I'm in the process of stringing two base-fed half wave verticals up in
a big beech tree, they're Dale Parfitt's End Fedz dipoles for 20 & 15M.
These antennas are described on this Web page:

http://www.universal-radio.com/catal...wire/4456.html

It seems to me that I have three options for feedline common mode
current minimization/elimination. Beads, coiled coax chokes which is a
quagmire I don't want to get into and plain old grounding. It's the
"plain old grounding" option I'd like to run past the gurus around here
for reality checks on my thinking.

The matching networks will be 12" - 18" inches above the the surface
and fed with 8X coax. The tops of eight foot ground rods will be
directly (+/-) below the matching network enclosures at the bases of
the verticals. I'd split open the jacket of the coax and solder
pigtails made from 3/8" flat braid to the coax shields just behind the
PL-259 fittings then tape/goop the joints to weatherproof them. The
other ends of the braid will be attached to the ground rods. There will
also be some "nominal" radials attached to the ground rods.

Will this arrangement eliminate the need for the usual types of 1:1
choke baluns by taking any I3 currents on the coax shields straight to
ground?

Thanks,

Brian w3rv

On 23 Oct 2006 17:41:37 -0700, "Brian Kelly" wrote:

I'm in the process of stringing two base-fed half wave verticals up in
a big beech tree, they're Dale Parfitt's End Fedz dipoles for 20 & 15M.
These antennas are described on this Web page:

http://www.universal-radio.com/catal...wire/4456.html

Hi Brian,

There are any number of curiosities about this link.
1. The antennas are marketed as half wave DIPOLES;
2. They have matching networks to 50 Ohms;
3. Some (if not all) have low power restrictions.

Why?

A half wave dipole already comes close enough to match as to beg the
question: what more is necessary?

Well, the best interpretation is they are not DIPOLES at all. They
are half wave monopoles which definitely demand matching. But with
tinker toy sized components in that small box? Now we see why they
are power restricted (those components would be toast).

The matching networks will be 12" - 18" inches above the the surface
and fed with 8X coax. The tops of eight foot ground rods will be
directly (+/-) below the matching network enclosures at the bases of
the verticals. I'd split open the jacket of the coax and solder
pigtails made from 3/8" flat braid to the coax shields just behind the
PL-259 fittings then tape/goop the joints to weatherproof them. The
other ends of the braid will be attached to the ground rods. There will
also be some "nominal" radials attached to the ground rods.

It sounds like it would be worth a try.

Will this arrangement eliminate the need for the usual types of 1:1
choke baluns by taking any I3 currents on the coax shields straight to
ground?

Skip it. Go straight path to ground, and make sure the coax hugs the
weeds all the way home. This will stabilize the match which is
notoriously wild if you have too much cable trailing around in the
open. Your concern for common mode is well founded.

Now, let's return to the technical howler of calling these antennas
DIPOLES. This is marketing to the stupid, or by the stupid. Buy your
own wire, and invest in quality components in a larger enclosure. This
will easily save half the cost and finding even a modest coil and cap
in the junk box will save you a trip to the post office (and the cost
of postage and handling). The worst you can do is equal the design.
(OK, so some could do much worse.)

Still and all, the price is set at the disposable income level; buy
two so you have a spare when the first one blows.

73's
Richard Clark, KB7QHC

Jeez RIchard, did we quaff a few too many pints of viper venom last
night? The guy asked for advice and got fanged...


Ignore Richard, Brian, his acerbic disembowling was aimed at the
purveyors of the antennas, not you...
However, having said that Richard is right as usual.. Forget those
guys...
Get some wire - Romex or THHN from Home Depot will work nicely... Or
any other source of #18 to #14 wire you can come up with...

Cut it to a half wave via formula:
983/F(mc) for 1 wave, then divide by 2 - exact length doesn't matter
because the tank circuit
will tune the antenna, just about no matter what..

Grab the nearest source of thin plastic bottle you can find that is
roughly 2" - 3" diameter...
- that bottle of designer water your sweetie carries around will work
just fine, just don't fess up when she asks if you have seen it...
And if you leave the water inside, you can tell the guys on the local
repeater, "Can you hear me now?" oops, wrong commercial
you can tell them that you are running so much power you had to water
cool the coils! -

Wind about 6 or 7 turns of bare wire on the bottle, spaced about a
wire diameter apart...
Get a variable cap, about 60 to 100 uuF will do nicely... Wire this
across the coil as a parallel tuned circuit...
Hook the braid of your coax to the bottom of the tank... The coax
center will have an alligator clip on it... The feed end of the antenna
goes to the top of the tank circuit obviously...
Tap the coil 1.5 to 2 turns up from the bottom with the alligator clip,
run low power, swing the cap and look for a dip (that is a 'dip' on the
SWR meter, not your fishing buddies)
Didn't dip did it? Probably because your tank didn't tune exactly to
the band you are on... Add or subtract turns to the tank coil until you
do see meter movement that says you are getting close... Then adjust
your tap point for that magic 1:1...

