Hi Mike, On 9/19/10, Mike Feher <mfe...@eozinc.com> wrote: > Well, if one just looks at the spec of the 10811A for relative performance, > it is -140 dBc/Hz at 100 Hz offset at 10 MHz. Realistically, probably a > little better. From that it would be real easy to generate the frequencies > Frank is looking for, obviously 20 would be easy but would be only -134 > dBc/Hz at 100 Hz away. 22 would be easy by diving the 10 and mixing it with > the 20, assuming the divide by 5 has a very small contribution, the PN of > the resultant at 2 MHz is also theoretically 20logN better, so, mixing will > also give close to -134 dBc at 100 Hz away. 42 can easily be generated by > doubling the 20, to get -128 dBc at 100 Hz and then mixing with the same 2 > MHz to get the 42 MHz, still resulting in almost -128 dBc/Hz at 42 MHz. > Obviously filters will have to be used to get rid of the unwanted lower > mixing products. Depending on the architecture used, as stated below, > further multiplications will again decrease these numbers by 20logN. > Filtering at the IF with a 250 to 500 Hz filter is not going to do anything > to the 100 Hz numbers. I assume the mode of communications here is CW, hence > the narrow filter at IF. 73 - Mike
this exact approach (well maybe mixing 20 and 22 to obtain 42 MHz instead of doubling 20 MHz then mixing) was my first choice but I'm afraid I wouldn't be able to do all these steps without making any mistake like chosing the right mixer, right filters and multiplier/dividers. It was really what I wanted to do, but looks like I could spend too much time doing it and ending with a poorer result than carefully chosen xtal oscillators. Thanks for suggesting it though :-) Frank IZ8DWF _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.