[Fwd: LF: Rcvr Sensitivy tests]
Mon, 04 Jan 1999 19:53:07 -0500
Mike Dennison wrote:
> Accordingly, I
> > use an external pre-amplifier with about 20 dB gain, and with good low
> > pass filtering to prevent MF AM broadcast signals from overloading
> > either the pre-amplifier or the following receiver (broadband RF
> > response on the lowest frequency range). So while it is handy to have a
> > receiver that does have good sensitivity on the LF band of interest, it
> > is also possible to build a suitable external pre-amp to compensate.
> > The ability to be able to detect QRN as the major component of noise is
> > a practical way of verifying that a receiver has adequate sensitivity.
> > Bob ZL2CA
> As many of you will know, one of my 'hobbyhorses' is the number
> of poor receivers there are in use on LF. It really is vital not to be
> misled by the idea that at these frequencies sensitivity is limited by
> man made noise (if it is you have a site problem).
> It is vital to have enough gain to receive - as Bob says - static at all
> times. Anyone with plenty of experience of receivers will recognise
> the term 'presence', that is the feeling that you are hearing all there
> is to hear, including band noise (also often known as a 'lively'
> receiver). This is important at LF where every decibel helps. Of
> course, with this sensitivity comes the need to have good filtering
> to keep out the extremely strong commercial signals (and any
> potential mixing products), and IF filtering to maximise the S/N
> I use a Datong LF Converter (available from Waters & Stanton
> www.waters-and-stanton.co.uk) which is extremely sensitive but
> needs some extra front end filtering. This gives an IF of 28-30MHz
> and I improve things by using an ATU at 28MHz to reduce the
> strength of out of (amateur) band signals coming from the converter.
> Mike, G3XDV (IO91VT)