Looking for FCC Part 15.35 Guru

[LewisCobb]

Hi - I have a rather specific question that someone may be able to answer with regard to the averaging of emissions for an on-off keyed transmitter under FCC part 15.35

According to the FCC documents and all that I have found through reading through it - the averaging can be used to gain up to a 20dB (10x received uV/m field strength) advantage by calculation of the average emissions over the busiest 100mS window.

An example - if the transmitter is putting out 100,000 uV/m at three meters and the duty cycle can be shown to be 10% - the averaged emission is 10,000 uV/m and will pass the emissions level.

I believe that the above averaging also holds true for the harmonics and their regulation levels.

My Question - for those harmonics that fall within the restricted bands - can this averaging also be applied to them, keeping in mind that the average must be equal or below the smaller emissions limit?

At 433.92MHz, the third harmonic is in a restricted band and has to be under 500uV/m at three meters. Does this mean that for a 50% on-off modulated data stream, the peak emisison can be 1000uV/m or are we resticted to a 500uV/m peak regardless of the duty cycle ?

Thanks for any assistance people can provide or perhaps pointers to a test house I can pose this question to.

Lewis
cobb@baseng.com

 

[Comcokid]

LewisCobb-
I looked up some testing performed some time back for a DSSS device in the 915 MHz ISM band, and harmonics in the GHz range. Our test lab applied the averaging factor to some harmonics that were slightly out in restricted bands bringing the product well within compliance.

For the question you posed, a maximum 50% on/off radiation (0.5) in a 100 msec period, this comes to 20*log(0.5) or -6.02 dB you can reduce your measured radiated harmonics by.