LF Radio Propagation, Aerials, Amplifiers, Transmitters, and Technical Talk
Alan Melia G3NYK
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Radio Amateurs were consigned to the 'useless' shorter wavelengths early in the last Century as the commercial interests annexed the the more useful 'Long Waveband' for long distance communication and broadcasting. This was the situation until very recently where the lowest frequency available to amaterus was around 1.8 MHz, known from its old classification as the 160 metre band. This is a great band and was the nursery of many a radio amateur. Gear was relatively easy to build for these frequencies as the transmitter power output was limited by the licence. I know I, and a lot of others, learned a lot of practical radio on 160 metres.
In 1996 after representations were made to the licencing authority by the Radio Society of Great Britain, a small segment of spectrum at about 73kHz was allocated to a limited number of amateurs who were required to apply for a Notice of Variation to their Class A licences. This was always intended as a stop-gap until European countries cooperated and agreed a contient-wide allocation. In the event the period of use was extended and the NoVs will now expire on the 30th June 2003. Fortunately the licencing authority (the Radio Communications Agency of the DTI) soon announced the allocation of a band at 136 kHz and several other countries quickly followed suit. There is now an actice and enthusiastic band of LFers in over twenty countries in Europe. For more detailed information follow the links to some of the well established LF web sites below.
FCC denies the US amateurs a slot at 136kHz. Instead it sees fit to "protect" a non-radiating data service carried on the power distribution. One can only be amazed at the strength of a commercial lobby, that is obviously technically illiterate. Particularly after the disaster of August 14th 2003 !!
US amateurs encouraged to apply for Part 5 licences to experiment on LF. The first licence granted to ex-pat Laurence Howell KL1X in Anchorage. Laurence has now transfered his location to Bartsville in Oklahma, from where he has achieved a report from New Zealand. Three other stations now licenced in the USA. First signals received (by CT1DRP and M0BMU) from John W1TAG using 100 watts to a loop aerial with the call WD2XES. Warren K2ORS has joined in with WD2XGJ which now has kW capability. Check the LWCA web site for the latest, to date (March 2006) WD2XDW, WD2XNS, WD2XKO have also been logged in Europe on QRSS. None has managed to crash the US power distribution network yet and several are running in excess of 1kW at the base of their aerials (sorry antennas)
Argentina now has an allocation and Brazil and Cuba have allocations under consideration. Poland has confirmed an allocation and SP5ZCC has made qsos with SM,UA,YU, and G, and there as listeners in Norway but no transmissions heard in the UK yet. Unsuccessful tests were organised in 2004 between Argentina and New Zealand
Probably the world record DX 2-way qso (10,300 km) so far was made this March 2004 between UA0LE in Vladivostok and ZM2E at Quartz Hill, New Zealand. Since then there have been signals heard from western Russia in New Zealand at about 16,000km. Laurence ( KL1X , GM4DMA ) running WD2XDW from Bartesville OK has been copied several times in ZL, but has considerably more trouble reaching Europe. Laurence has left Bartesville and is now in Shanghai and occasionally Singapore, with multi screen monitoring of course. Laurence left China in 2010 and is now back in the States.
Australian amateurs should have access to 137kHz by the end of 2008 !! This is just in time to coincide with what may be the best conditions for Eu<>VK tests on 137kHz
Not strictly LF but the ARRL MF experiment has been issued a licence recently (Sept 2006) by the FCC for operation on 505 to 510kHz. Station calls are WD2XSH/xx where xx is the two figure registered number of the location.
On 1March 2007 the UK regulatory body Ofcom issued a limited number of experimental permits to amateur full licencees allowing operation between 501 and 504 kHz with a maximum ERP of -10dBw (100mW). Europe wide reports have been received for night-time transmissions though absorption is limiting daytime range to 200 miles or so. At this power level which can be achieved with less than 10 watts RF in most cases, DX is confined to very narrow-band modes like QRSS and DFCW. However the fading period is short (30 to 90 seconds ) compared with 136kHz (10 minutes to 30 minutes) and these frequencies seem not stable enough for long-dot QRSS. Click here for links to the RSGB spectrum web site with recomendations and suggestions for applying for a permit. In 2008 Ofcom relaxed the power restrcyion to allow 1 watt ERP, and with the issue of a further extension in February 2009 the power allowed has risen to 10w ERP. This should be quite enough for regular two-way transatlantic hand-morse qsos, but may be difficult while only some of the Part 5 stations licenced in the States are authorised to contact foriegn amateurs and the Canadians have now got their allocation. In the Southern Hemisphere Argentina is active but I have not yet seen reports of reception outside their continent. I believe there are some Brazilian stations active as well. See Dave Pick's site (link below) for the latest situation on authorisations.
Great tutorials, a bibliography, and linked "Projects" file from Rik ON7YD at http://www.qsl.net/on7yd
LWCA (Long Wave Club of America ) web site http://www.lwca.org
Background, news, current topics, and an ARGO screen grabber from Dave Pick G3YXM who writes the Radcomm LF column at http://wireless.org.uk and a comprehensive list of links to other LF sites...also "rogues" gallery.
