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Re: An experiment 2.4 GHz SS Cordless vs Weak Signal



>From: "John P. Toscano" <tosca005@tc.umn.edu>
>"Edward R. Cole" wrote:
>> Here's an idea on how to make one:  Take a dead Drake convertor and
>> move the LO up to 2402 MHz (ala the "Dead Duck" article in a recent
>> Amsat Journal article).  That would give you maybe 0 to +5 dBm output.
>> Run that into a 20 dB mmic amp and you have your 100 mw beacon.  Want
>> more?  I believe DEMI has just announced a 10w amp for 2.3 GHz!  Run
>> that when you are not on AO-40 and it should clear a nice circle
>> around your neighborhood of such devices.  To be nice you should shut
>> it off when AO-40 is visible so your fellow satellite operators
>> aren't affected...but maybe it won't desense your preamp?
>
>Ed:
>
>Easy to build an illegal version.  To make it legal, it needs to send
>at least a valid callsign of the beacon operator's license, and to make
>it "ham friendly", should send a little more info such as 6-digit
>Maidenhead Grid Square, elevation, power, and antenna type.  CW would
>be the cheapest way to go.  For example,
>    AL7EB/B BP40IQ 10 WATTS TO LOOP AT 50 FEET
>
>Our local weak-signal group (Northern Lights Radio Society) is
>interested in getting members to operate beacons on some of the
>higher frequencies (or, if you prefer, lower microwave frequencies)
>like 902/903, 2304, 3456 MHz.  Any suggestions on how to cause the
>"Dead Drake" to generate CW, so it could send out a proper beacon
>message instead of simply illegal QRM?  I could put together a
>simple single-board computer interface using a ZWorld microprocessor
>board, to generate the ON/OFF control for each Morse Code character,
>but I'm not sure of the optimal way to actually modulate the RF
>generator you described with the ON/OFF (dit/dah/space) data.  This
>approach would allow you to go very simple or very sophisticated
>(just send callsign or send other telemetry data also with appropriate
>sensors added).  This seems to make more sense to me than setting up
>the Drake at 144 MHz away from the desired frequency and dedicating
>a 2 meter radio as a transverter IF rig.
>
>The other "issue" in my mind is the selection of a good
>omnidirectional antenna.  To accomplish Leslie's purpose, a
>quarter-wave vertical groundplane should be easy to build and suit
>the purpose, especially with a 10 Watt amp.  But for a weak-signal
>beacon, we would definitely want a horizontally-polarized omni
>antenna, since folks would be using their SSB/CW systems to listen
>for the beaccon and they will be horizontally polarized.  M-squared
>makes HOLoop antennas that serve the purpose, but only up to 432 MHz.
>Any idea how to construct a good horizontal omni, or better yet, a
>stacked pair (or two pair!) to give the signal a little more oomph?
>
>Not that I'm trying to suggest that anyone on this list would
>actually put up an illegal noise source instead of a legal beacon...
>
>73 de KB0ZEV
>

John,

Nor was it my intension to suggest that one set up a beacon illegally.  Yes
it should have the proper IDer.  Then it trully does provide a genuine
service as a propagation beacon*...completely legal and above the part-15
guys in the user hierarchy.

There are probably lots of ID circuits available.  One way to run it is to
place a pin diode in series between the "Dead Duck" Drake and any low power
amp.  You merely bias (using the output of the IDer) the pin diode to key
the 0-5 dBm signal.  BTW DEMI sells a nice little kit housed in a small
diecast box with pc-board, connectors, parts, and mmic.  I'm sure there is
one suitable for something like 50-200 mw at 2.4 GHz.  I made a couple of
these for 144 MHz IF amps and the cost was around $35, each.

As far as an antenna:  Take a one-pound coffee can, cut a rectangular slot
(1/2 by 1/4 WL) in the side of it, and install a coax connector with short
stub.  You need to make replacement for the metal can cover so it becomes a
metal cylinder...you have just made a waveguide slot antenna!  

Need gain?  Then stack several cans end-on-end!  I have a six-slot antenna
made from rectangular waveguide (wr-90) that is destined for a 10 Ghz
Beacon...I think it has about 10 dBi gain.

Although we have the legal foothold, the part-15 guys have the numbers!  So
don't think the FCC is actually going to do anything about the
interference.  This is what is great about the beacon...it's legal...and
effective if you are experiencing interference.  The part-15 consumer will
only know that his device doesn't work...or if it scans, it moves off our
freq.  Unlikely that he has a glimmer of your existence...and if he does
you have the legal high ground...A LICENSE!

Ed
PS:  I have had no local interference so this is merely theoretical for
me...but "Blue-Tooth" is coming! 
PSS:  *You may even want to get on 2.3-2.4 GHz with a transceiver...wow!
what a thought!  Hams operating on 13cm!

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