Originally Posted by rgburrill

As an EE who has worked with spread spectrum systems perhaps you can answer this question - do 2.4GHz RC systems use an IF in their receivers? One of the biggest problems that came about when 72MHz went to narrowband was the "23 channel" separation issue. Nearly all radios at the time, no matter what
band they operated in, used a final intermediate frequency of 455KHz before demodulation. The difference in frequencies between two radios 23 channels apart was 460KHz. So if both were on a "beat" frequency was generated that could interfere with wide-band receivers that were even on completely different channels.
I realize this is simplistic and may not represent what is happening at 2.4GHz but it shows that if an intermediate frequency is used ignition noise could be interfering with it since it is downstream from all the protection one gets from frequency hopping and spread spectrum RF transmission. Isn't that why the recommendation is to keep the ignition control unit 12 inches away from the receiver?
BTW, I saw this happen in a most unusual situation one day. I used channel 47 FM and another of our guys used channel 24 FM. Both of us had narrow-band equipment. However we had another guy who had an older 5 channel PCM system of channel 40. While the first two of us were operating he turned on his system and his plane started jittering on all surfaces. Since I was only doing ground tests I turned my system off and his jittering went away. After that all of us started pulling frequency pins that were 23 channels away from our frequency when we pulled our channel.