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Old August 31st 07, 03:40 AM posted to rec.radio.amateur.antenna
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Default Ferrite cores instead of a 1:1 current-choke UnUn for a Carolina Windom


The Carolina Windom uses a coax feedline from a 4:1 balun at the feedpoint
to a 1:1 current-type unun at the 22-foot point.

Do you guys think that some number of snap-on ferrite chokes of the type
Radio Shack sells at

http://www.radioshack.com/product/in...entPage=search

(Radio Shack part number 273-105), wrapped around the RG-8X feedline at
the 22-foot point, will be suitable in place of something like the MFJ-915
"RF Line Isolator" (unun)?

If so, how many should I use? I have four of them now and the local Radio
Shack claims to have some more in stock.

Each of those ferrite cores is about 1.25" long by 1" square. I have no
idea what type or grade of ferrite material they're made out of.

Thanks...


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Old August 31st 07, 04:08 AM posted to rec.radio.amateur.antenna
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Default Ferrite cores instead of a 1:1 current-choke UnUn for a Carolina Windom

On Thu, 30 Aug 2007 22:40:58 -0400, "Rick (W-A-one-R-K-T)"
wrote:


The Carolina Windom uses a coax feedline from a 4:1 balun at the feedpoint
to a 1:1 current-type unun at the 22-foot point.

Do you guys think that some number of snap-on ferrite chokes of the type
Radio Shack sells at

http://www.radioshack.com/product/in...entPage=search


Of undetermined parentage.

(Radio Shack part number 273-105), wrapped around the RG-8X feedline at
the 22-foot point, will be suitable in place of something like the MFJ-915
"RF Line Isolator" (unun)?


Could be. (There is every possibility that the UnUn that comes with
the commercial unit is not suitable - in spite of testimonials to the
contrary.)

If so, how many should I use? I have four of them now and the local Radio
Shack claims to have some more in stock.


Put a short length of wire through it, use an antenna analyzer to
measure the Z. Now, divide that number into as much Z as is necessary
to isolate the end of the 22-foot feed point. That is how many you
will need.

Each of those ferrite cores is about 1.25" long by 1" square. I have no
idea what type or grade of ferrite material they're made out of.


The previous suggestion renders that moot.

The real question devolves to the parenthetic statement made earlier:
How much Z do you need? It should be 3 to 10 times the Z found at
that drive point. However, with a wild card of the extra radiator
found in the 22 foot drop, it is no longer a simple 4:1 relationship
found at the upper end.

So, we again enter into the exciting world of amateur discovery
through experimentation. Keep choking up until you get the
performance you desire - then stop choking up.

This, then, raises the next real question: What performance are you
expecting?

73's
Richard Clark, KB7QHC
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Old August 31st 07, 07:00 AM posted to rec.radio.amateur.antenna
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Default Ferrite cores instead of a 1:1 current-choke UnUn for a CarolinaWindom

Richard Clark wrote:

...
This, then, raises the next real question: What performance are you
expecting?

73's
Richard Clark, KB7QHC


Well, I'd kinda like my ford explorer xlt 4WD with a 4.0L engine to
perform line a maserati, any chance? Any tweaks you could possible
suggest? Possibly new paint? :-)

Regards,
JS
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Old August 31st 07, 04:13 PM posted to rec.radio.amateur.antenna
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Default Ferrite cores instead of a 1:1 current-choke UnUn for a Carolina Windom

On Thu, 30 Aug 2007 20:08:07 -0700, Richard Clark wrote:

This, then, raises the next real question: What performance are you
expecting?


Good morning, Richard.

I would like it to work well. :-)

OK, more specifically, I'd like it to show a decent match (that is, a
match that's close enough for my TS-940S internal tuner to handle) on 80,
40, and 20, and work at least as well as my 160-meter inverted V that I
feed with ladder line and a manual tuner.

I have no way to define "expected performance" any way other than that.

Of course that leaves all kinds of unanswered questions regarding exactly
what I mean by "at least as well"... regional / NVIS? (Carolina Windom
may not work as well as the V) ... DX? (Carolina Windom may work better
than the V at least on 20) ... etc.

I also have no antenna analyzer and no means to acquire one any time
soon... best I can do is my transmitter (cranked way back in power) and an
SWR meter. No doubt 3/4 or more of my questions on this forum over the
last several weeks would have been answered by an antenna analyzer but
that's a luxury that's not currently available.

You mention the "UnUn that comes with the commercial unit"... not sure if
you meant a commercially-available CW antenna, but this one is being built
from scratch using a W2AU-type 4:1 balun and some lengths of insulated
copper-clad steel wire I have here.

