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[K3] KAT3 and 160 with 40m long doublet

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Stephen Prior

[K3] KAT3 and 160 with 40m long doublet

I have only just recently added the KAT3 and I'm very impressed with it, but
given the praise heaped upon it by others I'm slightly surprised that the
best VSWR I can get on 160m is about 8:1. The antenna is approximately a
doublet which is a half wave long on 80m I say 'approximately' as it's
slightly off-centre fed. I have about 7m of 300 ohm slotted down from the
feedpoint and then into a coaxial choke at roof level for the remaining 10m
into the back of the K3. Substituting the straight connection for a 4:1
balun (Guanella) at the transition between the slotted feeder and the coax
helps slightly but not by much.

Unfortunately I don't have a vector analyser, so I have no idea of the
nature of the reactance that the K3 is seeing. However, given the
wavelength involved, I would need to add a very significant length of
coaxial cable if I were to swing the point around the Smith Chart.

I have tried to manually tune the KAT3, but unless I am missing something,
I am am not able to change the L and C values at the same time as
transmitting, so it's a very tedious process.

Tomorrow I may well add some extra wire to hang vertically down from the
ends of the doublet. In the meantime I would be pleased to hear any
comments.

Happy New Year!

73 Stephen, G4SJP

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K5DNL

Re: [K3] KAT3 and 160 with 40m long doublet

Stephen,

What is the SWR without the tuner ?

73 Ken K5DNL
----------------------------------------------------------

--- On Sun, 1/2/11, Stephen Prior <[hidden email]> wrote:

> From: Stephen Prior <[hidden email]>
> Subject: [Elecraft] [K3] KAT3 and 160 with 40m long doublet
> To: "elecraft" <[hidden email]>
> Date: Sunday, January 2, 2011, 1:31 PM
> I have only just recently added the
> KAT3 and I'm very impressed with it, but
> given the praise heaped upon it by others I'm slightly
> surprised that the
> best VSWR I can get on 160m is about 8:1. The antenna
> is approximately a
> doublet which is a half wave long on 80m I say
> 'approximately' as it's
> slightly off-centre fed. I have about 7m of 300 ohm
> slotted down from the
> feedpoint and then into a coaxial choke at roof level for
> the remaining 10m
> into the back of the K3. Substituting the straight
> connection for a 4:1
> balun (Guanella) at the transition between the slotted
> feeder and the coax
> helps slightly but not by much.
>
> Unfortunately I don't have a vector analyser, so I
> have no idea of the
> nature of the reactance that the K3 is seeing.
> However, given the
> wavelength involved, I would need to add a very significant
> length of
> coaxial cable if I were to swing the point around the Smith
> Chart.
>
> I have tried to manually tune the KAT3, but unless I
> am missing something,
> I am am not able to change the L and C values at the same
> time as
> transmitting, so it's a very tedious process.
>
> Tomorrow I may well add some extra wire to hang vertically
> down from the
> ends of the doublet. In the meantime I would be
> pleased to hear any
> comments.
>
> Happy New Year!
>
> 73 Stephen, G4SJP
>
>
>
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Re: [K3] KAT3 and 160 with 40m long doublet

In reply to this post by Stephen Prior

That is a really tough antenna to match for 160 Stephen. The classic way to use
an 80 meter dipole on 160 is to short the feed line at a ground point and feed
it with the center conductor with the braid to the best counter poise you can
manage. This will make you a T topped Marconi which will probably tune for you.
Willis 'Cookie' Cooke
K5EWJ

________________________________
From: Stephen Prior <[hidden email]>
To: elecraft <[hidden email]>
Sent: Sun, January 2, 2011 1:31:06 PM
Subject: [Elecraft] [K3] KAT3 and 160 with 40m long doublet

I have only just recently added the KAT3 and I'm very impressed with it, but
given the praise heaped upon it by others I'm slightly surprised that the
best VSWR I can get on 160m is about 8:1. The antenna is approximately a
doublet which is a half wave long on 80m I say 'approximately' as it's
slightly off-centre fed. I have about 7m of 300 ohm slotted down from the
feedpoint and then into a coaxial choke at roof level for the remaining 10m
into the back of the K3. Substituting the straight connection for a 4:1
balun (Guanella) at the transition between the slotted feeder and the coax
helps slightly but not by much.

