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?

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.

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.

Thanks for your responses.

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.

Well, there are a few issues here.

First of all, most decent radios are superhets. This means that there must
be an intermediate frequency. Selecting an intermediate frequency, or two,
gets to be more of a problem the more frequencies you need to cover. Many
DC to daylight rigs are full coverage, which makes the problem a lot harder
than a ham band only radio, and adding more coverage obviously complicates
the problem.

Secondly, as you go up in frequency, the problem changes. Component layout
gets to be a bigger deal, and it is harder to get the gain you need. Many
HF only radios have only marginal performance at 10 meters. If you are
going to cover frequencies higher than 30 MHz, then you can't really fudge
the 10 meter performance because you need to go beyond it.

At 50 MHz, you are sort of in a no man's land. You can use HF techniques or
VHF techniques, but go firmly into VHF and you essentially are building
another radio for the frequencies above 50 MHz or so. The techniques and
parts are a lot different, even the problem you need to solve is different.
At HF, it is easy to get more gain than you can actually use. As you go up
in frequency, you need more gain but it gets harder to come by. Worse
still, at HF the relatively low gain requirement is caused by noise in the
atmosphere. Increase the gain and you get more noise, so it really doesn't
buy you anything. That atmsopheric noise becomes less of an issue as you go
up in frequency, but the noise in your circuitry becomes greater. As you
get to VHF and beyond, you are concerned with noise figure, something that
really doesn't matter at HF because it is orders of magnitude below the
atmospheric noise.

As far as transceivers vs. receivers, well, there is a little cost
differential, but perhaps not as much as you would expect. Part of that is
because a lot of the transmitter circuitry is shared with the receiver. In
particular, the expensive, critical parts are shared. The other dimension
is that there is only a tiny market for high-end receivers. There are lots
of SWLs out there, but very few SWLs who are willing to spend on a high end
receiver. On the other hand, hams need a lot out of a receiver for it to be
even useable, and they are more likely to buy a transceiver than a separate
transmitter and receiver, so the size of the market starts to come into
play.

Hope this sheds some light

...


"ShutterMan" wrote in message
ps.com...
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?

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.

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.

Thanks for your responses.

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?.... simple AM radio tank.... An AM/FM stereo
radio is cheaper in many cases than a similar radio with SW bands.....

Don't forget economy of scale.

I suspect many more HF-only compared to all-band receivers are sold.

AM or AM/FM radios are sold by the gazillions; undoubtedly many, many
more than are sold with a SW band. Don't know where you are from,
but just think of the ubiquitous AA5 (All American 5-tube AM radio)!
--
--Myron A. Calhoun.
Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge
NRA Life Member & Certified Instructor for Rifle, Pistol, & Home Firearm Safety
Also Certified Instructor for the Kansas Concealed-Carry Handgun (CCH) license

In article om,
ShutterMan wrote:

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?

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).

Well, there's cost, and then there's price. They aren't the same thing.

The cost may go up because:

- The general-coverage receiver may need additional "preselector"
stages in its RF front end (one per band), and

- The differences in the local oscillator stage may be more
involved than you think, in order to get an LO which tunes
reliably, smoothly, and stably over a very wide range of
frequencies, and

- The general-coverage receiver may need more sensitivity, as well
as a higher IP3 (i.e. ability to handle strong signals without
overloading) because it has to handle both local signals (which
are usually quite strong) as well as weak DX signals that are down
near the band's noise floor, and

- The general-coverage receiver may require multiple IF frequencies,
switching between them on a band-to-band basis, in order to ensure
that the IF, and the harmonics of the local-oscillator frequency
don't wipe out the signal you're trying to receive.

Then, there's price. Price is as much a marketing and perception
issue as it is a cost issue. The market for general-coverage radios
is smaller, there are fewer models made, there's less competition
between sellers, and the perceived value (the set of features or
capabilities) is greater. All of these contribute to the supply-and-
demand equation, and tend to cause the price to settle at a higher
level.

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.

That's partly because the receiver actually does incorporate most of
the signal-chain components present in the transmitter - power supply,
local oscillator and tuning electronics and mechanicals, case, front
panel, etc. - in many transceiver designs these are shared between the
transmit and receive pathways. There's some savings when you
eliminate the transmitter components, but less than you might imagine
(especially in today's highly-integrated designs).

