That sounds very good, Alan. As I say, I'm not very knowledgeable on signal processing so all of this is very interesting to me. I guess whether any of it ultimately turns out to be useful to anyone remains to be seen.
Regarding the multiple posts ... my ISP has been acting very flaky this afternoon and it kept telling me that the message upload had failed. Not sure what's going on there, but I'm sorry for the extra clutter. Thanks again es 73, Dave AB7E On 9/16/2010 1:55 PM, Alan Bloom wrote: > Hi Dave, > > For some reason I got several copies of your message. I'll go ahead and > post my reply to the reflector since it may be of wider interest. > > Yes, another way to get a constant phase shift at all frequencies is to > convert to an I/Q (in-phase/quadrature) signal. One way to do that is > to take the audio signal and run it through an all-pass network with a > constant 90-degree phase shift at all frequencies. That is then the "Q" > signal and the original non-shifted signal is the "I". You can then > obtain any desired phase shift by adding the two signals together with > the proper weighting factor for each. For example, if you weight I and > Q by the same factor you get 45 degrees. > > But that still requires a wide-band 90-degree phase shift network. It > can be done with a FIR or IIR digital filter. I think there are some > free filter design programs on the web that can design an all-pass > network. It may need to be a big filter (i.e. lots of coefficients) to > get good amplitude and phase accuracy over a 10:1 frequency range (300 > Hz to 3 kHz). > > The other way to get the I/Q signals is with an I/Q modulator. > Basically you run the baseband audio signal into two mixers whose local > oscillators are 90 degrees out of phase. Now you have two RF signals 90 > degrees out of phase. If you convert them back to baseband with the > same oscillator you get two audio signals 90 degrees out of phase and > can combine them as before. You then combine that signal with the > original to simulate rotation of the directional antenna. > > I still think the easiest method is what I first suggested. Like the > I/Q modulator except that, instead of a 90-degree phase shift, you > adjust the relative phase of the two oscillators. When you convert back > to baseband the two signals are already at the correct phase, ready to > be combined to simulate the directional antenna. > > Alan > > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
