Elecraft › [HAM]

OT: Need Antenna Tuning Help

Classic

List

Threaded

22 messages Options

Jim Bennett

OT: Need Antenna Tuning Help

I've got a K3 and a three month old KPA500. Trying to get 5BWAS; 80 meters is my biggest hurdle. I put up an 80 meter Inverted L several months ago - prior to getting the KPA500. The vertical part of the antenna is 40 feet in length. I had been using two radials, about 14 inches above ground - small lot, CC&R's, HOA, etc. The antenna worked fairly well with my K3 and the internal tuner. I had done some pruning of the radials to get it resonant on 3.550. The K3 tuner took care of the rest. Well, along came the KPA500 and as yet, no KAT500. So I started looking at the antenna to see what I could do. I opted to replace the two single radial wires with a K2AV Folded CounterPoise (FCP). Not sure if this was a mistake or not. Everything I've read said that the FCP approach on 80 / 160 meter Inverted L antennas would result in a greatly improved signal. What has happened is that I cannot for the life of me get this thing resonant around 3.520. And yes, I did build the isolation tran
sformer, per the instructions.

Here is what is happening and I am certainly perplexed. I'm using an MFJ-259B meter, at the shack end, to take my readings. I get TWO SWR nulls. Yes, two. One is at 3.461 and has R=35, X-0, and SWR of 1.3. The second null is at 3.654, R=0, X=1, SWR=1.0. In an attempt to get the antenna resonant at 3.520 or so, I started adjusting the length of the antenna. Adding wire to it makes the two "nulls" go down in frequency, as I would expect. If I instead shorten the antenna wire, the "resonant frequencies" both go up. However, there comes a point with both approaches where the change of frequency stops, but the SWR goes up.

As you can guess, I am NOT an antenna expert. Why do I get two different resonant frequencies, separated by only 200 KHz?

I've spent the better part of two days futzing around with this thing and am about at my wit's end. I don't necessarily want to toss the entire FCP assembly in the trash, and go back to the two radials, but this is not going as I'd hoped! If someone on this list who has a good handle on wire antenna tuning can give me some pointers and/or hints, off the list, I'd certainly appreciate it. :-)

Regards, Jim / W6JHB
______________________________________________________________
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

Fred Townsend

Re: OT: Need Antenna Tuning Help

Jim:
You need to pay attention to your numbers. "R=0, X=1, SWR=1.0" is a short
circuit with a short piece of wire. While it is possible to have multiple
resonances and multiple nulls this not the case here. You have a major
problem. Perhaps something is breaking down or perhaps you have made a
construction error. Recheck everything. Use a simple ohm meter to check for
shorts and continuity. If that doesn't find your problem prove your
transmission line by putting a 50 ohm dummy load at end of your coax
(antenna end) and check with your MFJ259. It should say 50 j0. If it does
inspect your antenna carefully. Make sure your insulators insulate.
Whatever you do don't hook up the KPA500 until you fix this problem. Let us
know how you come out.
73
Fred, AE6QL

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Jim Bennett
Sent: Tuesday, February 28, 2012 2:23 PM
To: [hidden email]
Subject: [Elecraft] OT: Need Antenna Tuning Help

I've got a K3 and a three month old KPA500. Trying to get 5BWAS; 80 meters
is my biggest hurdle. I put up an 80 meter Inverted L several months ago -
prior to getting the KPA500. The vertical part of the antenna is 40 feet in
length. I had been using two radials, about 14 inches above ground - small
lot, CC&R's, HOA, etc. The antenna worked fairly well with my K3 and the
internal tuner. I had done some pruning of the radials to get it resonant on
3.550. The K3 tuner took care of the rest. Well, along came the KPA500 and
as yet, no KAT500. So I started looking at the antenna to see what I could
do. I opted to replace the two single radial wires with a K2AV Folded
CounterPoise (FCP). Not sure if this was a mistake or not. Everything I've
read said that the FCP approach on 80 / 160 meter Inverted L antennas would
result in a greatly improved signal. What has happened is that I cannot for
the life of me get this thing resonant around 3.520. And yes, I did build
the isolation tran sformer, per the instructions.

Here is what is happening and I am certainly perplexed. I'm using an
MFJ-259B meter, at the shack end, to take my readings. I get TWO SWR nulls.
Yes, two. One is at 3.461 and has R=35, X-0, and SWR of 1.3. The second null
is at 3.654, R=0, X=1, SWR=1.0. In an attempt to get the antenna resonant at
3.520 or so, I started adjusting the length of the antenna. Adding wire to
it makes the two "nulls" go down in frequency, as I would expect. If I
instead shorten the antenna wire, the "resonant frequencies" both go up.
However, there comes a point with both approaches where the change of
frequency stops, but the SWR goes up.

As you can guess, I am NOT an antenna expert. Why do I get two different
resonant frequencies, separated by only 200 KHz?

I've spent the better part of two days futzing around with this thing and am
about at my wit's end. I don't necessarily want to toss the entire FCP
assembly in the trash, and go back to the two radials, but this is not going
as I'd hoped! If someone on this list who has a good handle on wire antenna
tuning can give me some pointers and/or hints, off the list, I'd certainly
appreciate it. :-)

Regards, Jim / W6JHB

______________________________________________________________
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

k6dgw

Re: OT: Need Antenna Tuning Help

In reply to this post by Jim Bennett

On 2/28/2012 2:22 PM, Jim Bennett wrote:

>
> I get TWO SWR
> nulls. Yes, two. One is at 3.461 and has R=35, X-0, and SWR of 1.3.
> The second null is at 3.654, R=0, X=1, SWR=1.0.

