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Old July 25th 16, 11:18 PM posted to rec.radio.amateur.antenna
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Default Anyone recommend a source of 36:50 ohm ununs?

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.

Thanks, Bob VE7HS
--
bobrsmits.ca

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Old July 26th 16, 12:26 AM posted to rec.radio.amateur.antenna
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Default Anyone recommend a source of 36:50 ohm ununs?

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.


One gotcha on this: before you add such an unun, make sure that your
feedpoint impedance is actually close to 36 ohms. It may not be,
depending on your actual soil and ground-plane impedance and losses,
and an unun of this sort might actually make matters worse.

One of the local ham clubs has a regular Field Day practice of sending
up a quarter-wave vertical wire, attached to a helium balloon, to
operate on 160 meters at night. They had planned to use an unun of
around that ratio to match it to the feedline... but when they tried,
it made the SWR at the transmitter rather worse.

I suggested that since they'd only run four radials (along the ground
surface), they had a rather poor ground plane and probably had quite a
few ohms of ground-loss resistance at the feedpoint. The simple
assumption of "quarter-wave vertical over a perfect ground plane" just
didn't apply very well. I think they just chose to drive the antenna
directly and live with the SWR on the line. It's possible that they
chose to hook up the unun "backwards".

Depending on the soil, and radials installed below your Inverted L,
you might encounter the same issue. And, depending on your soil type
and weather, it's possible that your ground losses might vary quite
a bit over the course of a year.

Adding an adjustable transmatch right at the base of the antenna would
have been a more flexible solution for them - not as broadband as an
unun, but more adaptable to different ground-loss conditions. Might
work for you, too (although I grant it's likely to need a rather large
inductor!)

Also... I'd suggest calculating the actual "excess loss" in your coax,
if you accept the mismatch at the feedpoint and match to 50 ohms at
the rig. At 2 MHz I'd guess that the excess loss from even a 2:1 SWR
would be quite low.

(My copy of "Reflections" is at home, and I can't recall whether
Walt Maxwell W2DU provides a winding formula for a 36:50, if
that's actually what you do turn out to need. I'll try to remember
to check. My guess is that you'd probably end up having to wind your
own.)




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Old July 26th 16, 01:02 AM posted to rec.radio.amateur.antenna
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Default Anyone recommend a source of 36:50 ohm ununs?

Dave Platt 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.


One gotcha on this: before you add such an unun, make sure that your
feedpoint impedance is actually close to 36 ohms. It may not be,
depending on your actual soil and ground-plane impedance and losses,
and an unun of this sort might actually make matters worse.


Yes, I'm considering that, and figure if it occurs I'll add more radials.

One of the local ham clubs has a regular Field Day practice of sending
up a quarter-wave vertical wire, attached to a helium balloon, to
operate on 160 meters at night. They had planned to use an unun of
around that ratio to match it to the feedline... but when they tried,
it made the SWR at the transmitter rather worse.

I suggested that since they'd only run four radials (along the ground
surface), they had a rather poor ground plane and probably had quite a
few ohms of ground-loss resistance at the feedpoint. The simple
assumption of "quarter-wave vertical over a perfect ground plane" just
didn't apply very well. I think they just chose to drive the antenna
directly and live with the SWR on the line. It's possible that they
chose to hook up the unun "backwards".

Depending on the soil, and radials installed below your Inverted L,
you might encounter the same issue. And, depending on your soil type
and weather, it's possible that your ground losses might vary quite
a bit over the course of a year.

Adding an adjustable transmatch right at the base of the antenna would
have been a more flexible solution for them - not as broadband as an
unun, but more adaptable to different ground-loss conditions. Might
work for you, too (although I grant it's likely to need a rather large
inductor!)


Large Inductors aren't a problem - keeping a tuner weathertight on BC's wet
coast is, however.

Also... I'd suggest calculating the actual "excess loss" in your coax,
if you accept the mismatch at the feedpoint and match to 50 ohms at
the rig. At 2 MHz I'd guess that the excess loss from even a 2:1 SWR
would be quite low.


How do I calculate "excess loss?


(My copy of "Reflections" is at home, and I can't recall whether
Walt Maxwell W2DU provides a winding formula for a 36:50, if
that's actually what you do turn out to need. I'll try to remember
to check. My guess is that you'd probably end up having to wind your
own.)


Thanks - I'll see if I can find a copy.
--
bobrsmits.ca
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Old July 26th 16, 01:25 AM posted to rec.radio.amateur.antenna
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Default Anyone recommend a source of 36:50 ohm ununs?

