Frequency interferance and TV stations

If TV channel 4 is transmitting in the area, then its audio carrier i

at 71.750 MHz. If any R/C transmitter is operating on channel 2 (72.190) or channel 21 (72.210), or if any local pager is operating o

72.200 then a strong 2nd order intermodulation product (differenc frequency) will be created inside all receivers that is very close t the 455 kHz intermediate frequency used by single conversion receivers

• Note that it does not matter what channel the single conversio receiver(s) are on. It could be on any channel in the 72 MHz band. I fact if there are 4 planes flying with single conversion receivers, an somebody getting ready to fly turns on their TX on channel 20 or 21 the could all crash simultaneously. In practice it is more hit and mis since RX's have various abilities to reject 2IM, plus th intermodulation product is not right at 455kHz

-- Iflyj

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This illustrates the problem of real world interactions, or the lack thereof, when using only /theory/mathmatics to prove a point. It does not take into account the effects of the brute strength field strength of the primary transmitter being used by the modeler.

A person that flies his/her model in close by normal operation, which is where most single conversion receivers are used, most likely will never notice a single glitch in the above outlined scenario. Don't worry about problems until you experience them.

Our model's receivers almost never operate in a clean RF environment. Microprocessors radiate lots of RF swarf into the environment.

How many microprocessors are in your home/apartment? JR's ABC/W single conversion receivers attack the problem by running only enough RF gain to do the job. This in conjunction with a tremendously strong primary control signal (your TX - relatively speaking), do a fair job at providing a solid link.

Ed Cregger

Speaking of receiver selectivity. Can anyone explain what the Berg receiver does? You can turn on your transmitter, then the Burg receiver and it will lock into your transmitter. Turn on another transmitter on the same frequency and it ignores it. I would not believe it but we actually tried it at the field. You have to be careful. If another transmitter on the same frequency is on and it will lock onto it first. You can't take control until that transmitter is shut off. We never did try to see what happened if BOTH transmitters were on at the same time and you turned on the Burg. We were so amazed that we didn't think to try that.

Red S.

Here is what they have to say about it: