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K3 power reduction due to high SWR

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vk4tux

K3 power reduction due to high SWR

I disagree, your coax suggestion has 32% loss against a good wl installation
which would provide 9% loss.
Use of RF ammeter on each leg can be used to balance the loading via antenna
leg adjustments if required.

A dedicated eg: Johnson matchbox or GQ balanced tuner etc at TX would give
good results.

The 450 ohm to 72 ohm connection is of no issue centre fed. The ladder line
length will have an impedance transformation effect.
Trying for common multiple of half wavelengths on FL length -vf at the
frequencies used will be a good idea if possible to represent the feedpoint
impedance at the TX end if possible. In any case the tuner will take care of
the transformation.

Any decent low loss coax on this length will cost lots.

I assume that the guy can't get the antenna closer, trees in the distance
etc probably, but I have seen many good examples from the USA of successful
long distance 450 ohm wl runs with wire antenna's.

A ladder line setup here will outperform your RG11 etc by 1.2dB.

When wet your RG11 setup will have a 1.4dB advantage. I guess it all depends
on the weather, and the guys bank balance.
213 is ordinary for coax, I much prefer lmr400, which I use with my BD
4115-ocf.

vk4tux

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Jim Brown
Sent: Thursday, 5 April 2012 3:26 PM
To: [hidden email]
Subject: Re: [Elecraft] K3 power reduction due to high SWR

> If I have to use your antenna, then my move would be to replace the 250'
> of75 ohm coax with 250' of 450 ohm ladder line, check the fan dipole
> legs are exactly the same to provide a balanced load.

You're on target about loss in the feedline, but ladder line is not a good
move here.David has resonant dipoles, so they are a pretty good match to 50
or 75 ohm cable. Folks think QRP, so they think small coax, But when the
line is as long as these are, the loss certainly gets out of hand unless
it's bigger coax. If I were to make ANY change in the feedline, it would be
to a decent RG8 or RG11. I would also look at ways to reduce the length of
the line by finding a shorter route to the shack. You don't need expensive
coax -- Davis 213 is about as good as it gets for the HF bands, and it's
fairly inexpensive.

Window line is NOT the cure for all ills -- it is as lossy as small coax
when it gets wet, and there's some loss (and cost) in any impedance
transforming balun. Further, most real antennas are unbalanced by their
surroundings, so they need a good ferrite common mode choke at the feedpoint
whether they're fed by coax or parallel wire line.

73, Jim Brown K9YC
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Vic Rosenthal

Re: K3 power reduction due to high SWR

Speaking of balanced lines and tuners, I recently did an experiment that surprised me.

I have a dipole fed with 600-ohm open-wire line (and some window line indoors). I usually
tune it with a Johnson Matchbox, a fully balanced link-coupled tuner.

I was lucky enough to get my hands on a massive, high-quality edge-wound rotary inductor
in a well-made aluminum enclosure. So I built a high-power T-network tuner with it. I
purchased a good (and expensive) 1:1 balun designed for use after a tuner from DX
Engineering, and compared the T-net + balun to the Matchbox. I didn't notice any
difference in the strength of received signals between the tuners.

But here is the surprising part: I expected that the Matchbox would provide better
balance, which would reduce radiation and pickup from the feedline. To test this, I
coupled a grid-dip oscillator to the feedline about 20 feet from the tuner.

To my great surprise, the signal from the oscillator was much weaker with the T-network +
balun than with the Matchbox!

Signals the same, 'noise' weaker. So much for the need for 'truly balanced' tuners!

On 4/5/2012 12:28 AM, Adrian wrote:

>
> I disagree, your coax suggestion has 32% loss against a good wl installation
> which would provide 9% loss.
> Use of RF ammeter on each leg can be used to balance the loading via antenna
> leg adjustments if required.
>
> A dedicated eg: Johnson matchbox or GQ balanced tuner etc at TX would give
> good results.
>
> The 450 ohm to 72 ohm connection is of no issue centre fed. The ladder line
> length will have an impedance transformation effect.
> Trying for common multiple of half wavelengths on FL length -vf at the
> frequencies used will be a good idea if possible to represent the feedpoint
> impedance at the TX end if possible. In any case the tuner will take care of
> the transformation.
>
> Any decent low loss coax on this length will cost lots.
>
> I assume that the guy can't get the antenna closer, trees in the distance
> etc probably, but I have seen many good examples from the USA of successful
> long distance 450 ohm wl runs with wire antenna's.
>
> A ladder line setup here will outperform your RG11 etc by 1.2dB.
>
> When wet your RG11 setup will have a 1.4dB advantage. I guess it all depends
> on the weather, and the guys bank balance.
> 213 is ordinary for coax, I much prefer lmr400, which I use with my BD
> 4115-ocf.
>
> vk4tux

--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
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Don Wilhelm-4

Re: K3 power reduction due to high SWR

Vic,

Where was the frequency of the GDO with respect to the band the tuner
was set to? If it was below the band of interest, I would expect
something like that - the T-Network is a high pass filter.

