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Author Topic: jug fishing transmitter?  (Read 18630 times)

Posts: 160

« on: March 27, 2011, 12:28:42 PM »

Just wanting to know if anybody has heard of or tried installing little battery operated oscillators in there jugs for tracking them down on the lake?  I want a better method than just the reflecting jug, I thought of using lighted ones but thought it might be a good idea to use low power transmitters and a beam and would also be fun. 

Posts: 17476

« Reply #1 on: March 27, 2011, 01:00:18 PM »

Actually folks are doing this on a much larger scale - we sometimes get QRM on 10m from
transmitters attached to drift nets in the south Atlantic.

There are a couple of approaches - commercial "canned" oscillators are available on a
number of frequencies, some of which mulitply up to 2m or other ham bands.  The odd
harmonics are  particularly strong - simply using a tuned circuit on the output to extract
the desired harmonic may be sufficient.  These are typically available in 5V and 3.3V
types and run a couple dollars for standard values.

There are also some One-Time Programmable (OTP) types where you can order the
specific frequency you want - these are less than $10.

Or you can build your own oscillators - a lot of baud rate crystals multiply up to
147.456 MHz (16.384, 12.288, 18.432 MHz, etc.)  so this is a convenient frequency
to use.  Scanner crystals for the 450 MHz range often operate on 2m / 440 MHz
and can be pressed into service.

Some practical considerations:

How long do you leave the jugs out?  (I've never heard of jug fishing before.)
You'll have to check the current draw of the oscillator and the battery capacity to get
a sense of how long they should last.  To save current draw the transmitters are often
pulsed - wildlife transmitters and others designed for light weight and long operation
use very short ON pulses, which make them more difficult to track.  A CMOS timer chip
such as the TLC555 makes it easy to control the ON and OFF times:  10 seconds should
be long enough to take a bearing with a yagi once you are experienced, and something
like an L'Per should work on 1 second pulses.

If you have multiple transmitters out, you may want some way to tell them apart.  Having
them all on the same frequency makes it easier since you don't have to change the
receiver tuning, but if they are on continuously you'll only be able to hear the closest
one.  A 5% duty cycle will make it easier to hear multiple transmitters on the same
frequency.  You can even modulate each with a different tone to tell them apart.

Of course, if the signal is strong enough to be heard at more than very short range,
they should send an callsign ID, and should be operated in the "Unattended Beacon"
portion of the bands.

Posts: 477

« Reply #2 on: April 13, 2011, 08:53:39 PM »

It would be awful expensive way to do it, but APRS comes to mind.  (I'm also sure that you'd make LOTS of 'friends' if you did that on 2 meters!)  Wouldn't have to 'DF' them at all, they'd tell you their positions.
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