The propagation of radio signals at frequencies around at136kHz is of a totally different nature to that experienced on the short wave bands. A lot of the basic professionall experimentation was done before 1930, and at a time when equipment was somewhat more crude, and the common recording device before the days of magnetic tape was a syphon pen recorder. Even in the 1950s when there was a further flurry of interest in the low frequencies for long range navigation, equipment for experiments was expensive complex and difficult to maintain in calibration over many months of obsevations. In all cases the general aim of the research was to refine ways of determining the ground-wave service area of a given station, and evaluate the severity of the interfering effects of night-time skywave (or ionospheric wave) on reception.
My initial interests were fired by some searching through bibliography and some 'back-of-envelope' calculations that indicated that with some luck and favourable conditions, communication might be possible across the Atlantic within the power limitations of the licence and the practical constraints of most amateur locations. My enthusiastic offerings in 1999 were greeted with a certain amount of well justified skepticism, because the record contact distance at that time was about 1800kms, which was less than half way across the 'pond'. We correctly identified the nightly appearance of an 'RTTY' signal at 137.00kHz as being from the Canadian Naval Station at Halifax, Nova Scotia. I started to monitor the signal regularly in a subjective way using some early soundcard software. After some prodding from Vaino, OH2LX an ex-professional in this field, I set up a proper calibrated receiver and a computer data logger to record the signal from Canada nightly. This was just in time to be able to correlate the signal profiles from the Navy station with the times of successful reception by John VE1ZJ, of Dave G0MRF and Peter G3LDO. These archive files are still available in zipped form on Rik ON7YD's web site. I have continued this project with the aim of trying to understand and be able to usefully predict the best times for Trans-Atlantic attempts. The continuation of reports is solely thanks to Brian CT1DRP who supplies me with daily 24hours logs of DCF39 signal strength as received in Porto. Plots of the Canadian station are posted, as and when it appears on the band. Some plots from mid 2001 of the Greek Naval station SXV are still available on Rik's ON7YD web site (URL elswhere on the page)
Propagation monitoring history.
The monitoring of the received signal strength of commercial and military LF stations has proved to be a very useful indicator of propagation conditions over longer paths. Unfortunately CFH (Halifax N.S.) ceased regular transmissions at Christmas 2000. The Greek Naval station SXV ceased regular transmissions around August 2001, but has recently started again (late 2002). Fortunately the path from DCF39 to CT1DRP has proved to be a reliable guide to conditions and Brian has supplied me with data for over 12 months from mid 2001 until his computer failed in Ocober 2002. He is on the verge of starting the monitoring process again now (Christmas 2002). Meanwhile several stations are starting to look eastwards from the USA . John Andrews W1TAG has posted real-time plots of HBG the standard frequency transmission on 75kHz.at http://webpages.charter.net/w1tag . Dexter McIntyre W4DEX has also monitored and posted near real-time plots of HBG on 75kHz. at http://www.w4dex.com . Dex is now ploting DCF39 daily (Feb 2003). Steve Dove W3EEE has set up a continuous monitoring station in DCF39 and is supplying me with raw data, as well as posting a real-time plot to his web site http://www.w3eee.com . This was good indication of the state of the Trans-Atlantic path, but Steve was away on business a lot and finally stalled his grabber in mid 2008. This is looking very exciting and shows occasional nights with large boosts in signal strength, similar to those I saw in late 2000 on CFH. The recent improvement (mid Jan 2003), seen by Steve W3EEE just after relatively long period of quiet solar activity, and caused by a minor rise in the Geomagnetic index Kp to 4, bodes well for DX capabilities of the band through the years of the solar minimum. Unfortunately the downward portion of the solar cycle is cited to have more geomagnetic activity than the upward slope. There has been almost continuous activity since late January and there has been no return to those good conditions seen in early January 2003 in 2004. However some long good spells of propagation have been experienced during the minimum. It now seems that a very quiet sun may allow the ionosphere to become slightly more "transparent" to 136kHz, so not producing expected good results. Often a small disturbance is required to perk condition up again. Now Scott Tilley VE7TIL has a capture of a Russian BC station on 153kHz which seems to be giving a good pointer to the effects on northern paths. This path is probably polar.
For more detailed descriptions of the logging system I used.
Propagation and monitoring links
Simple path-loss Calculation new Sept 2006 forget complex formulae here is a simple thumbnail calculation that gives accurate enough results to judge the likelyhood of a path being available, given the power available at each end. It can also be used to decide "should I be able to hear this beacon?"
Many of the articles and presentaions I have given in past years are linked below. bear in mind my ideas have changed slightly over the years as I have collected more data and gained practical ecxperience of the band. I have left the older papers in original form so that you can see how my ideas developed.
The presentaion given to the October 2001 HF Convention and a lot more updated material
Click here for a more detailed version of the presentation at the HF Convention 2002. "Simple Geometry applied to Propagation"
"Forecasting LF DX Windows" an attempt to devine the conditions over solar minimum years.
"Investigaton of Fading" an analysis of effects seen on the CT1DRP <> DCF39 path NEW..ideas on a possible mechanism
Forecasting 136kHz Propagation conditions a new paper on the use of the Dst Index
Download Excel file to go with an article by Mike ZL4OL in NZ mag "Break-in"
For my latest thoughts on LF propagation see the 2nd editions of "LF Today" by Mike Dennison available from the RSGB
Probably even more up to date is the article on Rik Stobbe's 472kHz pages http://www.472khz.org/pages/technical-topics/propagation.php
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