Talbot Andrew wrote:

[snip]
  Next project is a proper LF receiver with accurate and
repeatable signal measuring capability and built in A/D converter to
avoid having to use soundcards or external DSP for narrow band working.
[snip]

Andy,
          do you know these chips :  http://www.alesis-semi.com/index.html

From a first look they look quite useful for such a project. And they are

inexpensive, too.
Just a thought...

73
Alberto    I2PHD