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I read a recent post that said that, among hams, its become the consensus that return loss is a negative number. I respectfully disagree.



Regarding return loss, I understand some think its a negative number, some a positive. I am in the later camp. Why? When I was a young engineer I had the great fortune, in the early 1980s, to work for HP. Arguably the premier test and measurement company of its time. And equally arguably a leading if not THE leading microwave and rf company.



As new sales people, we were sent to 3, 3 week training sessions to learn the technology and the products so we might interact with our engineering customers in a technically sound way.



One thing HP taught, as I've said in a much earlier post, was that return loss was always a positive number. As someone on this list pointed out, negative loss is gain. And we KNOW that no return loss measurement, of a passive device, can exhibit gain.?



With respect, there is no gray area here. Return loss, is always a positive (or, perhaps better said, a non- signed) number.?


Even if you are at a hobby level of involvement, why not use the proper, and correct, terminology? If you're a private pilot, you are expected/ required to use the proper terminology. Same if you are an amateur road racer. Or "fill in your favorite" hobby.?













Sent using

its become the consensus that return loss is a negative number

IMO, "return loss" is a poor term.
Arguably, >>any<< return is loss, when sending power is the goal. In which case,
"return loss" might be power sent (since lost from return)..

On Fri, 4 Oct 2019 at 16:32, Oristo <ormpoa@...> wrote:

its become the consensus that return loss is a negative number

IMO, "return loss" is a poor term.

But one used very extensively. Personally, I don't have a problem with it.

Arguably, >>any<< return is loss, when sending power is the goal. In which

case,
"return loss" might be power sent (since lost from return)..

Not always. There are one-port amplifiers, such devices as Gunn diodes and
IMPATT diodes, but they are quite rare. For them, the signal returned is
greater than that sent to them. They work on the principle of negative
dynamic resistance. That means increasing the voltage, decreases the
current. They still have a positive resistance though. A device might draw
100 mA at 7 V, but 90 mA at 8 V. The voltage has increased, but the current
goes down.

I know what my opinion on the subject is (return loss is positive for any
passive device), but I am not going to try to force it on anyone else.

I'm an atheist, but I would never try to convince anyone of any religion
that their belief is silly. It is a waste of my time.

--
Dr David Kirkby Ph.D C.Eng MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, CHELMSFORD,
Essex, CM3 6DT, United Kingdom.
Registered in England and Wales as company number 08914892

Tel 01621-680100 / +44 1621-680100

I agree, return loss should be a positive number, and I can remember endless debates in our engineering-team about it, but when you tune filters on a Network analyzer, it is nice to have the insertion loss (S12) and return loss (S11) going the other way on a single screen. My memory is not too good after having a brain tumor and a couple of strokes, but I seem to recall the HP network analyzers (HP8712???) also showing S11 as a negative number, whilst S21 as a positive number. My memory is a bit fuzzy, bit I can remember the one graph, S12 going up (less negative), and S11 going more negative on the same screen, making it easy to tune. Whether it was the default mode for the HP8712 or whether it was a custom-mode, I can’t remember.

RL = -20 * log10( abs(gamma) )

where gamma is a complex reflection coefficient

In order to get negative RL, we needs abs(gamma) > 1, it means that reflected wave is higher than incident wave.

return loss is (almost always) a positive number. If one insists on negative numbers, just call it s11 (or s22). In essence the same property, but negative.

Op 4-10-2019 om 17:20 schreef Ron Spencer via Groups.Io:

Yes, I am G8WRB.

The problem is return loss is *often* used as a negative number in
professional academic publications. This one from an IEEE, has a
particularly amusing title;

Low-Return-Loss Printed Log-Periodic Dipole Antenna

Published in
IEEE Antennas and Wireless Propagation Letters
<>
( Volume: 13 )
Page(s)
503 - 506
ISSN Information
INSPEC Accession Number
14195004
DOI
10.1109/LAWP.2014.2310057 <>
Publisher:
IEEE
Sponsored by
IEEE Antennas and Propagation Society <>




and another, not published by the IEEE,


and another



As such, whilst I will continue to use a positive for all passive and most
active components, I really have no appetite for changing the mind of
others.



On Fri, 4 Oct 2019 at 20:26, Reinier Gerritsen <r.gerritsen@...>
wrote:

return loss is (almost always) a positive number. If one insists on
negative numbers, just call it s11 (or s22). In essence the same
property, but negative.

Op 4-10-2019 om 17:20 schreef Ron Spencer via Groups.Io:

I read a recent post that said that, among hams, its become the

consensus that return loss is a negative number. I respectfully disagree.

Regarding return loss, I understand some think its a negative number,

some a positive. I am in the later camp. Why? When I was a young engineer I
had the great fortune, in the early 1980s, to work for HP. Arguably the
premier test and measurement company of its time. And equally arguably a
leading if not THE leading microwave and rf company.

As new sales people, we were sent to 3, 3 week training sessions to

learn the technology and the products so we might interact with our
engineering customers in a technically sound way.

One thing HP taught, as I've said in a much earlier post, was that

return loss was always a positive number. As someone on this list pointed
out, negative loss is gain. And we KNOW that no return loss measurement, of
a passive device, can exhibit gain.

With respect, there is no gray area here. Return loss, is always a

positive (or, perhaps better said, a non- signed) number.

Even if you are at a hobby level of involvement, why not use the proper,

and correct, terminology? If you're a private pilot, you are expected/
required to use the proper terminology. Same if you are an amateur road
racer. Or "fill in your favorite" hobby.

