In rec.radio.amateur.antenna, you wrote:
On 7/26/2016 9:13 AM, Allodoxaphobia wrote:
On Mon, 25 Jul 2016 15:18:14 -0700, Robert Smits wrote:
Hi. Can anyone recommend a source of 36:50 ohm ununs?

I'm adding an inverted L for 160 meters and would like to add an
unun of 36
ohm to 50 ohms to reduce my SWR. EZNEC shows it would lower it
substantially and when you're running barefoot on 160 you need all
the help
you can get.

Just run two sections of 1/4 wavelength 72 ohm coax in parallel as
a matching section. KISS.

Where does the transformation to 50 ohms occur? If you have a 36 ohm
antenna and you build a 36 ohm transmission line with the paralleled 72
ohm lines (doesn't have to be 1/4 wavelength) you still have 36 ohms at
the transmitter end to deal with.

Ahhh... You are so correct!
I read the OP "intently" and then went off half-cocked.
Apologies!!

So, for a revised "suggestion" I would try parallel sections
of 93 ohm coax -- RG-62 -- and see how that plays out.

73
Jonesy W3DHJ

On 7/26/2016 8:20 PM, Allodoxaphobia wrote:
In rec.radio.amateur.antenna, you wrote:
On 7/26/2016 9:13 AM, Allodoxaphobia wrote:
On Mon, 25 Jul 2016 15:18:14 -0700, Robert Smits wrote:
Hi. Can anyone recommend a source of 36:50 ohm ununs?

I'm adding an inverted L for 160 meters and would like to add an
unun of 36
ohm to 50 ohms to reduce my SWR. EZNEC shows it would lower it
substantially and when you're running barefoot on 160 you need all
the help
you can get.

Just run two sections of 1/4 wavelength 72 ohm coax in parallel as
a matching section. KISS.

Where does the transformation to 50 ohms occur? If you have a 36 ohm
antenna and you build a 36 ohm transmission line with the paralleled 72
ohm lines (doesn't have to be 1/4 wavelength) you still have 36 ohms at
the transmitter end to deal with.

Ahhh... You are so correct!
I read the OP "intently" and then went off half-cocked.
Apologies!!

So, for a revised "suggestion" I would try parallel sections
of 93 ohm coax -- RG-62 -- and see how that plays out.

73
Jonesy W3DHJ


Errr... how does that help? Paralleled 93 ohm coax results in a 46.5 ohm
transmission line. It might as well be a single 50 ohm line instead.

John S wrote:
On 7/26/2016 8:20 PM, Allodoxaphobia wrote:
In rec.radio.amateur.antenna, you wrote:
On 7/26/2016 9:13 AM, Allodoxaphobia wrote:
On Mon, 25 Jul 2016 15:18:14 -0700, Robert Smits wrote:
Hi. Can anyone recommend a source of 36:50 ohm ununs?

I'm adding an inverted L for 160 meters and would like to add an
unun of 36
ohm to 50 ohms to reduce my SWR. EZNEC shows it would lower it
substantially and when you're running barefoot on 160 you need all
the help
you can get.

Just run two sections of 1/4 wavelength 72 ohm coax in parallel as
a matching section. KISS.

Where does the transformation to 50 ohms occur? If you have a 36 ohm
antenna and you build a 36 ohm transmission line with the paralleled 72
ohm lines (doesn't have to be 1/4 wavelength) you still have 36 ohms at
the transmitter end to deal with.

Ahhh... You are so correct!
I read the OP "intently" and then went off half-cocked.
Apologies!!

So, for a revised "suggestion" I would try parallel sections
of 93 ohm coax -- RG-62 -- and see how that plays out.

73
Jonesy W3DHJ


Errr... how does that help? Paralleled 93 ohm coax results in a 46.5 ohm
transmission line. It might as well be a single 50 ohm line instead.

