[Fwd: LF: RSGB HF & IOTA Convention 1998: LF Forum (amendment 1)]

[Andre' Kesteloot]

John W Gould wrote:

> The LF Forum was chaired by John Gould, G3WKL.
>
> The following attended
>
> Riki 4X4NJ, Peter DJ8WL/DA0LF, John G0AKN, David G0MRF, Roger G0UPU,
> Derek G3HEJ, John G3FBN, Derek G3GRO, Lech G3KAU, Peter G3LDO,
> Mike G3LYP, Walter G3JKV, John G3TDZ, Dave G3YMC, Stuart G3YSX,
> Dave G3YXM, Mike G3XDV, Graham G3XTZ, John G4GVC, Andy G4JNT, Linda,
> Mike G8AFN, Ian GI8AYZ/MI0AYZ, Andre N4ICK
>
> Everybody was invited to introduce themselves and say a few words about
> the interests in LF.
>
> Presentation of the Datong cup - the RSGB LF Experimenters Award
>
> The 1998 award was presented by the RSGB President Mr Ian Kyle, GI8AYZ /
> MI0AYZ to Mr John Hey, G3TDZ.  John had made significant contribution to
> amateur communications on the LF bands through his numerous experiments
> carried out in conjunction with the rugged caving environment. He had
> shared his designs, which have been proven by others.  His attention to
> detail and repeatability when noteworthy.
>
> John Gould, G3WKL, said that the HF Committee had commented on the high
> standard reached by all nominations for this year's award.  They had
> asked him to pass on a message of encouragement to all experimenters on
> these new amateur allocations.
>
> Presentation on underground LF communications by John Rabson, G3PAI
>
> John's presentation emphasised the particular difficulties faced by the
> amateur designing for the caving community.  Not only did the design
> have to meet the particular environment experience in caves, but the
> equipment also needed to be caver proof. He illustrated this with the
> help of the ruggisied transceiver designed by John Hey, G3TDZ.  He
> explained that as well as the range of amateur bands, the caver also had
> other specific frequencies available for underground communications.
>
> 136 kHz in Germany, Peter Bobek, DJ8WL / DA0LF
>
> Peter outlined the history of amateur LF activity in Germany.  He
> started with the spectrum survey which had identified many strong
> commercial stations that had led the DARC to request for LF frequencies,
> and the eventual compromise of the current 136kHz CEPT recommendation
> for Region 1. He explained that two temporary licenses had been issued,
> but that only his call DA0LF had been used for any length of time.
> Unfortunately his DA0LF licence expired during summer.  The authorities
> in Germany had not yet granted him further permission for 136 kHz
> transmissions, nor have they generally issued amateur access to that
> band.
>
> Peter outlined the experiments that he had carried out and the success
> that he had achieved. His transmissions, from a few miles south
> Frankfurt, had been received over 300km away using normal CW reception
> bandwidth and when running 10 watts initially.  The use of DSP
> processing, developed by G3PLX, enabled his transmissions to be received
> at over 900km from his QTH.  Strong intermodulation interference from
> the nearby Mainflingen LF radio site makes reception of weak signals
> difficult, thus 2-way QSOs are unlikely in the lower part of the band.
>
> Special 136 kHz permits in the US?, Andr Kesteloot, N4ICK
>
> Andr outlined the LF environments in the US.  He mentioned the
> excellent experimental work of the LOWFERS, and recommended reading
> their magazine "The Lowdown". He explained that the ARRL was in the
> process of filing a petition to the FCC for allocations in the 160 to
> 190 kHz band.  The ARRL had also recently added to that petition
> additional spectrum to harmonise with the 136 kHz amateur allocation in
> Region 1.
>
> Andr explained that he was a member and a past president of AMRAD, the
> AMateur radio Research and Development Corp. He explained that this is a
> world-wide club for amateur radio and computer experimenters.  They had
> recently added to their range of interests experimentation at the new LF
> amateur frequencies.  He added that about 20 Washington-based members of
> AMRAD have requested a special permit from the FCC to operate at 136kHz.
>
> Andr finished his short presentation with some viewfoils showing his
> role in an earlier AMRAD experiment for the development and deployment
> of an amateur satellite (AO-27).  He also showed his 1942 US Navy TRF
> receiver, signal sources, a VSWR meter, and a ferrite rod aerial
> intended for LF operation.
>
> Ground current communications, John Taylor, G0AKN.
>
> John outlined his experiments to launch a propagating LF signal from
> ground probes.  This had been proven to be a very successful, albeit
> unusual, way of launching a radiating signal at LF. His paper is at
> http://www.wireless.freeserve.co.uk
>
> In summary John is testing a hypothesis that ground probes placed at
> varying distances from 80 meters to 230 meters and beyond, can, by
> virtue of the low velocity factor of the ground, allow a resonant
> conduction current to be set up between the probes.
>
> Irrespective of the mechanism, transmissions from Devon have been
> received by G4GVC at Woburn Abbey, Bedfordshire using a standard loop
> aerial.
>
> LF policy issues
>
> A number of policy issues concerning the LF bands were discussed.  G3WKL
> said that he would feedback of Forum's views to the RSGB HF Committee.
>
> LF operating procedures
>
> Discussion took place about possible band planning, preferred
> frequencies for DX operating, testing, etc.  The consensus view was to
> retain flexibility by not having a rigid band plan.  In part this was
> because the parts of Europe would probably have different "DX Windows"
> and preferred times.  However, it was recommended that good operating
> practice would be to
>
> a) include a phone number in beacon messages
> b) conduct beacon transmissions below 136.0 kHz for transmitter testing
