Alt-BEAM Archive
Message #02274
To: "van Zoelen, Bram SSI-TSEA-352" Bram.A.A.vanZoelen@is.shell.com
From: Steven Bolt sbolt@xs4all.nl
Date: Tue, 13 Apr 1999 11:02:53 +0200 (CEST)
Subject: [alt-beam] Re: Help with AM/FM Transmitters
On Tue, 13 Apr 1999, van Zoelen, Bram SSI-TSEA-352 wrote:
> Just for my bare mind.
>
> A FM transmitter for the 3m band [88-109 MHz]
> All resistor values are just a blind guess!!!
> [font courier]
Here is an AM tx for 27MHz. The pcb layout shows two tone modulation
channels, but more can be added. Instead of 70 cm whip, you can
roll your own flexible, short antenna (what are these called
again?) from about 19 cm round mains cord. Remove the two wires
inside, and replace one of them with a thin bamboo rod. Then take
0.6mm enamelled wire and put about 61 evenly spaced windings on the
cord. Hold them in place with a bit of tape at each end while you
cover the coil with heat-shrinkable tubing. Remove a little isolation
from one end of the enamelled wire and use a mains cord
pull-relieve to mount the antenna. It'll look nice, and doesn't
seem to significantly reduce range.
http://www.xs4all.nl/~sbolt/Other/trsmit6.gif
http://www.xs4all.nl/~sbolt/Other/tsmtlay2.gif
The three coils are mounted at right angles to each other.
L1 is 27 windings of 0.2mm enamelled on a 1W resistor (> 1M).
L2 is 44 windings of 0.2mm enamelled on a 3W resistor (> 1M).
L3 is 14 windings of 0.6mm enamelled on an 8mm former with core;
these windings should be spaced by about 1 wire thickness.
Adjust L3 for maximum output using a field-strength meter.
Note that experimenting with transmitters like this may not be
legal in your country.
Best,
Steve
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# sbolt@xs4all.nl # Steven Bolt # popular science monthly KIJK #
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