On Oct 11, 2:57 am, ShutterMan wrote:

You know, a lot of the questions you ask here about "modern" radios
could have very similarly applied to radios of 20 or 40 years ago.
Some of the distinctions would have been different but not all that
many!

Hey folks,

A lurking SWL listener here. Was wondering something about receivers
in general. Why is it that all-band receivers are generally more
expensive than HF-only receivers? I know there are other circuits in
there, but in essence, aren't all receiver circuits basically the
same, just with the ability to tune to different frequencies?

Yes, but I think you underestimate the importance of front ends,
preselectors before the front end, and the variety of modes and
filters to be demodulated with associated different bandwidths, and
multiple IF stages in reducing intermod and reducing images.

I suppose another way of asking is this: a simple AM radio tank
circuit could be modified by adjusting the coil turns and/or variable
capacitor in order to pick up other frequencies. Why does this
(rather oversimplified) simple change cause the cost of the receiver
to go up nearly 50% in cost? (comparing a simple handheld AM radio
with one that includes a shortwave band or two). An AM/FM stereo
radio is cheaper in many cases than a similar radio with SW bands.
But you'd think that VHF reception would be slightly more expensive to
manufacture than AM's nearby neighbor SW. Confuses me.

The FM broadcast (88MHz-108MHz) band spans way way less than an
octave, and is nowhere near the IF frequency.

The SW bands (1.6MHz - 30 MHz inclusive) span more than 4 octaves and
usually overlap the best choice in IF frequency for filtering the most
popular modes.

Get to "all band" (which I think by your definition goes up to the
GHz) and you get like 8 more octaves for your front end to cover.

I also notice that HF transceivers can cost roughly the same as HF
receivers - you'd think a receiver WITH transmitter would be much more
expensive, but from what I can see its not. Something isn't
registering in my mind as to why all these cost differences.

Many really substantial parts of a transceiver - other than the finals
- are shared between the transmitter and receiver on low end models.
Frequency synthesis, sideband filtering, etc. I think all low-end
models share the receiver preselection with the transmit final
filtering. And if you're comparing a very low-end transceiver (say
$600) with an entry-level communications receiver in the same price
range (say the ICOM R75) you will note that the entry-level
communications receiver has many features not at all present on the
transceiver. Hams like me might might gloss over a lot of those
features because they aren't awfully relevant to ham band CW and SSB
operation but they must be important to somebody, otherwise they
wouldn't sell the radios, I guess!

I will note that the vast majority of SWL'ers seem to use radios
definitely below the entry-level communcations receiver level and are
typically in the under-$200 range.

For the past couple decades most ham transceivers were, out of the
box, of marginal utility for SWLing because the filters were chosen
for CW and SSB operation, not for AM. Yeah, they had a mode button on
the front marked "AM" in some cases but didn't have a really good
filter for AM installed from the factory. And all the preselection was
optimized for the ham bands, not the SWL bands (assuming that you
could tune outside the ham bands at all, not all could, but post-WARC
many began being general-coverage for receive.) On the high-end ham
transceivers I think this distinction is not really there anymore but
we're talking about the $2500 price range and the good high-end
transceivers are beginning to incoprorate *multiple* HF receivers into
them.

Tim.