In message , Jeff writes
On 29/09/2015 14:31, Jerry Stuckle wrote:
On 9/29/2015 4:40 AM, Jeff wrote:

Physicists and engineers do not mix gain and loss. Gain is always shown
as a positive number and loss as a negative number.

For instance - a system shows a gain and loss of +3, +5, +2, +1. What
is the total gain or loss of the system?


Of course they do, particularly when dealing with a quantity that is
defined as a LOSS.

I have never heard any engineer when asked the question 'what is that
attenuator' reply minus 3 dB. It is always 3dB. It is always called a
3dB attenuator, not a minus 3dB attenuator.

Jeff

Yes, and the power out is never +3db relative to the input. It is
always -3db.



Which is often referred to as 3dB loss (or 3dB down), ie a positive
quantity.

And Jerry still hasn't answered my question about him losing -$10.
--
Ian

On 9/30/2015 10:12 AM, Ian Jackson wrote:
In message , Jeff writes
On 29/09/2015 14:31, Jerry Stuckle wrote:
On 9/29/2015 4:40 AM, Jeff wrote:

Physicists and engineers do not mix gain and loss. Gain is always
shown
as a positive number and loss as a negative number.

For instance - a system shows a gain and loss of +3, +5, +2, +1.
What
is the total gain or loss of the system?


Of course they do, particularly when dealing with a quantity that is
defined as a LOSS.

I have never heard any engineer when asked the question 'what is that
attenuator' reply minus 3 dB. It is always 3dB. It is always called a
3dB attenuator, not a minus 3dB attenuator.

Jeff

Yes, and the power out is never +3db relative to the input. It is
always -3db.



Which is often referred to as 3dB loss (or 3dB down), ie a positive
quantity.

And Jerry still hasn't answered my question about him losing -$10.

Ever since he was presented with "reliable sources" he has been silent.
I was beginning to think that he would accept no source at all if it
didn't agree with him. However, his silence now is a plus for him.

On 9/30/2015 12:57 PM, John S wrote:
On 9/30/2015 10:12 AM, Ian Jackson wrote:
In message , Jeff writes
On 29/09/2015 14:31, Jerry Stuckle wrote:
On 9/29/2015 4:40 AM, Jeff wrote:

Physicists and engineers do not mix gain and loss. Gain is always
shown
as a positive number and loss as a negative number.

For instance - a system shows a gain and loss of +3, +5, +2, +1.
What
is the total gain or loss of the system?


Of course they do, particularly when dealing with a quantity that is
defined as a LOSS.

I have never heard any engineer when asked the question 'what is that
attenuator' reply minus 3 dB. It is always 3dB. It is always called a
3dB attenuator, not a minus 3dB attenuator.

Jeff

Yes, and the power out is never +3db relative to the input. It is
always -3db.



Which is often referred to as 3dB loss (or 3dB down), ie a positive
quantity.

And Jerry still hasn't answered my question about him losing -$10.

Ever since he was presented with "reliable sources" he has been silent.
I was beginning to think that he would accept no source at all if it
didn't agree with him. However, his silence now is a plus for him.

And no need to go on about the more dramatic aspects of this
conversation. If everyone is happy with the information indicating that
return loss is conventionally a positive dB value, let's move on.

While I may enjoy showing the "truth" to someone who is being obstinate,
I don't wish to make anyone feel like I'm rubbing their nose in it.

--

Rick

In message , rickman
writes
On 9/30/2015 12:57 PM, John S wrote:
On 9/30/2015 10:12 AM, Ian Jackson wrote:
In message , Jeff writes
On 29/09/2015 14:31, Jerry Stuckle wrote:
On 9/29/2015 4:40 AM, Jeff wrote:

Physicists and engineers do not mix gain and loss. Gain is always
shown
as a positive number and loss as a negative number.

For instance - a system shows a gain and loss of +3, +5, +2, +1.
What
is the total gain or loss of the system?


Of course they do, particularly when dealing with a quantity that is
defined as a LOSS.

I have never heard any engineer when asked the question 'what is that
attenuator' reply minus 3 dB. It is always 3dB. It is always called a
3dB attenuator, not a minus 3dB attenuator.

Jeff

Yes, and the power out is never +3db relative to the input. It is
always -3db.



Which is often referred to as 3dB loss (or 3dB down), ie a positive
quantity.

And Jerry still hasn't answered my question about him losing -$10.

Ever since he was presented with "reliable sources" he has been silent.
I was beginning to think that he would accept no source at all if it
didn't agree with him. However, his silence now is a plus for him.

And no need to go on about the more dramatic aspects of this
conversation. If everyone is happy with the information indicating
that return loss is conventionally a positive dB value, let's move on.

