The object is usually to keep energy from one generator from being coupled back into the second generator where the two signals can mix in the output stages and produce intermodulation products.
If for some particular purpose you don't care about intermoduation products in the output, you can likely just parallel the generators assuming you are not doing some potentially dangerous things like running one generator with a high DC offset and/or high output level, as these might damage the generator output.
As one poster said, for lower frequencies, an op-amplifier mixer will provide good isolation, as each generator operates into a load with a virtual ground.
Once you are above the op-amp frequency range, a resistive splitter/combiner can be used, but it has significant drawbacks. The isolation between ports is obtained by the resistive loss, so the greater the isolation you want/need between the two generators, the larger the attenuation between generator output and common port. The good features of a resistive mixer are (a) cheap and (b) can be built for a wide frequency range.
In RF engineering one normally uses a hybrid coupler / splitter to combine multiple signal sources. These are (in the lumped form configuration) a transformer that couples the input ports to the output port with little loss (usually 3 dB or 6 dB depending on the coupler design) whilst providing high isolation from generator to generator, 30 to 40 dB or more.
I've written about this at
http://www.cliftonlaboratories.com/6_db_hybrid_combiner.htm -- the circuits explored include resistive and hybrid couplers, both transformer based and the Wilkinson coupler.
Home
Help
Search
Login
Register
