From July 2005 QST © ARRLhere has been much excite-ment below our so-called topband at 1.8 MHz. At less thanone-tenth this frequency, near136 kHz, you will find many amateurs en-joying QSOs using a variety of modes. Al-though US and Canadian amateurs needspecial permission to transmit here, there isa 2200 meter amateur band in manyEuropean countries and in New Zealand.Aside from its low frequency, the most strik-ing thing about the 135.8-138.8 kHz band isits narrow width—only 2.1 kHz, barely wideenough to admit a single SSB transmission.Huge sources of interference are presentin the band. In Greece, the Navy transmitterSXV operates on 135.8 kHz, and in Canadaanother Navy transmitter (CFH) is on 137.0kHz. Just outside the band is the Germanstation DCF39 on 138.83 kHz. These sta-tions have effective radiated power (ERP)levels in the tens of kilowatts and can beheard on receivers thousands of miles away.At 100 kHz, there are the megawatt LORAN(long range aid to navigation) transmitterswith their perpetual clatter, and above 150kHz we have the commercial long waveband with powerful megawatt plus stations.How then can this band be of any use to theamateur experimenter?Amateurs have traditionally overcomemany obstacles in achieving their goals.When regulators restricted us to the “use-less wavelengths” below 200 meters, wespanned the globe. Now that we’re slowlybeing let above 200 meters again, we haveused some modern technology and old-fash-ioned persistence to achieve amazing featsin this challenging environment on the longwaves. We have even used the high powerinterference sources to our advantage.Propagation at 136 kHzIt is generally agreed amongst the pro-fessional propagation researchers that propa-gation between 50 kHz and 150 kHz isdifferent than both the bands above and be-low that region. The lower (VLF) frequen-cies are described as propagating by awaveguide mode between the ground and theionosphere. The waveguide mode dies outmainly above 30 kHz and certainly aboveabout 50 to 60 kHz. We believe this maydue the wavelength becoming short com-The Transatlantic on2200 MetersTFigure 1—On December 12, the Marconi and Poldhu radio clubs commemorateMarconi’s first transatlantic experiment. In 2003 they sent an LF signal fromNewfoundland to England using very slow speed CW with dots 30 seconds long(QRSS30). Here is a screen capture of that signal received at G3NYK using Argosoftware. If you look carefully, you can make out white Morse characters spelling outVO1NA against the noisy blue background. Argo uses Fast Fourier Transforms to getvery narrow effective bandwidths (fractions of a Hz) and is very popular with the LFcrowd. More information on Argo is available on the Web at www.weaksignals.com.Longing for the days when amateurs builttheir own gear and DX was big news?They’re back again...on the “top” top band.Joe Craig, VO1NA and Alan Melia, G3NYKpared with the thickness (about 30 km) ofthe daytime absorbing D-layer. Unlike HFfrequencies, LF has a substantial ground-wave service area, with the wave front beingbent to follow the curvature of the Earth tosome extent. In daytime, there is an absorb-ing ionized region, formed by photo-disso-ciation, which corresponds to the D-layer(50 to 90 km) and, in general, it is consid-ered that ionospheric propagation is not anelement of daytime signalsEarly in 1999 an FSK signal appearingnightly in the UK at 137.00 kHz was cor-rectly identified by Alan, G3NYK as thatfrom the Canadian Naval station, call signCFH, near Halifax in Nova Scotia. Roughearly estimates of the path loss suggestedthat an amateur transatlantic crossing wouldjust be possible with the allowed 1 W ERP.Many were dubious, but only a few weekslater Dave Bowman, GØMRF made the firstone-way LF crossing to John, VE1ZJ. Thendays later Peter, G3LDO managed a cross-band contact. Both of these events were co-incident with good received signal strengthfrom CFH. John was located near Big Pondin north Nova Scotia. Other, regularly heardcalls in the early days of tests was the wellknown MF station of Jack, VE1ZZ and thelate Larry Kayser, VA3LK.Daytime propagation is mainly groundwave, but at extreme range (in excess of1500 km) there is a significant daytimeionospheric component. This has been seenon the path between CT1DRP (Porto) andDCF39, a German utility station on 138.83kHz located near Magdeburg, and also oncertain occasions on the CFH to Europepath. The peak strength usually coincideswith the solar zenith at mid-path. This is atapproximately 1500 UTC for the CFH toEurope path, and around 1130 UTC for theCT to DCF path. The signal enhancementunder normal conditions on the 1950 kmDCF to CT path is about 10 dB. This en-hancement is caused by the sky-bound sig-nal being returned by the lower region ofthe D-layer. Penetration of the D-layer indaytime subjects the wave to absorption,so the enhancement is not as high asseen at night. Also, the apparent reflectionheight is sure to be lower.
