> Watts Reflected at the Mismatch.................At VSWR indicated of:
>
> ..........1 watt..................................................
> ......... 30 watts.................................................
> 3.4:1
> If you use an antenna tuner, most of the above indicated
> reflected power will be re-reflected back up to the antenna,
> and most of that will then be radiated! Losing only the
> indicated reflected percentages once again and a bit lost
> in I^2R loss in the transmission line (a real tiny amount).
> Antenna tuners also have some loss in the coil, again little.
> This is absolutely true even though the vswr between
> the tuner and the transmission line/antenna system will remain
> at the indicated numbers. The tuner "isolates" the rig from
> the returning reflected voltage, so the rig will continue
> to put out all the power it can at a set of control/drive/
> tune up settings.
My understanding (from reading Reflections II) is that this power is
re-reflected regardless of whether a tuner is present. Assuming that your
transmitter can handle the mismatch w/o folding back output power, there
should be no difference in performance SWR wise.
> And this explanation is the ENTIRE story/difference between
> an antenna which is resonant at a particular frequency, and
> another antenna which is not resonant and introduces the
> above examples of mismatch and vswr as a result. That is
> the ONLY difference between resonant and non-resonant
> antennas!
However, one thing I have noticed (empirical data only) is that the
radiation pattern of an antenna is affected when not operating at the
designed frequency. For example, I found that my 2 meter beam (vertically
polarized) did not have the same directivity when using it to receive FM
broadcast. Similarly, if you use an antenna tuner to "force" an antenna to
work on a band for which it is not designed, don't expect the radiation
pattern to be the same. Thus, while the antenna may be radiating almost all
the energy, the communication may not be as effective as some energy will be
radiated in other directions.
Mark
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|