73,
Don W3FPR

On 4/5/2012 12:28 PM, Vic K2VCO wrote:

> Speaking of balanced lines and tuners, I recently did an experiment that surprised me.
>
> I have a dipole fed with 600-ohm open-wire line (and some window line indoors). I usually
> tune it with a Johnson Matchbox, a fully balanced link-coupled tuner.
>
> I was lucky enough to get my hands on a massive, high-quality edge-wound rotary inductor
> in a well-made aluminum enclosure. So I built a high-power T-network tuner with it. I
> purchased a good (and expensive) 1:1 balun designed for use after a tuner from DX
> Engineering, and compared the T-net + balun to the Matchbox. I didn't notice any
> difference in the strength of received signals between the tuners.
>
> But here is the surprising part: I expected that the Matchbox would provide better
> balance, which would reduce radiation and pickup from the feedline. To test this, I
> coupled a grid-dip oscillator to the feedline about 20 feet from the tuner.
>
> To my great surprise, the signal from the oscillator was much weaker with the T-network +
> balun than with the Matchbox!
>
> Signals the same, 'noise' weaker. So much for the need for 'truly balanced' tuners!
>

Matt Murphy

Re: K3 power reduction due to high SWR

One related question, when speaking of the efficiency of a balanced
feedline + balun and tuner, what would be a best/worst case scenario for
the loss introduced by the balun+tuner? Would loss vary significantly by
frequency for a nonresonant antenna? I'm trying to develop an intuition
about the lossiness of the tuner+balun compared to, say, 50' of RG213.

I've opted to use a 1:1 balun at the end of 450 ohm ladder line, then a
short length of coax into a TenTec 229 tuner. In the informal test that I
performed, the homebrew 1:1 balun + coax jumper improved the performance of
the antenna compared with connecting it directly to the balanced line
connectors on the back of the tuner.

73,
Matt NQ6N

On Thu, Apr 5, 2012 at 12:23 PM, Don Wilhelm <[hidden email]> wrote:

> Vic,
>
> Where was the frequency of the GDO with respect to the band the tuner
> was set to? If it was below the band of interest, I would expect
> something like that - the T-Network is a high pass filter.
>
> 73,
> Don W3FPR
>
>
> On 4/5/2012 12:28 PM, Vic K2VCO wrote:
> > Speaking of balanced lines and tuners, I recently did an experiment that
> surprised me.
> >
> > I have a dipole fed with 600-ohm open-wire line (and some window line
> indoors). I usually
> > tune it with a Johnson Matchbox, a fully balanced link-coupled tuner.
> >
> > I was lucky enough to get my hands on a massive, high-quality edge-wound
> rotary inductor
> > in a well-made aluminum enclosure. So I built a high-power T-network
> tuner with it. I
> > purchased a good (and expensive) 1:1 balun designed for use after a
> tuner from DX
> > Engineering, and compared the T-net + balun to the Matchbox. I didn't
> notice any
> > difference in the strength of received signals between the tuners.
> >
> > But here is the surprising part: I expected that the Matchbox would
> provide better
> > balance, which would reduce radiation and pickup from the feedline. To
> test this, I
> > coupled a grid-dip oscillator to the feedline about 20 feet from the
> tuner.
> >
> > To my great surprise, the signal from the oscillator was much weaker
> with the T-network +
> > balun than with the Matchbox!
> >
> > Signals the same, 'noise' weaker. So much for the need for 'truly
> balanced' tuners!
> >
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

Vic Rosenthal

Re: K3 power reduction due to high SWR

In reply to this post by Don Wilhelm-4

All the tests -- signal comparison and noise tests -- were done on the same band, to which
the tuner was tuned (40m).

