SWR losses in coaxial cable depend on the frequency, the type of cable, its
length, as well as the SWR.  If you were running 50 feet of RG213 on 20
meters, you would probably lose 3 dB with a 9:1 SWR (this is just a wild
guess).  You won't lose all of your signal.  A remote tuner at the antenna
is the best way to go, but difficult to keep it running properly since it
needs power and is out in the weather.  

Lloyd Rasmussen, Kensington, Maryland
Home:  http://lras.home.sprynet.com
Work:  http://www.loc.gov/nls
 
> -----Original Message-----
> From: For blind ham radio operators [mailto:[log in to unmask]]
> On Behalf Of Howard Kaufman
> Sent: Tuesday, December 13, 2011 6:43 AM
> To: [log in to unmask]
> Subject: Re: imax-2000 continued.
> 
> I guess the theory is that on 20 it is a bit long for resonance, which now
> looks like a 3/8 wave.  Any antenna used on multiple bands will work
> differently on each band.
> I am trying to understand at what point the SWR drastically effects the
> efficiency of the vertical.  The variables seem to be reflected power and
> transmitter shut back when it sees the reflected power.  That can be
> eliminated with a tuner, but I don't know if doing that actually delivers
> more signal to the antenna or not.  Working with shielded line and a tuner
> is new to me.
> I am going to try a remote automatic tuner at the base of the antenna.
> That
> sounds like the best way to go for efficient multi-band operation.  I
> think
> that with coax, the tuned reflected power probably warms the coax rather
> than is radiated by the vertical.  It looks like stretching the efficient
> use of the antenna from 17 meters to 29.2 for A.M. Phone is asking a lot,
> which makes sense to me.