Unfortunately I don't have a vector analyser, so I have no idea of the
nature of the reactance that the K3 is seeing. However, given the
wavelength involved, I would need to add a very significant length of
coaxial cable if I were to swing the point around the Smith Chart.

I have tried to manually tune the KAT3, but unless I am missing something,
I am am not able to change the L and C values at the same time as
transmitting, so it's a very tedious process.

Tomorrow I may well add some extra wire to hang vertically down from the
ends of the doublet. In the meantime I would be pleased to hear any
comments.

Happy New Year!

73 Stephen, G4SJP

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Jim Brown-10

Re: [K3] KAT3 and 160 with 40m long doublet

In reply to this post by Stephen Prior

On 1/2/2011 11:31 AM, Stephen Prior wrote:
> In the meantime I would be pleased to hear any
> comments.

The condition you describe is not at all surprising for an antenna
that's half the length it needs to be for an acceptable match.

73, Jim K9YC
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Stephen Prior

Re: [K3] KAT3 and 160 with 40m long doublet

I guess I feel rather foolish. Why I should have expected the KAT3 to
cope I don't know, perhaps I have been swayed by the reports of others who
have claimed that the KAT3 would load anything anywhere! I shall have to
lengthen the antenna.

I don't have a good enough ground to feed the antenna as a Marconi so my
options other than lengthening the antenna are rather limited. I'm not
limited by space so much as by a very convenient distance between two tall
trees!

73 Stephen G4SJP

Let us consider the topic closed!

On 02/01/2011 19:51, "Jim Brown" <[hidden email]> wrote:

>
>On 1/2/2011 11:31 AM, Stephen Prior wrote:
>> In the meantime I would be pleased to hear any
>> comments.
>
>The condition you describe is not at all surprising for an antenna
>that's half the length it needs to be for an acceptable match.
>
>73, Jim K9YC
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David Cutter

Re: [K3] KAT3 and 160 with 40m long doublet

In reply to this post by Stephen Prior

I used a low and bent doublet of 2 x 88ft per section for a while and it
"tuned" up amazingly well on all bands 160 to 10 with the KAT3. As a rule I
like to use multi-band doublets away from any obvious in-band resonances, so
that it doesn't experience very high Z anywhere, so, adding a bit on each
end and stringing them wherever they will sensibly go should work for you.
A choke in the coax feed is good.

David
G3UNA

I have only just recently added the KAT3 and I'm very impressed with it, but
given the praise heaped upon it by others I'm slightly surprised that the
best VSWR I can get on 160m is about 8:1. The antenna is approximately a
doublet which is a half wave long on 80m I say 'approximately' as it's
slightly off-centre fed. I have about 7m of 300 ohm slotted down from the
feedpoint and then into a coaxial choke at roof level for the remaining 10m
into the back of the K3. Substituting the straight connection for a 4:1
balun (Guanella) at the transition between the slotted feeder and the coax
helps slightly but not by much.

Tomorrow I may well add some extra wire to hang vertically down from the
ends of the doublet. In the meantime I would be pleased to hear any
comments.

Happy New Year!

73 Stephen, G4SJP

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Dr. Detlef Petrausch

Re: [K3] KAT3 and 160 with 40m long doublet

In reply to this post by Jim Brown-10

That's not correct.
I use a 40.8 m long windom and it's no problem to tune to a swr abt. 1.2
with the KAT3 on the 160m band.

