Thanks for this response. I got a good laugh out of the signal moving so
fast that you don't care about phase.
When energy is reflected anywhere in a transmission line system, the
"reverse" portion that is reflected will have a varying phase relationship
with the signal that is traveling forward from the source. This causes peaks
and valleys in the voltage along the transmission line. Standing Wave Ratio
is a measurement of the ratio of the voltage peaks to the voltage valleys.
When the reflected power reaches the source, two things happen. If the
source is well-matched to the transmission line, the reverse signal is
dissipated in the source. If the source looks like a high impedance or low
impedance (that is, poorly matched) compared to the transmission line, the
signal will be re-reflected and again travel forward toward the antenna (or
whatever load is at the far end of the transmission line.) Depending on the
goodness of the match, there will generally be a combination of these two -
with some signal being dissipated and some being re-reflected.
73, Steve N6ST
steve@n6st.org
> -----Original Message-----
> From: owner-towertalk@contesting.com
> [mailto:owner-towertalk@contesting.com]On Behalf Of DavidC
> Sent: Tuesday, July 28, 1998 2:19 PM
> To: DOUG WALLER
> Cc: w8ji.tom@MCIONE.com; towertalk@contesting.com
> Subject: Re: [TowerTalk] Re. Impact of Reflected Power
>
>
>
> What about the timing issue some have explained at HF -- the signal is
> moving so fast that it obliterates the impact of phase concerns
> -- at least
> for the sort of narrow bandwidth signals we Hams use?
>
> I agree that it all sounds ugly, having our signal rattling up
> and down the
> feedline, but I guess it happens so fast that it is almost as though it
> hasn't happened at all.
>
> 73, DavidC AA1FA
>
> > Naaaahhh, cant be. If initial sig hits antenna, and part of energy is
> > reflected back to amp, then all of that is reflected back to
> ant, then we
> are
> > already getting these two sigs out of phase. then if part of that is
> reflected
> > back to amp, then reflected back, we are even more out of phase.
> Depending on
> > the transmission line length and its velocity coefficient, pwr
> nulling by
> > phaseout would seemingly take place. Even if this is wrong, I just dont
> like
> > it, i tell ya!
> > Peace, Doug - Nx4d
> > >
> > > So, are we agreeing to conclude that reflected power that is resolved
> by
> > > the final tuned circuit of an amp, rig, or antenna tuner is
> meaningless
> and
> > > to be ignored as irrelevant at HF frequencies?
> > >
> > > I am using "resolved" to mean that the amp or rig is protected from
> > > troublesome voltage, current and/or impedance's. I am also
> using it to
> > > mean that essentially all reflected is re-reflected back to
> the antenna
> and
> > > directed to its intended destination.
> > >
> > > One question: If one adds a group of toroid beads to the coax
> immediately
> > > exiting the amp or rig (some say this helps with impedance stability
> and
> > > eliminating rf in the shack), what is the actual result? Is any
> > > significant loss injected into the system design?
> > >
> > > Thanks & 73, DavidC AA1FA
> > >
> > > > Reflected POWER has little to do with anything except as it affects
> > > > voltages, currents, and impedances by presenting a different
> impedance to
> > > > the PA. 73 Tom
>
>
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