From July 2005 QST © ARRLAt night, the photo-dissociated elec-trons in the D-layer decay (or recombine)quickly, as the darkness removes the ion-izing radiation. The “apparent reflectionlevel” moves up to the base of the E-layerat around 90 to 100 km in altitude. The E-layer is a 24-hour layer, ionized, amongstother things, by high-energy cosmic rays.The atmospheric pressure is much lowerthan at the D-layer, so the chances of anelectron encountering an atom or positiveion are much reduced and their “lifetimes”are extended. Thus, the nighttime wavehas to travel through very little absorbingmaterial. The ionospheric wave, oftencalled the sky-wave, becomes strongerthan the ground wave at distances exceed-ing about 800 km. Thus, all long distancecontacts are due to ionospherically re-turned signals.These seemingly predictable conditionsare altered by the effects of Solar distur-bances. The initial check of the Solar indi-ces against known good nights drew a blank,but it was relatively easy to spot potentiallypoor conditions. These occurred about 2 to3 days after a geomagnetic event that liftedthe Kp index to 5 or above. This is about thesame level that leads to substantial auroraleffects. The conditions deteriorated more,and took longer to recover, the higher theKp rose. It is postulated, from the signalstrength plots, that Coronal Mass Ejections(CME) were responsible for injecting hotelectrons into the ionosphere. After thesehad time to diffuse to the D-layer region (thedelay), their presence was felt as long-livedFigure 2—Schematic and parts list forVO1NA’a class E LF transmitter. Asexplained in the text, transmitters atthis frequency tend to be unique,requiring some experimentation. Thistransmitter was based on design ideasof several LF experimenters andtailored for parts available fromVO1NA’s junk box. A very stable signalgenerator or TXCO may be used inplace of the Marconi XH100 receiver.See the text for component details.C1—27 nF capacitor.C2—18 nF capacitor.L1—88 µH air wound inductor.L2—0.4 mH air wound inductor.L3—0.3-1.3 mH variometer.M1—50 Ω ΩΩ ΩΩ wattmeter.M2—RF ammeter, 2 A full scale (seetext).M3—Drain current meter, 0-5 A dc.Q1, Q2—NPN small signal transistor,2N4401 or equiv.Q3— PNP small signal transistor,2N4403 or equiv.Q4—International Rectifier IRF640 N-channel MOSFET.RFC1—1.5 mH RF choke.T1—Impedance matching transformerwith 5 primary turns and 13secondary turns on a ferrite core.U1—7400 quad NAND gate.U2, U3—7490 decade counter.U4—7805 5-V regulator.
From July 2005 QST © ARRLFigure 3—This rack holds the IRF640power amplifier, power supply, antennamatching coil and variometer for VO1NA’s137-kHz transmitter. The variometer (L3)is the big red coil on the upper shelf nextto the wattmeter. The matching coil (L2) isabove the wattmeter. The power amplifieris on the next shelf down (with heat sink,L1, T1 and RFC1). Note that about 2000 Vis present at the feedthrough insulatorduring transmissions.RICK LINDQUIST N1RLFigure 4—The LF antenna at VO1NA used for several years (including his firsttransatlantic QSO) consists of two parallel wires 100 meters long, spaced 1 meterapart. The antenna is supported at the far end by a 25 meter tower, and the wiresslope down toward another tower near the shack where they are connected together.The antenna is fed at this point with another 50 meters of wire for a total length of150 meters and matched with the loading coil and variometer shown in Figure 5. Theantenna has since undergone several involuntary changes as Mother Nature took downone of the wires and then in January 2005 took the remaining wire and tower during anice storm. VO1NA is back on LF with 100 meters of wire about 10 meters off the ground.Joe was never very comfortable on the top of his tower and is most grateful he was notthere at the time it collapsed. A 30-meter-tall replacement is planned.1Notes appear on page 46.absorbing material in the D-layer, reducingthe nighttime signal strengths. This delay isreported in a number of professional paperson Solar disturbance to LF propagation. Sothe question remains: How to predict goodconditions?A more recent extensive series of DX testshave confirmed that the lesser-known index,Dst (disturbance storm time), is a fairly goodindicator. Dst is determined by measuring theeffect of ring of trapped ions and electronscirculating the equator in the Van Allen belt.Estimated values are published on the Internetby a number of observatories. It is thoughtthat ions and electrons are trapped from theCME plasma clouds and are gradually ex-changed with the ionosphere over a numberof days. These migrate to the D-layer andform a long-lived absorbing layer. This wouldexplain the prolonged period of poor condi-tions after a geomagnetic storm, even afterthe Kp index has returned to “quiet” condi-tions (< >
