This brings me nicely to the final bit of the puzzle: say, in a given location, you want to set up your own personal outdoor lab to make these measurements comparing various solutions. How do you create a constant noise source *which will most effectively demonstrate* the performance of one choke against another?
I suspect that, at the end of the day, this is probably going to be the cheapest and most conclusive of all tests. David G3UNA > >>Equally silly (and applicable here) is measuring a device in a 50-ohm >>environment and trying to determine attenuation, when in actual operation, >>neither the source or load impedance is known. > > Exactly. It is the 50 ohm environment that is the source of much of the > measurement error. Measuring S21, by one means or another, is an effective > solution, and the one I've used. > > Measuring shield current, as David has suggested, is an indication of the > effectiveness of a choke IN A PARTICULAR CIRCUIT -- for example, a > feedline > onto which it is inserted, the antenna to which the feedline is connected, > and the termination of the feedline at the receiver. The effectiveness of > a > choke in any given application depends upon the common mode impedances > within that particular circuit. > > These are two VERY different problems, and two very different > measurements. > Both are useful. Measuring the choke on the bench tells us about the > properties of the choke. Knowing that, we can optimize the choke for a > given frequency range and use, AND we can insert the properties of a choke > into a model and, if the model knows enough about the circuit of interest, > predict the effectiveness of the choke in reducing common mode current. > > There is, of course, another set of unknowns. They relate to the source(s) > of the noise, their location, polarization, directivity, proximity to the > feedline and to the antenna, the directivity of the antenna, etc. The > choke > will have little effect on the component of noise picked up on the antenna > -- it can suppress noise picked up only on the feedline. In general, the > choke will be most effective in suppressing noise that is much closer to > the feedline than to the antenna, and/or is rejected by antenna > directivity. > > 73, Jim K9YC > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