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Old August 31st 07, 04:54 PM posted to rec.radio.amateur.antenna
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Default Ferrite cores instead of a 1:1 current-choke UnUn for a CarolinaWindom

Rick (W-A-one-R-K-T) wrote:
If so, how many should I use? I have four of them now and the local Radio
Shack claims to have some more in stock.


You are trying to create a w2du current-choke-balun. Use the RS
devices along with some #77 or #43 ferrite beads from Amidon.
(Known characteristics for less than $5 seems to me to be
superior to unknown characteristics for more than $5.)

http://www.amidoncorp.com/aai_ferritesforrfi.htm
--
73, Cecil http://www.w5dxp.com


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Old August 31st 07, 05:22 PM posted to rec.radio.amateur.antenna
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Default Ferrite cores instead of a 1:1 current-choke UnUn for a CarolinaWindom

Rick (W-A-one-R-K-T) wrote:
I also have no antenna analyzer and no means to acquire one any time
soon... best I can do is my transmitter (cranked way back in power) and an
SWR meter.


What you are trying to do is minimize common-mode currents
between the choke and the transmitter. On the eznec.com
web page, Roy describes an inexpensive method of detecting
common-mode current amplitude using a simple toroidal pickup
coil. You could actually measure the relative effect of
your RS RFI devices.
--
73, Cecil http://www.w5dxp.com
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Old August 31st 07, 07:17 PM posted to rec.radio.amateur.antenna
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Default Ferrite cores instead of a 1:1 current-choke UnUn for a Carolina Windom

On Fri, 31 Aug 2007 11:13:41 -0400, "Rick (W-A-one-R-K-T)"
wrote:

I also have no antenna analyzer and no means to acquire one any time
soon... best I can do is my transmitter (cranked way back in power) and an
SWR meter.


Hi Rick,

Then using what you have, replace the antenna analyzer with the SWR
meter. That is, pass a short length of wire through the core you
intend to invest in (which begs the question: Why don't you simply go
to the right source and buy the right product?) and pour enough power
to this "load" to see what it measures in SWR.

If it is the right material (Amidon 73, 75, or 77 material). and the
right size (101 size bead) and the right frequency (60M or 12M); then
you should read something less than 2:1. Make it two beads, and it
would still read something less than 2:1 (but closer to 1:1).

You should note there are three variables above: material, bulk, and
frequency. Bulk adds isolation. Material and frequency go
hand-in-hand. As you have ferrite of unknown parentage you are adrift
on two counts and must accept what this ******* will have to offer.
You might be lucky, but it will undoubtedly cost more than doing it
the right way.

Anyway, returning to the practical investigation.... A 101 size bead
will support perhaps a Watt or two at 100% duty cycle and you can
raise that by the inverse proportion of DC. If you pour 100W into
this load to read the SWR, I doubt your meter will have a 10mS peak
reading capture time (unless you have a Daiwa). If you pour 1W into
it, you probably are not going to get a reading at all (that lends any
confidence at being accurate). 10W excitation should be adequate and
lest anyone complain that the SWR is indistinguishable from that
arising due to X (we are seeking R) - I will anticipate that as I have
in the past and ask you to grab onto the bead immediately after the
reading.

A blister on your finger and thumb will stand in telling corroboration
to the reading of nearly 1:1 that the bead exhibits an R of 50 Ohms. A
cool bead will be silent testimony to high X. It is sometimes a
wonder here how commonsense has to be spelled out.

Now, as you have none of the "right" variables, you need only judge
what you DO HAVE in relation to them. Merely repeat this with the
Radio Shack item. You need to balance the consideration that
bulk=Resistance and that your SWR reading may rise because it is
either:
1. Doing TOO good;
or
2. Doing TOO poorly.

The Radio Shack bulk may lend itself to presenting 100 Ohms (too good)
or is just sputtering along with 10 Ohms (too poor). As with
resistors, you can judge this through series/parallel combinations to
seek improved indications.

If two loads in parallel bring the SWR reading into 1:1, then you have
your baseline to build out to the proper sized Isolator. If two loads
in series bring the SWR reading into 1:1, then you have your baseline
to build out to the proper sized Isolator. (Amazing what knowledge
can do when you have just a little of it.)

This, of course, returns us to just how many Radio Shack clip-ons do
you need? My guess is they could handle 4W to 8W at 100% D.C. and if
one of them exhibits 50 Ohms you can do the math - depending on your
choking requirements.

I have no way to define "expected performance" any way other than that.


