On 9/28/2011 7:31 PM, Owen Duffy wrote:
The auto tuner can be a path to hiding shortcomings in an antenna
system, in search of the holy grail, low VSWR.

This is a 102' doublet with 40' of open wire balanced feed line.
Except for the input of the tuner looking like 50 ohms to make the
transmitter happy, there is no such thing as "low VSWR" on this
type of antenna.

Whilst you seem critical of the 4:1 voltage balun in the MFJ, it is my
perception that they are still the most popular balun. My theory on that
is that antenna systems that exhibit extreme impedance can often be
'matched' with that configuration, assisted by the loss in the balun.

It is an example of how the device's operation can be misunderstood.
There is little doubting the considerable anecdotal evidence that 4:1
voltage baluns work 'better', it is understanding what is meant by
'better' that is revealing.

Actually, the MFJ 949b Versa Tuner has an internal 4:1 voltage balun.
The reason for that is simple. One large toroid and you're done. There
isn't room inside the case for a 4:1 current balun.

If you disconnect the open wire line from the internal voltage balun
in an MFJ tuner and replace it with an external current balun you will
find that the tuning of the match on the tuner is a lot smoother as
opposed to almost erratic. (But still obtainable.)

Due to the location of my station on the 2nd floor over looking a
covered porch, having a "good RF ground" is not going to happen.
The current balun forces the antenna and feed line into a truly
balanced condition. No ground needed, other than a proper bonding
of all the related equipment to a common reference in the station.

The whole purpose of the tuner is to allow the transmitter to see
a 50 ohm unbalanced load that it was designed for. Accomplishing
that, allows the most power to be transferred to the antenna. The
102' doublet with open wire line seems to do a remarkable job at
radiating. (And equally well at receiving.)

That leads into the question of whether a 4:1 balun is 'better'.

Better than what? A 1:1 balun or none at all, which seems to be
the selling point of the G5RV antenna and it's clones.

Jeff-1.0
wa6fwi

--
"Everything from Crackers to Coffins"