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"

Jeffrey Angus wrote in news:j60h8s$ao0$1@dont-
email.me:

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.

Well to "make the transmitter happy" is jsut the new language for low
VSWR.

... There
isn't room inside the case for a 4:1 current balun.

But there is probably room for an effective 1:1 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.)

Ok, so in your experience, you haven't yet come across a load that could
be matched with the voltage balun, but not with an external current
balun.

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.

Ideal conditions like "forces" and "truly balanced" don't often exist in
the real world. It would be of more interest if you had measured and
reported the differential and common mode current at various
frequencies.

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

Yes. It is the meaning of "most" that is relevant. Most doesn't need to
mean 100%, or close to it, you make compromises for frequency agility
and multiband use, but "most" is often unknown. Perhaps some DX QSL
cards can substitute.

102' doublet with open wire line seems to do a remarkable job at
radiating. (And equally well at receiving.)

Yes, they can be a good antenna, but it is not a no-brainer.

For example, a correspondent recently reported problems with just such a
thing on 40m. Turns out his feed line length was such that at 800W into
the feed line, the voltage between the wires was some 4000+V and was
causing flashovers in a 3kW rated ATU. In this case, I recommended that
since he could not lengthen or shorten the feed line enough, that he
shorten the antenna so solve the problem.

He had previously smoked up a CWS Bytemark 5kW rated current balun on
80m with another antenna, caused by unlucky feed line length.


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

Better than what? A 1:1 balun or none at all,

1:1.

4:1 reduces the voltage impressed on the ATU components, which is good
for high impedance loads, and poor for low impedance loads.

There is no simple thing that always works best on a random set of loads
(which is the case for many multi band antennas).

which seems to be
the selling point of the G5RV antenna and it's clones.

Perhaps to some. There is good argument for use of a balun with a G5RV
and not-balanced transmitter. Varney conceded that in one of his later
articles. Most people who are adament about what Varney did or did not
describe have not read his articles. Antenna manufacturers are not a
good source of factual information.

Owen

On 9/28/2011 10:46 AM, Jeffrey Angus wrote:
It comes with an adapter cable for Icom radios, but it's a
4-pin Molex connector and the manual doesn't show what the
connections/signals are for the radio.

Multiple Homer Simpson "Do-oh!" moments.

LDG was kind enough to supply me with the application note for
the interface cable.

I have two Icom radios. An IC-761 with an internal tuner and an
IC-726 designed to use with an external tuner. The IC-726 has the
mating 4-pin Molex connector.

The two signals are essentially a "request to tune" and an "tune
complete". The IC-726 has a TUNE button on the front panel for
telling the external tuner to do it's thing. (By the way, I do
have the matching AT-150 auto-tuner for the IC-726.)

All three of the tuners, the IC-761 internal, IC-726 external and
LDG have an SO-239 connector for the output and would require an
external balun to connect to an open wire balanced feed line.

The reason I was using the MFJ Versa Tuner with the IC-761 was
fairly simple. It has an internal 4:1 balun and connections for
open wire balanced feed lines.

Since I had to purchase a balun to use the LDG tuner I realized
that "Oh, I can use the Icom tuners with the balun as well."
That was my first "Do-oh!" moment.

Subsequently on researching the interface signals to/from the
LDG I realized that the IC-761 doesn't have a TUNE button or the
signals externally because the tuner is already inside the radio.
That was my second "Do-oh!" moment.

Once the MFJ 4:1 current balun I ordered arrives, the only question
that remains is whether or not the specified matching range of the
Icom tuners is sufficient to deal with my antenna system.

The Icom tuners are specified at 16.7 to 150 ohms.
The LDG Z11 Pro II is specified as 2-1000 ohms.
Oddly enough, the MFJ Versa Tuner has no specified range.

Jeff-1.0
wa6fwi

--
"Everything from Crackers to Coffins"

Jeffrey Angus wrote in news:j64hp4$i7g$1@dont-
email.me:

The two signals are essentially a "request to tune" and an "tune
complete".

That is not quite correct.

Though the protocol is not published by Icom, and the implementation varies
a little from radio to radio, the four wires are usually labelled and none
are "tune complete".

Owen

On 9/30/2011 2:04 PM, Owen Duffy wrote:
Jeffrey wrote in news:j64hp4$i7g$1@dont-
email.me:

The two signals are essentially a "request to tune" and an "tune
complete".

That is not quite correct.