"One to one, one too one, we don't have no fun until it's one to
one"...

************************************************** ***************************************
A short break for Bruno to to give me my medicine and adjust my
restraints...
Now I feel better!
************************************************** ******************************************


Now the counterpoise... A ground rod will work after a fashion - so
will strychnine, but that is another story...
Better is radials, as many as you can put down - length does not
matter! Drop a wire from the bottom of your tank to the radials
center..
Better yet best! is an elevated counterpoise, half wave long, 2 feet
or higher above ground, the bottom of the tank/coax is tapped to the
center of the counterpoise... Ground rod is unnecessary, unless you
want to put an RF choke from the bottom of the tank to ground just to
bleed static electricity... Your call... The ground rod does nothing
otherwise, and may actually harm your antenna pattern if connected
directly to the tank...
(I know, I know, that's not what they taught you in Sunday School...
It's a cold, cruel world out there.)

Now the common mode choke... Well, you can order a premade choke from
WX0B (great folks, solid products, but definitely not cheap)
Or you can order a 0.5" X 4" iron powder rod from the usual suspects,
then get Formvar magnet wire and wind 6 bifilar turns on it... Then
solder this whole gaschmazz between the tank and the coax... It will
work nicely...
Or, you can stop reading all the Hennie Pennies who run around clucking
that the sky is falling down, wind 6 turns of your coax on a plastic
pail in about 90 seconds, and go for a beer because you are done - and
you have the best choke that money can buy...

BTW, you only have to put up one antenna for 20 because with a bit of
experimenting and a jumper or two, you can find the magic coil taps for
15 meters, also...

OK, Bruno says I will take a nap NOW, before I cause any more problems
on here....

denny / k8do

On 24 Oct 2006 06:15:34 -0700, "Denny" wrote:

Ignore Richard, Brian, his acerbic disembowling was aimed at the
purveyors of the antennas, not you...

Hi Denny,

Talk about new venom in old bottles. ;-)

Let's see, I offered several bits of advice:
one which you duplicated
another assuring
"Sure, go ahead!"
I also had a nod toward the vendor
"Priced to sell... Buy TWO"
and a river of tears flowed from all this; with Cecil reading from
scripture.

Is this rec.radio.amateur.DearAbby?

73's and thanx all for the entertainment,
Richard Clark, KB7QHC

Denny wrote:
Jeez RIchard, did we quaff a few too many pints of viper venom last
night? The guy asked for advice and got fanged...

I know how to fang back. Ask Cecil if I'm always a nice guy.

Ignore Richard, Brian, his acerbic disembowling was aimed at the
purveyors of the antennas, not you...

Understood.

However, having said that Richard is right as usual.. Forget those
guys...
Get some wire - Romex or THHN from Home Depot will work nicely... Or
any other source of #18 to #14 wire you can come up with...

Cut it to a half wave via formula:
983/F(mc) for 1 wave, then divide by 2 - exact length doesn't matter
because the tank circuit
will tune the antenna, just about no matter what..

Yup. Been there done all that many times.

Grab the nearest source of thin plastic bottle you can find that is
roughly 2" - 3" diameter...
- that bottle of designer water your sweetie carries around will work
just fine, just don't fess up when she asks if you have seen it...

.. . . I'm an unattached old hermit . . no broad in her right mind would
live here with me.

And if you leave the water inside, you can tell the guys on the local
repeater, "Can you hear me now?" oops, wrong commercial
you can tell them that you are running so much power you had to water
cool the coils! -

I like it!

Wind about 6 or 7 turns of bare wire on the bottle, spaced about a
wire diameter apart...
Get a variable cap, about 60 to 100 uuF will do nicely...

Been collecting variable caps for years for this purpose.

Wire this
across the coil as a parallel tuned circuit...
Hook the braid of your coax to the bottom of the tank... The coax
center will have an alligator clip on it... The feed end of the antenna
goes to the top of the tank circuit obviously...
Tap the coil 1.5 to 2 turns up from the bottom with the alligator clip,
run low power, swing the cap and look for a dip (that is a 'dip' on the
SWR meter, not your fishing buddies)
Didn't dip did it? Probably because your tank didn't tune exactly to
the band you are on... Add or subtract turns to the tank coil until you
do see meter movement that says you are getting close... Then adjust
your tap point for that magic 1:1...