You have something seriously wrong, 0+j1 ohms is a short circuit, or
extremely close to one. I'm sure the SWR reading at that point is
bogus, the MFJ was not designed to operate into a short circuit. In
fact, the apparent "short circuit" could be bogus, I've gotten some very
improbable results a few times with my MFJ.

I'd suggest:

1. Take your MFJ259 out to the feedpoint of the antenna and see what
you get.

2. Put a dummy load at the antenna end of your coax run and measure the
impedance at the shack end. It should be 50+j0 ohms everywhere [within
reason]

3. Check the SWR with your K3 with the tuner in bypass at 3501 and up
the band a few places and draw a graph of the readings. Keep the power
down, you can't really hurt the K3, it'll quit making RF if it gets
really annoyed. If the null at 3461 is really the resonant point of
your antenna, you should see the SWR climbing rapidly as you go up the band.

When really weird things happen in conflict with known physics, it's
almost always a simple error in the system or measurement configuration.
I'd look carefully at the wiring. Let us all know what you find, I'd
like to write it into my notebook for future ref.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2012 Cal QSO Party 6-7 Oct 2012
- www.cqp.org

______________________________________________________________
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

Jim Bennett

Re: OT: Need Antenna Tuning Help

Well, crud - my fat fingers messed up the original post. That reading at 3.654 should have been R=50, X=1, SWR=1.0. I'll take the MFJ out to the antenna base and see what I get.

On Tuesday, Feb 28, 2012, at Tuesday, 3:43 PM, Fred Jensen wrote:

> On 2/28/2012 2:22 PM, Jim Bennett wrote:
>
>>
>> I get TWO SWR
>> nulls. Yes, two. One is at 3.461 and has R=35, X-0, and SWR of 1.3.
>> The second null is at 3.654, R=0, X=1, SWR=1.0.
>
> You have something seriously wrong, 0+j1 ohms is a short circuit, or
> extremely close to one. I'm sure the SWR reading at that point is
> bogus, the MFJ was not designed to operate into a short circuit. In
> fact, the apparent "short circuit" could be bogus, I've gotten some very
> improbable results a few times with my MFJ.
>
> I'd suggest:
>
> 1. Take your MFJ259 out to the feedpoint of the antenna and see what
> you get.
>
> 2. Put a dummy load at the antenna end of your coax run and measure the
> impedance at the shack end. It should be 50+j0 ohms everywhere [within
> reason]
>
> 3. Check the SWR with your K3 with the tuner in bypass at 3501 and up
> the band a few places and draw a graph of the readings. Keep the power
> down, you can't really hurt the K3, it'll quit making RF if it gets
> really annoyed. If the null at 3461 is really the resonant point of
> your antenna, you should see the SWR climbing rapidly as you go up the band.
>
> When really weird things happen in conflict with known physics, it's
> almost always a simple error in the system or measurement configuration.
> I'd look carefully at the wiring. Let us all know what you find, I'd
> like to write it into my notebook for future ref.
>
> 73,
>
> Fred K6DGW
> - Northern California Contest Club
> - CU in the 2012 Cal QSO Party 6-7 Oct 2012
> - www.cqp.org
>
>
> ______________________________________________________________
> 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

Don Wilhelm-4

Re: OT: Need Antenna Tuning Help

In reply to this post by Jim Bennett

Jim,

I did a little chatting with Guy K2AV when he was starting to work on
that project (W0UCE lives only a few miles from me), and I recall that
changing the height above ground changed the behavior.
So if you do not have the lowest wire 8 feet above the ground, it will
not be tuned properly.
Maybe Guy will comment, he frequently posts on this reflector.

73,
Don W3FPR

On 2/28/2012 5:22 PM, Jim Bennett wrote:
> I've got a K3 and a three month old KPA500. Trying to get 5BWAS; 80 meters is my biggest hurdle. I put up an 80 meter Inverted L several months ago - prior to getting the KPA500. The vertical part of the antenna is 40 feet in length. I had been using two radials, about 14 inches above ground - small lot, CC&R's, HOA, etc. The antenna worked fairly well with my K3 and the internal tuner. I had done some pruning of the radials to get it resonant on 3.550. The K3 tuner took care of the rest. Well, along came the KPA500 and as yet, no KAT500. So I started looking at the antenna to see what I could do. I opted to replace the two single radial wires with a K2AV Folded CounterPoise (FCP). Not sure if this was a mistake or not. Everything I've read said that the FCP approach on 80 / 160 meter Inverted L antennas would result in a greatly improved signal. What has happened is that I cannot for the life of me get this thing resonant around 3.520. And yes, I did build the isolation tr
an
> sformer, per the instructions.
>
> Here is what is happening and I am certainly perplexed. I'm using an MFJ-259B meter, at the shack end, to take my readings. I get TWO SWR nulls. Yes, two. One is at 3.461 and has R=35, X-0, and SWR of 1.3. The second null is at 3.654, R=0, X=1, SWR=1.0. In an attempt to get the antenna resonant at 3.520 or so, I started adjusting the length of the antenna. Adding wire to it makes the two "nulls" go down in frequency, as I would expect. If I instead shorten the antenna wire, the "resonant frequencies" both go up. However, there comes a point with both approaches where the change of frequency stops, but the SWR goes up.
>
> As you can guess, I am NOT an antenna expert. Why do I get two different resonant frequencies, separated by only 200 KHz?
>
> I've spent the better part of two days futzing around with this thing and am about at my wit's end. I don't necessarily want to toss the entire FCP assembly in the trash, and go back to the two radials, but this is not going as I'd hoped! If someone on this list who has a good handle on wire antenna tuning can give me some pointers and/or hints, off the list, I'd certainly appreciate it. :-)
>

