[Elecraft] High power tuner

[Paul Christensen]

> An example of how the price of a tuner can grow astronomically with
> power level.
> At what point does it make more sense to spend the same $$ for antennas
> which don't require a tuner?

For some of us where only one HF antenna is feasible, it may make sense to 
put all the money in the tuner and *not* the antenna.  For example, I've 
gotten away with an 80m dipole at 60-ft in my gated community, only due to 
the natural antenna supports: pine trees.  For me, the optimal solution for 
80m-10m coverage, consists of a remote-controlled, symmetrical tuner built 
in a WX-proof enclosure and located at the base of an open feeder line. 
This offers me minimum system loss, minimum RFI leakage to my transmission 
line, and all band coverage.  Sure, I have no control over maximum lobes and 
minimum nulls at higher frequencies, but given the QTH constrains, it made 
sense to put all the money into a truly balanced tuner and nearly zero cost 
in the antenna.  Through 4Nec2 modeling and TLD, my antenna system losses 
are very low and in all cases, exceeds the performance of resonant mono-band 
dipoles fed with LMR-400.  My 600-ohm line length is optimized for all bands 
using an N2PK VNA.

The new RF Concepts tuner would not work well for me.  It's an unbalanced 
C-L-C design with a CM choke input, similar in design with several Palstar 
tuners, only with much more rugged components than what Palstar provides. 
W9CF, W7EL, and W8JI have analyzed a current choke placed at the input to a 
C-L-C tuner and have concluded that placement at the input is not as 
effective for maintaining line balance as a balun placed at the tuner's 
output.  The exception being if the CM choke is placed at the input of a 
symmetrical, balanced tuner (e.g., AG6K type).  My tuner is of this type and 
can be seen on my QRZ.com page.

Read through the eHam reviews and see just how gullible we are when it comes 
to tuner evaluation.  Nearly all accolades are based on: (1) the ability of 
the tuner to achieve an input VSWR of 1:1; (2) pretty layout; and (3) 
component size.  None of these factors tell us about the tuner's efficiency. 
When a tuner needs it own cooling and ventilation system to function, that 
should throw up red warning flags.

The new RF Concepts tuner has switched, 8pF to 800 pF output C.  Although 
better than most commercial tuners, it would have been even better to at 
least double that amount so long as minimum C is maintained through high 
isolation switched C.  The real *big* unknown with the new tuner is coil Q 
over its entire range.  I would like to see a Q plot of the coil mounted in 
the metal enclosure.  That's a critical piece of evidence in order to 
evaluate the tuner's efficiency, especially with low-Z line terminations. 
With both input and out C being vacuum types, I would expect high-Q for the 
C components.  I'm not too concerned about a tuner's ability to tune and 
match low-Z loads.  For base station operation, there are few combinations 
of full size wire antennas that place a low-Z at the line input, no matter 
the line length.  If I'm dealing with low-Z transmission line inputs, then 
its an antenna I probably don't want in the first place. For portable and 
mobile installations,  that a wholly different matter.

Finally, the new RF Concepts tuner has a slick Smith chart display on the 
front panel.  Only, the charting shows the Z at the input of the tuner which 
is of very limited value.  Since the input is always tuned and matched for 
50+j0, even the simple Monimatch circuit is sufficient for that purpose. 
So, it's nice "eye candy" but I see nearly no value in the display.

Paul, W9AC