Heterodyning Vs. Oscillator?

Discussion in 'General Electronics Chat' started by sjgallagher2, Apr 7, 2014.

  1. sjgallagher2

    Thread Starter Active Member

    Feb 6, 2013
    Let's say I want to make a 900MHz carrier signal to transmit an FM modulated digital signal. Do you think that the best way to accomplish this would be
    A) To use a negative resistance oscillator
    B) To create two LC oscillators, heterodyne them, and take the sum frequency?

    I would think the frequency stability might be more difficult to obtain, and if I go with a PLL type oscillator the hardware would definitely get pretty crazy. But negative resistance oscillators seem like they always use large pieces of hardware like gunn diodes. The issue being that, for example with a cell phone, you want to minimize size and including such hardware would make one hell of a bad cell phone. I've heard of negative resistance ICs but they're pretty scarce. Heterodyning on the other hand, and LC oscillators, are common and I've dealt with them at least theoretically before. Also, design of the amplifiers and other key components to the transmitter would be easier because they wouldn't have to deal with higher frequencies right? Less parasitics to compensate for and whatnot? But again, that means more real estate would be taken up. Again, we're going for small, compact.

    I need thoughts here!

    I can't make the decision on my own (not enough experience) and time is of the essence. I'm applying for college next fall and I'd really like to have this project, which has many other complex facets, designed and ready to be built by July. Thanks so much everyone!
  2. ian field

    AAC Fanatic!

    Oct 27, 2012
    A method frequently used by radio hams is to use frequency multipliers, basically an RF amplifier with a tuned collector circuit at the 2nd or 3rd harmonic of the input signal.
  3. sjgallagher2

    Thread Starter Active Member

    Feb 6, 2013
    Interesting, much better than heterodyning thats for sure! I came across these a while back but I must have forgotten about them :p it'll be a wonder if I make it through this project at this rate...