[Elecraft] Re: KAT100 with Ladder Line

[Don Wilhelm]

Yes, I fear that many hams do not realize how much loss is being 
introduced by their tuners.  It has been stated that MFJ makes good 
tuners, but my experience with their MFJ-963D and the MFJ-971 tuners say 
otherwise - the inductor is mounted too close to the enclosure which 
reduces the inductor Q and thereby reduces the efficiency.  BTW, there 
is no real need to have the tuner inside an RF proof enclosure, a tuner 
will not introduce harmonics or other spurious responses that have been 
adequately suppressed by the transceiver - a tuner built on a plain 
wooden board will work just great.
The fact that there are tuners and then there are tuners is true 
indeed.  The easy to manufacture T network tuners can have multiple 
setting combinations that produce a low SWR at the input, but many of 
those combinations will have a high loss factor due to RF currents 
circulating through the inductor.  This is a recognized problem with the 
easy to implement T section tuners.  The PI section and L network tuners 
do not have that ambiguity, but the only PI section tuner that I know of 
is the old Collins tuner - it is almost as efficient as the classic link 
coupled tuners, but due to the range of practical variable capacitors, 
its matching range is limited - the L network tuners similar to the 
Elecraft design are much more flexible and have a wide matching range.

Every tuner design has its limitations.  The T section, L network, and 
PI network tuner designs are nothing more than a transmission line 
section implemented with lumped components - the limits are defined by 
the range of adjustment for each of the components, and bandswitching 
with these designs is not difficult although the Pi network tuner does 
have limitations due to practical capacitor values.  Iin bandswitching 
tuners, the L network is the most efficient - the Elecraft tuners all 
use the L network configuration.

The link coupled tuner is usually the most efficient, but does not lend 
itself easily to bandswitching (the Johnson Matchbox is one link coupled 
bandswitching design that works well, but even it has a limited matching 
range).  When the going gets tough, I fall back onto the classic link 
coupled tuners - they are the most efficient by far, but the use of 
plug-in coils for bandswitching is a drawback to many hams.  With 
renewed interest in low loss tuners, it may be time to accept the 
reality that efficiency must be sacrificed for the convenience of 
bandswitching designs.   Unfortunately, there is no one correct answer, 
each situation must accept its own consequences.  I myself use the 
KPA100 in the shack for fine tuning of my coax fed resonant antennas at 
power levels up to 100 watts and an MFJ-962 tuner for times that I add 
the linear.  It is a compromise, but it does work well for me. Since I 
cannot have open wire line coming into the hamshack, any link coupled 
tuners must be fixed tuned and located remotely (relay switched).  That 
is not fully implemented yet, but is in the planning stages.

73,
Don W3FPR

Darrell Bellerive wrote:
> The big problem as I see it is that those who buy the tuners don't realize the 
> tradeoffs they have gotten. After all it tunes to a 1:1 SWR and contacts can 
> be made, so it must be working well. The reality could be quite different.
>
>