> c) avoid Saturday and Sunday mornings for long-duration transmitter
> testing on air
> d) make use of a good VFO, or ideally a synthesiser, so that common
> frequency working could be achieved by more stations.
> d) that the 6.6Hz band centered on 136458.18 Hz be used for narrow-band
> transmission (this is the largest "window" between adjacent LORAN C
> spurii within the 136Khz band).
>
> Activity co-ordination
>
> There was some agreement that more use should be made of the packet
> cluster network for notification of 136kHz DX.
>
> It was agreed that the RSGB LF Group reflector was being successful in
> co-ordinating future activity, however, as many users rely on their
> Internet connection at their place of work it was agreed that weekend
> operating schedules should be e-mailed to the reflector before midday on
> the Friday prior to the weekend.
>
> 80m and 160m SSB nets were discussed.  The 3720 kHz net (0900 UK local
> time every Saturday morning) would continue, though there was some
> possibility that the frequency may be difficult to acquire in the
> future.  G4GVC was concerned that some stations could not receive him
> too well, and asked whether he should continue as the net controller.
> All presents agreed that he was doing good job, and should continue.
>
> After some discussion about the 160 meter net it was agreed that G4GVC
> would raise the matter of the frequency with the group on the reflector.
> It was agreed that it should be below 1890kHz to enable the German
> amateurs to join the net. It was also agreed that the 160m net should
> move to the Sunday evening.
>
> LORAN C
>
> G3WKL thanked Walter Blanchard, G3JKV, for his excellent support in
> attempting to sort out the interference problem from the LORAN C
> transmitters. It was concluded we would be unlikely to get the spurii
> eliminated at source, although efforts would continue, so we would have
> to find ways of minimising the effects of the interference.  This would
> probably cause some 136 kHz experimenters to develop cancelling
> techniques.
>
> LF aerial modelling, Peter Dodd, G3LDO
>
> Peter demonstrated EZNEC, the aerial modelling computer programme.  He
> used the programme to show the difference in performance that it
> calculated for a number of different LF aerials. It could give some
> insights into how different configurations might compare.  Despite well-
> documented limitations, particularly at LF for the size of typical
> amateur aerials, the programme did provide some useful insights into
> aerial performance.
>
> Aerial lessons learnt
>
> It was generally agreed that the Marconi design was close to optimum.
> For a given the length of wire it was best to extend the span of the top
> section before adding additional wires in parallel to the top section.
> It was important that no part of the aerial came close to trees or other
> structures which were effectively a conducting path to earth.  The
> vertical part of the aerial needed to be as high as possible.
>
> Loops were seem to be an effective alternative in some locations,
> especially in areas of poor around conductivity.  The feed point
> position and capacity tuning position was not thought to be critical.
>
> All agreed that raising the loading inductor was beneficial in the
> Marconi configuration.  It was mentioned that G2FMI had an article
> published in a 1975 edition of QST.  The article suggested that the
> optimum position was immediately below the top section.
>
> Most considered that the safest way of matching to the aerial, from the
> point of view of amplifier protection, was to capacity couple the
> amplifiers low impedance output through a transformer, using a 3C85
> core, to the bottom of the loading coil and ground connections.  The
> transformer would match the amplifier output to about 100 ohms.  Link
> coupling to the loading inductor was best avoided as there was more
> likelihood of a very low impedance being presented to the amplifier when
> the aerial was off resonance.
>
> Kits
>
> G3PAI spoke of modifications that he had been making on the Howes DC2000
> direct conversion receiver.  It would be suitable for the caving
> application, and also as a simple general purpose receiver for the band.
>
> G0MRF mentioned his experience with the provision S-band receive
> converter kits for AMSAT. His 250W 136 kHz transmitter PA was now
> completed.  He could provide boards and difficult-to-obtain components
> at cost.
>
> General discussion about kits took place.  It was agreed that some basic
> kits would be of general benefit.  These should include an oscillator or
> synthesiser, a transverter, and a PA.  G0MRF agreed to consider the
> matter further and revert to G3WKL.
>
> Propagation
>
> Inconclusive discussion took place over the optimal time when long
> distance sky wave propagation occurs.  It was agreed that some proper
> measurements were required, which avoided variables such as transmitter
> power, changes in aerial configuration etc.
>
> DJ8WL suggested that the Germany transmitter (DBF39 near Magdeburg,
> 100km WSW of Berlin) on 138.822kHz (with a shift of about 360Hz) would
> be a suitable commercial station to use as a beacon.  It was situated
> near Berlin and thus would be approximately 600km from the UK.  G3JKV
> offered to consider what data would be required and how it should be
> formatted.  He agreed to discuss the matter with G3WKL.
>
> In relationship to a possible US to Europe QSO, G3JKV said that he had
> carried out calculations that suggested that communication might just be
> possible between Northwest Europe and the East Coast of the US in a 10Hz
> bandwidth. He asked N4ICK if he could confirm whether or not Loran-C
> could be received on 136 kHz in the U.S. emanating from U.S.
> transmitters.
>
> (any corrections e-mail to me directly)
> --
> John Gould, G3WKL
> G3WKL @GB7BEN.#43.GBR.EU
> g3wkl@pagnell.demon.co.uk