Then we once again enter into the fascinating world of Amateur
experimentation, an arena that comes with no guarantees and the
prospects of blistered fingers. As you have no way of quantifying
your goal, you have to judge it subjectively (no one else can do this
for you, as you are the subject in subjectivity).

Not knowing what Z is present at the distal end of the 20 Foot
transmission line drop can demand isolation from 500 Ohms to 50,000
Ohms. It is unlikely that the isolation will absorb all the power
your rig has to offer (but if it does, it will make a nice SWR match,
one of those glowing rewards for focusing on the wrong goal). So, by
these metrics, you can get along fine with 10 to 1000 of the mythical
50 Ohm Radio Shack clip-ons.

Start with 10 (adjusted in proportion to their actual R) and add more
until you have met your expected performance. Simple, n'est pas?

73's
Richard Clark, KB7QHC
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Old August 31st 07, 07:33 PM posted to rec.radio.amateur.antenna
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Default Ferrite cores instead of a 1:1 current-choke UnUn for a Carolina Windom

In article ,
Rick (W-A-one-R-K-T) wrote:

You mention the "UnUn that comes with the commercial unit"... not sure if
you meant a commercially-available CW antenna, but this one is being built
from scratch using a W2AU-type 4:1 balun and some lengths of insulated
copper-clad steel wire I have here.


For what it's worth - last year, I home-brewed a coaxial RF
isolator/choke, in an attempt to fix an RF-incursion problem involving
our RACES 40/80 trap dipole and the phone system in the building at
which the dipole is installed.

I used some fairly large-diameter ferrite beads - probably 43
material, if I remember the impedance readings I took correctly. They
were an inch or so long... I superglued a bunch of them together
(around 8 or 10, I think) to form a long ferrite cylinder. The ID was
large enough to let me get a length of RG-8X through the cylinder a
total of three times... in effect, making a very long, thin three-turn
choke. The whole thing was installed in a length of PVC pipe with end
caps and N connectors.

The common-mode impedance along the braid of the coax turned out to be
quite high. If I recall correctly, it was at the upper limit of my
MFJ-259's ability to read at 3.5 MHz (probably upwards of 1500 ohms,
mostly reactive) and was off-the-scale at 40 meters and all higher
frequencies. Whatever capacitive coupling occurred between the turns
didn't amount to enough to matter.

[Unfortunately, it didn't fix the RF incursion problem, which later
experiments proved was caused by near-field pickup by the phone lines
of RF from the antenna itself, and not due to feedline RF at all.]

You could probably build a similar unun using the Radio Shack
ferrites. If they aren't big enough to allow multiple turns of RG-8X,
you could use a short length of RG-58 or an even smaller-gauge 50-ohm
coax. Losses in this short a length of thin coax shouldn't amount to
enough at HF to matter, or to cause appreciable heating unless you're
running very high amounts of power.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
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Old August 31st 07, 11:48 PM posted to rec.radio.amateur.antenna
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Default Ferrite cores instead of a 1:1 current-choke UnUn for a Carolina Windom


Thanks to all for your help on this ferrite core question.

The objective was to see if I could put up the antenna with only what I
have on hand... and I have a 50-foot length of RG-8X and four of those
radio shack ferrite cores. I also have an MFJ unun and so I could cut the
coax at 22 feet and put in a couple of coax connectors, and use the unun,
I just hadn't gotten around to doing that and anyway I don't have the
connectors (but, the Radio Shack is just down the street).

Someone said "try it and see what works", so I did that... put up the
antenna this afternoon. Unfortunately it started raining and the XYL
started yelling at me to get my @$$ off of the roof before I fell off :-),
so I didn't get the unun OR the ferrite cores installed yet.

I figured what the heck, may as well try it without the choke and see what
happens. I inserted the unun into the line where the coax comes in the
window and fired it up. It actually seems to work better than my inverted
V on 20 meters (only band I've tried it on so far), though the difference
isn't exactly what one might call dramatic. Also the SWR is pretty poor
but nothing the rig's internal tuner can't handle.

I'll get the cores or the unun up there tomorrow and see how it acts then.

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Old September 1st 07, 03:09 AM posted to rec.radio.amateur.antenna
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Default Ferrite cores instead of a 1:1 current-choke UnUn for a Carolina Windom

"Rick (W-A-one-R-K-T)" wrote in
news
....
Someone said "try it and see what works", so I did that... put up the

....

Ah, you are well on the way to exploring the meaning of the term 'works' as
in 'my antenna works real well'.

Don't forget collecting a few DX QSL cards, that is often regarded as the
most conclusive evidence.

Owen
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