Ultra Heavy BCB Dx'ing
On Thu, 15 Apr 2010, Bob Dobbs wrote:
Geoffrey S. Mendelson wrote:
don't buy a SW, especially ham, receiver and expect it to perform
well on the AM BCB.
I didn't initially buy any of my HAM rigs for use on AMBCB,
however a couple have turned out to perform very nicely there.
They're very stable (TCXO), have adjustable IF bandwidth and shift,
one of them has a convenient band scan to spot stations,
another actually has a spectrum scope to look at the band.
And even though that band is always full at night
it helps to see what's out there during the day.
First, there was a long period when ham equipment wasn't particularly
good on AM, since most hams were using SSB. So no wider filters for
AM, sometimes there wasn't even an AM detector, and certainly no
synchronous detector that everyone seems to think should be mandatory
now. I suspect that has changed a bit recently, since some of the
techniques used to improve the design allows for adding better AM
reception without any real cost, and a lot of the ham manufacturers
like to be able to offer lots of bells and whistles, whether or not
they are needed.
Another obvious reason is that for a long time any receivers in amateur
radio equipment covered only the ham bands. That was a good thing,
since you got much better bandspread; if you wanted general coverage
you would have started with one of those to begin with. That too has
changed, now it's as easy to have a general coverage receiver as it is
to have a ham band only receiver, and again it's a selling point.
But, according to some, there may be attenuation that comes into play
on the AM broadcast band, or some other limitation as the frequency goes
down. Or, RF amplification may be left off, so the receiver can
better deal with the strong local signals.
I can't really imagine a manufacturer not using the existing receiver
circuitry for the AM broadcast band, since it's just a matter of
extending the frequency range. But maybe there are some out there
that toss in another IC for the AM band, resulting in no special
performance. I remember getting into an argument with a local about
whether their shortwave portable receiver would actually be outstanding on
the FM band. In that case, whatever great design is used on the shortwave
bands is lost, since a whole different circuit is needed for FM, and
thus they add a whole other FM receiver, usually an IC, which doesn't
have to be anything special; you are paying extra money for the shortwave,
not the FM band.
But, maybe the main reason was in the paragraph about the Superradio.
That one gets lost of praise, but it really is a pretty generic design.
The one thing it does have is a good loopstick antenna, and that's
certainly one area where ham equipment lacks. None will have any sort
of built in antenna, so one will need something external. That may often
be seen as some wire hanging off the antenna jack, and while that works, a
directional antenna is pretty useful on the AM broadcast band.
A receiver that has a built in antenna is going to be matched to that
small antenna, while a general coverage receiver with no built in antenna
may require external circuitry to best use a small antenna.