______________________________________________________________
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

Guy, K2AV

Re: OT: Need Antenna Tuning Help

In reply to this post by Jim Bennett

Guess FCP as a concept has hit the big time if it's being bandied on
Elecraft reflector. :>)

We do not have much feedback from 80 meter use at all. It's been 99.9%
about 160 meters where the huge space crunch hurts the worst.

You DO need to do all the measuring at the output of the isolation
transformer. Otherwise the coax can completely screw up the clues you need
to prune the thing. I'll wait to hear what you measure at the IsoT. The
only way you can correctly measure at the shack end of the coax is if you
are using an AIM 4170 and have run a remote calibration to the end of the
coax. There are some other analyzing devices that can do the remote
measure thing besides the AIM. The program that runs with the analyzer
keeps the calibration data for that specific piece of coax and then uses a
mathematical transformation to adjust out the effects of the coax. Cannot
do that with the MFJ analyzers.

On another issue, it was not clear from your post, but understand that a
+/- 33 foot FCP is a 160 meter device only and the isolation transformer
for that is 20 bifilar turns, and you will need something in the order of
magnitude of 125 feet in the "L" to resonate.

For 80 meters ONLY, the FCP is +/- 16 feet, and the isolation transformer
is 15 bifilar turns to work with something in the order of 60-65 feet.
You can use the 20 turn, but electrically it has a lot more leftover
inductance, and most likely runs with shorter L's for the "simple"
configuration. If you were doing that, you would be the first "guinea pig"
on how to use the 160 IsoT on 80 meters. Nobody has figured out how to do
a dual band FCP, nor can you just put them in parallel. You might get an
impedance dip, but the field cancelling effect that makes an FCP work is
simply absent off-band, and the ground loss is back.

The "simple" configuration is the FCP, the isolation transformer and
something approximately a quarterwave L, whose length gets adjusted to
bring the zero reactance crossing point where you want it. If you want to
get into the theory, there are more complex applications, like how to do a
4 square with FCPs, while not using any radials. We are talking here about
the "simple" configuration.

The actual value of the resistance at zero reactance a given person gets
depends on the specifics of the "L" that you have up. If you get the zero
reactance point right, significantly off-50 R values can be dealt with
using a series matching transformer of 50 ohm then 75 ohm, then 50 ohm coax
rest of the way, calculated by a little free program called SMC.EXE. Most
often the basic shape of the L is dictated by available trees, staying
hidden, or..., very specific to the individual. So we don't publish
"ideal" dimensions for the L.

The double dip is possible, but explaining why without a slide show of
EZNEC graphs ain't possible for us normal mortals. Or it could just be an
effect of your specifics and the length of your coax.

I would like to know the specific dimensions of your L.

If you are getting 50 +j1 at 3654, then the current wisdom is you need to
add length to force it down. But we don't have 80 meter information on how
far down you can force it before the FCP starts to "argue with you" and
won't move any more. Moving it from 3654 to 3535 is adding something like
4 and a half feet.

My current 160 meter antenna, up 90 out 105 over a 160 FCP, has a "sort of
half-way decent" spot down around 1700, but it's nowhere close to
adjustable to 50 +j0. It's also lossy, as the FCP has flipped out of its
cancellation mode. This leads me to believe the upper dip is the one you
want to manage.

For the extended audience here, the concept is on W0UCE's web page at
http://www.w0uce.net/K2AVantennas.html

Sorry about the OT. We don't have an "FCP reflector". Reflector
discussion has been entirely on TopBand.

73, Guy K2AV.

On Tue, Feb 28, 2012 at 6:51 PM, Jim Bennett <[hidden email]> wrote:

