Re: Elecrafts T-1

[John Harper AE5X]

Jerry,

I built one right after they came out and in one fell swoop, it made all my
monobanders much more easily portable. It has replaced my old workhorse,
Emtech's ZM-2 and has partially replaced the MFJ tuner I use on my 100-watt
rig (with power turned down to 25 watts or so). Easy band changes without
the "look at the meters while rotating the knob" routine.

Between home, field operation & Field Day 2005, I've used the T1 with all my
rigs and a borrowed K2 on various combinations of the following antennas:

ladder line-fed 40m dipole
80m G5RV
2 element 40m wire beam
30' wire + 1 radial
20m hamstick mobile whip (on 20 and 30m)

The T1 has tuned them all to a ratio of 1.4:1 or less, usually less. Soon
after building the tuner I would always go back and verify that the SWR
really was low. I did this buy disconnecting the rig and attaching a Bird
antenna analyzer.

A few months ago, QST had a review of 5 or 6 kilowatt tuners. The main gist
of the article was not whether or not the tuners would tune various antennas
on the HF bands for which they were designed, but with what efficiency the
mismatches could be transformed. This is my question on the T1 and every
tuner I use. For 5 watts out of the transmitter, how much of that goes to
the antenna when I use the T1 rather than the ZM-2, etc... That's what I
want to know, but darned if I know how to make such measurements.


John Harper AE5X
Portable QRP: http://www.ae5x.com


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[NR5A]

Well I broke down and ordered a T-1 to build and play with. EEK more
torroids to wind, yuk. Not a torroid winding person, but will not pay to
have them wound either. hi hi Yes, call me cheap. Anyway looking forward to
building it.

Jerry - NR5A - South Dakota


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[Coote, Jay]

All tuners will eat up some percentage of your RF output power.
The ones with toroid or smaller inductors may eat up more power.
Just how much power depends on the reactance/impedance transformation
required and the
Quality of the components.  
You can see that a test using a 50-ohm wattmeter on the input and
another on the output
Is not a true indication of the tuners capabilities- though that is
probably what
Some manufacturers to for their "tests".  The real test would be to
measure a wide
Number of resistive (and reactive) loads on a large number of
frequencies.

One good start might be to measure RF voltage VPP across the resistive
load after
The tuner has been adjusted. VPP on a good oscilloscope is more accurate
an RF
Power measurement than most wattmeters- especially for QRP.  

Some correct if I am wrong but I believe the formula is Pwatts = 0.35355
x VPP scope reading
Then square the results, Then divide the results by the load resistance
50- or the value that you chose for testing the tuner.

Jay
W6CJ

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of John Harper AE5X
Sent: Sunday, August 07, 2005 4:05 PM
To: Elecraft
Subject: [Elecraft] Re: Elecrafts T-1

Jerry,

I built one right after they came out and in one fell swoop, it made all
my monobanders much more easily portable. It has replaced my old
workhorse, Emtech's ZM-2 and has partially replaced the MFJ tuner I use
on my 100-watt rig (with power turned down to 25 watts or so). Easy band
changes without the "look at the meters while rotating the knob"
routine.

Between home, field operation & Field Day 2005, I've used the T1 with
all my rigs and a borrowed K2 on various combinations of the following
antennas:

ladder line-fed 40m dipole
80m G5RV
2 element 40m wire beam
30' wire + 1 radial
20m hamstick mobile whip (on 20 and 30m)

The T1 has tuned them all to a ratio of 1.4:1 or less, usually less.
Soon after building the tuner I would always go back and verify that the
SWR really was low. I did this buy disconnecting the rig and attaching a
Bird antenna analyzer.

A few months ago, QST had a review of 5 or 6 kilowatt tuners. The main
gist of the article was not whether or not the tuners would tune various
antennas on the HF bands for which they were designed, but with what
efficiency the mismatches could be transformed. This is my question on
the T1 and every tuner I use. For 5 watts out of the transmitter, how
much of that goes to the antenna when I use the T1 rather than the ZM-2,
etc... That's what I want to know, but darned if I know how to make such
measurements.


John Harper AE5X
Portable QRP: http://www.ae5x.com


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[wayne burdick]

Jay wrote:

> All tuners will eat up some percentage of your RF output power.
> The ones with toroid or smaller inductors may eat up more power.