While I may enjoy showing the "truth" to someone who is being
obstinate, I don't wish to make anyone feel like I'm rubbing their nose
in it.

So let's get back to the original question. Was it ever really answered?
I think it was made slightly more complicated by the fact that the
antenna feedpoint impedance was not purely resistive, but was actually
around 20-j130 (at 14 MHz),

Was there any advantage in having the coax paralleled (both for 20 ohms
resistive, and for 20-j130)?
--
Ian

"Ian Jackson" wrote in message ...

In message , rickman
writes
On 9/30/2015 12:57 PM, John S wrote:
On 9/30/2015 10:12 AM, Ian Jackson wrote:
In message , Jeff writes
On 29/09/2015 14:31, Jerry Stuckle wrote:
On 9/29/2015 4:40 AM, Jeff wrote:


So let's get back to the original question. Was it ever really answered? I
think it was made slightly more complicated by the fact that the antenna
feedpoint impedance was not purely resistive, but was actually around
20-j130 (at 14 MHz),

Was there any advantage in having the coax paralleled (both for 20 ohms
resistive, and for 20-j130)?

Expanding on the original question.... Antenna feedpoint approximately
20-j130
The ATU drives the antenna through about 15 feet of coax.
Assuming that the ATU provides a +j130 conjugate match, does that leave the
coax with a SWR of 50/20= 2.5:1?
If so, then I will not bother with considering 2 parallel coax.

Wayne wrote:

"Ian Jackson" wrote in message ...

In message , rickman
writes
On 9/30/2015 12:57 PM, John S wrote:
On 9/30/2015 10:12 AM, Ian Jackson wrote:
In message , Jeff writes
On 29/09/2015 14:31, Jerry Stuckle wrote:
On 9/29/2015 4:40 AM, Jeff wrote:


So let's get back to the original question. Was it ever really answered? I
think it was made slightly more complicated by the fact that the antenna
feedpoint impedance was not purely resistive, but was actually around
20-j130 (at 14 MHz),

Was there any advantage in having the coax paralleled (both for 20 ohms
resistive, and for 20-j130)?

Expanding on the original question.... Antenna feedpoint approximately
20-j130
The ATU drives the antenna through about 15 feet of coax.
Assuming that the ATU provides a +j130 conjugate match, does that leave the
coax with a SWR of 50/20= 2.5:1?
If so, then I will not bother with considering 2 parallel coax.

If I'm not mistaken, the aerial impedance will look a bit different at
the other end of about a quarter wave of coax. But that is probably
not going to alter your conclusion, just the matching network.


--
Roger Hayter

"Roger Hayter" wrote in message
...

Wayne wrote:

"Ian Jackson" wrote in message ...

In message , rickman
writes
On 9/30/2015 12:57 PM, John S wrote:
On 9/30/2015 10:12 AM, Ian Jackson wrote:
In message , Jeff
writes
On 29/09/2015 14:31, Jerry Stuckle wrote:
On 9/29/2015 4:40 AM, Jeff wrote:


So let's get back to the original question. Was it ever really answered?
I
think it was made slightly more complicated by the fact that the antenna
feedpoint impedance was not purely resistive, but was actually around
20-j130 (at 14 MHz),

Was there any advantage in having the coax paralleled (both for 20 ohms
resistive, and for 20-j130)?

Expanding on the original question.... Antenna feedpoint approximately
20-j130
The ATU drives the antenna through about 15 feet of coax.
Assuming that the ATU provides a +j130 conjugate match, does that leave
the
coax with a SWR of 50/20= 2.5:1?
If so, then I will not bother with considering 2 parallel coax.

# If I'm not mistaken, the aerial impedance will look a bit different at
# the other end of about a quarter wave of coax. But that is probably
# not going to alter your conclusion, just the matching network.

Good point. The impedance will move around the Smith constant swr circle to
something else that will need the ATU conjugate match.

I'll take a better look at the dimensions.

(but going "off the grid" for a while, so it will be a few days)

On 9/30/2015 3:31 PM, Wayne wrote:


"Ian Jackson" wrote in message ...

In message , rickman
writes
On 9/30/2015 12:57 PM, John S wrote:
On 9/30/2015 10:12 AM, Ian Jackson wrote:
In message , Jeff
writes
On 29/09/2015 14:31, Jerry Stuckle wrote:
On 9/29/2015 4:40 AM, Jeff wrote:


So let's get back to the original question. Was it ever really
answered? I think it was made slightly more complicated by the fact
that the antenna feedpoint impedance was not purely resistive, but was
actually around 20-j130 (at 14 MHz),

Was there any advantage in having the coax paralleled (both for 20
ohms resistive, and for 20-j130)?