> Well, crud - my fat fingers messed up the original post. That reading at
> 3.654 should have been R=50, X=1, SWR=1.0. I'll take the MFJ out to the
> antenna base and see what I get.
>
> On Tuesday, Feb 28, 2012, at Tuesday, 3:43 PM, Fred Jensen wrote:
>
> > On 2/28/2012 2:22 PM, Jim Bennett wrote:
> >
> >>
> >> I get TWO SWR
> >> nulls. Yes, two. One is at 3.461 and has R=35, X-0, and SWR of 1.3.
> >> The second null is at 3.654, R=0, X=1, SWR=1.0.
> >
> > You have something seriously wrong, 0+j1 ohms is a short circuit, or
> > extremely close to one. I'm sure the SWR reading at that point is
> > bogus, the MFJ was not designed to operate into a short circuit. In
> > fact, the apparent "short circuit" could be bogus, I've gotten some very
> > improbable results a few times with my MFJ.
> >
> > I'd suggest:
> >
> > 1. Take your MFJ259 out to the feedpoint of the antenna and see what
> > you get.
> >
> > 2. Put a dummy load at the antenna end of your coax run and measure the
> > impedance at the shack end. It should be 50+j0 ohms everywhere [within
> > reason]
> >
> > 3. Check the SWR with your K3 with the tuner in bypass at 3501 and up
> > the band a few places and draw a graph of the readings. Keep the power
> > down, you can't really hurt the K3, it'll quit making RF if it gets
> > really annoyed. If the null at 3461 is really the resonant point of
> > your antenna, you should see the SWR climbing rapidly as you go up the
> band.
> >
> > When really weird things happen in conflict with known physics, it's
> > almost always a simple error in the system or measurement configuration.
> > I'd look carefully at the wiring. Let us all know what you find, I'd
> > like to write it into my notebook for future ref.
> >
> > 73,
> >
> > Fred K6DGW
> > - Northern California Contest Club
> > - CU in the 2012 Cal QSO Party 6-7 Oct 2012
> > - www.cqp.org
> >
> >
> > ______________________________________________________________
> > 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
>

alsopb

Re: OT: Need Antenna Tuning Help

In reply to this post by Don Wilhelm-4

I think you have to identify which of the two resonances is due to the
antenna and not due to the antenna + feedline. Elevated radials that
exhibit resonances of their own can also be confounding.

The multiple resonance may be due to a fortunate length of coax that
presents a 50 ohm at the shack end.
You can identify which resonance is due to the antenna by attaching a
short length of coax at the antenna feed and find the resonance with
your antenna analyzer.

Then you will know if you have to add or subtract wire.

The fact that SWR "goes up" when you keep adding wires (@ complex part
=0) only means that the impedance at resonance is changing.

At resonance (complex part=0) different antennas have different values of Z

Inverted L's and verticals have Z's of 30 to 35 ohms at resonance with a
really good ground system. That isn't
an SWR of 1:1. A yagi may have a Z of 15 ohms-- hence a big SWR.

Once you have the antenna resonant where you want, then you have to deal
with the mismatch. A simple L network at the base of the antenna will
take care of the mismatch. 500 watts doesn't require monster components.

73 de Brian/K3KO

On 2/28/2012 7:20 PM, Don Wilhelm wrote:

> Jim,
>
> I did a little chatting with Guy K2AV when he was starting to work on
> that project (W0UCE lives only a few miles from me), and I recall that
> changing the height above ground changed the behavior.
> So if you do not have the lowest wire 8 feet above the ground, it will
> not be tuned properly.
> Maybe Guy will comment, he frequently posts on this reflector.
>
> 73,
> Don W3FPR
>
> On 2/28/2012 5:22 PM, Jim Bennett wrote:
>
>> I've got a K3 and a three month old KPA500. Trying to get 5BWAS; 80 meters is my biggest hurdle. I put up an 80 meter Inverted L several months ago - prior to getting the KPA500. The vertical part of the antenna is 40 feet in length. I had been using two radials, about 14 inches above ground - small lot, CC&R's, HOA, etc. The antenna worked fairly well with my K3 and the internal tuner. I had done some pruning of the radials to get it resonant on 3.550. The K3 tuner took care of the rest. Well, along came the KPA500 and as yet, no KAT500. So I started looking at the antenna to see what I could do. I opted to replace the two single radial wires with a K2AV Folded CounterPoise (FCP). Not sure if this was a mistake or not. Everything I've read said that the FCP approach on 80 / 160 meter Inverted L antennas would result in a greatly improved signal. What has happened is that I cannot for the life of me get this thing resonant around 3.520. And yes, I did build the isolation t

>>
> an
>
>> sformer, per the instructions.
>>
>> Here is what is happening and I am certainly perplexed. I'm using an MFJ-259B meter, at the shack end, to take my readings. I get TWO SWR nulls. Yes, two. One is at 3.461 and has R=35, X-0, and SWR of 1.3. The second null is at 3.654, R=0, X=1, SWR=1.0. In an attempt to get the antenna resonant at 3.520 or so, I started adjusting the length of the antenna. Adding wire to it makes the two "nulls" go down in frequency, as I would expect. If I instead shorten the antenna wire, the "resonant frequencies" both go up. However, there comes a point with both approaches where the change of frequency stops, but the SWR goes up.
>>
>> As you can guess, I am NOT an antenna expert. Why do I get two different resonant frequencies, separated by only 200 KHz?
>>
>> I've spent the better part of two days futzing around with this thing and am about at my wit's end. I don't necessarily want to toss the entire FCP assembly in the trash, and go back to the two radials, but this is not going as I'd hoped! If someone on this list who has a good handle on wire antenna tuning can give me some pointers and/or hints, off the list, I'd certainly appreciate it. :-)
>>
>>
> ______________________________________________________________
> 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
>
>
> -----
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 10.0.1424 / Virus Database: 2113/4837 - Release Date: 02/28/12
>
>
>

Guy, K2AV

Re: OT: Need Antenna Tuning Help

The original poster and I have a significant thread going off reflector,
and have been dealing with the tuning issues. A quarter-wave-ish wire over
an FCP and an isolation transformer is a complex, dual tuned impedance. It
sometimes does NOT prune simple like a dipole. We don't have a lot of
experience with the 80 meter version yet, but are making some adjustments
based on Jim's experience. We will post on the W0UCE web page when we have
it nailed down.