On 4/5/2012 12:23 PM, Don Wilhelm wrote:

> Vic,
>
> Where was the frequency of the GDO with respect to the band the tuner was set to? If it
> was below the band of interest, I would expect something like that - the T-Network is a
> high pass filter.
>
> 73,
> Don W3FPR
>
>
> On 4/5/2012 12:28 PM, Vic K2VCO wrote:
>> Speaking of balanced lines and tuners, I recently did an experiment that surprised me.
>>
>> I have a dipole fed with 600-ohm open-wire line (and some window line indoors). I usually
>> tune it with a Johnson Matchbox, a fully balanced link-coupled tuner.
>>
>> I was lucky enough to get my hands on a massive, high-quality edge-wound rotary inductor
>> in a well-made aluminum enclosure. So I built a high-power T-network tuner with it. I
>> purchased a good (and expensive) 1:1 balun designed for use after a tuner from DX
>> Engineering, and compared the T-net + balun to the Matchbox. I didn't notice any
>> difference in the strength of received signals between the tuners.
>>
>> But here is the surprising part: I expected that the Matchbox would provide better
>> balance, which would reduce radiation and pickup from the feedline. To test this, I
>> coupled a grid-dip oscillator to the feedline about 20 feet from the tuner.
>>
>> To my great surprise, the signal from the oscillator was much weaker with the T-network +
>> balun than with the Matchbox!
>>
>> Signals the same, 'noise' weaker. So much for the need for 'truly balanced' tuners!
>>

Vic Rosenthal

Tuners and baluns (was: Re: K3 power reduction due to high SWR)

In reply to this post by Matt Murphy

The efficiency of the T-network can be less than the Matchbox-type tuner or an L-network
because it is possible to find a suboptimal combination of component values that will give
you a 1:1 match. I believe that the most efficient match is achieved when the T inductance
is set to the minimum value that will give you 1:1.

This can require large values of capacitance in the T network for the lower bands. In my
case both input and output capacitors have maximum values of 600 pf. That is probably not
enough for a wide range on 160 meters.

The impedance range within which the T is efficient depends on the minimum and maximum
values of inductance and capacity that you can achieve. Using a pair of vacuum caps would
be best, but would be VERY hard to tune if you didn't know where to set them first!

I think the Tentec 229 tuner is an L network. It is as efficient as it can be when it is
adjusted for a 1:1 match. I don't know why you got better results with your balun than
Tentec's -- maybe yours was better!

On 4/5/2012 12:52 PM, Matt Murphy wrote:

> One related question, when speaking of the efficiency of a balanced feedline + balun and
> tuner, what would be a best/worst case scenario for the loss introduced by the
> balun+tuner? Would loss vary significantly by frequency for a nonresonant antenna? I'm
> trying to develop an intuition about the lossiness of the tuner+balun compared to, say,
> 50' of RG213.
>
> I've opted to use a 1:1 balun at the end of 450 ohm ladder line, then a short length of
> coax into a TenTec 229 tuner. In the informal test that I performed, the homebrew 1:1
> balun + coax jumper improved the performance of the antenna compared with connecting it
> directly to the balanced line connectors on the back of the tuner.
>
> 73,
> Matt NQ6N
>
>
>
> On Thu, Apr 5, 2012 at 12:23 PM, Don Wilhelm <[hidden email]
> <mailto:[hidden email]>> wrote:
>
> Vic,
>
> Where was the frequency of the GDO with respect to the band the tuner
> was set to? If it was below the band of interest, I would expect
> something like that - the T-Network is a high pass filter.
>
> 73,
> Don W3FPR
>
>
> On 4/5/2012 12:28 PM, Vic K2VCO wrote:
> > Speaking of balanced lines and tuners, I recently did an experiment that surprised me.
> >
> > I have a dipole fed with 600-ohm open-wire line (and some window line indoors). I
> usually
> > tune it with a Johnson Matchbox, a fully balanced link-coupled tuner.
> >
> > I was lucky enough to get my hands on a massive, high-quality edge-wound rotary
> inductor
> > in a well-made aluminum enclosure. So I built a high-power T-network tuner with it. I
> > purchased a good (and expensive) 1:1 balun designed for use after a tuner from DX
> > Engineering, and compared the T-net + balun to the Matchbox. I didn't notice any
> > difference in the strength of received signals between the tuners.
> >
> > But here is the surprising part: I expected that the Matchbox would provide better
> > balance, which would reduce radiation and pickup from the feedline. To test this, I
> > coupled a grid-dip oscillator to the feedline about 20 feet from the tuner.
> >
> > To my great surprise, the signal from the oscillator was much weaker with the
> T-network +
> > balun than with the Matchbox!
> >
> > Signals the same, 'noise' weaker. So much for the need for 'truly balanced' tuners!

