I've been following the VLF receiver threads with interest, particularly the need for remote operation to get away from noise. 

How much interest would there be in a digital remote receiver, linked via a UHF amateur band - or possibly the 868MHz / 2.4GHz licence-free band for SWLs?  

 

16 bit sigma-delta  A/D converters cost peanuts these days, and the resulting data could be streamed over 1.3 or 2.3GHz with low cost equipment and simple modulation.    Or perhaps an optical link

 

The ADS1113 A/D converter, for example, is specified for sample rates up 860kB/s, so in theory could even cope with 137kHz reception. 

However, for anything above audio I'd be inclined to downconvert first to get to a lower sampling rate to allow a more sensible link cpability.   137 and 503 witj their narrow bandwidths could be converted without much difficulty.   The output data rate is going to approach 1MB/s which is nothing for the 1.3/2.4GHz UHF modules that have been used by the Am TV community

 

One thing to watch out for is going to be frequency stability for very narrow band signalling.   The remote  A/D and downconverter will have to use a high stability reference - at least a TCXO for 1ppm stability.   Which is better than most sound cards anyway.

 

At the receiver end, you could either have a D/A converter for a transparant link, or find some way of reading the digits straight in - making them look like a .WAV file may be one way. 

 

A kit may be feasible

Thoughts please.   

Andy
www.g4jnt.com