As a lead in, I use a 16 ft vertical on 20-10 meters, mounted on a flat
metal roof. The antenna is fed with about 25 feet of RG-8, and there is a
tuner at the transmit end.

While I'm pretty happy with the antenna, I'd like to simplify the matching.

Thus, the question: what is the purpose of a 1:4 unun on a 43 foot vertical?
( I assume the "4" side is on the antenna side.)

I'd expect a better coax to antenna match when the antenna feedpoint is a
high Z (example, at 30 meters), but I'd also expect a worse coax to antenna
match when the feedpoint is a low Z (example, at 10 meters).

Is that the way it works, or is there other magic involved?

On 6/29/2015 10:48 AM, Wayne wrote:
As a lead in, I use a 16 ft vertical on 20-10 meters, mounted on a flat
metal roof. The antenna is fed with about 25 feet of RG-8, and there is
a tuner at the transmit end.

You use a 16ft vertical as a lead-in? For what and how is that done?

What are the dimensions of the metal roof?

While I'm pretty happy with the antenna, I'd like to simplify the matching.

To what matching do you refer? You don't want to use the tuner, or is
there some other stuff you have not mentioned?

Thus, the question: what is the purpose of a 1:4 unun on a 43 foot
vertical? ( I assume the "4" side is on the antenna side.)

You wrote that you were interested in a 16ft vertical. Now it is a 43ft
vertical?

I'd expect a better coax to antenna match when the antenna feedpoint is
a high Z (example, at 30 meters), but I'd also expect a worse coax to
antenna match when the feedpoint is a low Z (example, at 10 meters).

Is that the way it works, or is there other magic involved?

All this depends on your answers to the above questions.

"John S" wrote in message ...

On 6/29/2015 10:48 AM, Wayne wrote:
As a lead in, I use a 16 ft vertical on 20-10 meters, mounted on a flat
metal roof. The antenna is fed with about 25 feet of RG-8, and there is
a tuner at the transmit end.

You use a 16ft vertical as a lead-in? For what and how is that done?

Grammatically, the description of the vertical is a lead in for the
question, not an actual antenna lead.


What are the dimensions of the metal roof?

Somewhat irrelevant to my question. But it's about 20 by 35 feet.
I'm not looking for an analysis of the existing antenna.


While I'm pretty happy with the antenna, I'd like to simplify the
matching.

To what matching do you refer? You don't want to use the tuner, or is there
some other stuff you have not mentioned?

I want the tuner matching to be less awkward on some bands.
I'm willing to live with the existing high SWRs on the upper bands.


Thus, the question: what is the purpose of a 1:4 unun on a 43 foot
vertical? ( I assume the "4" side is on the antenna side.)

You wrote that you were interested in a 16ft vertical. Now it is a 43ft
vertical?

Please disregard all about the 16 ft vertical. I'm asking about a 43 ft
vertical 1:4 unun.


I'd expect a better coax to antenna match when the antenna feedpoint is
a high Z (example, at 30 meters), but I'd also expect a worse coax to
antenna match when the feedpoint is a low Z (example, at 10 meters).

Is that the way it works, or is there other magic involved?

All this depends on your answers to the above questions.

So, lets begin again, with no distractions.

What is the purpose (or benefit) of using a 1:4 unun on a 43 ft vertical.

In article ,
Wayne wrote:
So, lets begin again, with no distractions.

What is the purpose (or benefit) of using a 1:4 unun on a 43 ft
vertical.

http://www.eham.net/articles/21272 has a nice analysis.

It looks to me as if:

- Without a 4:1 unun, the antenna provides a very nice match at three
frequencies with in the HF band. At other frequencies, the SWR is
up over 10:1 much of the time - high enough that a coaxial feed
can be rather lossy.

- With a 4:1 unun, you do lose the excellent match at those three
frequencies... but the match gets better at most other
frequencies. The SWR across the HF band is much more uniform, and
lower on average... low enough to cut the coax losses somewhat and
(I think) within the matching range of many rigs' "line flattener"
built-in autotuners.

"Dave Platt" wrote in message ...

In article ,
Wayne wrote:
So, lets begin again, with no distractions.

What is the purpose (or benefit) of using a 1:4 unun on a 43 ft
vertical.

# http://www.eham.net/articles/21272 has a nice analysis.

# It looks to me as if:

# - Without a 4:1 unun, the antenna provides a very nice match at three
# frequencies with in the HF band. At other frequencies, the SWR is
# up over 10:1 much of the time - high enough that a coaxial feed
# can be rather lossy.

# - With a 4:1 unun, you do lose the excellent match at those three
# frequencies... but the match gets better at most other
# frequencies. The SWR across the HF band is much more uniform, and
# lower on average... low enough to cut the coax losses somewhat and
# (I think) within the matching range of many rigs' "line flattener"
# built-in autotuners.


Thanks Dave. I'll have to spend some more time studying it, but the article
is along the lines of what I was looking for.

I would assume that the 1:4 causes behavior just as you say....worse SWR at
nearly matched frequencies and better SWR elsewhere.

I'll have to pull out some textbooks and see how the math works out for a Z
seen through a 1:4 unun.

