Re: LF: RE: Todmorden receiver

[Andy Talbot <andy.g4jnt@gmail.com>]

As an alternative to SL and soundcards, if you're into building there are other solutions for ultra high stability digital receivers.

http://www.g4jnt.com/Coherent_LF_Receiver.pdf  gives details of a such a receiver that I have used in the past to sucessfully decode EbNaut transmissions (on 137kHz)

It uses a direct downconverter from RF  to 1kHz audio in a Softrock type receiver;  a DDS based LO is driven from a 10MHz master reference.  The 1kHz output is bandpass filtered and digitised in a PIC to give baseband I/Q channels each at 12 bit resolution at 1kHz sampling rate.   The digitised samples are fed over an RS422 interface to a PC (in practice this means a USB interconnection using FTDIChip devices)    GPS NMEA data is also fed into the receiver and used to timestamp the data to the PC to 1ms resolution

PC Software reads the serial data and filters / decimates the digital stream to use as wanted.   The beauty of using a serial RS422 format stream means any PC programming language can be used with ready made support for the COM port.

If your LF to HF shack receiver is locked to the same reference, only the digitiser is needed if the receiver is used in narrow filter CW mode with the BFO / pitch at 1kHz.   But note the need to pre-filter audio to the range 800 - 1200Hz so a normal SSB filter isn't suitable

Andy  G4JNT

On 4 January 2018 at 19:05, JACK ASKEW <va7jx@shaw.ca> wrote:

Thanks for the reply.  I too have problems fully understanding Spectrum Lab and envy those that use it daily.  But when you get to be 75 years old ones ability to absorb technical complex issues gets more problematic ;-)    I have been trying to use SL to receive signals at QRSS600 but it doesn't work for me, best I can do is get QRSS120 and it's obviously just not enough for weaker signals.  I guess what I don't understand is how this program you are using receives the data real time and or how to generate that data so it can be seen later using this software.

73, Jack  

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From: "Paul Nicholson" <vlf0403@abelian.org>
To: "rsgb lf group" <rsgb_lf_group@blacksheep.org>
Sent: Wednesday, January 3, 2018 9:48:27 PM
Subject: Re: LF: RE: Todmorden receiver

 > Is that software you use for the spectrum plot display
 > available on line?

Easy, it is all in your browser.  It is all html and
_javascript_, and it is not compiled or minified.

Just save the page to you local drive.

Perhaps others can use it?  I try to keep the code simple
and tidy to encourage that.   It is necessary to provide
spectrum data on your web server in the right format.  I'll
document the simple format and how to generate the data.

--
Paul Nicholson
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