Expanding on the original question.... Antenna feedpoint approximately
20-j130
The ATU drives the antenna through about 15 feet of coax.
Assuming that the ATU provides a +j130 conjugate match, does that leave
the coax with a SWR of 50/20= 2.5:1?
If so, then I will not bother with considering 2 parallel coax.

The ATU will have no effect on the SWR in the 15ft of coax. The SWR is
determined entirely by the mismatch between the coax and your antenna.
The ATU simply transforms the impedance it sees to give the transmitter
the load it needs (50 + j0).

Using a Smith chart, I estimate that your load (antenna) will be
transformed to 6.67 + j52.5 through the 15ft of coax. So, that's what
your ATU will see for a load. The chart also shows about 17:1 SWR in the
coax and there is nothing I can do at the transmitter to change it.

If I now change the coax to Zo of 25 ohms, the impedance at the
transmitter end changes to 1.55 +j18.5 ohms and the coax SWR becomes
about 40:1.

It seems to me that you would only be hurting yourself.

Does this help?

On 9/30/2015 9:10 PM, John S wrote:
On 9/30/2015 3:31 PM, Wayne wrote:


"Ian Jackson" wrote in message
...

In message , rickman
writes
On 9/30/2015 12:57 PM, John S wrote:
On 9/30/2015 10:12 AM, Ian Jackson wrote:
In message , Jeff
writes
On 29/09/2015 14:31, Jerry Stuckle wrote:
On 9/29/2015 4:40 AM, Jeff wrote:


So let's get back to the original question. Was it ever really
answered? I think it was made slightly more complicated by the fact
that the antenna feedpoint impedance was not purely resistive, but was
actually around 20-j130 (at 14 MHz),

Was there any advantage in having the coax paralleled (both for 20
ohms resistive, and for 20-j130)?

Expanding on the original question.... Antenna feedpoint approximately
20-j130
The ATU drives the antenna through about 15 feet of coax.
Assuming that the ATU provides a +j130 conjugate match, does that leave
the coax with a SWR of 50/20= 2.5:1?
If so, then I will not bother with considering 2 parallel coax.

The ATU will have no effect on the SWR in the 15ft of coax. The SWR is
determined entirely by the mismatch between the coax and your antenna.
The ATU simply transforms the impedance it sees to give the transmitter
the load it needs (50 + j0).

I will plead ignorance of ATUs, but wouldn't they also be designed to
match the impedance seen at the cable?


Using a Smith chart, I estimate that your load (antenna) will be
transformed to 6.67 + j52.5 through the 15ft of coax. So, that's what
your ATU will see for a load. The chart also shows about 17:1 SWR in the
coax and there is nothing I can do at the transmitter to change it.

If I now change the coax to Zo of 25 ohms, the impedance at the
transmitter end changes to 1.55 +j18.5 ohms and the coax SWR becomes
about 40:1.

It seems to me that you would only be hurting yourself.

Are you calculating the SWR based on the cable to ATU match or the cable
to antenna match? Using an online calculator I get 20:1 VSWR with a 50
ohm cable and 36:1 with a 25 ohm cable. Were you just rounding your
numbers? I used Z = 20 -j130 ohms for the antenna.

--

Rick

In message , Wayne
writes


"Ian Jackson" wrote in message ...

In message , rickman
writes
On 9/30/2015 12:57 PM, John S wrote:
On 9/30/2015 10:12 AM, Ian Jackson wrote:
In message , Jeff writes
On 29/09/2015 14:31, Jerry Stuckle wrote:
On 9/29/2015 4:40 AM, Jeff wrote:


So let's get back to the original question. Was it ever really
answered? I think it was made slightly more complicated by the fact
that the antenna feedpoint impedance was not purely resistive, but was
actually around 20-j130 (at 14 MHz),

Was there any advantage in having the coax paralleled (both for 20
ohms resistive, and for 20-j130)?

A quick model.

A vertical antenna about 4.2m long with a wire radius of 0.5mm
approximates to what you have . The devil is in the j130 If you use a
1.5uH series L the SWR for the parallel 50ohm line is 1.19: 1 and not a
bad match over the band

Expanding on the original question.... Antenna feedpoint approximately
20-j130
The ATU drives the antenna through about 15 feet of coax.
Assuming that the ATU provides a +j130 conjugate match, does that leave
the coax with a SWR of 50/20= 2.5:1?
If so, then I will not bother with considering 2 parallel coax.

No the line SWR is still about 36:1. If you run a bit of poke, you might
melt the coax.

If you want a single 50 ohm feed, extend the antenna to 5.7m ( ~50+
j87) and use a series C ~130pf to take out the the +j87. You have to
do this at the antenna end.

It goes without saying you need a good ground.

Brian

--
Brian Howie