The line needs to be sqrt(Zi*Zo) = sqrt(50*36) = 42.4 ohm.

Paralleled 93 ohm is probably the closest you can get using off-the-shelf
cable.

Rob wrote:

John S wrote:
On 7/26/2016 8:20 PM, Allodoxaphobia wrote:
In rec.radio.amateur.antenna, you wrote:
On 7/26/2016 9:13 AM, Allodoxaphobia wrote:
On Mon, 25 Jul 2016 15:18:14 -0700, Robert Smits wrote:
Hi. Can anyone recommend a source of 36:50 ohm ununs?

I'm adding an inverted L for 160 meters and would like to add an
unun of 36
ohm to 50 ohms to reduce my SWR. EZNEC shows it would lower it
substantially and when you're running barefoot on 160 you need all
the help
you can get.

Just run two sections of 1/4 wavelength 72 ohm coax in parallel as
a matching section. KISS.

Where does the transformation to 50 ohms occur? If you have a 36 ohm
antenna and you build a 36 ohm transmission line with the paralleled 72
ohm lines (doesn't have to be 1/4 wavelength) you still have 36 ohms at
the transmitter end to deal with.

Ahhh... You are so correct!
I read the OP "intently" and then went off half-cocked.
Apologies!!

So, for a revised "suggestion" I would try parallel sections
of 93 ohm coax -- RG-62 -- and see how that plays out.

73
Jonesy W3DHJ


Errr... how does that help? Paralleled 93 ohm coax results in a 46.5 ohm
transmission line. It might as well be a single 50 ohm line instead.

The line needs to be sqrt(Zi*Zo) = sqrt(50*36) = 42.4 ohm.

Paralleled 93 ohm is probably the closest you can get using off-the-shelf
cable.

How about 75 ohm in parallel with 93 ohm giving a theoretical 41.5 ohm?
Or doesn't this work?

--

Roger Hayter

On Tue, 26 Jul 2016 22:06:12 -0500, John S wrote:
On 7/26/2016 8:20 PM, Allodoxaphobia wrote:
In rec.radio.amateur.antenna, you wrote:
On 7/26/2016 9:13 AM, Allodoxaphobia wrote:
On Mon, 25 Jul 2016 15:18:14 -0700, Robert Smits wrote:
Hi. Can anyone recommend a source of 36:50 ohm ununs?

I'm adding an inverted L for 160 meters and would like to add an
unun of 36
ohm to 50 ohms to reduce my SWR. EZNEC shows it would lower it
substantially and when you're running barefoot on 160 you need all
the help
you can get.

Just run two sections of 1/4 wavelength 72 ohm coax in parallel as
a matching section. KISS.

Where does the transformation to 50 ohms occur? If you have a 36 ohm
antenna and you build a 36 ohm transmission line with the paralleled 72
ohm lines (doesn't have to be 1/4 wavelength) you still have 36 ohms at
the transmitter end to deal with.

Ahhh... You are so correct!
I read the OP "intently" and then went off half-cocked.
Apologies!!

So, for a revised "suggestion" I would try parallel sections
of 93 ohm coax -- RG-62 -- and see how that plays out.

Errr... how does that help? Paralleled 93 ohm coax results in a 46.5 ohm
transmission line. It might as well be a single 50 ohm line instead.

We only have a "guess" in the OP that the "inverted L for 160 meters"
has a feedpoint impedance of 36 ohms -- probably from a book relying on
theoretical perfect conditions. This is AMATEUR RADIO! Try it.
See it it helps or hurts. Learn something from the experience.

Jonesy

On 7/27/2016 9:35 AM, Allodoxaphobia wrote:
On Tue, 26 Jul 2016 22:06:12 -0500, John S wrote:
On 7/26/2016 8:20 PM, Allodoxaphobia wrote:
In rec.radio.amateur.antenna, you wrote:
On 7/26/2016 9:13 AM, Allodoxaphobia wrote:
On Mon, 25 Jul 2016 15:18:14 -0700, Robert Smits wrote:
Hi. Can anyone recommend a source of 36:50 ohm ununs?