73, Guy.

On Thu, Mar 1, 2012 at 12:11 PM, briana <[hidden email]> wrote:

> I think you have to identify which of the two resonances is due to the
> antenna and not due to the antenna + feedline. Elevated radials that
> exhibit resonances of their own can also be confounding.
>
> The multiple resonance may be due to a fortunate length of coax that
> presents a 50 ohm at the shack end.
> You can identify which resonance is due to the antenna by attaching a
> short length of coax at the antenna feed and find the resonance with
> your antenna analyzer.
>
> Then you will know if you have to add or subtract wire.
>
> The fact that SWR "goes up" when you keep adding wires (@ complex part
> =0) only means that the impedance at resonance is changing.
>
> At resonance (complex part=0) different antennas have different values of Z
>
> Inverted L's and verticals have Z's of 30 to 35 ohms at resonance with a
> really good ground system. That isn't
> an SWR of 1:1. A yagi may have a Z of 15 ohms-- hence a big SWR.
>
> Once you have the antenna resonant where you want, then you have to deal
> with the mismatch. A simple L network at the base of the antenna will
> take care of the mismatch. 500 watts doesn't require monster components.
>
> 73 de Brian/K3KO
>
> On 2/28/2012 7:20 PM, Don Wilhelm wrote:
> > Jim,
> >
> > I did a little chatting with Guy K2AV when he was starting to work on
> > that project (W0UCE lives only a few miles from me), and I recall that
> > changing the height above ground changed the behavior.
> > So if you do not have the lowest wire 8 feet above the ground, it will
> > not be tuned properly.
> > Maybe Guy will comment, he frequently posts on this reflector.
> >
> > 73,
> > Don W3FPR
> >
> > On 2/28/2012 5:22 PM, Jim Bennett wrote:
> >
> >> I've got a K3 and a three month old KPA500. Trying to get 5BWAS; 80
> meters is my biggest hurdle. I put up an 80 meter Inverted L several months
> ago - prior to getting the KPA500. The vertical part of the antenna is 40
> feet in length. I had been using two radials, about 14 inches above ground
> - small lot, CC&R's, HOA, etc. The antenna worked fairly well with my K3
> and the internal tuner. I had done some pruning of the radials to get it
> resonant on 3.550. The K3 tuner took care of the rest. Well, along came the
> KPA500 and as yet, no KAT500. So I started looking at the antenna to see
> what I could do. I opted to replace the two single radial wires with a K2AV
> Folded CounterPoise (FCP). Not sure if this was a mistake or not.
> Everything I've read said that the FCP approach on 80 / 160 meter Inverted
> L antennas would result in a greatly improved signal. What has happened is
> that I cannot for the life of me get this thing resonant around 3.520. And
> yes, I did build the isolation t
> r
> >>
> > an
> >
> >> sformer, per the instructions.
> >>
> >> Here is what is happening and I am certainly perplexed. I'm using an
> MFJ-259B meter, at the shack end, to take my readings. I get TWO SWR nulls.
> Yes, two. One is at 3.461 and has R=35, X-0, and SWR of 1.3. The second
> null is at 3.654, R=0, X=1, SWR=1.0. In an attempt to get the antenna
> resonant at 3.520 or so, I started adjusting the length of the antenna.
> Adding wire to it makes the two "nulls" go down in frequency, as I would
> expect. If I instead shorten the antenna wire, the "resonant frequencies"
> both go up. However, there comes a point with both approaches where the
> change of frequency stops, but the SWR goes up.
> >>
> >> As you can guess, I am NOT an antenna expert. Why do I get two
> different resonant frequencies, separated by only 200 KHz?
> >>
> >> I've spent the better part of two days futzing around with this thing
> and am about at my wit's end. I don't necessarily want to toss the entire
> FCP assembly in the trash, and go back to the two radials, but this is not
> going as I'd hoped! If someone on this list who has a good handle on wire
> antenna tuning can give me some pointers and/or hints, off the list, I'd
> certainly appreciate it. :-)
> >>
> >>
> > ______________________________________________________________
> > 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
> >
> >
> > -----
> > No virus found in this message.
> > Checked by AVG - www.avg.com
> > Version: 10.0.1424 / Virus Database: 2113/4837 - Release Date: 02/28/12
> >
> >
> >
>
>
> ______________________________________________________________
> 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
>

Jim Bennett

Re: OT: Need Antenna Tuning Help

In reply to this post by Jim Bennett

Folks - back on the 28th of Feb I started this thread, looking for assistance getting the K2AV Folded CounterPoise (FCP) to work on my 80 meter Inverted L antenna. Got several good suggestions and wound up having a long series of off-line email exchanges with Guy, K2AV. With his help, we got the thing working perfectly. I now have an antenna that has a 100 kHz wide segment of the band with zero reactance, and an SWR that is 1.5:1 or below for 125 kHz.

