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Author Topic: Generate RF through pc parallel port ?  (Read 3148 times)
MSTRAM
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Posts: 26




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« on: April 20, 2016, 02:07:41 AM »

Have any of  you guys generated RF by directly programming the parallel port ?

From what little info I've found, it seems a pc parport has a max speed of  ~2meg /sec  ?

So transmission on medium wave, to ~160 meters should be possible ?

With no hardware other than a random wire antenna, I would think transmission range would only be a few feet at best ?

However, I've also found info to suggest that trying to program the port under any non real time os is going to yield only a few hundred Khz at best.

If so, I'm thinking maybe a custom boot program that might be the solution ?

I've found a few examples of RF / AM, FM transmitting using microcontrollers, and I then wondered if a PC could do something similar with either the parallel, USB or serial ports for either medium wave or ham frequencies.

Serial looks too slow, and USB not doable without some kind of USB dev board / custom device, so that leaves
the parallel port.
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N3QE
Member

Posts: 5128




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« Reply #1 on: April 20, 2016, 06:26:26 AM »

If you want to generate a RF signal from a PC, sound card (up to 192kHz available in many consumer cards) and video cards (even old SVGA bandwidths were in the 10's of MHz) seem like a better solution.
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MSTRAM
Member

Posts: 26




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« Reply #2 on: April 20, 2016, 08:09:22 AM »

The svga idea looks interesting.

Do you have any links or further info?

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MSTRAM
Member

Posts: 26




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« Reply #3 on: April 20, 2016, 06:19:44 PM »

I  guess I was over thinking the complications of how to use a vid card for rf.

Turns out all I have to do is put my sw radio's antenna (Grundig YB 400) near my computer screen, open a cmd prompt, then press ALT-ENTER and I'm getting a "morse beep"  Smiley

And either or my LCD screen (Dell Flat .. not sure which model# will check) is really "noisy", or the YB is not very sensitive.

At first I tried the "precise" solution, figuring out the calcs for the res /
herz : and 800*600*60 works out to 28,800,000 which is covered by my sw radio.

I first  tried a batch file alternating 'dir' /'cls'. No effect heard on the sw recvr.

 I thought "CLS" / dir would be a good "toggle" ?

Then I tried switching the cmd window from windowed to full screen (ALT-ENTER),
and I'm getting a two-tone peep with my radio tuned to 28.8M

I then discovered that by tuning the radio (Grundig YB 400) to 1.8MHZ, and repeating
the ALT-ENTER in a cmd window is producing a LOVELY "bell like" "morse beep" !

And the signal is WAY STRONGER than with the radio tuned to the "matching" 28.8M !

Holding the radio / antenna ~ 5 feet from the *screen*   (*not* the vid cable
as  I first guessed) gives a clear "morse like tone" !

The flat screen monitor (DELL 15") is putting out a VERY WIDE band signal !

I can detect my "ALT-ENTER" on almost every ham band on the radio, as well as the top of the AM band !

Albeit that's with the radio antenna  ~5 feet from the monitor or less Smiley

But with some filtering, amplification, could this be the simplest CW transmitter possible ?

The signal is coming from the MONITOR though, not the cable as I first expected.

But the cable is probably heavily shielded, right ?

Gonna see if I have a spare monitor cable, and strip off the outer insulation / shielding, see if the signal will be there without a monitor connection.

Or maybe a "dummy monitor" will always be necessary, even an old junker might do, with the cable split to the radio filter/amplifier ?

I also have an ancient CRT monitor here, will give that a try and see what happens.

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N3QE
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Posts: 5128




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« Reply #4 on: April 23, 2016, 04:35:22 AM »

The signal is coming from the MONITOR though, not the cable as I first expected.

You might try reading up on "Tempest Compliance" (was a big deal in the 80's). Also called, in the old enough literature, "Van Eck radiation".

Mostly this was written for CRT-type technologies, not LCD. Any point in the video chain could leak enough RF, but usually the biggest contributor (due to lack of shielding and highest power levels) were the "video drivers" (usually low-watt high-bandwidth transistors) driving the CRT.

There is at least one article on applying same principles to LCD type displays: http://www.cl.cam.ac.uk/~mgk25/pet2004-fpd.pdf
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KJ4TX
Member

Posts: 16




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« Reply #5 on: April 26, 2016, 09:15:08 PM »

I think you are trying to invent "RFI".  With enough effort and power, you can go far... very far.  Wink

Mike
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