Dear Mr. Gil Simon:

To get greater distance out of ultrasonic range finders, the secret is in the transmitter. You have to think in amps rather than Milli Amps. The following circuit (located at the below web site) does a good job of blasting a tweeter with a strong signal. The output section of this circuit almost wipes out the transducer with the current you pump thru it but it get the job done.

http://www.reconnsworld.com/ir_ultras...witch.html

Good luck,

Charles Bannister