[TowerTalk] Mismatch Loss and Tuners [2)

[sbest@cushcraft.com]

     Just a follow up to Jim's comments:
     
     
     >     SUMMARY -  A matched antenna will significantly outperform a
     >     mismatched antenna with a tuner.  A tuner cannot introduce      
     "reflection
     >     gain" to change this fact.
     
     >That summary is not correct!!  Other wise most broadcast stations,  
     >most of which use antenna tuners would be wasting a lot of money!!  
     >Their vertical radiating towers are not 1/4 wave tall,  in most 
     cases,  
     >forexample.
     
     This statement is made without any background information.  To have an 
     adequate discussion on the performance of broadcast stations, we would 
     have to know the transmitter output power, the tuner loss, the total 
     cable attenuation, the antenna VSWR, the antenna pattern, the antenna 
     gain, the communications distance, the reciever sensitivity, etc., 
     etc.
     
     Also, I never once said that a tuner does not the improve performance 
     of a mismatched antenna.  
     
     
     >In this overly wordy argument put forth by Steve,  he omits one tiny
     >detail:  the tiny amount of time that these reflections within the
     >transmission line between the antenna and the tuning network exist,
     >both initial and  following about which he belabors!
     >These reflections  are over and done with in  nanoseconds,  in even 
     >the
     >lowest propagation velocity coax where  the speed of the signal is
     >only 60 some % of the speed of light in space!
     
     I do not disagree with Jim's statement about the short time involved 
     for all of the voltage reflections and interactions to occur.  The 
     real issue is that they occur.  Their practical impact on signal 
     quality in amateur communications may not be significant but the 
     re-reflections at the antenna are still echoes of previous signals.  
     The background theory and operation of a tuner does not change because 
     the time involved is short. 
     
     As far as my summary regarding a matched antenna performing better 
     than a mismatched antenna and tuner:  First, if the cable attenutaion 
     between the tuner and the antenna is 0 dB, then a signal strength 
     meter will not detect the power difference as Jim stated.  This is not 
     inconsistent with any statements I made in my previous e-mail.  
     However, as the cable attenuation increases, a field strength meter 
     should be able to detect the difference between the two set ups.  This 
     would be the best experiment to verify what really happens.
     
     73 Steve Best, VE9SRB   

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