[TenTec] Orion LO phase question

[Bill L. Fuqua]

Sounds like you have a difficult task ahead of you. If you want to compare phases of the outputs of 2 receivers  you must use the same oscillators. Unless there is a way  to sync. the DDS references and the PLL oscillators they  may start up at any phase even though they may be the exact same frequency.  You could use a standard signal to inject to both receiver inputs at the same time after a frequency change to check the phase shift between the receivers and use that to correct your measurement. 

Also it is best take the measurement at a single frequency, the same as you reference. If you are measuring wide bandwidth you will need to sweep the entire bandpass and normalize the whole set of data. 

The results are quite unpredictable and a reference sweep may will solve that problem. But that will require a programable reference source or a harmonic (comb)  generator. 

    Lots of things can change the phase shift (delay) thru a receiver. Phase shift often changes with RF or IF gain changes.  This is due to the fact that gain changes are (unless switched attenuators are used) by changes in some devices impedance. It does not matter if it is pin diodes or semiconductor devices ( such as differential amplifiers ). 
   Filters also will change noticeably with temperature as well. 

    Also you may want to intercept the signal before the digital signal processing. There is no telling what the DSP IF will do to phase. Fortunately this is done at a low frequency and you may be able to do in your PC.  
   A useful tool is available free. Check out “Spectrum Lab”. I have had a great deal of fun with it and have used it to demonstrate various RF processing principles in my classes. 

http://www.qsl.net/dl4yhf/spectra1.html

If you have some questions I would be happy to help. I have delt with sort of problem before. 

73
Bill wa4lav
elay) thru a receiver. Phase shift often changes w