开云体育

i have been quitely following hans' travails on rec.radio.amateur.homebrew
with his digital counter experiments. i dug out a counter from my junk
box. it consists of just a 74HC4020. the output of the fed to the sound
card of my PC. on the PC i wrote an application to count the zero
crossings and multiply the result by 1024. it gave a rough indication of
where my VFOs were. the counting took a second. but it is a rough and
ready instrument. like most amateur intrumentation. but that brings us to
an often overlooked piece of equipment that is present in almost every
shack. the PC.

i know that a number of us cannot live without spice. i haven't figured
out how to use it. but for many of us, designs do start with spice. "can i
spice it?" is a regular refrain on the net. a number of excellent design
tools written by hams are useful around the home lab. i use a large number
of small code snippets to calculate inductances and capacitances from a
test oscillator's frequency readout.

another useful application of the PC is as spectrum analyser workng at
audio frequencies. while this may not seem much at first glance, if you
feed the output of direct conversion receiver to the PC's sound card and
run a DSP software on it, it turns into a fairly useful measurement. for
instance, you can evaluate the crystal filters, tune the front-ends etc. a
half unfinished project at my shack is a spectrum analyser that uses this
principle.

the PC is a powerful a DSP as you can hope to own. the problem is in
getting signals in and out of it. the only available means of doing it is
via audio (baseband). i have used a PC based scope too. but that is a
costly option. costlier than the PC itself. but it might be interesting to
see how useful can the ordinary PC become by strapping some home made
circutis around it.

does anybody have more stories about using PCs in the home lab?

- farhan

On Jun 24, 2004, at 5:37 AM, Ashhar Farhan wrote:

the PC is a powerful a DSP as you can hope to own. the problem is in
getting signals in and out of it. the only available means of doing it is
via audio (baseband). i have used a PC based scope too. but that is a
costly option. costlier than the PC itself. but it might be interesting to
see how useful can the ordinary PC become by strapping some home made
circutis around it.

does anybody have more stories about using PCs in the home lab?

"Back in the day" ...

A decade or more ago, it was trivial to get ISA-bus prototype boards to wire up new gadgets like A/D converters. With the limited bandwidth of ISA and the low frequency of consumer-affordable A/D chips, board layout was not an issue. In fact, some of us were building MIDI interfaces/audio digitizers for Macintosh out of a single A/D chip and a couple of connectors. And it's trivial to use the PC printer port (LPTx) as a data interface.

A PCI breadboard is a lot harder to come by nowadays, and it's not even something that an enterprising hobbyist could etch up himself. However, PCI has the bandwidth and the newest consumer-grade A/D chips have sampling rates that were almost unheard of just 5 years ago. But it would be (relatively) simple to design and build a PCI A/D board. The biggest challenge would be to equalize the signal traces from the A/D chip to the PCI connector. Assuming one could etch a PCI connector, this could be done at home.

An easier interface would be USB 2.0 or FireWire (IEEE 1394). Most PCs built since 1999 have USB 1.0 or higher; some PCs since 2002 have FireWire (Macs introduced since 1998 or so all have FireWire). The significant advantage to USB is that most consumer OSes besides Mac OS X have drivers for most USB devices built in, so there's a good chance that for any given USB interface chip, the OS will recognize its data stream and be able to provide it _somewhere_. This isn't as easy to implement as an LPTx scheme under DOS, but there are a number of simple programming environments for Windows such as Visual BASIC (yecch) or National Instruments' LabView (hurrah!) that make data acquisition and manipulation easy to set up.

And Linux has at least as many drivers, plus the ability to drop to a command-line interface, which makes accessing machine-level functions a whole lot easier than under an MS OS, now that DOS has been effectively buried under Wind0ze.

Theoretically, all you need for data capture is -- suitable conditioning and buffering circuitry to deliver your analog signal to your A/D converter, a buffer/interface to your bus, and a suitable bus connector. In the case of USB and FireWire, which are serial interfaces, you need as part of the bus buffer/interface from the A/D -- a data serializer. This would be any scheme that would take the parallel-bus output from the A/D and convert it to a serial stream compatible with USB or FireWire.

