For about signal bending at 41 (transport tires monitoring pressure). From my experience with ax-25 I was initially wonder, why transmission usually includes large delay on turning On and large delay on turning off (each about 300ms, some people recommend even 1500ms).<p>So, idea is, when transmitter turned on, it spend some time to become stable, for modern high-tech equipment this could be faster, I measured less then 50ms on modern Japanese desktop radios, but for older it could really be more than second.<p>For example, GSM solves this with brute force way - all GSM have high power load, CB guys usually call it "equivalent" and switch, and when GSM 2.0 make call, it turn transmitter on at begin of call and connect it to antenna only when need to transmit, all other time power spent on load, and transmitter turned off after call finished.<p>When GSM MT working with GPRS or 3G, things are more complicated, but it is usually "half-duplex" communication, most traffic received from network, upload usually limited, so MT could save power, turning on transmitter only when have large batch of data in buffers and turning it off when pause appear. But "equivalent" used anyway.<p>Returning to tires, their transmitters usually in very harsh environment, and batteries are not always give enough power (I think, batteries are weakest tech in this case), and yes, this could be reason, why transmitter frequency become unstable.<p>Other may possible reason, but probability is not high, if signal reflected from plane or if some interference happen.<p>What I mean on interference, I still sometimes see old radios, which don't have good enough filters, and they could retransmit distorted signals with their heterodyne circuit.