Did you miss the word essentially?

Since it bothers you. From LDG "Start Line." Ground this from an
external switch or open collector to initiate a tuning sequence by
the external tuner.

And "Key Line" This is similar to a PTT line to the transmitter,
but in this case tells the transmitter (which is capable of doing
it) to, regardless of mode, transmit a low lever CW carrier.

When the key line changes state because of a request to tune, it
turns on the transmitter. When tuning is complete, the key line
toggles back to it's normal state.

Though the protocol is not published by Icom, and the implementation varies
a little from radio to radio, the four wires are usually labelled and none
are "tune complete".

If you put an indicator such as an LED on the key line watching it
change state is a pretty good indication of "I'm tuning" and "Tune
complete" regardless of what it's called.

Jeff

--
"Everything from Crackers to Coffins"

Jeffrey Angus wrote in
:

On 9/30/2011 2:04 PM, Owen Duffy wrote:
Jeffrey wrote in news:j64hp4$i7g$1@dont-
email.me:

The two signals are essentially a "request to tune" and an "tune
complete".

That is not quite correct.

Did you miss the word essentially?

Since it bothers you. From LDG "Start Line." Ground this from an
external switch or open collector to initiate a tuning sequence by
the external tuner.

And "Key Line" This is similar to a PTT line to the transmitter,
but in this case tells the transmitter (which is capable of doing
it) to, regardless of mode, transmit a low lever CW carrier.

When the key line changes state because of a request to tune, it
turns on the transmitter. When tuning is complete, the key line
toggles back to it's normal state.

Though the protocol is not published by Icom, and the implementation
varies a little from radio to radio, the four wires are usually
labelled and none are "tune complete".

If you put an indicator such as an LED on the key line watching it
change state is a pretty good indication of "I'm tuning" and "Tune
complete" regardless of what it's called.

The /KEY line can be used to initiate a tune carrier, it is used to
sustain the tune carrier until the tx aborts or the tuner ends the
process, and it is used by the tuner to signal whether the tune was or
was not successful.

Owen

Jeffrey Angus wrote in news:j64hp4$i7g$1@dont-
email.me:

The Icom tuners are specified at 16.7 to 150 ohms.
The LDG Z11 Pro II is specified as 2-1000 ohms.
Oddly enough, the MFJ Versa Tuner has no specified range.

Impedance is not a simple scalar quantity as expressed above. The
'specification' is incomplete, you would need to ask the sellers what
they meant.

If for example, they mean the R component only, do they imply that X
must be zero, or that X can be any value?

If they mean the magnitude, do they imply that any angle of impedance is
acceptable?

Also missing is any bounds on efficiency.

I have heard from time to time on air, OMs boast that their tuner is so
good, they have matched it up with no antenna plugged in. Obviously,
efficiency is zero in that case. A tuner with lower internal losses
might not achieve the same feat.

Owen

On 9/30/2011 3:03 PM, Owen Duffy wrote:
Jeffrey wrote in news:j64hp4$i7g$1@dont-
email.me:

The Icom tuners are specified at 16.7 to 150 ohms.
The LDG Z11 Pro II is specified as 2-1000 ohms.
Oddly enough, the MFJ Versa Tuner has no specified range.

Impedance is not a simple scalar quantity as expressed above. The
'specification' is incomplete, you would need to ask the sellers what
they meant.

If for example, they mean the R component only, do they imply that X
must be zero, or that X can be any value?

If they mean the magnitude, do they imply that any angle of impedance is
acceptable?

Do you just like to argue? These are published specifications from
the manufacturer. If you have an issues with the validity of their
claims, take it up with them.

I suspect both Icom and LDG took the time to play with resistive
loads to verify the tuning range. If that is the case, then yes,
it's a simple scalar quantity. I doubt they took the time to fiddle
around adding a reactive components to the test loads otherwise they
would haved published a Smith Chart with a "We can match anything
within these bounds" as the specification for tuning range.

Also missing is any bounds on efficiency.

I have heard from time to time on air, OMs boast that their tuner is so
good, they have matched it up with no antenna plugged in. Obviously,
efficiency is zero in that case. A tuner with lower internal losses
might not achieve the same feat.

I am aware that a frightening majority of licensed amateurs wouldn't
be able to pour **** out of a boot with the instructions printed on
the heel. Perhaps you're unaware tha I'm not one of them.

Jeff-1.0
wa6fwi

--
"Everything from Crackers to Coffins"