I learned quite a bit about antenna tuning, and the fact that the MFJ-259B does NOT show minus reactance. When I put the Resistance ( R ) and Reactance ( X ) figures on a graph - they were quite whacky. Turns out that there were several negative values that I'd "assumed" as being positive. Once adjusted, the chart looked reasonable. I also had another antenna on the property, resonant on 80 meters, that was messing up the works. With Guy's guidance, I adjusted dimensions of the FCP and the Inverted L radiator and bingo - it works great!

I opted to build my own isolation transformer, saving a couple bucks. The FCP is mounted about five inches out from a property line wooden fence, about five feet off the ground. I used schedule 40 PVC pipe for the FCP wire supports. The PVC and enclosure for the isolation transformer were purchased at a local Ace Hardware. The powdered iron core and teflon wire insulation came from Amidon and the wire for the FCP and isolation transformer came from The Wireman. The W0UCE web site has detailed information, including parts information.

If you don't have room for a bazillion radials on 80 or 160 meters, by all means look into using an FCP with your Inverted L.

Many thanks to K2AV for his gracious help and his putting up with my lack of technical knowledge!
______________________________________________________________
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

Tony Estep

Re: OT: Need Antenna Tuning Help

On Thu, Mar 8, 2012 at 2:19 AM, Jim Bennett <[hidden email]> wrote:
>... the MFJ-259B does NOT show minus reactance....
===========
Gee whiz! That's pretty lame. As my favorite soccer announcer says
when a guy misses from short range, "Me pongo las manos en la cabeza."

Tony KT0NY

--
http://www.isb.edu/faculty/facultydir.aspx?ddlFaculty=352
______________________________________________________________
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

Re: OT: Need Antenna Tuning Help

I think the original statement was incorrect. The MFJ-259B does show reactance, both positive and negative, but it does not show polarity, so you have to experiment a little or add some knowledge to find out the polarity of the reactance. That is one of the reasons that the MFJ-259B is not the best antenna analyzer on the market, just a cost effective, but inexpensive antenna analyzer. My German professor when asked to explain how the science students with only 8 hours of German aced the senior German students on a major test "Man muss hab kopf!" which translates to "One must have a head" or better "One needs a brain!"

Willis 'Cookie' Cooke
K5EWJ & Trustee N5BPS, USS Cavalla, USS Stewart

________________________________
From: Tony Estep <[hidden email]>
To: [hidden email]
Sent: Thursday, March 8, 2012 9:07 AM
Subject: Re: [Elecraft] OT: Need Antenna Tuning Help

On Thu, Mar 8, 2012 at 2:19 AM, Jim Bennett <[hidden email]> wrote:
>... the MFJ-259B does NOT show minus reactance....
===========
Gee whiz! That's pretty lame. As my favorite soccer announcer says
when a guy misses from short range, "Me pongo las manos en la cabeza."

Tony KT0NY

--
http://www.isb.edu/faculty/facultydir.aspx?ddlFaculty=352
______________________________________________________________
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

Re: OT: Need Antenna Tuning Help

In reply to this post by Jim Bennett

Congratulations Jim! I have been watching this thread with interest to see how it worked out. I would like to know a bit more. Is your feed point at the same elevation as your counterpoise, or at ground level? If at ground level, describe your transition to five feet for the counterpoise. What do you use for a support and how high is your transition to horizontal? Is your transformer a true isolation transformer with two windings and DC isolation or an UnUn wound transformer? Is your powdered iron core a rod or toroid? What is the Amidon model number?

Again, congratulations! I love this kind of dialog! 73!

Willis 'Cookie' Cooke
K5EWJ & Trustee N5BPS, USS Cavalla, USS Stewart

________________________________
From: Jim Bennett <[hidden email]>
To: [hidden email]
Sent: Thursday, March 8, 2012 2:19 AM
Subject: Re: [Elecraft] OT: Need Antenna Tuning Help

Folks - back on the 28th of Feb I started this thread, looking for assistance getting the K2AV Folded CounterPoise (FCP) to work on my 80 meter Inverted L antenna. Got several good suggestions and wound up having a long series of off-line email exchanges with Guy, K2AV. With his help, we got the thing working perfectly. I now have an antenna that has a 100 kHz wide segment of the band with zero reactance, and an SWR that is 1.5:1 or below for 125 kHz.

I learned quite a bit about antenna tuning, and the fact that the MFJ-259B does NOT show minus reactance. When I put the Resistance ( R ) and Reactance ( X ) figures on a graph - they were quite whacky. Turns out that there were several negative values that I'd "assumed" as being positive. Once adjusted, the chart looked reasonable. I also had another antenna on the property, resonant on 80 meters, that was messing up the works. With Guy's guidance, I adjusted dimensions of the FCP and the Inverted L radiator and bingo - it works great!

I opted to build my own isolation transformer, saving a couple bucks. The FCP is mounted about five inches out from a property line wooden fence, about five feet off the ground. I used schedule 40 PVC pipe for the FCP wire supports. The PVC and enclosure for the isolation transformer were purchased at a local Ace Hardware. The powdered iron core and teflon wire insulation came from Amidon and the wire for the FCP and isolation transformer came from The Wireman. The W0UCE web site has detailed information, including parts information.

If you don't have room for a bazillion radials on 80 or 160 meters, by all means look into using an FCP with your Inverted L.

