[Fwd: LF: The Loran problem]
Fri, 31 Jul 1998 09:37:18 -0400
Paul Keinanen wrote:
> At 09:20 31.7.1998 +0100, Peter Dodd <email@example.com> wrote:
> >I would like to start a discussion of way as to deal with the
> >pollution from the spurious sidbands from the Loran transmitter at in
> >northern France, which appears to be getting worse.
> I am not familiar with the exact pulse structure, but I assume that the
> spurious response at 136 kHz are synchronous with the main pulse emisssion
> at 100 kHz. What about adopting the synchronous noise blanker principle,
> which is sometimes used to get rid of impulse noise from arcing mains
> insulators (or other arcing devices) which generate the blanking pulse from
> the mains phase (with adjustable phase shift).
> If a separate wide band "Loran" receiver is tuned to the Loran transmission
> frequency and the signal is simply envelope detected with minimum filtering.
> The recovered Loran pulse is then used to control a switch, that grounds the
> 136 kHz receiver antenna input. The blanking pulse from the wide band
> "Loran" receiver will have short (and well defined) raise and fall times,
> much better than any internally derived blanking in a narrow band receiver.
> It would be interesting to look at the pulse with a dual trace oscilloscope,
> one channel showing the main Loran pulse and the other showing the output
> from the 136 kHz receiver (without noise blanking). If the spurious
> sidebands is simply due to too steep pulse edges (which is preferable for
> accurate navigation) i.e. "key click", then the spurious emission will only
> be present at the pulse edges and the noise blanker should be modified
> Just an idea.
> Paul OH3LWR