In practice, I've had good results with SWRs even in the 30:1 range with
short coax feeds.

More research...and thanks.

On Monday, June 29, 2015 at 8:46:47 PM UTC-4, Wayne wrote:
"Dave Platt" wrote in message ...

In article ,
Wayne wrote:
So, lets begin again, with no distractions.

What is the purpose (or benefit) of using a 1:4 unun on a 43 ft
vertical.

# http://www.eham.net/articles/21272 has a nice analysis.

# It looks to me as if:

# - Without a 4:1 unun, the antenna provides a very nice match at three
# frequencies with in the HF band. At other frequencies, the SWR is
# up over 10:1 much of the time - high enough that a coaxial feed
# can be rather lossy.

# - With a 4:1 unun, you do lose the excellent match at those three
# frequencies... but the match gets better at most other
# frequencies. The SWR across the HF band is much more uniform, and
# lower on average... low enough to cut the coax losses somewhat and
# (I think) within the matching range of many rigs' "line flattener"
# built-in autotuners.


Thanks Dave. I'll have to spend some more time studying it, but the article
is along the lines of what I was looking for.

I would assume that the 1:4 causes behavior just as you say....worse SWR at
nearly matched frequencies and better SWR elsewhere.

I'll have to pull out some textbooks and see how the math works out for a Z
seen through a 1:4 unun.

In practice, I've had good results with SWRs even in the 30:1 range with
short coax feeds.

More research...and thanks.

I know that what I am about to say is provocative to some but I still think it is worth saying. If you look at the way that commercial and military radios are matched to antennas you will notice that most of the matching is done as close to the feed point as practical.

Since only the power that actually reaches the antenna can be radiated I have a hard time seeing the point of matching the transmitter to the feed line. Matching at the feed line connection point will prevent damage to the transmitter but if that were the main objective a dummy load would accomplish that.

When you couple the antenna to the load at the feed point you can have extremely low losses in the feed line. When you do the matching at the feed point you will transfer the most energy possible to the antenna and will get the highest available effective radiated power. Since the objective is the transfer of the highest practical amount of power to the antenna the place to do that is at the feed point were possible.

I do realize that it is often simpler and easier to match at the feed line connection but I felt obliged to point out that is is not the most effective place to do the job.

Tom

On 6/29/2015 3:47 PM, Wayne wrote:


"John S" wrote in message ...

On 6/29/2015 10:48 AM, Wayne wrote:
As a lead in, I use a 16 ft vertical on 20-10 meters, mounted on a flat
metal roof. The antenna is fed with about 25 feet of RG-8, and there is
a tuner at the transmit end.

You use a 16ft vertical as a lead-in? For what and how is that done?

Grammatically, the description of the vertical is a lead in for the
question, not an actual antenna lead.


What are the dimensions of the metal roof?

Somewhat irrelevant to my question. But it's about 20 by 35 feet.
I'm not looking for an analysis of the existing antenna.


While I'm pretty happy with the antenna, I'd like to simplify the
matching.

To what matching do you refer? You don't want to use the tuner, or is
there some other stuff you have not mentioned?

I want the tuner matching to be less awkward on some bands.
I'm willing to live with the existing high SWRs on the upper bands.


Thus, the question: what is the purpose of a 1:4 unun on a 43 foot
vertical? ( I assume the "4" side is on the antenna side.)

You wrote that you were interested in a 16ft vertical. Now it is a
43ft vertical?

Please disregard all about the 16 ft vertical. I'm asking about a 43 ft
vertical 1:4 unun.


I'd expect a better coax to antenna match when the antenna feedpoint is
a high Z (example, at 30 meters), but I'd also expect a worse coax to
antenna match when the feedpoint is a low Z (example, at 10 meters).

Is that the way it works, or is there other magic involved?

All this depends on your answers to the above questions.

So, lets begin again, with no distractions.

What is the purpose (or benefit) of using a 1:4 unun on a 43 ft vertical.

Ok. Well, 43ft is a half wavelength at about 12MHz. The vertical will be
very high impedance at that frequency and a 1:4 unun will theoretically
bring that impedance down closer to the feed line impedance.

Does this help?

In message , John S
writes
On 6/29/2015 3:47 PM, Wayne wrote:


"John S" wrote in message ...

On 6/29/2015 10:48 AM, Wayne wrote:
As a lead in, I use a 16 ft vertical on 20-10 meters, mounted on a flat
metal roof. The antenna is fed with about 25 feet of RG-8, and there is
a tuner at the transmit end.

You use a 16ft vertical as a lead-in? For what and how is that done?

Grammatically, the description of the vertical is a lead in for the
question, not an actual antenna lead.


What are the dimensions of the metal roof?

Somewhat irrelevant to my question. But it's about 20 by 35 feet.
I'm not looking for an analysis of the existing antenna.


While I'm pretty happy with the antenna, I'd like to simplify the
matching.

To what matching do you refer? You don't want to use the tuner, or is
there some other stuff you have not mentioned?

I want the tuner matching to be less awkward on some bands.
I'm willing to live with the existing high SWRs on the upper bands.