Jay, John, etc.:

The physical size of the inductors would only be a factor if they were
also inefficient (dissipating a lot of heat). In all of our tuners,
including the T1, we use high-Q toroidal inductors with core and wire
sizes appropriate for the intended RF current. In addition, we use
high-Q capacitors (NP0/C0G ceramic or in some cases silver mica).

In lab tests of the T1, I used loads from 3 to 1000 ohms, calculating
the power into and out of the L-network. The T1's efficiency was on a
par with other tuners of this type, including those with much larger
toroids. For typical matches, losses range from 0.1 to 1 dB. A tuner
using very large air-wound inductors and air-variable capacitors might
cut these values in half, and would have an advantage at very high or
low impedances. But such a unit would also not be very portable, so
it's a tradeoff.

A much bigger factor in most antenna installations is ground loss,
which usually dwarfs any L-network losses. This is especially true of
portable antennas. If your goal is to radiate the best possible signal,
you can reduce ground losses by using *lots* of radials, or consider a
dipole or inverted V with its feedpoint as high off the ground as
possible.

When I'm in casual operating mode I simply toss a wire in a tree, lay
out one radial, use no feedline at all, and accept the inevitable
ground loss. If I'm "serious," I string a wire between two trees such
that the center is 20 to 30 feet high, feed it with 300-ohm low-loss
twinlead, and use a low-loss balun between the feedline and the tuner
(the Elecraft BL1 is quite small and works well in this application).
In this cases I use a wire that's at least 1/2-wavelength long on the
lowest band of operation.

The T1 finds a low-SWR match on most or all HF bands with either
"casual" or "serious" antennas  :)

73,
Wayne
N6KR


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[Bob Cunnings NW8L]

So far I've not bothered with a balun when running my KX1 into a
dipole fed with balanced line (using the internal tuner to match) and
seem to have pretty good results, better than the random wire and
counterpoise so far (portable operation over poor ground). My thinking
was that since the whole system is floating with respect to ground
(I'm usually sitting on a slab of rock), it wouldn't really matter. I
find little in the literature about this topic, except older
references to "floating" single ended antenna tuners to drive balanced
lines. I certainly understand the necessity of the balun when the
single ended output is truly ground referenced via a good ground
system, etc.

Whats the truth?

Bob NW8L

On 8/8/05, wayne burdick <[hidden email]> wrote:

> Jay wrote:
>
> > All tuners will eat up some percentage of your RF output power.
> > The ones with toroid or smaller inductors may eat up more power.
>
> Jay, John, etc.:
>
> The physical size of the inductors would only be a factor if they were
> also inefficient (dissipating a lot of heat). In all of our tuners,
> including the T1, we use high-Q toroidal inductors with core and wire
> sizes appropriate for the intended RF current. In addition, we use
> high-Q capacitors (NP0/C0G ceramic or in some cases silver mica).
>
> In lab tests of the T1, I used loads from 3 to 1000 ohms, calculating
> the power into and out of the L-network. The T1's efficiency was on a
> par with other tuners of this type, including those with much larger
> toroids. For typical matches, losses range from 0.1 to 1 dB. A tuner
> using very large air-wound inductors and air-variable capacitors might
> cut these values in half, and would have an advantage at very high or
> low impedances. But such a unit would also not be very portable, so
> it's a tradeoff.
>
> A much bigger factor in most antenna installations is ground loss,
> which usually dwarfs any L-network losses. This is especially true of
> portable antennas. If your goal is to radiate the best possible signal,
> you can reduce ground losses by using *lots* of radials, or consider a
> dipole or inverted V with its feedpoint as high off the ground as
> possible.
>
> When I'm in casual operating mode I simply toss a wire in a tree, lay
> out one radial, use no feedline at all, and accept the inevitable
> ground loss. If I'm "serious," I string a wire between two trees such
> that the center is 20 to 30 feet high, feed it with 300-ohm low-loss
> twinlead, and use a low-loss balun between the feedline and the tuner
> (the Elecraft BL1 is quite small and works well in this application).
> In this cases I use a wire that's at least 1/2-wavelength long on the
> lowest band of operation.
>
> The T1 finds a low-SWR match on most or all HF bands with either
> "casual" or "serious" antennas  :)
>
> 73,
> Wayne
> N6KR

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[wayne burdick]

On Aug 8, 2005, at 9:29 AM, Bob Cunnings wrote:

> So far I've not bothered with a balun when running my KX1 into a
> dipole fed with balanced line (using the internal tuner to match) and
> seem to have pretty good results, better than the random wire and
> counterpoise so far (portable operation over poor ground). My thinking
> was that since the whole system is floating with respect to ground
> (I'm usually sitting on a slab of rock), it wouldn't really matter.

