# [Fwd: LF: SLow CW between the LORAN lines]

**André Kesteloot**
akestelo@bellatlantic.net

*Sat, 23 May 1998 18:16:41 -0400*

Looks to me like a job for the DSp Wallahs...
Andre
********************************************
Peter Martinez wrote:
>* >From Peter Martinez G3PLX Kendal Cumbria.
*>*
*>* Following some discussion on the 80m net about how to avoid the
*>* LORAN spurii for very low-signal working, I thought I would dig out
*>* some calculations I did a while ago and feed them into the group.
*>*
*>* The LORAN signal is centred on 100.000... kHz (as many zeroes as
*>* you like). The one we hear splattering across the 136 kHz band
*>* radiates pulses with two different repetition rates. The RF waveform
*>* in the pulses starts at exactly the same point in the RF cycle on
*>* each pulse. This means that the carrier frequency must be a
*>* whole-number multiple of the pulse repetition frequency and that the
*>* spectrum consists of two arrays of closely-spaced carriers, each
*>* array having a carrier spacing equal in Hz to the p.r.f. and at 100
*>* kHz exactly, the two arrays of carriers line up.
*>*
*>* With this information and a few measurements, I was able to work
*>* out absolutely the values of the two p.r.f's, and hence the carrier
*>* spacings. They are 100000/14998 Hz and 100000/13462 Hz, or
*>* about 6.67Hz and 7.42 Hz. We can work out where the spurii come
*>* in the 135.7 to 137.8 kHz band by noting that one set of frequencies
*>* is the series N*100000/14998, where N goes from 18268 to 18551,
*>* and the other set of frequencies is M*1000/13462, where M goes
*>* from 20352 to 20667.
*>*
*>* What we want to do is find the gaps! The biggest gaps will be found
*>* either side of the places where the two sets line-up as closely as
*>* possible. They never line up exactly within the band. There are 7
*>* spots where they line up closer than 0.1Hz, so the best gaps are
*>* about 6.5Hz wide centred 3.3Hz either side of these spots. I give
*>* these spot frequencies below.
*>*
*>* 135938.1
*>* 136198.2
*>* 136458.2
*>* 136718.2
*>* 137045.0
*>* 137305.0
*>* 137565.0
*>*
*>* 73
*>* Peter G3PLX
*