Classic all the way and very much in the direction I plan to go. A few
points though. I have an MFJ-259B analyzer which makes antenna tuning a
piece of cake. By the time I get around to building any tuners I'll
also have a grid dip meter which will take care of getting the tank
circuit in-band on the bench instead of having to do it out in the
weeds. And I'll probably see if I can wind coils like B&W does just
because I've always admired them and it would be a challenge.

"One to one, one too one, we don't have no fun until it's one to
one"...

Whoever invented SWR worship needs to be shot.

************************************************** ***************************************
A short break for Bruno to to give me my medicine and adjust my
restraints...
Now I feel better!
************************************************** ******************************************


Now the counterpoise... A ground rod will work after a fashion - so
will strychnine, but that is another story...

Back when I was furiously chasing an early five band DXCC from another
location here in town I had an end-fed 130 foot inverted L and one
ground rod and no radials. Used the antenna on 80 & 40 and didn't have
much competition in the pileups with 500W. I've been attributing the
success of that antenna to ground conditions. Dark, heavy Pennsylvania
loam. This location should be even better in this respect because it's
the same soil but it's damper. I have to cut down a lot of bamboo to
make room around the tree for the two antennas. There's a message in
that.

Better is radials, as many as you can put down - length does not
matter! Drop a wire from the bottom of your tank to the radials
center..

Oops: Hold on right there. I live on a rather strange patch of ground.
The property is only 65' x 45' (roughly) and it's overpopulated by five
huge old hardwood trees all of them well over 75' tall, and one small
cedar cabin. Radial farms are out, some radials, ground rods and
voltage-fed half wave verticals are in.

. . . . The ground rod does nothing
otherwise, and may actually harm your antenna pattern if connected
directly to the tank...
(I know, I know, that's not what they taught you in Sunday School...
It's a cold, cruel world out there.)

I don't even start to understand this one.

Now the common mode choke... Well, you can order a premade choke from
WX0B (great folks, solid products, but definitely not cheap)
Or you can order a 0.5" X 4" iron powder rod from the usual suspects,
then get Formvar magnet wire and wind 6 bifilar turns on it... Then
solder this whole gaschmazz between the tank and the coax... It will
work nicely...

Never read about that one before except as they apply to filament
chokes, looks like a good alternative to a pile of beads.

Or, you can stop reading all the Hennie Pennies who run around clucking
that the sky is falling down, wind 6 turns of your coax on a plastic
pail in about 90 seconds, and go for a beer

Scotch.

because you are done - and
you have the best choke that money can buy...

BTW, you only have to put up one antenna for 20 because with a bit of
experimenting and a jumper or two, you can find the magic coil taps for
15 meters, also...

'Druther be able to twist a switch inside the nice warm house to change
bands than go outside and futz with coil taps in the snow.

OK, Bruno says I will take a nap NOW, before I cause any more problems
on here....

Entertainement is where one finds it. Or creates it.

denny / k8do

Thanx,

Brian w3rv

Richard Clark wrote:
Well, the best interpretation is they are not DIPOLES at all. They
are half wave monopoles which definitely demand matching.

From the IEEE Dictionary:
"dipole antenna - any one of a class of antennas having
a radiation pattern approximating that of an elementary
electric dipole."

Is the reflector on a single-band Yagi a dipole?
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:

Is the reflector on a single-band Yagi a dipole?

No, or yes, depending on semantics.

ac6xg

Richard Clark wrote:

Hello Richard ~ Nice to hear from you.

On 23 Oct 2006 17:41:37 -0700, "Brian Kelly" wrote:

I'm in the process of stringing two base-fed half wave verticals up in
a big beech tree, they're Dale Parfitt's End Fedz dipoles for 20 & 15M.
These antennas are described on this Web page:

http://www.universal-radio.com/catal...wire/4456.html

Hi Brian,

There are any number of curiosities about this link.
1. The antennas are marketed as half wave DIPOLES;
2. They have matching networks to 50 Ohms;
3. Some (if not all) have low power restrictions.

Why?

Why am I going to use them? Because they only cost fifty bucks apiece
delivered, I only have a barefoot 100W HF xcvr and I don't have to buy
or build two tuners before it gets too cold to mess with antennas.

A half wave dipole already comes close enough to match as to beg the
question: what more is necessary?

If I could install classic center-fed dipoles I would. But because of
the space-restricted installation geometry I'm dealing with I can't
pull the coax off at anywhere near a 90º angle to the vertical wire,
the coax would have to droop close to and parallel to the radiators
which would cause all sorts of problems.

Well, the best interpretation is they are not DIPOLES at all.