Bob,

Operating in this "floating" mode without a balun may be satisfactory
in many cases. But a balun should be helpful with antennas that present
a high impedance to the tuner, for two reasons: (1) it steps the
impedance down by a factor of 4, which may help if the tuner's range is
limited; (2) it reduces the RF voltage appearing on the chassis. The
latter is more of an issue at higher power and in SSB mode, where it
might prevent "hot mic" syndrome.

73,
Wayne
N6KR


---

http://www.elecraft.com

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[Darrell Bellerive]

On August 8, 2005 09:48 am, wayne burdick wrote:
> But a balun should be helpful with antennas that present
> a high impedance to the tuner, for two reasons: (1) it steps the
> impedance down by a factor of 4, which may help if the tuner's range is
> limited;

Doesn't the impedance conversion degrade as the balun is used away from it's
designed impedance. If I recall the BL1 was designed for a 200 ohm load. Will
it still do a 4:1 conversion if the load is 1000 or 2000 ohms?

--
Darrell Bellerive
Amateur Radio Stations VA7TO and VE7CLA
Grand Forks, British Columbia, Canada
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[n6wg]

Bob
The idea of a balun is to provide balanced drive to the transmission line
so that it will not radiate, saving that for the antenna.  Part of the
idea is to reduce TVI etc due to feedline radiation, and part is to
preserve the directivity pattern of the antenna.  A radiating feedline
tends to an omnidirectional pattern, spoiling a good directional antenna
pattern.

Out in thw boonies, this is a nonissue, as you want to raidate anywhere you
can.
Just go out and enjoy.

73, Bob N6WG

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]]On Behalf Of Bob Cunnings
Sent: Monday, August 08, 2005 9:30 AM
To: Elecraft
Subject: Re: [Elecraft] ATU efficiency and the Elecraft T1


So far I've not bothered with a balun when running my KX1 into a
dipole fed with balanced line (using the internal tuner to match) and
seem to have pretty good results, better than the random wire and
counterpoise so far (portable operation over poor ground). My thinking
was that since the whole system is floating with respect to ground
(I'm usually sitting on a slab of rock), it wouldn't really matter. I
find little in the literature about this topic, except older
references to "floating" single ended antenna tuners to drive balanced
lines. I certainly understand the necessity of the balun when the
single ended output is truly ground referenced via a good ground
system, etc.

Whats the truth?

Bob NW8L

On 8/8/05, wayne burdick <[hidden email]> wrote:

> Jay wrote:
>
> > All tuners will eat up some percentage of your RF output power.
> > The ones with toroid or smaller inductors may eat up more power.
>
> Jay, John, etc.:
>
> The physical size of the inductors would only be a factor if they were
> also inefficient (dissipating a lot of heat). In all of our tuners,
> including the T1, we use high-Q toroidal inductors with core and wire
> sizes appropriate for the intended RF current. In addition, we use
> high-Q capacitors (NP0/C0G ceramic or in some cases silver mica).
>
> In lab tests of the T1, I used loads from 3 to 1000 ohms, calculating
> the power into and out of the L-network. The T1's efficiency was on a
> par with other tuners of this type, including those with much larger
> toroids. For typical matches, losses range from 0.1 to 1 dB. A tuner
> using very large air-wound inductors and air-variable capacitors might
> cut these values in half, and would have an advantage at very high or
> low impedances. But such a unit would also not be very portable, so
> it's a tradeoff.
>
> A much bigger factor in most antenna installations is ground loss,
> which usually dwarfs any L-network losses. This is especially true of
> portable antennas. If your goal is to radiate the best possible signal,
> you can reduce ground losses by using *lots* of radials, or consider a
> dipole or inverted V with its feedpoint as high off the ground as
> possible.
>
> When I'm in casual operating mode I simply toss a wire in a tree, lay
> out one radial, use no feedline at all, and accept the inevitable
> ground loss. If I'm "serious," I string a wire between two trees such
> that the center is 20 to 30 feet high, feed it with 300-ohm low-loss
> twinlead, and use a low-loss balun between the feedline and the tuner
> (the Elecraft BL1 is quite small and works well in this application).
> In this cases I use a wire that's at least 1/2-wavelength long on the
> lowest band of operation.
>
> The T1 finds a low-SWR match on most or all HF bands with either
> "casual" or "serious" antennas  :)
>
> 73,
> Wayne
> N6KR

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[wayne burdick]

On Aug 8, 2005, at 10:01 AM, Darrell Bellerive wrote:

> If I recall the BL1 was designed for a 200 ohm load. Will
> it still do a 4:1 conversion if the load is 1000 or 2000 ohms?