Matt Murphy

Re: K3 power reduction due to high SWR

In reply to this post by Matt Murphy

Thanks Ron for the great explanation. 73

On Thu, Apr 5, 2012 at 1:41 PM, Ron D'Eau Claire <[hidden email]> wrote:

> Most tuner losses occur in the same way as feed line losses - resistive
> losses in the conductors. In a tuner, that is usually in the inductance.
> The
> higher the current, the greater the resistive losses.
>
> That's why high impedance feed lines such as open wire line have typically
> much less loss than 50 ohm coaxial line. Higher impedance means higher
> voltages and less current for a given power. (Excepting the use of some
> "ladder line" that has very small gauge conductors which offset at least
> some of its advantage).
>
> Tuners that must feed very low impedance loads often suffer losses in the
> inductors due to the high currents required.
>
> Some tuners such as the popular T-network type may have more than one
> combination of settings that will provide a match. One setting can produce
> much more current and so greater loss than the other. W9CF wrote a Java
> simulator that lets you see the predicted losses for various conditions.
> Just twirl the knobs and watch the SWR or let it "auto-tune" for a given
> load and frequency:
>
> http://fermi.la.asu.edu/w9cf/tuner/tuner.html
>
> 73, Ron AC7AC
>
>
>
>
>
> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Matt Murphy
> Sent: Thursday, April 05, 2012 12:53 PM
> To: [hidden email]
> Cc: Vic K2VCO; [hidden email]
> Subject: Re: [Elecraft] K3 power reduction due to high SWR
>
> One related question, when speaking of the efficiency of a balanced
> feedline
> + balun and tuner, what would be a best/worst case scenario for the loss
> introduced by the balun+tuner? Would loss vary significantly by frequency
> for a nonresonant antenna? I'm trying to develop an intuition about the
> lossiness of the tuner+balun compared to, say, 50' of RG213.
>
> I've opted to use a 1:1 balun at the end of 450 ohm ladder line, then a
> short length of coax into a TenTec 229 tuner. In the informal test that I
> performed, the homebrew 1:1 balun + coax jumper improved the performance of
> the antenna compared with connecting it directly to the balanced line
> connectors on the back of the tuner.
>
> 73,
> Matt NQ6N
>
>
>
> On Thu, Apr 5, 2012 at 12:23 PM, Don Wilhelm <[hidden email]> wrote:
>
> > Vic,
> >
> > Where was the frequency of the GDO with respect to the band the tuner
> > was set to? If it was below the band of interest, I would expect
> > something like that - the T-Network is a high pass filter.
> >
> > 73,
> > Don W3FPR
> >
> >
> > On 4/5/2012 12:28 PM, Vic K2VCO wrote:
> > > Speaking of balanced lines and tuners, I recently did an experiment
> > > that
> > surprised me.
> > >
> > > I have a dipole fed with 600-ohm open-wire line (and some window
> > > line
> > indoors). I usually
> > > tune it with a Johnson Matchbox, a fully balanced link-coupled tuner.
> > >
> > > I was lucky enough to get my hands on a massive, high-quality
> > > edge-wound
> > rotary inductor
> > > in a well-made aluminum enclosure. So I built a high-power T-network
> > tuner with it. I
> > > purchased a good (and expensive) 1:1 balun designed for use after a
> > tuner from DX
> > > Engineering, and compared the T-net + balun to the Matchbox. I
> > > didn't
> > notice any
> > > difference in the strength of received signals between the tuners.
> > >
> > > But here is the surprising part: I expected that the Matchbox would
> > provide better
> > > balance, which would reduce radiation and pickup from the feedline.
> > > To
> > test this, I
> > > coupled a grid-dip oscillator to the feedline about 20 feet from the
> > tuner.
> > >
> > > To my great surprise, the signal from the oscillator was much weaker
> > with the T-network +
> > > balun than with the Matchbox!
> > >
> > > Signals the same, 'noise' weaker. So much for the need for 'truly
> > balanced' tuners!
> > >
> > ______________________________________________________________
> > Elecraft mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:[hidden email]
> >
> > This list hosted by: http://www.qsl.net Please help support this email
> > list: http://www.qsl.net/donate.html
> >
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>

vk4tux

K3 power reduction due to high SWR

In reply to this post by Matt Murphy

The external balun you are using is probably better than the one built into
the tuner. An English ham did research some time back and found using a 1:1
current balun less lossy that a 4:1 or others, despite the line mismatch the
tuner made up for it with tested less total loss.

