In article ,
Carsten Hjorth wrote:
Hello!

I just bought this: http://www.rustindustries.co.uk/remote.htm
The range is only 10-15 meters in free air, only 5-7 meters indoor.
Is it possible to connect a whip type antenna?
I have calculated a length ca 17 cm.
But i cannot see where to connect the antenna.
The transmitter has a loop style antenna, powered by one transistor and a
oscillator of some sort, i have drawn a schematic:
http://media.openbloc.com/1tpwr
I have tried to connect the antenna to the collector, but that gave me no
output at all.

I looked at the design of a similar 433 MHz nonlicensed transmitter a
couple of months ago (it was for an IR-remote-to-RF repeater system).

It looked to me as if it was using the loop both as part of a tuned LC
tank circuit, and as the radiating element. I suspect that the same
is true of the circuit in your transmitter.

Adding a length of wire to it would very probably de-tune the tank
circuit. At best, it'd oscillate and transmit on the wrong frequency.
At worst, the wire loading would de-Q the tank to the point that it
wouldn't oscillate at all.

To boost the transmitter power or the antenna gain (if doing so is
even legal under your RF-use rules) would probably require a
significant redesign of the circuit.

In your situation, would it be adequate to boost the _receiver_ gain
instead? You can probably do anything you want, legally, to the
receiver... add a collinear antenna, change to a Yagi, use a corner
reflector, etc.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
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