Yes, although the higher the impedance, the more the balun's own strays
will come into play. (Note also that at QRP levels, a large balun such
as the BL1 should have negligible heating loss over a very wide
impedance range.)

I'd suggest experimenting ahead of time with the tuner, balun, and
typical antennas.

73,
Wayne
N6KR


---

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[Darrell Bellerive]

On August 8, 2005 10:29 am, wayne burdick wrote:
> at QRP levels, a large balun such
> as the BL1 should have negligible heating loss over a very wide
> impedance range.

I would have thought that the heating is a result of inefficiency. The heat is
lower at QRP levels than at higher power levels since there is less power to
produce heat. If a balun is converting 10% of energy into heat, then more
heat is produced with 100 watts than 5 watts, but the loss is still the same
10%. Am I wrong?

--
Darrell Bellerive
Amateur Radio Stations VA7TO and VE7CLA
Grand Forks, British Columbia, Canada
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[wayne burdick]

Darrell,

My comment about heating was in regards to saturation, which greatly
increases loss. At QRP levels a BL-1 will never saturate, even if it is
working into a very low or high impedance. OTOH, at high power, a
severe mismatch really *will* heat up the balun, and if it saturates,
it will become a lot less efficient, making losses much greater.

You're correct that efficiency of impedance transformation is the same
at any power level -- as long as the balun isn't in saturation.

73,
Wayne


On Aug 8, 2005, at 10:57 AM, Darrell Bellerive wrote:

> On August 8, 2005 10:29 am, wayne burdick wrote:
>> at QRP levels, a large balun such
>> as the BL1 should have negligible heating loss over a very wide
>> impedance range.
>
> I would have thought that the heating is a result of inefficiency. The
> heat is
> lower at QRP levels than at higher power levels since there is less
> power to
> produce heat. If a balun is converting 10% of energy into heat, then
> more
> heat is produced with 100 watts than 5 watts, but the loss is still
> the same
> 10%. Am I wrong?
>

---

http://www.elecraft.com

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[Stuart Rohre]

L. B. Cebik, W4RNL, explored the "im balance" of the end fed Zepp antenna,
a half wave with open wire feed where one side of the wire connects to
nothing, and the other to the antenna end element.

That would seem to be the extreme case of current imbalance but he found
typically, there is only 10 per cent less current in one conductor at the
rig end, than the other.  The line seems to divide the power available,
rather than one wire being a true zero current.

This was done for a floating system, or a closed system, ie dipole in space,
no other ground.  That would pretty well approach the floating system you
have used on rock.

Stuart
K5KVH



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[Bob Cunnings NW8L]

On 8/8/05, Stuart Rohre <[hidden email]> wrote:

> This was done for a floating system, or a closed system, ie dipole in space,
> no other ground.  That would pretty well approach the floating system you
> have used on rock.
>

Well, my thinking went like this:

Imagine I connected a 3/4 wavelength wire to the ant output on the
KX1, and a 3/4 wavelength counterpoise to the rig's chassis (which is
floating with respect to ground). A current maximum would exist at the
2 points of attachment and equal and opposite currents would flow into
the two wires. Now if the first 2/3 of each wire were paralleled to
form a transmission line with the remaining 1/3 arranged to form a
dipole antenna, nothing really changes except that now only the dipole
elements radiate, since the currents on the 2/3 of the wire formed
into a transmission line are (still) equal and opposite in phase. The
system remains balanced with respect to ground, by virtue of the fact
that the chassis is floating. As noted by others, this arrangment does
have a drawback - RF voltage will be present on the chassis. I hadn't
thought about that. Since I'm using resonant dipoles with balanced
feedlines cut to 1/2 wavelength the voltages probably aren't that
high, but upon reflection I can see why the balun would be nice to
have for that reason alone. Oh well, just an oz. or two more weight to
carry if I want to use one.

