[Elecraft] Ferrite transformer losses, 43-foot vertical and the K3

[Don Wilhelm]

Sandy,

You are correct that using a balun (either 4:1 or 1:1) is not 
necessarily the most efficient solution.  The 'old fashioned' link 
coupled tuner will most always be more efficient.

When the feedline input impedance (and that has nothing to do with the 
characteristic impedance of the feedline) is close to the output 
impedance of the balun, the balun will be just almost as efficient as 
the link coupled balanced tuner, but that rarely happens in practice.

Yes, using a balun following an unbalanced transmatch is a compromise.  
It lends itself to easy bandswitching and its associated convenience.  
If one is searching for the most efficient antenna tuning mechanism, 
then either dedicated resonant antennas are required, or one must accept 
the inconveniences of changing coils in a simple balanced link coupled 
tuner or accept the compromises of an easy bandswitching system.  The 
old Johnson Matchbox was an effort to provide bandswitching convenience 
with a link coupled balanced tuner, but even it has limited matching 
range compared to the simple single-band tuner designs. 

Bottom line, one must either accept the compromises dictated by the 
conveniences of bandswitching or accept the inconveniences of using the 
most efficient tuners that can be constructed.  There is no 'best of all 
worlds'.

73,
Don W3FPR

Sandy wrote:
> When a high VSWR exists with a toroid ferrite balun due to a high 
> inductive or capacitive reactance and the toroid begins to heat, the 
> losses will rise to quite unacceptable losses and can possibly destroy 
> the balun itself, even tough the tuner used appears to have reduced 
> the VSWR on the input side of the circuit to a very low value.
>
> Generally a 4:1 or 1:1 transformer type balun should be preferably 
> used for just a resistance transformation, not where there is a 
> highly  reactive component on the output side of the balun.  Lots of 
> people "get away" with this situation, but it isn't a very good idea.  
> I commonly did this for years with very large ferrite cores and a 
> vanilla high pass "T" network tuner (like the many MFJ and other "T" 
> network tuners)
>
> For the last 15 years I have used nothing but the common Parallel type 
> balanced line link coupled tuner configuration and had extremely good 
> results with the old fashioned and sometimes very cranky to get setup 
> right circuit.
>
> "choke" type baluns (the ones that traditionally use a large number of 
> ferrite beads on a length of coaxial cable) are much less troublesome 
> than the transformer type.  If your "balun" setup runs cool, then you 
> probably have hit upon a length of feeder that is "just right" and you 
> are "OK".  If it is running warm then you are treading on dangerous 
> ground and things may be getting ready to surprise you one day with a 
> catastrophic failure, especially when you run the legal limit!
>
> This no matter what the VSWR meter says between the tuner and the 
> ferrite balun in question.
>
> 73,
>