In message , John S
writes
On 9/27/2015 1:42 PM, John S wrote:
On 9/27/2015 1:20 PM, Wayne wrote:


"rickman" wrote in message ...

On 9/27/2015 10:41 AM, kg7fu wrote:

Matching the antenna won't make the Return Loss go away but it will
make
the transmitter happy.

Can you explain this? I thought matching the antenna would *exactly*
make the return loss go away because it would eliminate the mismatch.

Not wanting to put words in his mouth....
I read that to mean that the high SWR between the ATU and the antenna
would remain, but the transmitter would be happy with the SWR on the
transmitter/ATU coax.


Rick is correct. If the antenna (load) is matched to the line, there is
no return loss, hence no SWR. The ATU will be adjusted (hopefully) to
make the transmitter operate properly with the impedance as seen at the
transmitter end of the line.

I apologize. My statement that "there is no return loss" above is
technically incorrect. The return loss with matched conditions is
maximum. It will peg your meter.

Are you both getting this right?

With a perfect match, the return loss is infinite (ie there is
absolutely no reflection). Your SWR meter will read 1:1.

With a total mismatch, the return loss is zero (ie the reflection is as
strong as the forward signal). Your SWR meter will be pegged hard over
at FSD.



--
Ian

In message , John S
writes
On 9/29/2015 1:45 PM, Wayne wrote:



We always used positive numbers and viewed RL as the difference in dB
between the forward and reflected power.

That makes perfect sense. You could never have a negative dB.

It might be instructive for us all to have a quick look at this
information (especially the last sentence!):

http://www.microwaves101.com/encyclopedias/vswr

"Thus in its correct form, return loss will usually be a positive
number. If it's not, you can usually blame measurement error. The
exception to the rule is something with negative resistance, which
implies that it is an active device (external DC power is converted to
RF) and it is potentially unstable (it could oscillate). Not something
you have to worry about if you are just looking at coax cables! However,
many engineers often omit the minus sign and talk about "-9.5 dB return
loss" for example. People that find it necessary to correct engineers
who do this have underwear that is too tight."

.




--
Ian

On 9/29/2015 5:05 PM, Ian Jackson wrote:
In message , John S
writes
On 9/27/2015 1:42 PM, John S wrote:
On 9/27/2015 1:20 PM, Wayne wrote:


"rickman" wrote in message ...

On 9/27/2015 10:41 AM, kg7fu wrote:

Matching the antenna won't make the Return Loss go away but it will
make
the transmitter happy.

Can you explain this? I thought matching the antenna would *exactly*
make the return loss go away because it would eliminate the mismatch.

Not wanting to put words in his mouth....
I read that to mean that the high SWR between the ATU and the antenna
would remain, but the transmitter would be happy with the SWR on the
transmitter/ATU coax.


Rick is correct. If the antenna (load) is matched to the line, there is
no return loss, hence no SWR. The ATU will be adjusted (hopefully) to
make the transmitter operate properly with the impedance as seen at the
transmitter end of the line.

I apologize. My statement that "there is no return loss" above is
technically incorrect. The return loss with matched conditions is
maximum. It will peg your meter.

Are you both getting this right?

With a perfect match, the return loss is infinite (ie there is
absolutely no reflection). Your SWR meter will read 1:1.

With a total mismatch, the return loss is zero (ie the reflection is as
strong as the forward signal). Your SWR meter will be pegged hard over
at FSD.

You are correct, of course. I was thinking of a dB meter that reads from
0 to some large value (say, 100) full scale. It is not an SWR meter. I
have probably just confused the whole thing. Sorry.

On 9/29/2015 8:19 AM, Jerry Stuckle wrote:
On 9/29/2015 3:47 AM, Ian Jackson wrote:
In message , Jerry Stuckle
writes
On 9/28/2015 7:12 PM, John S wrote:
On 9/28/2015 1:51 PM, Jerry Stuckle wrote:
On 9/28/2015 1:42 PM, rickman wrote:





You said return loss increases with lower SWR. It does not.


It does.

Sorry, a lower SWR does not increase the amount of loss.

Of course it doesn't. No one said it did. It does the opposite, ie a
lower SWR gives less loss on the feeder.

Please cite a reliable reference that says it does. Even the table Rick
cited shows a negative value for return SWR.

What is this 'Return SWR'? I'm not familiar with it.


Sorry, writing too quickly. I meant return loss.

Do you mean Return Loss Ratio (RLR)? This is a simple, easily
measurable, and meaningful statement of how strong the returning
reflected signal is compared with the outgoing forward signal.

The reflected signal is a weaker version of the forward signal. It's
expressed as a loss, an attenuation, or relatively how much down the
level of the reflection is. You can express this as a numerical ratio -
the reflection coefficient (rho) - or (as often more convenient) rho in dB.

As others have suggested, what is apparently a negative sign in the
chart is presumably more artistic licence than scientific accuracy. If
you lose $10, you don't say that you lost 'minus $10'. Similarly, when
you lose 10dB of signal, you don't say you lost 'minus 10dB'.

Which is greater - 10db or -30db?


Which is greater: -20dB or +20dB?

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.

"Ian Jackson" wrote in message ...

In message , John S
writes
On 9/29/2015 1:45 PM, Wayne wrote:



We always used positive numbers and viewed RL as the difference in dB
between the forward and reflected power.

That makes perfect sense. You could never have a negative dB.

It might be instructive for us all to have a quick look at this information
(especially the last sentence!):

http://www.microwaves101.com/encyclopedias/vswr

"Thus in its correct form, return loss will usually be a positive number.
If it's not, you can usually blame measurement error. The exception to the
rule is something with negative resistance, which implies that it is an
active device (external DC power is converted to RF) and it is potentially
unstable (it could oscillate). Not something you have to worry about if you
are just looking at coax cables! However, many engineers often omit the
minus sign and talk about "-9.5 dB return loss" for example. People that
find it necessary to correct engineers who do this have underwear that is
too tight."

LOL. Yes I have run into people like that.

Years ago, I worked with a young engineer who would ask me the following
question when I said "SWR".
He would ask "Do you mean VSWR?"

After a few of his questions, I constructed a nomograph that would convert
SWR to VSWR for him.
And I even wrote an equation for him. SWR=10(VSWR)/10

hope this doesn't start a new thread

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.