With a well designed tuner/balun combo the circulating current is much less,
and it is only the resistance component that provides loss, not inductive
nor capacitive.

vk4tux

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Matt Murphy
Sent: Friday, 6 April 2012 5:53 AM
To: [hidden email]
Cc: Vic K2VCO; [hidden email]
Subject: Re: [Elecraft] K3 power reduction due to high SWR

One related question, when speaking of the efficiency of a balanced feedline
+ balun and tuner, what would be a best/worst case scenario for the loss
introduced by the balun+tuner? Would loss vary significantly by frequency
for a nonresonant antenna? I'm trying to develop an intuition about the
lossiness of the tuner+balun compared to, say, 50' of RG213.

I've opted to use a 1:1 balun at the end of 450 ohm ladder line, then a
short length of coax into a TenTec 229 tuner. In the informal test that I
performed, the homebrew 1:1 balun + coax jumper improved the performance of
the antenna compared with connecting it directly to the balanced line
connectors on the back of the tuner.

73,
Matt NQ6N

On Thu, Apr 5, 2012 at 12:23 PM, Don Wilhelm <[hidden email]> wrote:

> Vic,
>
> Where was the frequency of the GDO with respect to the band the tuner
> was set to? If it was below the band of interest, I would expect
> something like that - the T-Network is a high pass filter.
>
> 73,
> Don W3FPR
>
>
> On 4/5/2012 12:28 PM, Vic K2VCO wrote:
> > Speaking of balanced lines and tuners, I recently did an experiment
> > that
> surprised me.
> >
> > I have a dipole fed with 600-ohm open-wire line (and some window
> > line
> indoors). I usually
> > tune it with a Johnson Matchbox, a fully balanced link-coupled tuner.
> >
> > I was lucky enough to get my hands on a massive, high-quality
> > edge-wound
> rotary inductor
> > in a well-made aluminum enclosure. So I built a high-power T-network
> tuner with it. I
> > purchased a good (and expensive) 1:1 balun designed for use after a
> tuner from DX
> > Engineering, and compared the T-net + balun to the Matchbox. I
> > didn't
> notice any
> > difference in the strength of received signals between the tuners.
> >
> > But here is the surprising part: I expected that the Matchbox would
> provide better
> > balance, which would reduce radiation and pickup from the feedline.
> > To
> test this, I
> > coupled a grid-dip oscillator to the feedline about 20 feet from the
> tuner.
> >
> > To my great surprise, the signal from the oscillator was much weaker
> with the T-network +
> > balun than with the Matchbox!
> >
> > Signals the same, 'noise' weaker. So much for the need for 'truly
> balanced' tuners!
> >
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net Please help support this email
> list: http://www.qsl.net/donate.html
>

______________________________________________________________
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______________________________________________________________
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Matt Murphy

Re: K3 power reduction due to high SWR

Interesting! The balun I made is just a basic core type current balun
modeled after the one listed here (but made with high temp wire inside
teflon tubing):

http://vk5ajl.com/projects/baluns.php#current

On Thu, Apr 5, 2012 at 2:15 PM, Adrian <[hidden email]> wrote:

