[Lowfer] newbie questions / receivers

[Steve Dove]

Hi Tom,

Let me weigh in support for the Icom R-75, too.  I recently got one
based on John's recommendation of some time past.

For 'Lowfer'ing, one needs adequate sensitivity and stability, and
a decent front-end.  The latter is because of the ease with which
broadcast-band signals get mushed into a grungy pulp at LF when
using anything other than a high-Q tuned antenna.

The R-75 has as mentioned the two preamps which make the 
sensitivity probably better than anything else, *provided* a low-pass
filter to get rifd of the BCB stuff, or a tuned loop is used.  Stability
would be OK provided you left it on all the time;  the optional but
fabulously expensive OCXO does work a treat.

Widely regarded especially in EU is the receiver in the Kenwood
TS-850, which would possibly be available for not much more money
than a new R-75.  On a monitoring setup, I use its kid brother,
a TS-140, which has no LF-specific front-end filter (so one is
vital externally) and decent enough sensitivity, although this is
starting to get iffy by 100kHz or so.  In common with most modern
radios, it uses a single reference oscillator from which all its 
required internal frequencies are generated  -  this is important for
stability.  The receivers in the Icom 751a, and the receive only R-71a
are both excellent, *except* their use of multiple crystals, which 
makes the degree of stability required nearly impossible.

Most hambone transceiver's receivers are miserably insensitive
at LF;  with the notable exception of the ones mentioned above
they are to be avoided.  Oh, the rx in the Icom 781 is the best 
for LF I've used, but it ought to be!  Apart from the need for some
additional selectivity (implicit in a tuned loop) the R-75 is its equal,
in fact more sensitive.

Filters:  I like good filters;  in the monitoring TS-140 and in the 
R-75 there are International Radio 125Hz 455kHz filters.  Great as 
microscopes, useless for anything general purpose.  Suggest
either the IR 400Hz for the 9MHz IF, or the Icom FL-232, which
is nominally 350Hz at 9MHz.  You do need *something*, even
though for the most part you'll be letting the FFT programs do
the walking.

         73,

                Steve        W3EEE



>
>Message: 3
>From: "Tom Smith" <tsmith@hal-pc.org>
>
>Hi,
>I'm sort of new at this and have a question about receiving hardware. =
>Understanding from the different Lowfer sites the stability needed to be =
>effective, I need to upgrade my equipment. I currently use a Collins =
>
>
>Tom  N5AMA=20
>