> David asks:
>
> >Is this because once the energy is lost (gone as heat or radiated by the
> >pre-antenna components) there is no longer anything stimulating a
mismatch
> >at the antenna?
>
> No, it is because very high, many, many dB of return loss translates
> to nearly a perfect impedance match through out the system carrying
> the RF energy. It "means" the reflected power is many, many dB below
> the forward power on the line, hence a very high loss is suffered by
> the return power, get it?
>
> I can give you the timing of all this if you are interested; consider a
> 30 wpm CW "dit": lasts about 43 milliseconds. Several reflection/
> re-reflection pairs in 100 feet of typical coax transmission line
> are all over and done with in only 3 or 4 microseconds! So neither
> you nor the guy on the rcv'g end can possibly hear, nor can the
> rigs amateurs use, possibly tell anything about this slightly later
> radiated energy. The "dit" tone, after all, is 43,000 times
> longer in time duration! You will never know that these
> reflection phenomena are occuring, nor will your rig.
>
> All perfectly clear now, I'll bet, yeah, right! 73, Jim, KH7M
Actually, much clearer!
So the conclusion becomes, if we grant that loss issues will vary greatly,
reflected energy due to mismatch is not inherently bad.
Would you say that the issues now center around:
1. System loss.
2. Misdirected radiated energy prior to the antenna.
3. Strange loads imposed on the antenna.
4. Strange loads presented to the TX (presumably mitigated by a tuner).
5. Harm to components designed for 1500 watts perhaps exposed to bursts way
over
that.
Thanks for helping! 73, DavidC AA1FA
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|