Thanks all,

Bob NW8L
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[Darrell Bellerive]

On August 8, 2005 01:39 pm, Stuart Rohre wrote:

> L. B. Cebik, W4RNL, explored the "im balance" of the end fed Zepp antenna,
> a half wave with open wire feed where one side of the wire connects to
> nothing, and the other to the antenna end element.
>
> That would seem to be the extreme case of current imbalance but he found
> typically, there is only 10 per cent less current in one conductor at the
> rig end, than the other.  The line seems to divide the power available,
> rather than one wire being a true zero current.
>
> This was done for a floating system, or a closed system, ie dipole in
> space, no other ground.  That would pretty well approach the floating
> system you have used on rock.
>

So how would the Elecraft BL1 Balun do with the End-Fed Zepp? Depending on the
ground losses, the impedance could be 5000 ohms or so. Would the 4:1
transformation ratio still hold true? What would the efficiency of the balun
be? Would 100 watts from a K2/100 cause saturation of the balun core?

--
Darrell Bellerive
Amateur Radio Stations VA7TO and VE7CLA
Grand Forks, British Columbia, Canada
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[Don Wilhelm-3]

Darrell,

It all depends on the electrical length to the feedline at the frequency of
operation.  Sorry, but no better answer exists.

If your antenna is end fed (like the example of an end fed dipole), the
impdance at the antenna feedpoint will be high, but if the feedline is an
odd multiple of a 1/4 wave (elecrtical), the impedance presented to the
shack loaction should be low.  At other lengths, the impedance at the input
to the feedline will be high or low or something in between and will depend
on the length of the feedline.  Whether it is better to use a 1:1 balun or a
4:1 balun depends on the answer to these questions.

73,
Don W3FPR

> -----Original Message-----
> > L. B. Cebik, W4RNL, explored the "im balance" of the end fed
> Zepp antenna,
> > a half wave with open wire feed where one side of the wire connects to
> > nothing, and the other to the antenna end element.
> >
> > That would seem to be the extreme case of current imbalance but he found
> > typically, there is only 10 per cent less current in one
> conductor at the
> > rig end, than the other.  The line seems to divide the power available,
> > rather than one wire being a true zero current.
> >
> > This was done for a floating system, or a closed system, ie dipole in
> > space, no other ground.  That would pretty well approach the floating
> > system you have used on rock.
> >
>
> So how would the Elecraft BL1 Balun do with the End-Fed Zepp?
> Depending on the
> ground losses, the impedance could be 5000 ohms or so. Would the 4:1
> transformation ratio still hold true? What would the efficiency
> of the balun
> be? Would 100 watts from a K2/100 cause saturation of the balun core?
>
> --
> Darrell Bellerive

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[Darrell Bellerive]

On August 8, 2005 07:03 pm, W3FPR - Don Wilhelm wrote:
> If your antenna is end fed (like the example of an end fed dipole), the
> impdance at the antenna feedpoint will be high, but if the feedline is an
> odd multiple of a 1/4 wave (elecrtical), the impedance presented to the
> shack loaction should be low.  At other lengths, the impedance at the input
> to the feedline will be high or low or something in between and will depend
> on the length of the feedline.  Whether it is better to use a 1:1 balun or
> a 4:1 balun depends on the answer to these questions.

So lets take a worst case example of a 160 meter half wave antenna, and use it
on all bands 160 through 10 meters including the WARC bands to align with the
capabilities of the K2/100.
As the electrical length of the antenna and feedline will vary with frequency,
different bands will have very different characteristics. I suspect that on
some bands this antenna system including the BL1 balun will be very efficient
and will be able to be matched by the KAT100, however I also expect that on
other bands it will be problematic. I would worry that a BL1 balun would
become quite inefficient at some frequencies. Do I understand this correctly?


--
Darrell Bellerive
Amateur Radio Stations VA7TO and VE7CLA
Grand Forks, British Columbia, Canada
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[Ron D'Eau Claire-2]

Darrell asked:
So how would the Elecraft BL1 Balun do with the End-Fed Zepp? Depending on
the
ground losses, the impedance could be 5000 ohms or so. Would the 4:1
transformation ratio still hold true? What would the efficiency of the balun

be? Would 100 watts from a K2/100 cause saturation of the balun core?

------------------------------------------------

Dipole = 1/2 wavelength radiator.  

Zepp = dipole radiator fed at one end with 1/4 wavelength of open wire feed
line. The 1/4 wavelength feed line converts that high impedance to a low
impedance at the rig end.