Thus, the question: what is the purpose of a 1:4 unun on a 43 foot
vertical? ( I assume the "4" side is on the antenna side.)

You wrote that you were interested in a 16ft vertical. Now it is a
43ft vertical?

Please disregard all about the 16 ft vertical. I'm asking about a 43 ft
vertical 1:4 unun.


I'd expect a better coax to antenna match when the antenna feedpoint is
a high Z (example, at 30 meters), but I'd also expect a worse coax to
antenna match when the feedpoint is a low Z (example, at 10 meters).

Is that the way it works, or is there other magic involved?

All this depends on your answers to the above questions.

So, lets begin again, with no distractions.

What is the purpose (or benefit) of using a 1:4 unun on a 43 ft vertical.

Ok. Well, 43ft is a half wavelength at about 12MHz. The vertical will
be very high impedance at that frequency and a 1:4 unun will
theoretically bring that impedance down closer to the feed line
impedance.

Does this help?

It was been pointed out to me that the figures for feeder loss with an
imperfect SWR are only correct when the length is fairly long (at least
an electrical wavelength?). How much loss does 25' of RG-8 really have
at 12MHz, when there's a halfwave hanging on the far end?
--
Ian

On 7/1/2015 10:56 AM, Ian Jackson wrote:
In message , John S
writes
On 6/29/2015 3:47 PM, Wayne wrote:


"John S" wrote in message ...

On 6/29/2015 10:48 AM, Wayne wrote:
As a lead in, I use a 16 ft vertical on 20-10 meters, mounted on a
flat
metal roof. The antenna is fed with about 25 feet of RG-8, and
there is
a tuner at the transmit end.

You use a 16ft vertical as a lead-in? For what and how is that done?

Grammatically, the description of the vertical is a lead in for the
question, not an actual antenna lead.


What are the dimensions of the metal roof?

Somewhat irrelevant to my question. But it's about 20 by 35 feet.
I'm not looking for an analysis of the existing antenna.


While I'm pretty happy with the antenna, I'd like to simplify the
matching.

To what matching do you refer? You don't want to use the tuner, or is
there some other stuff you have not mentioned?

I want the tuner matching to be less awkward on some bands.
I'm willing to live with the existing high SWRs on the upper bands.


Thus, the question: what is the purpose of a 1:4 unun on a 43 foot
vertical? ( I assume the "4" side is on the antenna side.)

You wrote that you were interested in a 16ft vertical. Now it is a
43ft vertical?

Please disregard all about the 16 ft vertical. I'm asking about a 43 ft
vertical 1:4 unun.


I'd expect a better coax to antenna match when the antenna feedpoint is
a high Z (example, at 30 meters), but I'd also expect a worse coax to
antenna match when the feedpoint is a low Z (example, at 10 meters).

Is that the way it works, or is there other magic involved?

All this depends on your answers to the above questions.

So, lets begin again, with no distractions.

What is the purpose (or benefit) of using a 1:4 unun on a 43 ft
vertical.

Ok. Well, 43ft is a half wavelength at about 12MHz. The vertical will
be very high impedance at that frequency and a 1:4 unun will
theoretically bring that impedance down closer to the feed line
impedance.

Does this help?

It was been pointed out to me that the figures for feeder loss with an
imperfect SWR are only correct when the length is fairly long (at least
an electrical wavelength?). How much loss does 25' of RG-8 really have
at 12MHz, when there's a halfwave hanging on the far end?

A *resonant* half wave at 12MHz is about 36.7 feet long and it presents
an impedance of about 1063 + j0 ohms to the RG-8 at the antenna end. The
current at the antenna end is 0.0245A while one watt is applied at the
source end. This means that the power applied to the antenna is about
0.687W. So, about 68% of the applied power reaches the antenna.

So, about 32% of the power is lost in the RG-8 for this example.

Does this help?

On 6/29/2015 10:48 AM, Wayne wrote:
As a lead in, I use a 16 ft vertical on 20-10 meters, mounted on a flat
metal roof. The antenna is fed with about 25 feet of RG-8, and there is
a tuner at the transmit end.

While I'm pretty happy with the antenna, I'd like to simplify the matching.

Thus, the question: what is the purpose of a 1:4 unun on a 43 foot
vertical? ( I assume the "4" side is on the antenna side.)

I'd expect a better coax to antenna match when the antenna feedpoint is
a high Z (example, at 30 meters), but I'd also expect a worse coax to
antenna match when the feedpoint is a low Z (example, at 10 meters).

Is that the way it works, or is there other magic involved?

I think we strayed off the path to answering your original question.

The short answer is that you are correct and there is no magic involved.
A bit longer answer is:

A 43ft vertical will present a feed impedance of 1010 + J 269.2 ohms at
30 meters. Using a 1:4 transformer at the feed point will reduce that to
253 + J 67 ohms. That is a bit closer to your 50 ohm line.

At 10 meters, the antenna will present a 147 + J 133 ohms impedance. A
1:4 transformer will reduce that to 37 + J 33 ohms.

There are several disclaimers I could include, but I think you
understand that the answers cannot be exact with the info presented.

I hope this helps.