> The external balun you are using is probably better than the one built into
> the tuner. An English ham did research some time back and found using a
> 1:1
> current balun less lossy that a 4:1 or others, despite the line mismatch
> the
> tuner made up for it with tested less total loss.
>
> With a well designed tuner/balun combo the circulating current is much
> less,
> and it is only the resistance component that provides loss, not inductive
> nor capacitive.
>
> vk4tux
>
>
> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Matt Murphy
> Sent: Friday, 6 April 2012 5:53 AM
> To: [hidden email]
> Cc: Vic K2VCO; [hidden email]
> Subject: Re: [Elecraft] K3 power reduction due to high SWR
>
> One related question, when speaking of the efficiency of a balanced
> feedline
> + balun and tuner, what would be a best/worst case scenario for the loss
> introduced by the balun+tuner? Would loss vary significantly by frequency
> for a nonresonant antenna? I'm trying to develop an intuition about the
> lossiness of the tuner+balun compared to, say, 50' of RG213.
>
> I've opted to use a 1:1 balun at the end of 450 ohm ladder line, then a
> short length of coax into a TenTec 229 tuner. In the informal test that I
> performed, the homebrew 1:1 balun + coax jumper improved the performance of
> the antenna compared with connecting it directly to the balanced line
> connectors on the back of the tuner.
>
> 73,
> Matt NQ6N
>
>
>
> On Thu, Apr 5, 2012 at 12:23 PM, Don Wilhelm <[hidden email]> wrote:
>
> > Vic,
> >
> > Where was the frequency of the GDO with respect to the band the tuner
> > was set to? If it was below the band of interest, I would expect
> > something like that - the T-Network is a high pass filter.
> >
> > 73,
> > Don W3FPR
> >
> >
> > On 4/5/2012 12:28 PM, Vic K2VCO wrote:
> > > Speaking of balanced lines and tuners, I recently did an experiment
> > > that
> > surprised me.
> > >
> > > I have a dipole fed with 600-ohm open-wire line (and some window
> > > line
> > indoors). I usually
> > > tune it with a Johnson Matchbox, a fully balanced link-coupled tuner.
> > >
> > > I was lucky enough to get my hands on a massive, high-quality
> > > edge-wound
> > rotary inductor
> > > in a well-made aluminum enclosure. So I built a high-power T-network
> > tuner with it. I
> > > purchased a good (and expensive) 1:1 balun designed for use after a
> > tuner from DX
> > > Engineering, and compared the T-net + balun to the Matchbox. I
> > > didn't
> > notice any
> > > difference in the strength of received signals between the tuners.
> > >
> > > But here is the surprising part: I expected that the Matchbox would
> > provide better
> > > balance, which would reduce radiation and pickup from the feedline.
> > > To
> > test this, I
> > > coupled a grid-dip oscillator to the feedline about 20 feet from the
> > tuner.
> > >
> > > To my great surprise, the signal from the oscillator was much weaker
> > with the T-network +
> > > balun than with the Matchbox!
> > >
> > > Signals the same, 'noise' weaker. So much for the need for 'truly
> > balanced' tuners!
> > >
> > ______________________________________________________________
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> > Post: mailto:[hidden email]
> >
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> >
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Geoffrey Mackenzie-Kennedy-3

Re: K3 power reduction due to high SWR

In reply to this post by Vic Rosenthal

Vic,

Before you write off "truly balanced tuners" in favour of the T-network +
balun <g>, it would be interesting to measure and compare the current in
each wire of the feeder (while transmitting a carrier) when using the
Matchbox and then the T-network + balun?

73,
Geoff
LX2AO

On April 05, 2012 18:28 +0200, Vic K2VCO wrote:

<snip>

> But here is the surprising part: I expected that the Matchbox would
> provide better
> balance, which would reduce radiation and pickup from the feedline. To
> test this, I
> coupled a grid-dip oscillator to the feedline about 20 feet from the
> tuner.
>
> To my great surprise, the signal from the oscillator was much weaker with
> the T-network +
> balun than with the Matchbox!
>
> Signals the same, 'noise' weaker. So much for the need for 'truly
> balanced' tuners!

Vic Rosenthal

Re: K3 power reduction due to high SWR

I am not sure I know how to do this. I have a device that I made
<http://www.qsl.net/k2vco/sniffer/rfsniffer.html>
to measure current but it gave me anomalous results when I tried it on the matchbox. I
found that when I measured the currents about 4 inches from the matchbox they were equal,
but when I measured them two feet away they were significantly different. So there is
something I don't understand about this process.

On 4/6/2012 9:16 AM, Geoffrey Mackenzie-Kennedy wrote:

> Vic,
>
> Before you write off "truly balanced tuners" in favour of the T-network + balun <g>, it
> would be interesting to measure and compare the current in each wire of the feeder (while
> transmitting a carrier) when using the Matchbox and then the T-network + balun?
>
> 73,
> Geoff
> LX2AO
>
>
> On April 05, 2012 18:28 +0200, Vic K2VCO wrote:
>
>
> <snip>
>
>> But here is the surprising part: I expected that the Matchbox would provide better
>> balance, which would reduce radiation and pickup from the feedline. To test this, I
>> coupled a grid-dip oscillator to the feedline about 20 feet from the tuner.
>>
>> To my great surprise, the signal from the oscillator was much weaker with the T-network +
>> balun than with the Matchbox!
>>
>> Signals the same, 'noise' weaker. So much for the need for 'truly balanced' tuners!
>