That's why the balance in such an antenna is not bad even though one side of
the open wire line connects to the end of the dipole radiator and the other
side connects to nothing at all. Very little current flows into the end of
the dipole and very little current flows from the end of the unconnected
feeder (some current flows due to losses in the insulators at the end).

Such an antenna is a "piece of cake" for a balun and you may find the feeder
currents are equal even without one. After all, that arrangement is simply a
3/4 wavelength long wire connected to the "hot" side of the rig output and a
1/4 wave "counterpoise" connected to the other side, only the counterpoise
and the first 1/4 wavelength of the radiator run in parallel to minimize
radiation (that was important in Zeppelins where they were used).

Many Hams try to use lengths other than 1/2 wave for the radiator and 1/4
wave for the feeders. When you do that, all bets are off. It's like any
"non-resonant" doublet or end-fed wire. They can work well, but you must
have a matching network that can handle some potentially extreme impedances.
Actually at any but the exact lengths for a proper Zepp, the feeder will
radiate as much as the antenna. That's why non-resonant antennas fed with
open wire line are usually center fed (so-called doublets). Such center fed
arrangements hold decent balance regardless of frequency.  

Ron AC7AC


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[Darrell Bellerive]

On August 8, 2005 07:30 pm, Ron D'Eau Claire wrote:
> Many Hams try to use lengths other than 1/2 wave for the radiator and 1/4
> wave for the feeders. When you do that, all bets are off. It's like any
> "non-resonant" doublet or end-fed wire. They can work well, but you must
> have a matching network that can handle some potentially extreme
> impedances. Actually at any but the exact lengths for a proper Zepp, the
> feeder will radiate as much as the antenna. That's why non-resonant
> antennas fed with open wire line are usually center fed (so-called
> doublets). Such center fed arrangements hold decent balance regardless of
> frequency.

Even with a center fed multiband doublet, a balun would be presented with an
extreme set of impedances. I would suspect that on some bands or frequencies
the whole antenna system would be quite inefficient. But as QRPer's have
proved it doesn't take much power to make contacts. A 100 watts into an
antenna system that is only 5% efficient is still 5 watts ERP. Combine that
with an antenna that is long in terms of wavelengths and the nulls and peaks
of the lobes will be substantial.

Perhaps I am way behind the times, but I still think that a link coupled
balanced tuner is the proper way to feed a balanced antenna, whether center
fed or end fed. Modern L or T antenna tuners with a balun on the output may
be easier and cheaper to build, but just don't seem to be designed for the
multiband balanced antennas.

--
Darrell Bellerive
Amateur Radio Stations VA7TO and VE7CLA
Grand Forks, British Columbia, Canada
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[Paul Gates]

My only comment is, first of all I am not an engineer and I am not savvy
always on the ins and outs of antennas,  but my gut feeling is that a "L"
network tuner is the better for all circumstances than a "T" network tuner.

Paul Gates
K1  #0231
KX1 #1186
XG1
[hidden email]


----- Original Message -----
From: "Darrell Bellerive" <[hidden email]>
To: <[hidden email]>
Sent: Monday, August 08, 2005 10:49 PM
Subject: Re: [Elecraft] ATU efficiency and the Elecraft T1

> On August 8, 2005 07:30 pm, Ron D'Eau Claire wrote:
> > Many Hams try to use lengths other than 1/2 wave for the radiator and
> > 1/4
> > wave for the feeders. When you do that, all bets are off. It's like any
> > "non-resonant" doublet or end-fed wire. They can work well, but you must
> > have a matching network that can handle some potentially extreme
> > impedances. Actually at any but the exact lengths for a proper Zepp, the
> > feeder will radiate as much as the antenna. That's why non-resonant
> > antennas fed with open wire line are usually center fed (so-called
> > doublets). Such center fed arrangements hold decent balance regardless
> > of
> > frequency.
>
> Even with a center fed multiband doublet, a balun would be presented with
> an
> extreme set of impedances. I would suspect that on some bands or
> frequencies
> the whole antenna system would be quite inefficient. But as QRPer's have
> proved it doesn't take much power to make contacts. A 100 watts into an
> antenna system that is only 5% efficient is still 5 watts ERP. Combine
> that
> with an antenna that is long in terms of wavelengths and the nulls and
> peaks
> of the lobes will be substantial.
>
> Perhaps I am way behind the times, but I still think that a link coupled
> balanced tuner is the proper way to feed a balanced antenna, whether
> center
> fed or end fed. Modern L or T antenna tuners with a balun on the output
> may
> be easier and cheaper to build, but just don't seem to be designed for the
> multiband balanced antennas.
>
> --
> Darrell Bellerive
> Amateur Radio Stations VA7TO and VE7CLA
> Grand Forks, British Columbia, Canada
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[Ron D'Eau Claire-2]