Well . . this is a semantics & definitions issue as an ME I'll leave
for you EEs to sort out. I'm just another hobbyist who calls any
conductive structure with it's first resonance at a half wavelemgth of
some specific frequency a "dipole" independent of where it's fed and
how it's oriented. Which of course lays me open to the prospect of
getting gored good by purists and others who have copies of the IEEE
dictionary. But that's OK, I have scars all over m'bod and have
survived nicely.

They are half wave monopoles which definitely demand matching.

Yes, they're two of Dale's "dipoles"installed as half wave monopoles.

But with
tinker toy sized components in that small box? Now we see why they
are power restricted (those components would be toast).

I don't have an amp and they're well known for being considerably
underrated as far as power handing is concerned.

The matching networks will be 12" - 18" inches above the the surface
and fed with 8X coax. The tops of eight foot ground rods will be
directly (+/-) below the matching network enclosures at the bases of
the verticals. I'd split open the jacket of the coax and solder
pigtails made from 3/8" flat braid to the coax shields just behind the
PL-259 fittings then tape/goop the joints to weatherproof them. The
other ends of the braid will be attached to the ground rods. There will
also be some "nominal" radials attached to the ground rods.

It sounds like it would be worth a try.

OK, good.

Will this arrangement eliminate the need for the usual types of 1:1
choke baluns by taking any I3 currents on the coax shields straight to
ground?

Skip it. Go straight path to ground, and make sure the coax hugs the
weeds all the way home. This will stabilize the match which is
notoriously wild if you have too much cable trailing around in the
open. Your concern for common mode is well founded.

That's what I'm looking for. I've been concerned about missing
something fundamental. Apparently I have not. Onward.

Now, let's return to the technical howler of calling these antennas
DIPOLES.

With all due respect Richard I've babbled on enough on that topic so
I'l leave it alone and let you work it out with Dale since he done it


This is marketing to the stupid, or by the stupid.

I wouldn't touch that comment with a ten foot pole!

http://www.eham.net/reviews/detail/3632

Buy your
own wire, and invest in quality components in a larger enclosure. This
will easily save half the cost and finding even a modest coil and cap
in the junk box will save you a trip to the post office (and the cost
of postage and handling). The worst you can do is equal the design.
(OK, so some could do much worse.)

I've built some number of tuners which could handle 2kW and then some
including one which used a 4" edge-wound roller inductor and a variable
cap with 1/4" plate spacing both remotely operated by giant Navy
surplus five-phase selsyns. Etc., etc., etc . . ad nauseam.

But right now all I want out of life is to get on 20 & 15 to snipe some
of the expeditions coming up this winter without having to fiddle with
the soldering iron. At some point after it warms up I'll do just what
you're suggesting, build robust tuners, use #10 wire for the radiator
and store the 100W "dipoles" for portable operations.

Still and all, the price is set at the disposable income level; buy
two so you have a spare when the first one blows.

I just might do that.

Thanks Richard.

73's
Richard Clark, KB7QHC

Brian w3rv

Brian Kelly wrote:
Well . . this is a semantics & definitions issue as an ME I'll leave
for you EEs to sort out. I'm just another hobbyist who calls any
conductive structure with it's first resonance at a half wavelemgth of
some specific frequency a "dipole" independent of where it's fed and
how it's oriented. Which of course lays me open to the prospect of
getting gored good by purists and others who have copies of the IEEE
dictionary.

Actually Brian, the IEEE Dictionary seems to agree with you.
It doesn't say a thing about the feedpoint position of dipoles.
Is an OCF a dipole? Is it a dipole if one of the poles is only
one inch long? The IEEE Dictionary seems to say that anything
that walks like a dipole, talks like a dipole, and radiates
like a dipole *is* a dipole, by definition. :-)
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
Brian Kelly wrote:
Well . . this is a semantics & definitions issue as an ME I'll leave
for you EEs to sort out. I'm just another hobbyist who calls any
conductive structure with it's first resonance at a half wavelemgth of
some specific frequency a "dipole" independent of where it's fed and
how it's oriented. Which of course lays me open to the prospect of
getting gored good by purists and others who have copies of the IEEE
dictionary.

Actually Brian, the IEEE Dictionary seems to agree with you.
It doesn't say a thing about the feedpoint position of dipoles.
Is an OCF a dipole? Is it a dipole if one of the poles is only
one inch long? The IEEE Dictionary seems to say that anything
that walks like a dipole, talks like a dipole, and radiates
like a dipole *is* a dipole, by definition. :-)

Heh. Somewhere along the line a long time ago some sage somewhere
stated that there are only two basic types of antennas, point radiators
which are really difficult to build and dipoles and their variants. The
concept stuck and I've been wearing it ever since.

73, Cecil http://www.w5dxp.com

Brian w3rv