What a great little tool !!! Range testing my unit showed that with my Futaba 9CAP transmitter turned on, inside my garage, but with the antenna fully withdrawn into the Tx, I could trigger the frequency checker for a very limited distance....approximately thirty feet...just about the end of my driveway. That is without any external antenna attached to the checker.
The next test was with the Tx antenna fully extended, as it would be when flying,...but still no external antenna on the checker...I was able to walk down the street and see that the unit was registering my channel as active, for a distance of approximately a good 200 feet...not actually measured...just an approximation of the distance. That appears to be sensitive enough to detect any active transmitter at my flying field...in the impound, on the flight line...or even out in the parking lot.
Next, I fully collapsed the transmitter antenna once again, and plugged in a random length of wire to the antenna jack on the checker...(just using a handy stereo headphone cord whose plug nicely fitted the antenna jack)...Now with the external antenna, I am able to see this very low level signal as an active channel for approximately 200 feet away...even though the Tx antenna is fully collapsed inside the Tx! The addition of the external antenna really increases the sensitivity of the unit. I have not tried this test with both the Tx antenna extended...and the external antenna plugged into the checker....I'll have to pack a lunch for such a long trip. heh heh. Out at the field, I was positioned about 100 feet from the pilots boxes. From that distance, the checker accurately told me which channels were active...with or without the external antenna.
This little gizmo, which easily fits into a shirt pocket, is more than just an interesting novelty....it is immediately a standard necessary item in my field box.
At the price....it seems to be quite a bargain.
Jim