I have checked the local walmart shelves, nope, nothing like I have
mentioned...

Warmest regards,
John
--
When Viagra fails to work--you are DOOMED!!!

wrote in message
oups.com...
| From: Paul Keinanen on Sun,May 8 2005 11:54 pm
|
| On Sun, 08 May 2005 10:44:27 -0700, Tim Wescott
| wrote:
|
| The basic difference is that with a digital system you either end up
| with a clean signal or a useless signal. In an analog system the
| character and purity of the signal must be carefully guarded, at
| least
| until you manage to digitize it. This means that there will be a
| much
| greater chance that adding a new card to the radio will degrade not
| only
| the function of the new card, but the function of all the other
| cards.
|
| Second, the PC market is a huge one, with great advantages to be
| derived
| from common equipment and software, and much smaller advantages to be
|
| derived from commonality. This is the exact obverse of the radio
| market, including homebrew radios. To make a "card" radio would be
| to
| define a basic radio architecture, probably down to the IF frequency
| (or
| at least to the point of forcing you to match your IF and front end).
|
| While improvements could be made within this structure an independent
|
| experimenter couldn't play around with such things as
| direct-conversion,
| different IF schemes, etc., without extensive modification.
|
| I agree that it would be quite hard to make a good quality radio with
| some common backplane structure. However, connecting various
| functional modules with 50 ohm input and output impedance could be
| used to make quite different radios with good specifications.
|
| That's already been done in the RF industry for a half
| century.
|
| As one example, take the U.S.' AN/PRC-8, -9, -10 series
| of manpack transceivers covering high-HF into low-VHF.
| Still in the vacuum tube era, all of the IF modules
| included the IF tuned circuits as well as the subminiature
| tube. If the tube filament burned out, the entire module
| was replaced. NO alignment tweaking was required. Design
| was done back around 1950.
|
| As for standards on control...start with the ATLAS (for
| USAF test equipment) and continue on to the IEEE-488
| interface. Those standards worked with "modular"
| components capable of testing receiver sensitivity down
| to noise level with KNOWN signal levels. By the way,
| test equipment for RF has been standardized at 50 Ohms
| since WW2 days.
|
| For
| instance Mini-Circuits also makes various diode ring mixers,
| amplifiers and apparently also VCOs that are boxed and have BNC or SMA
| connectors. With each functional module in a metallic enclosure,
| controlling the spurious radiation between modules is much easier. I
| don't know that anyone would make filter modules, which would be
| required to build a complete radio. Also SSB-Electronics sold separate
| amplifier, mixer, frequency multiplier and crystal oscillator modules
| mainly intended for a 10 GHz transverter.
|
| Unfortunately the cost of these modules is quite high, apparently due
| to low production volumes and large amount of manual labour needed to
| assemble them. If there would be a large demand for such modules, it
| would make sense to design them to require less manual labour to
| assemble them and hence get the price to more affordable levels.
|
| Define "more affordable." :-)
|
| "Filter modules" have and are built to order by dozens
| (if not hundreds worldwide) of companies. The costs
| ARE high because they are built TO specifications and
| such have to be TESTED to meet those specifications.
| Is there comparable KNOWN/calibrated test equipment
| in the average homebrewer's hobby workshop that is
| comparable...even at "low" frequencies of HF? Actually,
| Kaylie's Mini-circuits DOES use calibrated, automatic
| test equipment to check out each module, small
| quantities to large quantities. Mini-Circuits doesn't
| have the market demand to do production runs in the
| 10,000-lot quantities.
|
| The mystique on L-C filters is largely that...mystique.
| Without some good, calibrated test equipment, it is
| very difficult to determine what a "filter module"
| has for performance. Synthesis (design) of the values
| for a particular filter type was arduous until folks
| came out with computer-aided design. I have a working
| freeware program for PCs on that...send a message in
| private e-mail if you want one transmitted to you.
|
| As to cost, just look at a cellular telephone handset.
| Those can cost around US$ 50 each, new. They work in
| a band roughly centered at 1.0 GHz. Microwaves.
| Complete microwave Rx-Tx with synthesized tuning.
| For half a hundred US dollars here. A mere 30 years
| ago that would be almost inconceivable. Three years
| ago the U.S. Census Bureau said that one in three
| Americans have a cell phone subscription. That's
| roughly 100 MILLION units either out there or waiting
| to be used. Market quantity and competition in that
| market are the key to bringing down costs. Radio
| hobbyists just cannot possibly get close to such
| market quantities.
|
| While a backplane would not be suitable for running the RF signals, it
| would be a good idea to have a common control interface standard. This
| might be some sort of serial interface or perhaps a CANbus interface
| as used on some AMSAT satellites.
|
| Who says a "backplane would not be suitable?" :-)
| Those PC backplanes carry terribly broad spectra of
| RF...from (literally) DC on up to the low microwaves.
| No "perhaps" about it. Thing is, the layout can NOT
| be done as if it were wire-wrap; i.e., in random
| order of wire placement. With broadbanding anything,
| every single adjacent trace becomes a COUPLER and
| unwitting layouts can produce remarkable crosstalk
| effects. Designers have known that for decades and
| handle it...all kinds of Application Notes and info
| out in public access available for anyone...just too
| specialized for the "weekender" small-project
| assembler hobbyist.
|
| The IEEE-488 is a mature standard for control and
| interface for computer-controlled, interconnected
| systems. Would be a bit TOO all-inclusive for a
| special-purpose new design. The "interface" does
| NOT have to be some kind of "new" thing used on the
| latest whatever out in space. It's just a control-
| and-response avenue carrying signals of a standardized
| kind...a few wires/traces perhaps...laid out properly
| if required to be broadbanded or broad in dynamic
| signal range. Not a big thing, but needs some
| THOUGHT before becoming hardware.
|
|
|