water navigation aids, plus a few teletype stations in between. Many may even hear the sounds of European and Middle East long wave broadcasters, particularly if you are located near the Eastern Coastal areas. To assist you in the monitoring of these lower frequencies , here are some suggested targets to aim for in order to find interesting stations to log. For those who wish to expand their monitoring skills, stations in the VLF range are also listed. We will also provide information for those who wish to move beyond monitoring about the growing group called "Lowfers", who are experimenting with low frequency, low power, radio transmission using all of the conventional modes of communications, such as CW, SSB and even digital ! Other topics of interest to those wishing to know more about LF and VLF radio are also listed with references to the World Wide Web.

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Frequency Allocations for LF and VLF operation

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Some Active LF Broadcast Radio Stations
(Source The Lowdown June 1996 - compiled by Richard Morris)

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Target Frequencies below 100Khz (Note: freq. change without notice - list may not be up to date)

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Listening to LF Beacons

When first monitoring the LF (100 to 535Khz Range) of frequencies one is often left wondering exactly what are those tones and slow Morse code Ids that are heard. Many will know that they have something to do with radio direction, but is there any way that I can find out where they are, and how they are used ? For the beginner there are several tools available to enable them to actively find and identify navigational beacons. In some ways this is the purist of DX listening, because the reception and identification of the signal is the sole aim. While there may be no "message" in the signal, the pursuit of this part of the radio listening hobby is to be part of the original "fox hunt" technology.

Most people use air and marine navigational charts to locate and identify beacons and there are a number of groups who specialise in monitoring beacons and provide good advice to their members on how to log and get QSL cards from these stations. It should be noted that with the advent of GPS and other new navigational aids, the age of the beacon may be ending soon, so this may be the last chance to hear these "radio lighthouses" until the beginning of the next century when the majority will be decommissioned.

To find out more about navigational beacons and utility stations operating in the LF range, see these Web Pages:

http://members.aol.com/RKDX/N9MBK-Publications.html      - N9MBK Publications Longwave Targets of the North Atlas

http://members.aol.com/us66soft/lfutil.htm     - Longwave Club of America Utility database

and

http://pw1.netcom.com/~spmcgrvy/artoftoc.html - ON THE ART OF NDB DXING by Sheldon Remington, NI6E

Very Low Frequency Time Signals in the US

The National Institute of Standards and Technology operates WWVB, the Longwave counterpart of the better known WWV and WWVH. Using a protected frequency of 60 kHz, a time signal that is more accurate than the HF versions is transmitted from Fort Colins CO. For more information is the NIST web page at: http://www.boulder.nist.gov/timefreq/

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Finding out more about Lowfer radio

Under FCC part 15 rules regarding the use of low powered radios, it is legal to operate a low frequency transmitter in the frequency range of 160 to 190 kHz, though this must be done on a shared basis with other licensed stations found in those frequencies. The main restriction placed upon Lowfer operation is that the station must be operated with a limitation of 1 watt input power to an antenna systems that does not exceed a total length for lead, antenna and ground of 15 meters. Despite these limitations, many people are operating CAW, SST, TTY and even digital stations in two way communications with other Lowfer operators. Commercial (kit and built) sets are available at about the same cost as a good CB radio station. Depending upon conditions, a Lowfer station can expect a transmitting radius of between 5 to 50 miles. For more information you can write the Longwave Club of America, 45 Wildflower Rd. Levittown, PA 19057 or see their Web Page at http://members.aol.com/lwcanews/index.html and also be certain to check http://members.aol.com/part15/lfmfbcns.txt - for a list of articles on operating a Lowfer station.

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Tuning in the last operating Anderson Generator Transmitter site

About once a year the last remaining Anderson high frequency alternating transmitter, located in Grimeton Sweeden, is tuned up and used to transmit VLF (16.7 kHz) CW signals. At one time this type of transmitter was the only way that reliable trans-Atlantic radio communications could be maintained, and many of these transmitters were operating up into the 1960's. A few VLF transmitters still exist (such as NAA at Annapolis MD, and the Jim Creek site in the State of Washington to name a few), but these are now using modern solid state transmitters. The Anderson transmitter, named after the General Electric engineer who perfected them, uses a high frequency AC generator rather than a vacuum tube (or even spark gap) oscillator. These generators were able to operate at the very high speeds needed to reach into the radio frequency spectrum in order to generate the radio waves frequencies. For more information on when, where and how to listen for these special transmissions, and how to get a QSL if you are able receive them, see the stations webpage at: http://www.telemuseum.se/Grimeton/Grimeen.HTML

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LORAN vs. GPS - what are the facts today

Marine navigators have used the LORAN system for years, and while the system has gone from using the
1.8 - 2.0 MHz range of frequencies, and has moved down to 100 kHz, it is still in active use around the world today. Yet what about the newly emerging GPS (Global Positioning System) that uses satellites. We know that the main limitation to GPS is the inclusion of a randomising factor in the results in order to prevent the system being used by hostile military forces. In this regards LORAN may still be more accurate due to its reliability and proven technology. What are the facts ? Will LORAN become obsolete or can it be used with GPS for even greater accuracy. What equipment is available, and how is it used ? What are the costs involved ? See the United States Navel Observatory web site at http://www.tyco.wno.navy.mil

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The new 76 kHz Ham band in England: a model for the US ?

Hams in the British Isles have been given a "per-use" access to LF spectrum at 76 kHz. This is an experimental band that has the interesting characteristic of being usable underground. At 76Khz radio waves are able to penetrate rock for considerable distances, and several hams are combining "Spelunking" (Cave exploration) with their ham radio hobby. Power is restricted to 1 watt, and the antenna system is also no longer than 15 Meters in total. Still, many Hams have been working towards breaking distance records above and below ground, and even working mobile ! There is a movement in the entire European community to open up new LF spectrum for experimentation, particularly as beacons (the traditional users of these frequencies) become less important for navigation. For more information see the 76Khz home page at: http://www.stonix.demon.co.uk/73kHz/

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The ELF frequencies: Transmitting at 76 cycles and below !

The US Navy, and other military groups around the world, have been working with extremely low frequencies to communicate with submerged submarines. These low frequencies are capable of forming strong wavefronts that are able to dip deep below the ocean waves. The efficiency of the these transmitters are very poor, and considerable amounts of RF energy are wasted as heat, and likewise the antenna systems are huge, covering many many miles in the rocky area of Wisconsin and Michigan. To get more information on one of the strangest radio technologies to emerge from the cold war period see the US Navy web page on the site at http://www.mtifwb.com/navy.html

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