73 Detlef, DL7NDF

Am 02.01.2011 20:51, schrieb Jim Brown:

> On 1/2/2011 11:31 AM, Stephen Prior wrote:
>> In the meantime I would be pleased to hear any
>> comments.
> The condition you describe is not at all surprising for an antenna
> that's half the length it needs to be for an acceptable match.
>
> 73, Jim K9YC
> ______________________________________________________________
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>
>

Jim Brown-10

Re: [K3] KAT3 and 160 with 40m long doublet

In reply to this post by Stephen Prior

On 1/2/2011 12:03 PM, Stephen Prior wrote:
> I don't have a good enough ground to feed the antenna as a Marconi so my
> options other than lengthening the antenna are rather limited.

Don't give up so easily. In Chicago, I used a big wrought iron fence
plus a dozen or so 30 ft long wires as counterpoise for a Marconi; KK9H
has used the HVAC ducts in his home. ANY counterpoise is better than NO
counterpoise. In another installation, I've run as many fairly short
wires as I could from the base of the antenna, connected them together,
and to the coax shield. Was it as good as 70 quarter-wave radials? Of
course not. Did the antenna work well enough for me to have a lot of
fun? Yup!

My Marconi was a 100 ft long center-fed dipole with loading coils to
resonate it on 80M. Just for fun, I tried loading it as a dipole on 160.
Performance was wretched. Using it as a Marconi gave me signal reports
at least 10dB better.

73, Jim K9YC
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Re: [K3] KAT3 and 160 with 40m long doublet

Jim, a large iron deposit lies north and west of Chicago, so verticals work very
well in many areas around Chicago. I live on the Texas Gulf Coast which is salt
laden gumbo from an ancient sea and verticals work very well here. I don't know
about Stephen's area of the UK, but I will easily accept his experience that
verticals don't work well there.
Willis 'Cookie' Cooke
K5EWJ

________________________________
From: Jim Brown <[hidden email]>
To: [hidden email]
Sent: Sun, January 2, 2011 3:42:12 PM
Subject: Re: [Elecraft] [K3] KAT3 and 160 with 40m long doublet

On 1/2/2011 12:03 PM, Stephen Prior wrote:
> I don't have a good enough ground to feed the antenna as a Marconi so my
> options other than lengthening the antenna are rather limited.

Don't give up so easily. In Chicago, I used a big wrought iron fence
plus a dozen or so 30 ft long wires as counterpoise for a Marconi; KK9H
has used the HVAC ducts in his home. ANY counterpoise is better than NO
counterpoise. In another installation, I've run as many fairly short
wires as I could from the base of the antenna, connected them together,
and to the coax shield. Was it as good as 70 quarter-wave radials? Of
course not. Did the antenna work well enough for me to have a lot of
fun? Yup!

My Marconi was a 100 ft long center-fed dipole with loading coils to
resonate it on 80M. Just for fun, I tried loading it as a dipole on 160.
Performance was wretched. Using it as a Marconi gave me signal reports
at least 10dB better.

73, Jim K9YC
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Tony Estep

Re: [K3] KAT3 and 160 with 40m long doublet

In reply to this post by Dr. Detlef Petrausch

On Sun, Jan 2, 2011 at 3:18 PM, Dr. Detlef Petrausch <[hidden email]>wrote:

> I use a 40.8 m long windom and it's no problem to tune to a swr abt. 1.2
> with the KAT3 on the 160m band....

Yep, similar results here. I have used 7 different ATUs and the KAT3 is the
best by far. The antenna can be way shorter than 1/2 wave and still tune up
fine. No loading scheme is needed. A short antenna just presents a
capacitive reactance (a -j value) to the tuner, which in my experience the
KAT3 has always been able to deal with.

According to my antenna analyzer, on some frequencies my antennas present
reactive loads that put an SWR on the coax up to about 20:1. But I have only
a short run of coax between balun and transmitter, so the loss is low.

However, when the load presents a lot of reactance, I have found that it has
been helpful in certain antenna setups to have a good counterpoise
arrangement where the balanced feedline comes into the shack and goes into
the balun. The counterpoise doesn't have to be resonant, nor does it need to
be elaborate.