In article ,
Robert Smits wrote:

Large Inductors aren't a problem - keeping a tuner weathertight on BC's wet
coast is, however.


Understood :-)

Also... I'd suggest calculating the actual "excess loss" in your coax,
if you accept the mismatch at the feedpoint and match to 50 ohms at
the rig. At 2 MHz I'd guess that the excess loss from even a 2:1 SWR
would be quite low.


How do I calculate "excess loss?


http://www.qsl.net/co8tw/Coax_Calculator.htm seems to work nicely.

Plug in the coax-cable type and length, the frequency, the load SWR,
and your input power. It's an approximation (the actual losses depend
not just on the SWR, but the actual load) but it should give you a
good idea of the tradeoffs.

It'll calculate:

- Matched loss (what you'd lose in the coax even if you have a
perfect 1:1 match at the antenna) in dB
- SWR loss (what I referred to as excess loss - additional power
lost in the coax due to the higher currents caused by a higher
SWR) in dB
- Total loss (the sum of the two)
- Actual power into the antenna

As an example: Belden 8237 (RG-8 type), 200 feet, at 2 MHz, into a
3:1 load. The program calculates a matched loss of .487 dB, and an
SWR loss of .281 dB, for a total of .768 dB.

Not a whole lot. If you had a perfect lossless match at the antenna
base, you'd cut your coax loss by about 40%, and gain .281 dB of
signal.

Then, compare that to ground losses. Based on a cursory glance at
some figures on the web, it looks as if a quarter-wave vertical
monopole installation can easily lose 2-3 dB in the ground, even with
as many as 24 radials. Might need up to 60 radials to get down to 1
dB of ground loss. Matching or not-matching the antenna to the
feedline won't affect these losses significantly.

So, it may be that SWR loss in your coax isn't the best place to spend
your efforts... at least, not at first. Adding more radials, or
elevating the radials above ground may have a greater payback.


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Old July 26th 16, 03:15 AM posted to rec.radio.amateur.antenna
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Default Anyone recommend a source of 36:50 ohm ununs?

On 7/25/2016 5:18 PM, 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.

Thanks, Bob VE7HS


I don't have a source, but I have Jerry Sevick's book,
"Transmission Line Transformers"fourth edition.
On pages 7-4 thru 7-15 are descriptions of how to wind
32 ohm to 50 ohm UNUNs.
I found this,
http://documents.mx/documents/amidon...shandbook.html
Go to page 39 of the book (pg 61 of the docslide) and see the 5 winding
configuration to give you 32 ohm to 50 ohm.


If you search W2FMI-2:1-HU50 using Google it is the first hit
and show several approaches. I think this is the same as above.

Mikek




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Old July 26th 16, 08:54 AM posted to rec.radio.amateur.antenna
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Posts: 344
Default Anyone recommend a source of 36:50 ohm ununs?

Robert Smits wrote:
Dave Platt 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.


One gotcha on this: before you add such an unun, make sure that your
feedpoint impedance is actually close to 36 ohms. It may not be,
depending on your actual soil and ground-plane impedance and losses,
and an unun of this sort might actually make matters worse.


Yes, I'm considering that, and figure if it occurs I'll add more radials.


Wouldn't it be easier and better to first measure the impedance?
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Old July 26th 16, 03:13 PM posted to rec.radio.amateur.antenna
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Default Anyone recommend a source of 36:50 ohm ununs?

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.

73
Jonesy
--
Marvin L Jones | W3DHJ | W3DHJ | http://W3DHJ.net/
Pueblo, Colorado | @ | Jonesy | __
38.238N 104.547W | jonz.net | DM78rf | 73 SK
* Killfiling google & XXXXbanter.com: jonz.net/ng.htm
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Old July 26th 16, 04:17 PM posted to rec.radio.amateur.antenna
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Posts: 539
Default Anyone recommend a source of 36:50 ohm ununs?

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.

73
Jonesy


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.



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Old July 26th 16, 04:27 PM posted to rec.radio.amateur.antenna
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Default Anyone recommend a source of 36:50 ohm ununs?

On 25/07/16 23:18, 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.

Thanks, Bob VE7HS

================================================
Ref:Building and using Baluns and Ununs
(Practical designs for the experimenter ) by Jerry Sewick , W2FMI SK

Publisher : CQ Communications .Inc in 1994 ISBN 0-943016-09-6

On page 71 (Chapter 8) a dual-ratio Unun 32 and 18 Ohm to 50 Ohm.

A very useful book possibly available from a library or perhaps via eBay

I bought it in the 1990s from Ham Radio Outlet (HRO) in the USA


Frank , GM0CSZ / KN6WH in IO87AT



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