It's also likely that receivers sold as receivers, may have a somewhat
more sophisticated receiver design (and better performance) than the
receiver stages built into all-in-one transceivers, and thus may
actually cost more to build.

Then, add the smaller-marketplace and this-is-a-special-purpose-box
issues, and the market price floats up.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Good answers from everyone, thank you. In looking at the simplest of
tank circuits for radio, I just couldnt understand why you just cant
add more coil windings and different capacitance to increase frequency
coverage.....but it looks like its alot more complicated than that.
Thanks again.

In the old days, this is exactly how it was done, but even so, think of it
this way.............what had to be done was to use the same tuning
capacitor, but switch different resonating inductors for each tuning range.
The different tuning range inductors needed different ferrite mixes for the
different frequency ranges. Then, there was the R&D.......I believe that
much of this research data was taken from repeated experimantation. Even
today, in my own experiences with RF simulation programs, we would still
have to build and fine tune the circuit under development. Just to do a new
synthesizer design from start to finish would take between 6 to 18 months
(these are optimistic values). Figure an engineering team of at least 3
people that are being paid between 60k to 120k a year each, and it becomes a
little bit clearer just how high engineering costs can be. This doesn't
count the cost of multiple iterations of the design before the engineering
review team deems things to be complete.
This is one of the reasons that I decided to homebrew many different
receiver designs. This is a good way to learn "the hard way" many of the
things that a manufacturer must go through when working through a design,
from conception to final product.
Newer designs are a little bit easier now that upconversion topologies can
be used. This type of design became practical, once VHF crystal filters
became viable. The stumbling block with VHF crystal filters was that in
order to work, the crystal elements had to be ground so thin that they
became quite fragile. Enter the overtone mode crystal filter..........now,
you could use a much thicker filter blank, and resonate this crystal element
on one of its overtone modes.
What VHF crystal filters allowed one to do is use these filters at the 1st
I.F. The significance here is twofold. First of all, single
conversion receivers with a high I.F. and good selectivity could be
designed. Second, in a multiple conversion design, these same crystal
filters, because of their selectivity, are able to have good 2nd image
rejection (2 X 2nd I.F.)
If you look at the specifications of todays roofing filters (the filters
that follow the 1st mixer in a receiver), you will notice that a 910kHz
rejection spec is given. The reason for this is because the 1st I.F. is
always at some high frequency between 40 and 120MHz, while the 2nd I.F. is
almost 450, 455, or 460kHz (image response would be at 900, 910, or 920kHz
respectively).
After this is all done, the intermediate frequencies (I.F.) have to be
chosen very carefully, with spur chart analysis of the various mixers for
inband spurs (this had already been done by many manufacturers, so this step
can be pretty much considered done).
To make a long story short, upconversion eliminates the need for multiple
bandswitched coils in the LO section of a radio, because with a high I.F. a
synthesizer can be designed that will operate over less than a 1 octave
range.
The significance here is that you can now operate the Varactor diodes in the
VCO portion of the synthesizer over the most linear part of their range.
This allows you to have a VCO that has a K/V characteristic of less than 2:1
over its tuning range. When designing a loop filter for a synthesizer, the
K/V characteristic is one component of the design equations. This is very
important, so that the settling time of the synthesizer will be relatively
constant over its entire tuning range. With synthesizers designed for
frequency hop communications or digital modes, bandswitched Varactor diodes
are sometimes used for a small portion of the tuning range. Other times, a
dual mode loop filter is used, with a wide bandwidth loop filter used while
the PLL is acquiring lock, switching to a narrow bandwidth loop filter once
the system acquires lock. This improves the close-in phase noise of the
synthesizer, thus minimizing reciprocal mixing effects.
Today, settling time is not as much a factor as it used to be, since the
advent of Fraction N synthesizers. This design opens another can of worms,
since you now have to deal with different types of spurs. One approach that
has been used is what is called a Modulated Fractional Divider. This type of
design translated the Fractional N mixing spurs further out from the LO
carrier. This way, these spurs can be more easily filtered.
As an example, consider a radio with a 1st I.F. of 70MHz. To tune from 0 to
30MHz with high-side injection from the 1st LO, the tuning range of this LO
will tune from 70 to 100MHz. The lower sideband range from the 1st mixer
will be used in this case for receiving. The only tuned circuits required
for good image rejection will be a low pass filter that cuts off at about
35MHz.
Since your image band will be 140MHz away (140 to 170MHz), this response
will be far down on the low pass filter's skirts, as long as this filter
provides good out of band attenuation. Good shielding is important here.
Mind you, this only covers the LO portion of the receiver. In order to have
good strong signal handling performance, a good 1st mixer with good IMD
performance is required. Suboctave input bandpass filtering also improves
IMD performance of the receiver, because by limiting the aperture of how
much spectrum space the 1st mixer is actually seeing, you are limiting the
integrated power that is being applied to this mixer.
I could go on and on, but I don't want to hog too much bandwidth. I have
touched on only a very small part of the design challenges that a receiver
designer faces. I haven't covered roofing filter bandwidth options (the
other limiting factor besides phase noise performance that limits what is
sometimes referred to as dynamic selectivity). The 2nd mixer is where much
of this limitation occurs.
Oh, then there is the AGC system design. Typically, a receiver with AGC
applied only to the I.F. system will overload at around 3000 to 10000uV. To
extend the dynamic range of the AGC system, AGC needs to be applied the the
RF / 1st mixer stages so that it takes over at a level where the I.F. AGC
"runs out of steam". If you are not careful when you design this part of the
receiver, the two AGC systems can oscillate. Drake '7 Line
owners...........think about how critical that AGC adjustment is on your
units. If it is not set according to Drake's specifications, the AGC will
oscillate when in the fast mode.
I hope this small bit of "scratching the surface" helps. I still haven't
even covered the demodulator design and the audio stage design. And then,
there are the challenges of designing a low noise power supply!
Thanks to all of the other posters, for all of your good information!