Many thanks to K2AV for his gracious help and his putting up with my lack of technical knowledge!
______________________________________________________________
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

Jim Bennett

Re: OT: Need Antenna Tuning Help

In reply to this post by Cookie

I stand corrected. I should have said that it simply shows numbers and it is up to the user to figure out the correct polarity. Thanks for the input.

> I think the original statement was incorrect. The MFJ-259B does show reactance, both positive and negative, but it does not show polarity, so you have to experiment a little or add some knowledge to find out the polarity of the reactance. That is one of the reasons that the MFJ-259B is not the best antenna analyzer on the market, just a cost effective, but inexpensive antenna analyzer. My German professor when asked to explain how the science students with only 8 hours of German aced the senior German students on a major test "Man muss hab kopf!" which translates to "One must have a head" or better "One needs a brain!"
>
> Willis 'Cookie' Cooke
> K5EWJ & Trustee N5BPS, USS Cavalla, USS Stewart
>
>
> ________________________________
> From: Tony Estep <[hidden email]>
> To: [hidden email]
> Sent: Thursday, March 8, 2012 9:07 AM
> Subject: Re: [Elecraft] OT: Need Antenna Tuning Help
>
> On Thu, Mar 8, 2012 at 2:19 AM, Jim Bennett <[hidden email]> wrote:
>> ... the MFJ-259B does NOT show minus reactance....
> ===========
> Gee whiz! That's pretty lame. As my favorite soccer announcer says
> when a guy misses from short range, "Me pongo las manos en la cabeza."
>
> Tony KT0NY
>
>
> --
> http://www.isb.edu/faculty/facultydir.aspx?ddlFaculty=352
> ______________________________________________________________
> 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

Re: OT: Need Antenna Tuning Help

I wouldn't have mentioned it Jim, except Tony's funny comment muddied the water some. I like humor, but I also don't want anyone to be confused by humorous dialog. I am sure Tony knows how the analyzer works. In your case, there were enough confusing factors to leave some doubt about the polarity that was not resolved without a lot of thought and experimentation. It usually is not that difficult to reason the polarity of the reactance.

Willis 'Cookie' Cooke
K5EWJ & Trustee N5BPS, USS Cavalla, USS Stewart

________________________________
From: Jim Bennett <[hidden email]>
To: Elecraft Reflector <[hidden email]>
Sent: Thursday, March 8, 2012 10:44 AM
Subject: Re: [Elecraft] OT: Need Antenna Tuning Help

I stand corrected. I should have said that it simply shows numbers and it is up to the user to figure out the correct polarity. Thanks for the input.

______________________________________________________________
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

Jim Bennett

Re: OT: Need Antenna Tuning Help

In reply to this post by Cookie

The feed point is at exactly the same elevation as the FCP - just around five feet off the ground. The FCP should have been eight feet high, but that would put it in the neighbor's cross-hairs and we live in a CC&R / HOA area, so stealth is best for me. The isolation transformer unit is loosely strapped (in it's box, of course) to the side of a redwood tree, about three feet horizontally from the FCP, which is a few inches off of the wooden property line fence. When I built the FCP, I left several feet of extra #12 AWG copper wire at the bottom end for connection to the FCP. It is that wire that runs over to one binding post on the isolation transformer. The other binding post connects to the vertical part of the Inverted L, which runs up through the limbs of the tree, approximately 31 feet, and then around 40 feet or so horizontal across the back yard. It is not perfectly horizontal - comes down on a slight angle. The antenna wire I used is #13 AWG "Silky Coat" from The Wire
man.

The transformer is a true isolation transformer - 15 bifilar turns of #14 AWG Polyimide Insulated Wire with teflon sleeving, wound on an AmidonT300A-2 powdered iron toroid. All part numbers, pictures, and a complete description can be found at: http://www.w0uce.net/K2AVantennas.html

This is really cool for me, as I'm waiting for that elusive KAT500, but I can now freely roam around the CW part of 80 meters and the KPA500 happily follows me!

Jim / W6JHB

On Thursday, Mar 8, 2012, at Thursday, 8:34 AM, WILLIS COOKE wrote:

> Congratulations Jim! I have been watching this thread with interest to see how it worked out. I would like to know a bit more. Is your feed point at the same elevation as your counterpoise, or at ground level? If at ground level, describe your transition to five feet for the counterpoise. What do you use for a support and how high is your transition to horizontal? Is your transformer a true isolation transformer with two windings and DC isolation or an UnUn wound transformer? Is your powdered iron core a rod or toroid? What is the Amidon model number?
>
> Again, congratulations! I love this kind of dialog! 73!
> Willis 'Cookie' Cooke
>

______________________________________________________________
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

Tony Estep

Re: OT: Need Antenna Tuning Help

In reply to this post by Cookie

On Thu, Mar 8, 2012 at 10:54 AM, WILLIS COOKE <[hidden email]> wrote:
> I wouldn't have mentioned it Jim, except Tony's funny comment muddied the water...
===========
Yeah, there's always some smart-aleck to confuse the issue. But
seriously, I don't see why MFJ couldn't put a minus sign or something
on the display. My cheapo Autek gadget (<$100 on ebay) tells you
series and parallel reactance with sign, equivalent C, equivalent L,
phase angle, and some other stuff as well as SWR. I'm not an
MFJ-basher; I have been happy with all the MFJ stuff I have. But in
this case IMHO they left out some worthwhile functionality.