From July 2005 QST © ARRLfor the purpose. Let’s illustrate this withan example of a simple LF transmitter. Theschematic shown in Figure 2 is based ondesigns of several amateurs.A temperature controlled crystal oscil-lator generates a carrier at 100 times the in-tended frequency—in this case, 13.77770MHz. This signal is fed into U1. Logic ma-nipulations are performed on the carrier os-cillator signal and the keying inputs topreclude a sustained positive output at thedivider circuit. Such a level would destroythe final amplifier in microseconds. Addi-tionally, it prevents any emissions while thetransmitter is not keyed. This is importantduring receiving.The output from U3, a square wave at137 kHz, is fed to an inverting switch (Q1)which converts the TTL signal to a 12 Vsquare wave. This is fed to a low-imped-ance-output totem pole driver circuit com-prising Q2 and Q3, which switches the gateof final amplifier Q4 between 0 and 12 V.The operation of a class E amplifier is dis-cussed in detail elsewhere and methods offinal tuning are outlined.2 It is not difficultto tune properly using a ’scope to check thewaveforms and meters to monitor the inputpower.The final amplifier evolved from a15 W circuit with a P-channel MOSFET,but when efforts to increase the power to100 W at 12 V resulted only in fried FETsand frustration, a new strategy was sought.The next step was to try a higher voltagedevice, an N channel IRF640.Using G3NYK’s spreadsheet program toget approximate values for the tuning com-ponents simplifies the design considerably.The process entails selecting a power out-put and voltage within the specifications ofthe MOSFET you wish to use. C1 is calcu-lated based on the required power output.The values of the remaining components, L1and C2, are provided by the spreadsheet, butwill usually require a small bit of adjust-ment to achieve optimal efficiency. The out-put transformer, T1, can be adjusted bychanging the turns ratio to get the desiredoutput impedance, usually 50 Ω. The trans-mitter signal then goes through a wattmeterand on to the antenna tuning network(L2, L3).High quality capacitors should be usedfor C1 and C2. Parallel combinations of sil-ver mica or pulse rated metalized polyeth-ylene capacitors are recommended. RFC1and T1 are both wound on 2.75 inch squareferrite cores such as those used in flybacktransformers. RFC1 is 28 turns for about1.5 mH of inductance. The number of turnsdepends on the core material, which shouldbe selected to avoid saturation and exces-sive heating. L1 was constructed using twoconcentric air wound inductors. The innernant antenna. A large amount of capacitivereactance and a very small radiation resis-tance are the facts of life for any practicalLF antenna.The first step in tuning the antenna is tocancel the capacitive reactance by insertinga large amount of inductance, often severalmillihenrys, in series with the antenna. Thisis simplified by using a variometer (L3),which allows a continuous variation of in-ductance. Next, the remaining resistive com-ponent has to be transformed to the outputimpedance of the transmitter, which is nor-mally 50 Ω. This is usually achieved by us-ing an autotransformer (L2) to step up theresistance, or if you are fortunate, to step itdown. The ultimate goal is to get the effi-ciency of the transmitter and the antennacurrent as high as possible at the same time.It’s a little more challenging than erectingan antenna and running coax from it to therig as we do so easily on the wavelengthsbelow 200 meters.The inductance needed to achieve reso-nance is obtained fromC ) f 2 (1L2π =[Eq 1]where C is the antenna capacitance, whichcan be roughly estimated as 5 pF per meterof antenna length. For example, if your an-tenna is 100 meters long, its capacitance willbe about 500 pF and the total inductanceneeded is about 2.7 mH. Fine tuning is doneby adjusting the variometer and matchingtransformer for maximum antenna current.The LF antenna that VO1NA used for thetransatlantic experiments is shown in Fig-ure 4. The antenna is about 150 meters long,including 100 meters of horizontal wire andanother 50 meters of wire between the shackand feed point acting as a feed line. The useof two parallel wires increases the antennacapacitance and efficiency.To match VO1NA’s parallel-wireantenna, L2 is air wound, with 100 space-wound turns for a total inductance of about0.4 mH. It