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Non-Resonant Antennas and Chokes

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johnpierce

Non-Resonant Antennas and Chokes

I haven't read all the comments on this thread and thus may requesting
redundant info. My antenna, for 40 mtr's, is a 67' wire up about 25'. I
have 30' of 450 ohm ladder line connected to the end of the antenna and
bringing the antenna into my basement. So I guess you could say that I have
a non-resonant end fed Zepp.

I can check the impedance at the end of the ladder line, where one side is
the antenna and the other side is connected to a ground rod at the point of
entering the house. I can measure the impedance of the antenna in the
basement, using Mini60 without an antenna tuner . The ladder line is then
connected to a MFJ 926B remote antenna tuner The tuner is fed by about 30'
of RG58 coax from my transmitter. When I see a reactive component to the
impedance of the ladder line, without the tuner connected, should I have
some choke inserted in one side of the ladder line or not? Should the tuner
be able to handle the reactive component?

John

AD2F

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Wes Stewart-2

Re: Non-Resonant Antennas and Chokes

Why don't you cut the dipole in the center, add an insulator and feed it with
coax? Put a CM choke at the feedpoint if you insist and lose the ladderline and
tuner. Prune the wire length for resonance.

Wes N7WS

On 1/15/2019 7:15 PM, John Pierce wrote:

> I haven't read all the comments on this thread and thus may requesting
> redundant info. My antenna, for 40 mtr's, is a 67' wire up about 25'. I
> have 30' of 450 ohm ladder line connected to the end of the antenna and
> bringing the antenna into my basement. So I guess you could say that I have
> a non-resonant end fed Zepp.
>
>
>
> I can check the impedance at the end of the ladder line, where one side is
> the antenna and the other side is connected to a ground rod at the point of
> entering the house. I can measure the impedance of the antenna in the
> basement, using Mini60 without an antenna tuner . The ladder line is then
> connected to a MFJ 926B remote antenna tuner The tuner is fed by about 30'
> of RG58 coax from my transmitter. When I see a reactive component to the
> impedance of the ladder line, without the tuner connected, should I have
> some choke inserted in one side of the ladder line or not? Should the tuner
> be able to handle the reactive component?
>
>
>
> John
>
> AD2F
>
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Vic Rosenthal

Re: Non-Resonant Antennas and Chokes

In reply to this post by johnpierce

I have three suggestions:

1) If you are feeding the antenna at the precise end of the wire, move
the feedpoint out a few feet. That's because you need "the other half of
the antenna." Because of the high impedance at this point, only a few
feet are needed.

2) Don't connect one side of the ladder line to a ground rod. It doesn't
help and will probably hurt. If you want to ground something, ground the
shield of the coax at the tuner.

3) Use a good 1:1 balun designed for antenna tuner use between the tuner
and the ladder line. Yes, people say you should use a 4:1 balun. Don't
listen to them. The impedance at the end of the ladder line will be low
on 40m (it's transformed by the near 1/4 wave ladder line). If you use
the antenna on other bands it will vary all over the map.

73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5
http://www.qsl.net/k2vco/
On 16/01/2019 4:15, John Pierce wrote:

KEN-3

Re: Non-Resonant Antennas and Chokes

In reply to this post by Wes Stewart-2

On 1/16/19 12:11 AM, Wes Stewart wrote:
> Why don't you cut the dipole in the center, add an insulator and feed
> it with coax? Put a CM choke at the feedpoint if you insist and lose
> the ladderline and tuner. _Prune the wire length for resonance. _

You do realize that "pruning" for resonance will rarely give a flat SWR
and pruning for low SWR does not mean the antenna is resonant?

Of course, if you cut an end fed Zepp and feed it in the center with
coax, it becomes a single band dipole instead of a multi band antenna.

Ken WA8JXM

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Ignacy

Re: Non-Resonant Antennas and Chokes

In reply to this post by Vic Rosenthal

You have several choices.

1. Add voltage or current balun at tuner output. Voltage 4:1 is simpler.

2. Connect the ladder line directly but loop the coax by the tuner a few
times around a large toroid. This is equivalent to adding a balun. Do not
ground the tuner.

The first option guarantees balance but may add some losses. The second one
is trivial to do. Most likely you will not be able to tell a difference.

I used to have 70ft dipole at 25 ft fed with ladderline all the way to the
shack. Matched by MFJ-962C, which had internal balun. Never a problem with
up to 500W and even worked coast to coast on 160m!

Ignacy, NO9E

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Wes Stewart-2

Re: Non-Resonant Antennas and Chokes

In reply to this post by KEN-3

Oh dear. Of course I know that stuff. BTW, except for very lossy RX antennas
the only thing I know of that gives a "flat" SWR is a dummy load.

The OP said, "My antenna, for 40 mtr's, is a 67' wire up about 25'." Why should
he make a 40-meter dipole so complicated?

Wes N7WS

On 1/16/2019 9:37 AM, Ken wrote:

>
> On 1/16/19 12:11 AM, Wes Stewart wrote:
>> Why don't you cut the dipole in the center, add an insulator and feed it with
>> coax? Put a CM choke at the feedpoint if you insist and lose the ladderline
>> and tuner. _Prune the wire length for resonance. _
>
>
> You do realize that "pruning" for resonance will rarely give a flat SWR and
> pruning for low SWR does not mean the antenna is resonant?
>
>
> Of course, if you cut an end fed Zepp and feed it in the center with coax, it
> becomes a single band dipole instead of a multi band antenna.
>
>
> Ken WA8JXM