Here's my setup: My FT-817 feeds an LDG Z100 autotuner. The
output from the tuner goes to a nearby window via 8' of RG-58
coax. There the coax is formed into a coil. The coil form was one
of those round CD-R cases (you know, the cake shaped 50 packs
you see at Wal-mart). I wound 12 turns of coax neatly around
this form, glued the turns together with superglue and baking
soda then removed the form.

The output from this choke attaches to 50' of 450 ohm ladder
line which connects to a 134' inverted V with an apex of 35'
and ends at 15'. Without the tuner, I get 2:1 SWR points at:

2.125-2.375 Mhz
3.995-4.305 Mhz
4.905-5.595 Mhz
9.335-10.605 Mhz
12.145-13.725 Mhz
16.545-18.685 Mhz
20.475-21.785 Mhz
23.765-26.725 Mhz
28.615-30.125 Mhz

Now - this morning I was talking on the phone with Barry, W4WB
of W4RT electronics and I described the antenna system to him.
His opinion was that while the choke was surely doing it's job, I
would get better performance (radiation efficiancy) if between the
ladder line and choke I would install a 4:1 balun.

What do you guys think? Kinda makes sense to me.

Ken KG0WX

On Thu, 15 Jan 2004 08:28:40 -0700, "Ken Bessler"
wrote:
I get 2:1 SWR points at:

2.125-2.375 Mhz
3.995-4.305 Mhz
4.905-5.595 Mhz
9.335-10.605 Mhz
12.145-13.725 Mhz
16.545-18.685 Mhz
20.475-21.785 Mhz
23.765-26.725 Mhz
28.615-30.125 Mhz

Now - this morning I was talking on the phone with Barry, W4WB
of W4RT electronics and I described the antenna system to him.
His opinion was that while the choke was surely doing it's job, I
would get better performance (radiation efficiancy) if between the
ladder line and choke I would install a 4:1 balun.

What do you guys think? Kinda makes sense to me.

Hi Ken,

Sounds like Barry wants to sell a BalUn if that is the sense you get.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message

Hi Ken,

Sounds like Barry wants to sell a BalUn if that is the sense you get.

73's
Richard Clark, KB7QHC

1) If you knew Barry, you would not think that
2) W4RT dosen't sell baluns

The question still stands - would adding a 4:1 balun at
the transition between coax and ladder line improve the
system or is a coax choke good enough?

73's de Ken KG0WX

On Thu, 15 Jan 2004 11:07:39 -0700, "Ken Bessler"
wrote:


"Richard Clark" wrote in message

Hi Ken,

Sounds like Barry wants to sell a BalUn if that is the sense you get.

73's
Richard Clark, KB7QHC

1) If you knew Barry, you would not think that
2) W4RT dosen't sell baluns

The question still stands - would adding a 4:1 balun at
the transition between coax and ladder line improve the
system or is a coax choke good enough?

73's de Ken KG0WX


Hi Ken,

The value of the coax choke is found in its ability to snub common
mode currents. Given the proximity of earth such currents are an
almost certainty - however, suffering from them is arguable. You
haven't complained of it forcing you to use this as a solution have
you? If so, I missed that.

The coax choke does not perform an Z transformation. Do you
anticipate that the antenna will present 200 Ohms to you somewhere
(especially so close to earth)? Does your data support this
expectation (in other words, howcum why a 4:1 BalUn with all the 2:1
SWRs)?

Do you anticipate that the antenna will present 12.5 Ohms to you
somewhere? Does your data support this expectation? (Notice the
parallel development to the question above.) Will you be connecting
this BalUn backwards to support this notion? (Was it even mentioned?)

The sales clerk's suggestion seems mostly gratuitous. Back in the
30's W.C. Fields would have offered "Go away son, you bother me!"

73's
Richard Clark, KB7QHC

If you knew Barry, you would not think that

If Barry said it would, and you know Barry, I don't think I would bother asking
anyone else.

The question still stands - would adding a 4:1 balun at
the transition between coax and ladder line improve the
system or is a coax choke good enough?

I assume you are to use this antenna on all bands. The reason for adding a
choke balun is that you are going from an unbalanced coax to a more or less
balanced antenna system. The choke attempts to maintain that balance by
presenting a high impedance path to any current that attempts to flow on the
outside of the coax shield.

Adding a 4:1 balun might help the tuner see a more easily tuned (less tuner
loss) impedance on some frequencies. However, this is an all band antenna, so
the Z is all over the place. A 4:1 impedance transformer most of the time
won't help, and can even make things worse. I wouldn't bother.
If the tuner balks on a certain frequency, change the length of 450 ohm line
a little till she will tune. About that 25' of RG-58 between the tuner and the
450 ohm line. (8' to the window+17' in the choke) That will transform the Z at
the 450 ohm termination to something completely different at the tuner. The
exception is that the Z at the 450 ohm line is 50 ohms resistive, then it is a
true 1:1.
You can see all this stuff in action if you model your antenna and
transmission line on Eznec, or Reg Edwards Dipole1.


73 Gary N4AST

Ken Bessler wrote:
The question still stands - would adding a 4:1 balun at
the transition between coax and ladder line improve the
system or is a coax choke good enough?

The highest impedance possible with an SWR of 2:1 is 100
ohms. All impedances that cause an SWR of 2:1 or less, in
a 50 ohm environment, are less than 100 ohms. Therefore,
a 4:1 balun would yield the same SWR for 100 ohms and a
worst SWR for all other impedances less than 100 ohms.
A 4:1 balun is a bad idea in this case.
--
73, Cecil, W5DXP

Ken,
Very simply, I doubt if a balun would do you much
good.
'Doc

"'Doc" wrote in message ...


Ken,
Very simply, I doubt if a balun would do you much
good.
'Doc

Thanks for the simple answer - I think I'll keep
on going with what I've got.....

Ken KG0WX

The coax choke does not perform an Z transformation.

Hi Richard,
I was wondering about that when I tried to answer Ken's question. The choke
he described was 13 turns of RG-58 on about a 5" form. That is about 17' of 50
ohm coax. That will transform the heck out of impedances other than 50 ohms
resistive.

This implies the coax choke does perform a Z transformation. I think a true
1:1 balun can best be realized with a W2DU type with a 100 or so ferrite beads
on about a foot of coax. What do you think?
73 Gary N4AST

JGBOYLES wrote:
The coax choke does not perform an Z transformation.

I was wondering about that when I tried to answer Ken's question. The choke
he described was 13 turns of RG-58 on about a 5" form. That is about 17' of 50
ohm coax. That will transform the heck out of impedances other than 50 ohms
resistive.

Yep, on 30m that's just about a 1/4WL series section transformer.
--
73, Cecil http://www.qsl.net/w5dxp



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