is tapped for the best resistivematch.L3 is the tuning variometer with an in-ductance range of about 0.3 to 1.3 mH. Thevariometer is wound with 12 gauge insulatedcopper wire. The insulation is used as a con-venient means of spacing the turns to reducelosses.A good ground connection is very im-portant and this will take some experimen-tation. The ground resistance can beestimated from2 gIPR=[Eq 2]where P is the power of the transmitterand I is the antenna current. At VO1NA itis about 40 Ω.Figure 5—After almost two years oftuning the antenna from inside the shack,in January 2005 VO1NA moved theloading coil and variometer outside to thetower. A smaller variometer, about 60-250 µH, was used in series with a tappedloading coil. This moves the RF and highvoltages away from the house. A standard50 Ω ΩΩ ΩΩ coaxial cable runs back to thetransmitter in the shack.one is 2.75 inches diameter by 6.25 incheslong. The outer one is 3.125 inches diam-eter by 2 inches long. You can adjust theinductance by taking taps and fine tune itby sliding the coils. L1 conducts largeamounts of current and should be built ac-cordingly with wire no smaller than no. 16.The finished transmitter is shown inFigure 3. Increasing the voltage made itmuch easier to get high efficiency. Within ashort time 100 W at about 80% efficiencywas achieved and there seemed little pointin further tinkering. It was very gratifyingto see that the only hot thing on the bench(besides the soldering iron!) was the dummyantenna. The MOSFET, mounted on aheatsink about 3 × 3 × 4 inches, was barelywarm after several minutes of steady car-rier. For those interested in even higherpower, a 700 W transmitter has been de-scribed in QEX.3Some form of filtering may be neededat the transmitter output to reduce the har-monic content of the signal, but it is worthnoting that a properly tuned class-E stagehas less distortion (and harmonics) than aclass-C or class-D stage. Amplifiers arediscussed in Peter Dodd’s excellent LowFrequency Experimenter’s Handbook.4The Antenna andTuning NetworksBecause ¼ λ is more than 500 meters at136 kHz, it is not likely that you will havethe good fortune to be able to erect a reso-
From July 2005 QST © ARRLThese Web pages offer a wealth ofadditional information about Ama-teur Radio LF experiments, hard-ware, software and propagation.Argo Softwarewww.weaksignals.comCT1DRP Web sitehomepage.esoterica.pt/~brian/G3YXM LF Newswww.wireless.org.ukG3NYK Web sitewww.alan.melia.btinternet.co.ukKL1X Web sitemyweb.cableone.net/flow/Long Wave Club of Americawww.lwca.orgNOAA Space Environment Centerwww.sec.noaa.govON7YD Web site www.qsl.net/~on7yd/VE7SL Web site imagenisp.ca/jsm/INDEX.htmlW1TAG Web site www.w1tag.comW3EEE Web site www.w3eee.comW4DEX Web site www.w4dex.comWeb Pages for the LFExperimenterDanger: High Voltage! Please note thatthere are very dangerous voltages presenton the antenna end of the tuning coil andthe antenna itself. Special precautions arenecessary to prevent electric shocks andburns, as well as arcing. Low frequencyRF can be deadly lethal when it uses yourbody as the ground lead.Getting the Message Outon the Long WavesKeying the transmitter can be done inseveral ways. For slow speed CW (0.04WPM) one has to be very persistent formanual operation. Most of us aren’t thatpatient so we use a diode matrix identi-fier or program a computer to do the job.A matrix (or EPROM/PIC) is very conve-nient for beacon operation, but a computeroffers more versatility for making slowspeed QSOs. VO1NA’s IDer is a CMOSversion of the circuit published by TomMcMullen, W1SL, many years ago.5A variety of modes is used on LF, butby far the most popular are FSK or slowspeed CW (QRSS) in which the dots aresent on one frequency and the dashes on aslightly higher frequency. For long dis-tance work, dots are 30 to 60 seconds long,so the QSOs do not involve the exchangeof a lot of details other than the call signsand the signal reports.Transatlantic Experiments onLong WaveVO1NA’s initial transmissions werewith a 5 W transmitter used for long waveexperiments on 180 kHz in 1992. He re-tuned it for 136.269 kHz and coupled it toa 30 meter wire antenna. Signals wereheard 7 km away. Next he built a 15 Wclass E transmitter using a P-channelMOSFET. Contacts were had with severalmembers of the Marconi Radio Club ofNewfoundland including VO1FB,VO1HD, VO1HP and VO1XP.Signals were finally radiated outsidethe country when the 150 meter wire an-tenna shown in Figure 4 was raised andsignals were detected by John Andrews,W1TAG in Holden, Massachusetts, about1600 km away. This success encouragedthe attempt