I'm adding an inverted L for 160 meters and would like to add an
unun of 36
ohm to 50 ohms to reduce my SWR. EZNEC shows it would lower it
substantially and when you're running barefoot on 160 you need all
the help
you can get.

Just run two sections of 1/4 wavelength 72 ohm coax in parallel as
a matching section. KISS.

Where does the transformation to 50 ohms occur? If you have a 36 ohm
antenna and you build a 36 ohm transmission line with the paralleled 72
ohm lines (doesn't have to be 1/4 wavelength) you still have 36 ohms at
the transmitter end to deal with.

Ahhh... You are so correct!
I read the OP "intently" and then went off half-cocked.
Apologies!!

So, for a revised "suggestion" I would try parallel sections
of 93 ohm coax -- RG-62 -- and see how that plays out.

Errr... how does that help? Paralleled 93 ohm coax results in a 46.5 ohm
transmission line. It might as well be a single 50 ohm line instead.

We only have a "guess" in the OP that the "inverted L for 160 meters"
has a feedpoint impedance of 36 ohms -- probably from a book relying on
theoretical perfect conditions. This is AMATEUR RADIO! Try it.
See it it helps or hurts. Learn something from the experience.

Jonesy


There is no harm in using the tools available to get guidance. If the
results do not agree, then okay, you learned something about
simulations. Trying it and simulating it are both learning experiences.
It is nice when they connect even a little bit.

Thanks for all the suggestions.

I'll see what it's like with 50 ohm coax first, and then make other changes.

--
bobrsmits.ca

In message , Robert Smits
writes
Thanks for all the suggestions.

I'll see what it's like with 50 ohm coax first, and then make other changes.

What about making the antenna somewhat longer than a quarterwave (which
presumably is what it is)? This will make the feedpoint impedance higher
resistive, and inductive. Make it long enough to get the resistance
close to 50 ohms, and then add series C to cancel the inductance.
--
Ian

On 7/27/2016 4:43 PM, Ian Jackson wrote:
In message , Robert Smits
writes
Thanks for all the suggestions.

I'll see what it's like with 50 ohm coax first, and then make other
changes.

What about making the antenna somewhat longer than a quarterwave (which
presumably is what it is)? This will make the feedpoint impedance higher
resistive, and inductive. Make it long enough to get the resistance
close to 50 ohms, and then add series C to cancel the inductance.

Or, rather than fussing with the antenna, just use a 50 ohm .051
wavelength open stub located 0.113 wavelengths from the antenna. Use a
T-connector. Wavelengths are electrical lengths. Good for 1.8Mhz.

Feel free to check my numbers.

In message , John S
writes
On 7/27/2016 4:43 PM, Ian Jackson wrote:
In message , Robert Smits
writes
Thanks for all the suggestions.

I'll see what it's like with 50 ohm coax first, and then make other
changes.

What about making the antenna somewhat longer than a quarterwave (which
presumably is what it is)? This will make the feedpoint impedance higher
resistive, and inductive. Make it long enough to get the resistance
close to 50 ohms, and then add series C to cancel the inductance.

Or, rather than fussing with the antenna, just use a 50 ohm .051
wavelength open stub located 0.113 wavelengths from the antenna. Use a
T-connector. Wavelengths are electrical lengths. Good for 1.8Mhz.

Feel free to check my numbers.

I'll believe you, as my Smith chart skills are rusty at the moment!

However, has it been determined why the OP wants to try and achieve a
perfect match?

If it is to reduce losses in the coax, unless the coax is really long,
on 160m the losses due to having a 2:1 SWR are probably negligible.

If it is to present the TX with a perfect 50 ohm load, this can be done
at the shack end with the appropriate simple matcher.
--
Ian