[Antennas]efficient antenna tuning

[DJED1 at aol.com]

N8DE has suggested leaving the antenna alone and operating- while that  has 
it's benefits, I thing the original poster was looking into how he could  
operate over the entire 40M band without climbing on the roof to retune the  
bugcatcher.  Since my comments caused some confusion with N8DE, I'll try  and 
clarify for the benefit of all.
In general, it is known in the technical community that an untuned  antenna 
should either be tuned for a match to the transmitter at the antenna, or  using 
a low-loss transmission line, at the rig.  Open wire line is commonly  
recommended for a low-loss line.  The issue is that the loss on the line  increases 
with SWR, even if you have a tuner at the rig so that the rig sees an  
impedance match. 
 
In this case the coax loss is only about 0.4 dB for a matched line, but can  
go above 1 dB for a SWR of 8 or so. (For N8DE's benefit, the SWR on the line 
is  related only to the antenna impedance and the impedance of the coax.   A 
tuner at the rig matches the impedance of the line-antenna combination to  50 
ohms, but doesn't change the SWR on the line. Calculators for cable loss vs  SWR 
are available on the net and in ARRL publications.)
So the first choice of several posters was to put the tuner at the  antenna.  
Costs about $200, and has about 1 dB of loss for the tuner and  0.4 dB of 
cable loss.  I agree, and I use an ICOM AH4 tuner with a whip on  my portable rig.
Given that the original requirement was for QRP and low cost, I considered  a 
small QRP tuner at the rig, which may cost less than an AH4.  In this  case, 
the cable dissipation will be more, depending on how high the SWR of the  
antenna is at the ends of the band.  Even with a 10:1 SWR, however, the  cable 
loss increases to only about 1 dB, with the tuner adding another 1  dB. So this 
is the best tradeoff of performance and cost.  
Finally, I suggested detuning the antenna if all that was available for  
tuning was a capacitor.  To answer the question about series or  parallel would 
require some assumptions about the antenna impedance and  some transmission line 
calculations (remember Smith charts?), which I'm too lazy  to do right now.  
however, the added cable loss make this a poor choice.
So my recommendation is to set the antenna at the center of the band, get  an 
inexpensive tuner and install it at the rig, and go have fun.
Just my .02 based on 25 years as an Extra and 35 years as an RF  engineer
Ed