Tony KT0NY
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David Cutter

Re: [K3] KAT3 and 160 with 40m long doublet

In reply to this post by Cookie

It's very patchy: there are areas of huge clay deposits stretching for miles
and very deep; I've forgotten the geological term for it, but I understand
it was pushed into place by the last ice age; good for low loss low angle
radiation I understand. There are also large areas of sand stone which is
pretty hopeless for anything radio they tell me. Looking at the geology
around Stephen I'd say it wasn't too good, however the sea isn't far away so
the take off to the States is quite good if the immediate area around the
antenna could be made efficient. Isn't the internet wonderful?

David
G3UNA

I don't know
about Stephen's area of the UK, but I will easily accept his experience that
verticals don't work well there.
Willis 'Cookie' Cooke

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Guy, K2AV

Re: [K3] KAT3 and 160 with 40m long doublet

The real issue with verticals over bad "ground" of that sort is to
couple as little of it as possible. There is good evidence that DENSE
elevated radials are effective over really bad earth. Since "dense"
and "elevated" coupled together can easily be one of those
easy-to-say-and-don't-dare-do situations practically, the possibility
may make little difference.

73, Guy.

On Sun, Jan 2, 2011 at 6:07 PM, David Cutter <[hidden email]> wrote:

> It's very patchy: there are areas of huge clay deposits stretching for miles
> and very deep; I've forgotten the geological term for it, but I understand
> it was pushed into place by the last ice age; good for low loss low angle
> radiation I understand. There are also large areas of sand stone which is
> pretty hopeless for anything radio they tell me. Looking at the geology
> around Stephen I'd say it wasn't too good, however the sea isn't far away so
> the take off to the States is quite good if the immediate area around the
> antenna could be made efficient. Isn't the internet wonderful?
>
> David
> G3UNA
>
>
>
> I don't know
> about Stephen's area of the UK, but I will easily accept his experience that
> verticals don't work well there.
> Willis 'Cookie' Cooke
>
> ______________________________________________________________
> Elecraft mailing list
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Don Wilhelm-4

Re: [K3] KAT3 and 160 with 40m long doublet

In reply to this post by Tony Estep

The length of the radiator is only half the story. Unless the
feedline is matched to the impedance at the antenna feedpoint, there
will be SWR on the transmission line.
When there is SWR on the transmission line, the type of line and its
length become important when comparing whether any given antenna will
work the same as any other antenna of the same length.
So if you do not state the type and length of your feedline, it is like
comparing apples to oranges.
If you do not understand this phenomenon, take a look at the Antenna,
Transmission Line, Tuner article on y website www.w3fpr.com.

*If* it just so happens that the KAT3 cannot tune a particular antenna,
then the impedance in the shack may be very low or very high (out of the
range of the tuner). Adding or subtracting a 1/8 wavelength of feedline
will often bring it into range, and that is normally the easiest
solution if the only thing you are considering is the ability of the
tuner to produce a match.

73,
Don w3FPR

On 1/2/2011 5:39 PM, Tony Estep wrote:
> On Sun, Jan 2, 2011 at 3:18 PM, Dr. Detlef Petrausch<[hidden email]>wrote:
>
>> I use a 40.8 m long windom and it's no problem to tune to a swr abt. 1.2
>> with the KAT3 on the 160m band....
>
> Yep, similar results here. I have used 7 different ATUs and the KAT3 is the
> best by far. The antenna can be way shorter than 1/2 wave and still tune up
> fine.
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Kok Chen

Re: [K3] KAT3 and 160 with 40m long doublet

On Jan 2, 2011, at 4:01 PM, Don Wilhelm wrote:

> Adding or subtracting a 1/8 wavelength of feedline
> will often bring it into range, and that is normally the easiest
> solution if the only thing you are considering is the ability of the
> tuner to produce a match.