Pete

"ShutterMan" wrote in message
oups.com...
Good answers from everyone, thank you. In looking at the simplest of
tank circuits for radio, I just couldnt understand why you just cant
add more coil windings and different capacitance to increase frequency
coverage.....but it looks like its alot more complicated than that.
Thanks again.

On Oct 11, 11:21 pm, ShutterMan wrote:
Good answers from everyone, thank you. In looking at the simplest of
tank circuits for radio, I just couldnt understand why you just cant
add more coil windings and different capacitance to increase frequency
coverage.....but it looks like its alot more complicated than that.
Thanks again.

That works over a limited range. It can be pressed into service to
cover 3.5MHz - 30MHz, which is (not too surprising) the range of bands
traditionally covered by a ham-band transceiver. Going down to 1.8MHz
or up to 54 MHz is possible with some cleverness and a number of
recent radios cover those bands too.

All that said, using traditional techniques to do the bandswitching
from the front panel involved a bandswitch shaft running through the
length of the radio coupled to multiple switch wafers for each section
that required switching components for different bands. Some even have
multiple shafts for the bandswitching run by chains or gears.

Since this is the "homebrew" group, I should point out that some
homebrewers with mechanical cleverness have done this sort of
bandswitching in the homebrew receivers, transmitters, and (egads!)
transceivers. But a more popular technique going back at least half a
century is to build a base radio that works in one band (which may not
even be a ham band) and use converters/transverters to use that radio
in the band of interest. Some call this the "tunable IF" technique and
in ham bands the tunable IF typically covers a span of 50,100,150 kHz
(if CW or SSB sub-bands only) or 500kHz (if intended to cover a whole
band). There are gotchas related to images/leakthrough based on choice
of IF, too, but these have been overcome with few compromises with
several popular choices. The result is usually not a DC-to-daylight
radio but one that works on the desired ham bands; this is counter to
what a SWL'er typically expects out of their radio. (It seems that
most today expect to key in a frequency on the front panel and go
right to it). So the "first IF at 45 MHz" approach is more popular
there.

Tim.

In article .com,
ShutterMan wrote:

Good answers from everyone, thank you. In looking at the simplest of
tank circuits for radio, I just couldnt understand why you just cant
add more coil windings and different capacitance to increase frequency
coverage.....but it looks like its alot more complicated than that.
Thanks again.

One thing that I didn't see mentioned, was that many Short-wave
Broadcast stations are using Synchronous AM transmission. I understand
this is a form of double sideband with reduced carrier. It can be tuned
by a Single Sideband receiver, but it is difficult to tune music so it
sounds right. It sounds somewhat distorted on an AM radio.

For SWL use, I would look for a Short-wave Receiver that had a true
Synchronous AM detector in addition to the other modes. I don't think
you will find that in many Ham Radio transceivers!

Fred
K4DII