[Fwd: LF: Re: Loran Signal From Lessay]
Fri, 14 Aug 1998 19:22:57 -0400
DEREK ATTER wrote:
> Re: E-Mail from Peter, G3LDO (08/08/98) regarding Loran QRM at 136Khz. and
> request from Walter, G3JKV for further observations :
> Herewith confirmation of Peter's observations re pulse splatter at G3GRO
> QTH in Crawley (IO91VC)
> The relative signal level of the pulse interference at 136/137Khz does not
> seem to vary with weather but I confirm but it is subject to diurnal
> variation during the day, generally decreasing from it's early morning
> level (S4-S6) by perhaps as much as 6dB towards evening time by which time
> it is often masked or partially masked by QRN or local noise. The headings
> of both the QRM and of the main Loran signal are the same at 216 deg.
> magnetic from Crawley measured by an indoor loop.This is very close to the
> actual bearing to Lessay of 211 deg magnetic,
> Further confirmation of the source of the interference as being the Lessay
> transmitter is given from observation of the signals on a dual-beam digital
> storage oscilloscope which confirm :
> (a) The main Loran signal received here on 100Khz is very strong
> (S9+20dB) and is clearly a dual master/slave station
> judging by the interlaced trains of 9 and 8 pulse groups of
> essentially equal amplitude.
> (b) The group repetition interval (GRI) of the master station was
> measured as 64mS and the slave GRI as 75mS which
> corresponds to the published data for Lessay.
> (c) The interference at 136Khz is time synchronous with the pulse
> bursts from the main Loran station.
> Relative signal strength measurements today comparing the level of the
> noise sidebands at 137Khz with the signal level of the main Loran signal at
> 100 Khz using a calibrated step attenuator and with the 40ft top-loaded
> vertical antenna resonated at the two measurement frequencies in turn,
> showed the splatter to be only around -40dB with respect to the main signal
> measured in a 2Khz IF bandwidth. The actual signal levels in a 2Khz BW were
> 5 microvolts (S4) and 500 microvolts (S9+20dB) respectively into 50 ohms
> calibrated by a signal generator. This is a very poor performance
> considering the relatively narrow antenna bandwidths usually involved at
> the transmitting station and that the splatter is observed at a separation
> of over 30% of the centre frequency.
> It's good to hear that a dialog has been established with MegaPulse
> and hopefuuly they may be able to effect a cure. Thanks for your help
> 73 , de Derek, G3GRO