[Antennas] VSWR on Log Periodic.

[George, W5YR]

If the properties of the coax - Zo, loss, length (electrical), etc. - are
known, then there is no advantage that I can see to climbing to the top of
the tower with instrumentation, sitting there in the near field and
distorting all the properties of the antenna attempting to make "real"
measurements!   <:}

Those line properties are readily measured with a good "antenna analyzer"
and once known can make the shack measurements just as meaningful and
probably more accurate than those made in some ideal fashion at the
antenna.

The whole point here is that there is nothing magic or arcane about
translating the line impedance and other line properties to its load.
People have been doing this for the better part of 100 years, and with
great ease since Mr. Smith published his chart in 1945. 

The same theory that allows the antenna to work and to have power
transmitted to it from a transmitter via a transmission line also allows
the shack measurements to be related with little or no error to the load
end of the line.

Why should one want to complicate matters by placing instrumentation at
both ends? Theoretically, they both give the same information about the
antenna, and again theoretically and practically, it is a relatively simple
matter to make measurements in the shack and translate them to the antenna
- again the results are the same as far as determining such antenna
properties as driving-point impedance, SWR bandwidth, etc.

I guess there is a point here going right over my head!   <:}

73/72/oo, George W5YR - the Yellow Rose of Texas         
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe   
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771 I-LINK 11735
Icom IC-756PRO #02121  Kachina 505 DSP  #91900556  Icom IC-765 #02437


A10382 wrote:
> 
> Measuring at the transmitter gives a good indication of how 'friendly' the
> transmission system (everything after the rig) is to the transmitter or amp.
> 
> Measuring at the antenna (power AND vswr) is the real indication of how
> friendly everything else is to the antenna.
> 
> How about a remote control meter at the antenna feed.  Of course this
> remotely operated device would have to have almost no effects itself on the
> system when not 'reading'.  Then you can measure at BOTH ends.
> 
> This would seem ideal.  Is this thinking 'in band' or 'out of it' ?