[Lf] [Fwd: LF: US FCC NOTICE OF PROPOSED RULE MAKING, Comments]

[Andre Kesteloot]

James Moritz wrote:

> Dear Andre, LF Group,
>
> Regarding ERP and so on, significant points that can be drawn from European
> experience on LF are:
>
> Measurements by several people have shown that the efficiencies achieved by
> typical amateur LF antennas are rarely better than 0.1%, and normally
> rather less. So a 100W PEP TX power limit in practice would limit EIRP to
> less than 0.1W for the vast majority of amateur stations - experience shows
> that to get 1W EIRP with 100W transmit power probably requires a favourably
> located antenna around 30m high. Even with unlimited transmitter power
> available, EIRP greater than 1W would be difficult to achieve from many
> amateur locations due to electrical breakdown of the antenna. Only a small
> minority of European stations approach our 1W ERP limit, in spite of the
> fact that transmitter powers are normally well over 100W. A TX power
> limited to 100W seems unnecessarily restrictive. In Europe, the
> availability of higher transmit powers means that less well-off amateurs
> can generate usable signal levels without having to acquire large tracts of
> real estate for antennas!
>
> It is certainly possible to make consistent measurements of ERP, although
> difficult for the average amateur station. However, an estimate can easily
> be made from a knowledge of the antenna geometry (effective height or area)
> and a measurement of the antenna current. The actual ERP determined by
> field strength measurements is invariably lower than the figure given by
> this estimate by an amount depending on environmental factors, usually in
> the range 0-10dB. So a safely conservative (from the regulatory point of
> view) estimate of ERP can be made from very simple measurements.
>
> In the European context, signal levels are present in the range of
> kilowatts to megawatts ERP from numerous broadcast and utility transmitters
> throughout the LF frequency range. There seems to be little interference
> caused to the operation of other electronic systems by breakthrough of
> these high level signals, which are obviously vastly greater than any
> feasible amateur signal level. Short range RF tagging systems using the
> 125kHz and 134kHz frequencies seem to be successfully in use over here, in
> spite of these large signal levels, so amateur LF operation would seem to
> pose little threat to these systems. I don't know if the power utilities in
> Europe use the same type of LF PLC systems (perhaps that is what the
> "Watford Whistle" carrier on 136.647kHz I D/F'ed to some power lines a
> while ago is.)
>
> The other side to the above is that, because they are relatively of
> extremely low power, amateur LF signals experience high levels of
> unintentional interference from numerous sources - for instance noise
> sidebands and intermodulation from high power LF transmitters (especially
> Loran), and switching noise from a wide range of mains driven appliances.
> These are often a severe limitation on amateur operation at LF, and would
> be considerably more of a problem with the proposed US power limits.
>
> Do you think it would be useful to send this type of comment directly to
> the FCC, or would it be better to do it via AMRAD/LWCA/ARRL etc?
>
> Cheers, Jim Moritz
> 73 de M0BMU