Guy, K2AV

Re: K3 power reduction due to high SWR

Vic et al,

The currents on a particular wire of a two wire feedline, will always
be the vector sum of differential current and common mode current.
This is not the same thing as forward and reflected, which are both
expressed in the differential current. The tuner will be able to
control the differential current "leaving" the tuner. It will NOT be
able to control the common mode current. The common mode current can
occur because the TERMINATION of the feedline is flawed at the antenna
or a balanced to coax junction. Or common mode current can occur
simply because it is induced by the antenna, because the feedline is a
conductor in the vicinity of the antenna and the relationship of the
physical placements of antenna and feedline favor induction.

The tuner IMHO is least likely to be the major malefactor in a case of
unbalanced currents on a feedline. What occurs out at and toward the
feedpoint has been mildly astounding in cases I have helped solve. I
have had that problem personally, and had to deal with beating a
common mode issue on a balanced line that was putting 900 volts RF
across a balun blocking path at QRO and destroying the balun in the
process.

The common mode path of a balanced feedline is a big antenna, and THE
ENTIRE LENGTH of the feedline should be modeled as a single conductor
along with the antenna, just to see what is being induced. This
includes grounding in the shack if your tuner has a grounded center
point which effectively grounds common mode current. Other tuners
will present anything from a brute force common mode block to a
resistive path to ground. From the tuner's treatment of incoming
common mode, its direct grounding, or resistive path to ground, or
open circuit to ground, needs to be put in the model.

I had to do all of that to dig my way out of my problem.

Note, you can't buy broadband RF common mode blocks for balanced line
at Radio Shack. Nor anywhere else, for that matter, that I've been
able to find.

73, Guy.

On Fri, Apr 6, 2012 at 12:24 PM, Vic K2VCO <[hidden email]> wrote:

> I am not sure I know how to do this. I have a device that I made
> <http://www.qsl.net/k2vco/sniffer/rfsniffer.html>
> to measure current but it gave me anomalous results when I tried it on the matchbox. I
> found that when I measured the currents about 4 inches from the matchbox they were equal,
> but when I measured them two feet away they were significantly different. So there is
> something I don't understand about this process.
>
>
> On 4/6/2012 9:16 AM, Geoffrey Mackenzie-Kennedy wrote:
>> Vic,
>>
>> Before you write off "truly balanced tuners" in favour of the T-network + balun <g>, it
>> would be interesting to measure and compare the current in each wire of the feeder (while
>> transmitting a carrier) when using the Matchbox and then the T-network + balun?
>>
>> 73,
>> Geoff
>> LX2AO
>>
>>
>> On April 05, 2012 18:28 +0200, Vic K2VCO wrote:
>>
>>
>> <snip>
>>
>>> But here is the surprising part: I expected that the Matchbox would provide better
>>> balance, which would reduce radiation and pickup from the feedline. To test this, I
>>> coupled a grid-dip oscillator to the feedline about 20 feet from the tuner.
>>>
>>> To my great surprise, the signal from the oscillator was much weaker with the T-network +
>>> balun than with the Matchbox!
>>>
>>> Signals the same, 'noise' weaker. So much for the need for 'truly balanced' tuners!
>>
>
> --
> Vic, K2VCO
> Fresno CA
> http://www.qsl.net/k2vco/
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

Geoffrey Mackenzie-Kennedy-3

Re: K3 power reduction due to high SWR

In reply to this post by Vic Rosenthal

Did the "Sniffer" give you similar anomalous results when you were using the
T-network + balun? Also I assume that the indoor run of 450 ohm window line
well clear of any object which could affect it.

I suggest that we "go off List" should you like to discuss this further.

73,
Geoff
LX2AO

On April 06, 2012 at 18:24 +0200, Vic K2VCO wrote:

>I am not sure I know how to do this. I have a device that I made
> <http://www.qsl.net/k2vco/sniffer/rfsniffer.html>
> to measure current but it gave me anomalous results when I tried it on the
> matchbox. I found that when I measured the currents about 4 inches from
> the matchbox they were equal, but when I measured them two feet away they
> were significantly different. So there is something I don't understand
> about this process.

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