2.4 GHz failure mode ***READ THIS***
Posted: Sat Jun 05, 2010 2:50 pm
A few of you witnessed my recent Chipmunk crash, where the plane got up about 25m, perhaps 50m from the transmitter, and then totally lost control with motor shut off and dead sticks,flew itself into the mud. Fortunately, crash damage was fixable (repairs are going slowly)
So in order to recreate the failure i devised a little test. 150 m separation, line of sight, 2.4GHz HK el cheapo 4 ch transmitter and two HK receivers (with remote receiver antenna at non parallel orientation, if a 3cm 1/4 wave qualifies as an antenna)
With transmitter antenna folded at 90 degrees, full control. At 45 degrees, full control.
However, with antenna straight out, pointed at the receiver, NO CONTROL.
This result was repeated exactly with two different receivers, the crashed one itself and another identical.
I did have the antenna straight at the time of the crash, unintentionally. Obviously the out-of-phase problem is much less of an issue than the dead spot straight above an omnidirectional 1/4 wave transmitter. I believe the radiation pattern is toroidal around such a configuration, and the nodes are deeper for higher frequencies, which is why you can do this with 72MHz without problems, but not at 2.4GHz.
So in order to recreate the failure i devised a little test. 150 m separation, line of sight, 2.4GHz HK el cheapo 4 ch transmitter and two HK receivers (with remote receiver antenna at non parallel orientation, if a 3cm 1/4 wave qualifies as an antenna)
With transmitter antenna folded at 90 degrees, full control. At 45 degrees, full control.
However, with antenna straight out, pointed at the receiver, NO CONTROL.
This result was repeated exactly with two different receivers, the crashed one itself and another identical.
I did have the antenna straight at the time of the crash, unintentionally. Obviously the out-of-phase problem is much less of an issue than the dead spot straight above an omnidirectional 1/4 wave transmitter. I believe the radiation pattern is toroidal around such a configuration, and the nodes are deeper for higher frequencies, which is why you can do this with 72MHz without problems, but not at 2.4GHz.