You can see what Don means by taking a look at this figure (KAT3 at 1.8 MHz, with Smith Chart centered at 50+i0 ohms):

http://homepage.mac.com/chen/Technical/Tuner/tuner1.8.png

Each point on the Smith Chart is a point that the KAT3 can be brought to an precise SWR of 1.0:1. The blue points are for the KAT3 cap on one side of the inductor and the green points are for the cap switch to the other end of the inductor (the KAT3 is an L tuner, with a relay K17, that switches the caps to one or the other side of the inductor).

The center of the Smith Chart circle represents an antenna with an SWR of 1.0:1. As you go out towards the circumference, you have growing circles with the same centers, with ever increasing SWR.

Notice (as Don mentioned) that when the SRW is large (towards the circumference of the Smith Chart), there are huge swaths of empty spots in the Smith Chart. These are terminations that the KAT3 can never bring to an SWR of 1.0:1.

However (again, as Don mentioned), there are large areas beyond the blue region where you can rotate yourself along on a constant SWR circle and drop yourself right into where the dense green dots are! Voila, ability to tune to an SWR of 1.0:1 while you could not do so without rotating.

How do you rotate yourself? A length of transmission line, of course!

If you remember your transmission line theory, adding a transmission line will move you along a constant radius circle centered at SWR = 1.0:1. The 1/8 wavelength that Don mentioned will rotate you by 90 degrees. In the case of the K3, you may have to try everything up to about 3/4 of a wavelength since the green and blue parts are not symmetrical. (Yes, 3/4 wavelength at 160m is no fun :-).

By the way, if you look carefully, there are SWR values outside of the blue-green Yin-Yang looking region, that are not occupied. I.e., there *will* be antennas that you will never be able to tune even if you try different transmission lines until you are blue in the face. But this plot (again, with reference center at 50 ohms) should quickly tell you which antenna is tunable at 1.8 MHz.

If you want to look at the full resolution PDF of the above plot (warning: 9.4 MB), you can use this link:

http://homepage.mac.com/chen/Technical/Tuner/tuner1.8.pdf

The points are computed by using the capacitor and inductor values of the KAT3. The KAT-100 uses slightly different L and C -- if you are interested in seeing how that tuner works, and can run Xcode on a Mac, I am more than glad to send you the source code that you can modify to produce the PDF chart for a KAT100.

The interesting thing about the KAT3 is that as you go up in frequency, the dots become sparser, but do cover the most of the Smith Chart circle out to very high SWR circles. That means that as you go up in frequency, you might not be able to tune to exactly SWR 1.0:1 but you can get close enough that it should not be a problem to tune "any" load well enough practically. For example, the KAT3 looks like this on 20m:

http://homepage.mac.com/chen/Technical/Tuner/T14080.jpg

Again, if you have Xcode loaded on your Mac (Xcode is on every Mac OS X Installer DVD, but you have to ask for it to be installed), I will be glad to send you the Xcode project so you can generate plots for any frequency that you wish.

Vy 73
Chen, W7AY

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Kok Chen

Re: [K3] KAT3 and 160 with 40m long doublet

On Jan 2, 2011, at 5:52 PM, Kok Chen wrote:

> You can see what Don means by taking a look at this figure (KAT3 at 1.8 MHz, with Smith Chart centered at 50+i0 ohms):
>
> http://homepage.mac.com/chen/Technical/Tuner/tuner1.8.png

I should add that, if memory serves (it has been a while ago that I wrote the program), the blue and green points are what an SWR 1.0:1 is transformed to by the KAT3.

An antenna that will produce a match is actually the complex conjugate of one of the blue or green points (easy to figure out on the Smith Chart).

73
Chen, W7AY

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Kok Chen

Re: [K3] KAT3 and 160 with 40m long doublet

In reply to this post by Kok Chen

On Jan 2, 2011, at 5:52 PM, Kok Chen wrote:

> In the case of the K3, you may have to try everything up to about 3/4 of a wavelength since the green and blue parts are not symmetrical. (Yes, 3/4 wavelength at 160m is no fun :-).