Paul, KD3JF wrote:

My only comment is, first of all I am not an engineer and I am not savvy
always on the ins and outs of antennas,  but my gut feeling is that a "L"
network tuner is the better for all circumstances than a "T" network tuner.

----------------------------------------

Good 'gut' feelings, Paul.

I try to minimize the number of reactive elements (coils & caps) in the
circuit on the theory that all such elements have SOME loss.

Measurements show that there is little difference between L and T networks
at nominal impedance levels. However, when transforming to very low
impedances, the losses in a T-network tuner go up very quickly compared to
other types. Also, T-networks will typically show a match at more than one
combination of settings, some of which will show much higher losses in the
tuner (usually in the inductor) than others.

In their defense, T-networks do a great job of fixing nominal impedance
mismatches. They became very popular some years ago when the popular tunable
pi-network outputs in our rigs were no longer adequate. Of course,
pi-network outputs were very versatile, allowing us to not only handle just
about any SWR we might encounter on a coaxial feedline, but even to load up
quite an array of end-fed wires and other "casual" antennas.

But tunable pi-network output were doomed by two problems. One problem was
that, here in the USA at least, the FCC tightened up the specifications for
spurious radiations beyond what pi-nets could provide. The other problem was
the solid-state RF power amplifier. The circuit values required for a
pi-network were beyond that available with reasonable parts. More complex
networks were needed. So rig manufacturers started building rigs with
fixed-tuned output networks.

>From a marketing viewpoint they were heralded as "no-tune" rigs. No longer
did we need to dip the plate current and then set the loading for every QSY.
That was sort of true. They were no-tune as long as our antenna provided a
very good 50-ohm match to the rig on every frequency we wanted to use. Open
wire feeders and end-fed wires virtually disappeared from most Hamshacks in
favor of a variety of trap verticals, trap dipoles and multi-band beams. But
that didn't fix the problem for everyone. Many Hams found it very difficult
to erect antennas that provided the low-SWR required by their 'no-tune' rigs
on all bands.

Companies like MFJ and other tuner manufacturers stepped in to fill that
gap. They chose the T-network because it was simple and cheap to implement
to cover a wide frequency range and, when used to correct nominal mismatches
in a 50-ohm line, they are very efficient. Typically a 4:1 balun was
included for those wanting to feed antennas with balanced lines like the
popular folded dipoles that required a 300 ohm feed. The 4:1 impedance
matching ration provided a good match for such an antenna to the most
efficient working range of the T-network.

But, Hams being Hams, some of us decided to use them to load up all manner
of strange random wires and antennas. And Marketing folks being Marketing
folks, the manufacturers didn't exactly discourage that, although if one
reads the MFJ manuals there are plenty of warnings about the limitations of
the T-network and its tendency to become very lossy under certain
conditions.

Things really got crazy when the WARC bands were made available. The Ham
bands no longer had a simple harmonic relationship to each other, so the
design of a single antenna that would provide a low SWR on ALL the HF bands
became very complex. Doublets and random end-fed wires and a whole bunch of
"untuned" multiband  antennas started appearing on the scene again, and the
tuners designed to correct minor mismatches in coax lines were simply not
adequate for the job. Really efficient wide-range tuners were needed.

To handle these new requirements, Elecraft has opted for the L-network with
its wide matching range and good efficiency in all of its tuners, even
though it requires a more complex switching system to handle all of the
possible combinations of inductance and capacitance that might be needed.
But we don't really notice the more complex tuning since it's now done
automatically for us by controller systems that were only available on Star
Trek back in 1960.

So things have come full-circle. Instead of dipping the plate current and
adjusting the loading for the output power, we now adjust the tuner for a
low SWR on the link to the rig to make sure the transmitter's output network
is working efficiently.

And, with fully-automatic ATU's like Elecraft gives us, we still don't have
to twiddle with any knobs when we QSY. We just listen to the latching relays
go "crrrrrrick!"  <G>.

Ron AC7AC


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