Some newer A/Ds now have serial outputs, so the interface would be as simple as doing level conditioning and perhaps some timing adjustment. The stuff's out there -- try TI or National Semiconductor. Both companies have reasonable sample policies if you know how to ask. It's harder to design the board than it is to get free parts. (N.B. -- Some parts are US export-restricted, even though they're made or assembled outside the US.)

And -- if you have lots of money to throw at the problem, National Instruments has already solved it. Reverse-engineering their hardware at lower performance levels should be within the scope of most savvy home builders -- their catalog offers ample design solutions that show you what CAN be done. After that, it's just a matter of software.

Or, if your signal of interest is 20 kHz or narrower, you merely need to convert it to baseband and feed it to your sound card. There's a lot of amateur DSP software available. And again, if you have a lot of money to throw at the problem, there's also MatLab for developing your own DSP software.

And -- the modulation characteristics and core DSP source routines to match those characteristics are freely available on the Internet if you are a diligent searcher. Programming in C is an advantage here. If you choose to explore this avenue, you'll soon find that having a stereo input sound card opens up a huge new world of capabilities.

Most of them beyond the scope of HF SSB, CW, or PSK31.

Jim N6OTQ

does anybody have more stories about using PCs in the
home lab?

Farhan, I don't have a PC at home at all, except an old laptop my XYL uses
for internet access. I prefer to do everything without a PC. I even built my
crazy 30m QRSS beacon project with no PC or microcontroller, see
and
. I sit in front of a
computer here in the office every day and somehow prefer that when I am at
home I don't have to be attached to one.

There's also the problem of the "homebrew only" law which rules my station.
So far the only exception to it is my old 5MHz oscilloscope and my DVM. Some
day I will get my Z80 computers up and running, and will be able to write
some homebrew software for QRSS and PSK31 etc.

73 Hans G0UPL

On Jun 25, 2004, at 8:34 AM, Hans Summers wrote:

There's also the problem of the "homebrew only" law which rules my station.

We should not look askance at ALL "store-bought" technology. Sometimes, recycled gear is nearly as satisfying as homebrewed, especially if it's recycled from the dust bin.

A few months back, I was challenged to write a book describing how to build a transmitter and receiver starting from ZERO technology. So far, I've outlined sections on how to knap flint, how to make fire with sticks, and how to develop the most rudimentary tools for metallurgy.

It appears that the shortest route to homebrewing a radio station essentially from dirt is to use gold for the wiring ... so far, I've found much more gold in the dust bin than lying about on the ground.

Jim N6OTQ

There's also the problem of the "homebrew only" law which
rules my station.

We should not look askance at ALL "store-bought" technology.
Sometimes, recycled gear is nearly as satisfying as
homebrewed, especially if it's recycled from the dust
bin.

Don't get me wrong, I don't look askance at store-bought technology at all,
nor have anything against it or any other aspect of amateur radio. Some
people are committed QRP enthusiasts. I am mostly QRP but sometimes if condx
are bad and I want to get through to a friend I turn the 80m CW TX
up to its maximum 10W and I
don't feel bad about it.

There are so many aspects to amateur radio, each ham has his own areas of
interest. Some hate CW, others operate it exclusively. To each his own! But
my own passion is to homebrew everything.

For really extreme homebrew, I hope one day to build a valve transmitter and
matching receiver using components which are all constructed from household
items or things that can be purchased from the hardware store. Every
component: valves from baby food jars, capacitors from kitchen foil, etc
etc. See for
the capacitor I built, the only part so far.

But that's just me - people who operate QRQ QRO black box contest stations
don't bother me either. Unless it's a time such as once happened when I was
in QSO with an SM6 on 80m, 2-way QRP CW and both about 339 or something
rather marginal, and midnight GMT comes around and suddenly the whole place
explodes with contest traffic and the SM6 and myself, well we both got
practically vapourised by the volume of the audio in our receivers. Had to
curse them a bit then ;-)

73 Hans G0UPL

I thought this forum was focused on the BITX20.
Have I gotten into the wrong forum by accident?

Hey it wasn't *that* far off topic! Have a look back in the archives... It
stems from Farhan's questions about PC use which also relates to his telling
us previously about him using his computer for some audio and AGC
processing.

Several people have asked for possible AGC circuits for the BITX20. I'll see
what I can find over the weekend.

73 Hans G0UPL