My mistake, that should be "everything up to 3/8 of a wavelength...". Sorry -- brain shorted to ground; aftereffects of champagne. 1/2 a wavelength will rotate you completely through 360 degrees.

73
Chen, W7AY

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k6dgw

Re: [K3] KAT3 and 160 with 40m long doublet

In reply to this post by Tony Estep

On 1/2/2011 2:39 PM, Tony Estep wrote:

> A short antenna just presents a
> capacitive reactance (a -j value) to the tuner, which in my experience the
> KAT3 has always been able to deal with.

Well ... I think it sort of depends on the antenna and the length of the
feedline if it's surge impedance isn't matched to the antenna feedpoint.
Short Marconi-T's and Inv-L's typically will have some inductive
reactance when fed at the bottom, hence the usual series cap. And, what
Z appears at the TX end of the coax depends both on the mismatch at the
feedpoint, and the length of the coax. W3FPR has suggested multiple
times that, if all you're looking for is a match by the KAT3 so your K3
will be happy and exude power, try adding 1/8 wave of coax to the line.

Of course, just getting a KAT3 match doesn't mean you're getting a lot
of power into a short antenna or that it will radiate [or receive] well.

I guess there's a reason why those old coastal marine stations had such
huge antennas :-)

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2011 Cal QSO Party 1-2 Oct 2011
- www.cqp.org
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Don Wilhelm-4

Re: [K3] KAT3 and 160 with 40m long doublet

In reply to this post by Kok Chen

Chen

Thanks for that supporting addition, and for your work on the Smith
Chart showing the KAT3 matching range for 160 meters. It is all a
matter of the physics of the situation.

As you mentioned, the matching range of the KAT3 becomes greater as the
frequency is increased.
That fact is often overlooked by many hams. It is all about the amount
of L and C available in the tuner, but the inductive or capacitive
reactance is really what counts in producing the match. If the
feedpoint in the shack has 1000 ohms of inductive reactance, and the
tuner has only 600 ohms capacitive reactance to attempt to cancel that
inductance, then a match will never happen.

For a given L, the reactance increases with frequency, and with a given
C, the reactance decreases with frequency. That can be easily seen from
the formulas for inductive and capacitive reactance - for inductance,
the "f: term is a multiplier, and for capacitors, it is a divisor.

The limiting factor for L-network tuners is usually the largest
inductance available. The capacitive component is not normally the
limiting factor because that can be made quite small (high reactance).

The KAT3 (and KAT100 and KAT2, and KAT1 and KXAT1) uses an L-match
tuning section. The required L and C values can easily be computed
using the standard formulas for an L-matching section. If the L and C
values required are greater than that available in the tuner, you have
exceeded the range of the tuner.

Instead of adding additional feedline, it is also possible to add
parallel or series capacity or inductance at the feedline connection
point to bring things into a tunable range. For those who want to
pursue the "fine points", study a bit about L-networks and conjugate
matching.

73,
Don W3FPR

On 1/2/2011 8:52 PM, Kok Chen wrote:

> On Jan 2, 2011, at 4:01 PM, Don Wilhelm wrote:
>
>> Adding or subtracting a 1/8 wavelength of feedline
>> will often bring it into range, and that is normally the easiest
>> solution if the only thing you are considering is the ability of the
>> tuner to produce a match.
> You can see what Don means by taking a look at this figure (KAT3 at 1.8 MHz, with Smith Chart centered at 50+i0 ohms):
>
> http://homepage.mac.com/chen/Technical/Tuner/tuner1.8.png
>
> Each point on the Smith Chart is a point that the KAT3 can be brought to an precise SWR of 1.0:1. The blue points are for the KAT3 cap on one side of the inductor and the green points are for the cap switch to the other end of the inductor (the KAT3 is an L tuner, with a relay K17, that switches the caps to one or the other side of the inductor).
>
> The center of the Smith Chart circle represents an antenna with an SWR of 1.0:1. As you go out towards the circumference, you have growing circles with the same centers, with ever increasing SWR.
>
> Notice (as Don mentioned) that when the SRW is large (towards the circumference of the Smith Chart), there are huge swaths of empty spots in the Smith Chart. These are terminations that the KAT3 can never bring to an SWR of 1.0:1.
>
> However (again, as Don mentioned), there are large areas beyond the blue region where you can rotate yourself along on a constant SWR circle and drop yourself right into where the dense green dots are! Voila, ability to tune to an SWR of 1.0:1 while you could not do so without rotating.
>
> How do you rotate yourself? A length of transmission line, of course!
>
> If you remember your transmission line theory, adding a transmission line will move you along a constant radius circle centered at SWR = 1.0:1. The 1/8 wavelength that Don mentioned will rotate you by 90 degrees. In the case of the K3, you may have to try everything up to about 3/4 of a wavelength since the green and blue parts are not symmetrical. (Yes, 3/4 wavelength at 160m is no fun :-).
>
> By the way, if you look carefully, there are SWR values outside of the blue-green Yin-Yang looking region, that are not occupied. I.e., there *will* be antennas that you will never be able to tune even if you try different transmission lines until you are blue in the face. But this plot (again, with reference center at 50 ohms) should quickly tell you which antenna is tunable at 1.8 MHz.
>
> If you want to look at the full resolution PDF of the above plot (warning: 9.4 MB), you can use this link:
>
> http://homepage.mac.com/chen/Technical/Tuner/tuner1.8.pdf
>
> The points are computed by using the capacitor and inductor values of the KAT3. The KAT-100 uses slightly different L and C -- if you are interested in seeing how that tuner works, and can run Xcode on a Mac, I am more than glad to send you the source code that you can modify to produce the PDF chart for a KAT100.
>
> The interesting thing about the KAT3 is that as you go up in frequency, the dots become sparser, but do cover the most of the Smith Chart circle out to very high SWR circles. That means that as you go up in frequency, you might not be able to tune to exactly SWR 1.0:1 but you can get close enough that it should not be a problem to tune "any" load well enough practically. For example, the KAT3 looks like this on 20m:
>
> http://homepage.mac.com/chen/Technical/Tuner/T14080.jpg
>
> Again, if you have Xcode loaded on your Mac (Xcode is on every Mac OS X Installer DVD, but you have to ask for it to be installed), I will be glad to send you the Xcode project so you can generate plots for any frequency that you wish.
>
> Vy 73
> Chen, W7AY
>

n7ws

Re: [K3] KAT3 and 160 with 40m long doublet

In reply to this post by Tony Estep

Don't you mean "to the transmission line"?

A quarter-wavelength line between the antenna and tuner makes that -j into a +j.

Wes N7WS

--- On Sun, 1/2/11, Tony Estep <[hidden email]> wrote:

>
> The antenna can be way shorter than 1/2 wave
> and still tune up
> fine. No loading scheme is needed. A short antenna just
> presents a
> capacitive reactance (a -j value) to the tuner,.............

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n7ws

Re: [K3] KAT3 and 160 with 40m long doublet

In reply to this post by Don Wilhelm-4

Sort of sounds logical.... but it's wrong.

Let the load in the shack be 50 +j1000.

A low-pass L-net with a shunt Xc = -j501 and series Xl = j1000 will do it.

Wes N7WS

--- On Sun, 1/2/11, Don Wilhelm <[hidden email]> wrote:

> As you mentioned, the matching range of the KAT3 becomes
> greater as the
> frequency is increased.
> That fact is often overlooked by many hams. It is all
> about the amount
> of L and C available in the tuner, but the inductive or
> capacitive
> reactance is really what counts in producing the
> match. If the
> feedpoint in the shack has 1000 ohms of inductive
> reactance, and the
> tuner has only 600 ohms capacitive reactance to attempt to
> cancel that
> inductance, then a match will never happen.