Tony KT0NY

--
http://www.isb.edu/faculty/facultydir.aspx?ddlFaculty=352
______________________________________________________________
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

Ian Wilson

Re: OT: Need Antenna Tuning Help

The basic bridge in the MFJ - and lots of other impedance analyzers - is
insensitive to the sign of the reactive impedance. You can figure it out by
making a "small" change in frequency and seeing whether the reactance
increases or decreases. However, this takes additional software in the uP,
increases the measurement time, and guessing how large a small step
you can get away with is not trivial.

So I think that the original designer made a reasonable tradeoff. I wonder
who that was - the design was purchased by MFJ from Vectronics, I think).

73, ian K3IMW

On Thu, Mar 8, 2012 at 6:51 PM, Tony Estep <[hidden email]> wrote:

> On Thu, Mar 8, 2012 at 10:54 AM, WILLIS COOKE <[hidden email]> wrote:
> > I wouldn't have mentioned it Jim, except Tony's funny comment muddied
> the water...
> ===========
> Yeah, there's always some smart-aleck to confuse the issue. But
> seriously, I don't see why MFJ couldn't put a minus sign or something
> on the display. My cheapo Autek gadget (<$100 on ebay) tells you
> series and parallel reactance with sign, equivalent C, equivalent L,
> phase angle, and some other stuff as well as SWR. I'm not an
> MFJ-basher; I have been happy with all the MFJ stuff I have. But in
> this case IMHO they left out some worthwhile functionality.
>
> Tony KT0NY
>
>
> --
> http://www.isb.edu/faculty/facultydir.aspx?ddlFaculty=352
> ______________________________________________________________
> 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
>

Don Wilhelm-4

Re: OT: Need Antenna Tuning Help

In reply to this post by Tony Estep

Tony,

There is more to it than just putting a + or - sign on the display. The
instrument must have adequate measurements starting at the front end
reflectometer to determine the sign of the reactance. The MFJ does not
have that.

If there were a microprocessor in the instrument, and it had the
capability of electrically varying the frequency, it could move the
frequency up or down to determine the sign. The MFJ259 manual tells you
how to determine the sign by moving the frequency up or down while
watching the reactance.

73,
Don W3FPR

On 3/8/2012 1:51 PM, Tony Estep wrote:
> But seriously, I don't see why MFJ couldn't put a minus sign or
> something on the display. My cheapo Autek gadget (<$100 on ebay) tells
> you series and parallel reactance with sign, equivalent C, equivalent
> L, phase angle, and some other stuff as well as SWR. I'm not an
> MFJ-basher; I have been happy with all the MFJ stuff I have. But in
> this case IMHO they left out some worthwhile functionality. Tony KT0NY
______________________________________________________________
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

Don Wilhelm-4

Re: OT: Need Antenna Tuning Help

In reply to this post by Ian Wilson

I think you will find the original designer was Tom Rauch W8JI.

73,
Don W3FPR

On 3/8/2012 2:15 PM, Ian Wilson wrote:
> So I think that the original designer made a reasonable tradeoff. I wonder
> who that was - the design was purchased by MFJ from Vectronics, I think).
>
>
______________________________________________________________
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

Jim Bennett

Re: OT: Need Antenna Tuning Help

In reply to this post by Jim Bennett

Gary,

My L wire started out from the formula L (ft) = 234 / f (mHz). Wasn't quite long enough and wound up adding a couple feet to it. But first, we had to get to a zero reactance spot, and that meant (for my installation) adding two feet to the total wire length of the FCP, as compared to what was on the W0UCE web page. That "may" have been because my FCP is only five feet off the ground, as opposed to the recommended eight feet. You didn't say if you were making one for 80 or 160 meters. Mine was for 80, so your figures may be different. When we lengthened my L, we also added the length to the FCP. But - and I highly recommend this - make a graph of your antenna's X, R, and SWR readings before doing any pruning / tuning, after installing the FCP.

My graph showed exactly where the whole thing reached zero reactance, and it was a matter of bringing it down a few kHz from there. It also showed that I had another 80 meter antenna on my property that was being coupled to the inverted L, screwing up the entire thing! I eliminated THAT problem, and everything with the FCP and inverted L fell into place!

It is my understanding that the vertical part of an inverted L is the most important, and the more of it in the up and down plane, the better.

Good luck, and let us know how it works out for you.

73, Jim / W6JHB

On Thursday, Mar 8, 2012, at Thursday, 12:14 PM, Gary Hinson wrote:

> ... and thank YOU Jim for your encouraging words. I do have the space for
> several quadrillion radials but not the energy to cut them all into the
> ground below sheep/cattle/deer foot level. So I'm waiting for the postman
> to deliver some cores from Amidon, and I'll give an FCP a go.
>
> One thing is not v clear on W0UCE's site is the antenna: he shows an
> inverted L coupled directly in - it looks v simple but my inv-L will be
> different so aside from trimming the length and maybe configuration of the
> L, are there any other tricks to achieving system resonance? I have tall
> fir trees to hang the antenna from, so mine will be close to a quarter wave
> vertical I hope.
>
> 73
> Gary ZL2iFB www.G4iFB.com
>
> PS Please don't feel compelled to respond - I'm going to enjoy
> experimenting with it in any case!
>
>