Sent using

--

Dr. David Kirkby,
Kirkby Microwave Ltd,
drkirkby@...

Telephone 01621-680100./ +44 1621 680100

Registered in England & Wales, company number 08914892.
Registered office:
Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United
Kingdom

Oops,
This was not meant to be sent to the list, but privately to someone who
emailed me on the subject.

Anyway, I stand by what I said
1) Return loss should be positive for passive components.
2) I have no desire to try to convince others to my way of thinking.

Dave

On Fri, 4 Oct 2019 at 20:55, Dr. David Kirkby <
drkirkby@...> wrote:

Yes, I am G8WRB.

The problem is return loss is *often* used as a negative number in
professional academic publications. This one from an IEEE, has a
particularly amusing title;

Low-Return-Loss Printed Log-Periodic Dipole Antenna

Published in
IEEE Antennas and Wireless Propagation Letters
<>
( Volume: 13 )
Page(s)
503 - 506
ISSN Information
INSPEC Accession Number
14195004
DOI
10.1109/LAWP.2014.2310057 <>
Publisher:
IEEE
Sponsored by
IEEE Antennas and Propagation Society <>




and another, not published by the IEEE,


and another



As such, whilst I will continue to use a positive for all passive and most
active components, I really have no appetite for changing the mind of
others.



On Fri, 4 Oct 2019 at 20:26, Reinier Gerritsen <r.gerritsen@...>
wrote:

return loss is (almost always) a positive number. If one insists on
negative numbers, just call it s11 (or s22). In essence the same
property, but negative.

Op 4-10-2019 om 17:20 schreef Ron Spencer via Groups.Io:

I read a recent post that said that, among hams, its become the

consensus that return loss is a negative number. I respectfully disagree.

Regarding return loss, I understand some think its a negative number,

some a positive. I am in the later camp. Why? When I was a young engineer I
had the great fortune, in the early 1980s, to work for HP. Arguably the
premier test and measurement company of its time. And equally arguably a
leading if not THE leading microwave and rf company.

As new sales people, we were sent to 3, 3 week training sessions to

learn the technology and the products so we might interact with our
engineering customers in a technically sound way.

One thing HP taught, as I've said in a much earlier post, was that

return loss was always a positive number. As someone on this list pointed
out, negative loss is gain. And we KNOW that no return loss measurement, of
a passive device, can exhibit gain.

With respect, there is no gray area here. Return loss, is always a

positive (or, perhaps better said, a non- signed) number.

Even if you are at a hobby level of involvement, why not use the

proper, and correct, terminology? If you're a private pilot, you are
expected/ required to use the proper terminology. Same if you are an
amateur road racer. Or "fill in your favorite" hobby.

Sent using

--

Dr. David Kirkby,
Kirkby Microwave Ltd,
drkirkby@...

Telephone 01621-680100./ +44 1621 680100

Registered in England & Wales, company number 08914892.
Registered office:
Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT,
United Kingdom

--
Dr. David Kirkby,
Kirkby Microwave Ltd,
drkirkby@...

Telephone 01621-680100./ +44 1621 680100

Registered in England & Wales, company number 08914892.
Registered office:
Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United
Kingdom

What "a can of worms" this subject opens up.?I noticed the Hewlett Packard rarely if ever referred to return loss as a hardware specification; it was always specified in terms of SWR. Personally I prefer using return loss, with a negative sign. I know this results in misunderstandings, such as referring to a low SWR wideband antenna as having a low return loss. IEEE uses the negative return loss as a standard for their publications. I suppose that correct or not, the most used sign (negative) has became the standard. As long as we are all on the same page, it tends to work out.?All of my network analyzers will output either SWR or return loss, and an iPhone app will convert from one standard to the other.

Stuart K6YAZLos Angeles, USA

Steven Maas if I recall in one of his little texts, mentions, I dis like the term return loss.

Its one of those EE crazy terms!

That said, I never discuss return loss with any thought whatsoever. All return loss numbers that ever roll off my lips are positive. Per the IEEE definition. I feel fine with this for the simple reason as follows:

A filter... its passive... generates no power, lousy filter, 2 dB return loss, ugh. Good filter, great match in the pass band, 20 dB return loss. I'll take it.

I just finished a power amplifier design. Output power 500 W and oh by the way, the return loss is 15 dB. Wow.... Is that 15 dB or -15 dB sir? Hey all my power amplifiers are UNCONDITIONALLY stable. I don't build oscillators here, sir!

Alan

Hi All,

Well, my initial post certainly raised some 'interest', however I'm not sure that we have actually concluded anything, other than it is problematic :-)

Personally, I think it's worthwhile trying to get these parameters correct, so that bad practice is not further propagated, especially amongst newcomers to VNA's and RF measurements in general, which the Nano VNA is likely to expose them to for perhaps the first time.

Anyway, my thanks to everyone who responded.

Regards,

Martin - G8JNJ

Return loss is a measure of the loss of incident power that is not being returned because it is being "lost" to the load resistance.

The easiest way to imagine it is to place a 3dB attenuator on the CH0 port and measure the Return Loss with nothing connected to the other side of the attenuator so that is open circuit.

The power will flow one way and be subject to 3dB attenuation (approx) and then reflected back from the open circuit and experience another 3dB of attenuation, making it 6dB in total.

The same happens if the other side of the attenuator is short circuit.

With higher values of attenuation, the actual value, when incorrectly terminated at one port gets closer to the theoretical value, so there is a closer relationship between the measured RL as being twice the value of attenuation.

Regards,

Martin - G8JNJ