to span the Atlantic, and the100 W transmitter described earlier wasbuilt from parts in the old junk box.Arrangements were made betweenG3NYK and VO1NA based on Alan’s pre-dictions of conditions. After a few tries,signals were finally copied and the Atlan-tic spanned for the first time from VOland. Alan used an indoor 1.25 meter loopmade out of 16 turns of 25-pair telephonecable, tuned and amplified with the simplepreamp shown on his Web site. On June 12, 2003, 1011/2 years afterMarconi spanned the Atlantic, a two-wayQSO was completed with Jim Moritz,MØBMU, near London—more than 3700km away. Jim used a 2 meter loop to re-ceive Joe’s very slow CW signals on137.777 kHz. Other transatlantic contacts have beencompleted, including a couple withG3LDO. To date, the best DX fromVO1NA has been RN6BN at 6600 km.We’ve copied each other’s signals and arestill hoping for a two-way QSO. A longwave listener, Hartmut Wolff in Germanyhas copied VO1NA’s 137 kHz signals anumber of times, as well as his QRP (5 W)beacon on 189.81 kHz. Closer to home,and at even higher CW speeds FrankDavis, VO1HP, while operating theMarconi Radio Club station VO1MRC,completed the first two-way conventionalCW QSO in Canada by working VO1NAat 20 WPM. With a recent reception byHartmut of a 10 W signal, transatlanticexperimentation promises to be very in-teresting and gratifying for upcoming win-ter seasons. More information on ourexperiments appeared in The CanadianAmateur.6ConclusionBefore transmitting on the 2200 meterband, please note that Canadian amateursare required to obtain a Letter of Authori-zation (LOA) from Industry Canada. Thiscan be done through Radio Amateurs ofCanada. American amateurs are requiredto obtain an experimental license underPart 5 of the FCC Regulations. We hopethat this band will be allocated to the ama-teur service on a worldwide basis.Amateurs who seek technical challengesand new excitement have a fascinating newfrontier at 2200 m. With the aid of theInternet, you can become part of a growingfraternity with some very competent andknowledgeable fellow amateurs. State-of-the-art software has been developed andmade readily available for all to use. Newdevelopments are surfacing all the time.AcknowledgmentsWe wish to acknowledge the supportof members of LF community, RadioAmateurs of Canada, the Marconi RadioClub of Newfoundland and the Radio So-ciety of Great Britain for their LF Internetreflector.Notes1J.S. Belrose, W.L. Hatton, C.A. McKerrowand R.S. Thain, “The Engineering ofCommunications Systems for Low RadioFrequencies,” Proc. IRE, Vol 47, No 5,May 1959, pp 661-680.2N. Sokal, “Class E Power Amplifiers,” QEX,Jan/Feb 2001, pp 9-20.3A. Talbot, “A 700 W Switch-Mode Transmit-ter for 137 kHz,” QEX, Nov/Dec 2002,pp 16-26.4P. Dodd, The Low Frequency Experimenter’sHandbook (Radio Society of Great Britain,2000).5T. McMullen, “A Low Cost CW Identifier,”QST, Apr 1975, pp 34-36.6J. Craig, R. Dodge and R. Peet, “LF In New-foundland and Labrador,” The CanadianAmateur, Sep/Oct 2004, p 39.Photos by Joe Craig, VO1NA, unless otherwisenoted.Joe Craig, VO1NA, was first licensed in 1976. Heis the son of VO1FB, husband of VO1RL, andfather of Julia. Joe completed his Bachelors andMasters degrees at Memorial University of New-foundland and works with the Government ofCanada as a physicist. He has lectured at theUniversity and at conferences in radio and physi-cal science and has authored dozens of techni-cal and research papers as well as several pub-lications in the primary literature. Joe is a mem-ber of the Baccalieu and Poldhu Amateur RadioClubs, the Marconi Radio Club of Newfound-land, Radio Amateurs of Canada and a life mem-ber of the Quarter Century Wireless Association.He has both CW and 160 meter DXCC. Joe alsoenjoys swimming and fitness, music, traveling,photography and astronomy. He can be contactedat jcraig@mun.ca.Alan Melia became interested in AmateurRadio at school about 1955 and obtained hislicense, G3NYK, while at Liverpool Universityin 1960. He graduated with a BSc (Hons) inPhysics in 1961 and joined the then Post OfficeResearch Department (later British Telecom Re-search Labs) where he worked for 30 years ontransistor and IC test and reliability. He thenjoined a small local two-way radio company,retiring 5 years ago. He started on 160 m, andhas become addicted to LF, particularly propa-gation effects. He is a member of the RSGBPropagation Studies Committee, and still holdsmembership in the Institute of Physics asa Chartered Physicist. He can be contactedat 67A Deben Ave, Martlesham, Heath,Ipswich IP5 7QR, UK or alan.melia@btinternet.com.