Confusing wording?

[Martin James Smith]

On Sat, 08 Feb 2020 21:15:18 +0000, Cursitor Doom
<curd@notformail.com> wrote:

On Sat, 08 Feb 2020 19:17:55 +0200, Mikko OH2HVJ
mikko.syrjalahti@nospam.fi> wrote:

Nope, it works exactly like that. 1dB is relation (multiply) and 1dBm is
absolute power.

Agreed.

If you increase power from 9dBm by 1dB, that equals 10^(0.1)=1.25
multiplication, i.e. 9dBm + 1dB = 8mW * 1.25 = 10mW = 10dBm.

Agreed. But that's just the "cumbersome method" I used myself earlier
up the thread.

But if you combine 9dBm and 1dBm, you get 8mW+1mW=9mW=9.6dBm.

Which differs from your own answer further up the thread! And I have
no idea what you mean by "combine" either.

Decibels are great for calculating the overall gain of an amplifier,
you just add together the individual stage gains in dB and Bob's your
uncle. Unfortunately, however, whenever you see something like "10dBm
plus or minus 1dB" there's no alternative to translating the figures
back to absolute quantities, performing the multiplication (x1.26 in
the case of 1dB) then translating the answer back into dB again.

 

Unfortunately, however, whenever you see something like "10dBm
plus or minus 1dB" there's no alternative to translating the figures
back to absolute quantities, performing the multiplication (x1.26 in
the case of 1dB) then translating the answer back into dB again.

Why? It's not as though Âą1 dB is a precision instrument. 'Plus or minus 25%' is close enough.

Cheers

Phil Hobbs
(percentages don't have to be translated to absolute units either)

 

[John S]

On 2/8/2020 6:01 PM, amdx wrote:

On 2/8/2020 5:58 PM, amdx wrote:
On 2/6/2020 4:31 PM, Cursitor Doom wrote:
Gentlemen,

I came across this instruction in a service manual and for some reason
find it hard to understand its meaning. It's probably my fault, but
I'd appreciate confirmation of that.

The wording is:

13.  "Adjust output dBm until the power meter indicates +9dBm.
14.  "Adjust tuning slowly through the range 100kHz to 3Ghz and note
the meter readings at 25Mhz intervals. The difference between the
readings should not be greater than 1.0dB."

Are they trying to say all the readings should lie between 7.74dBw and
10.26dBw?? It's far from clear - to me at any rate!

Thanks,

CD

I see it as,

The spread between you highest and your lowest measurement should not
have more than 1db difference.
  It could be a lowest reading of 8.5db and highest of 9.5db or a low
of 8db and high of 9db or a low of 9db and a high of 10db.

  But I don't even know what you are working on.

                                           Mikek

OK, add m to all those db.


 It could be a lowest reading of 8.5dbm and highest of 9.5dbm or a low of
 8dbm and high of 9dbm or a low of 9dbm and a high of 10dbm.

                            Mikek

I don't think you need to add m to your statement. The m is simply the
reference. It could be anything such a volt, watt, amp, or any other
reference. Disregard it.

Think in terms of recording data as suggested from 100kHz to 3GHz every
25MHz into a spreadsheet. That's about 120 data points. Now find the
highest and lowest. What is the difference between the two? The spec
says not more than 1dB. It doesn't matter whether it is dBV, dBW, dBI,
or any other reference.

 

[Jeroen Belleman]

On 2020-02-09 11:29, Martin James Smith wrote:

On Sat, 08 Feb 2020 21:15:18 +0000, Cursitor Doom
curd@notformail.com> wrote:

On Sat, 08 Feb 2020 19:17:55 +0200, Mikko OH2HVJ
mikko.syrjalahti@nospam.fi> wrote:

Nope, it works exactly like that. 1dB is relation (multiply) and 1dBm is
absolute power.

Agreed.

If you increase power from 9dBm by 1dB, that equals 10^(0.1)=1.25
multiplication, i.e. 9dBm + 1dB = 8mW * 1.25 = 10mW = 10dBm.

Agreed. But that's just the "cumbersome method" I used myself earlier
up the thread.

But if you combine 9dBm and 1dBm, you get 8mW+1mW=9mW=9.6dBm.

Which differs from your own answer further up the thread! And I have
no idea what you mean by "combine" either.

Decibels are great for calculating the overall gain of an amplifier,
you just add together the individual stage gains in dB and Bob's your
uncle. Unfortunately, however, whenever you see something like "10dBm
plus or minus 1dB" there's no alternative to translating the figures
back to absolute quantities, performing the multiplication (x1.26 in
the case of 1dB) then translating the answer back into dB again.

I'm surprised that this generates so much discussion. It's really
that simple. A figure in dBm is a power. A figure in dB is a gain.
So x dBm + y dB = (x+y) dBm.

Adding dBm to dBm is a different animal altogether. There you
have to convert back to watts. So for example 10dBm + 10dBm =
13dBm because 10mW + 10mW = 20mW, but that isn't what the
original question was about.

Jeroen Belleman

 

[RheillyPhoull]

On 7/02/2020 7:52 am, Cursitor Doom wrote:

On Fri, 7 Feb 2020 07:41:04 +0800, RheillyPhoull
Rheilly@bigslong.com> wrote:



I would take it to mean the taken readings should not be above or below
each other than 1db.

That wording's even worse than the original!

Don't give up your day job

 

[amdx]

On 2/9/2020 8:22 AM, John S wrote:

On 2/8/2020 6:01 PM, amdx wrote:
On 2/8/2020 5:58 PM, amdx wrote:
On 2/6/2020 4:31 PM, Cursitor Doom wrote:
Gentlemen,

I came across this instruction in a service manual and for some reason
find it hard to understand its meaning. It's probably my fault, but
I'd appreciate confirmation of that.

The wording is:

13.  "Adjust output dBm until the power meter indicates +9dBm.
14.  "Adjust tuning slowly through the range 100kHz to 3Ghz and note
the meter readings at 25Mhz intervals. The difference between the
readings should not be greater than 1.0dB."

Are they trying to say all the readings should lie between 7.74dBw and
10.26dBw?? It's far from clear - to me at any rate!

Thanks,

CD

I see it as,

The spread between you highest and your lowest measurement should not
have more than 1db difference.
  It could be a lowest reading of 8.5db and highest of 9.5db or a low
of 8db and high of 9db or a low of 9db and a high of 10db.

  But I don't even know what you are working on.

                                           Mikek

OK, add m to all those db.


  It could be a lowest reading of 8.5dbm and highest of 9.5dbm or a
low of
  8dbm and high of 9dbm or a low of 9dbm and a high of 10dbm.

                             Mikek

I don't think you need to add m to your statement. The m is simply the
reference. It could be anything such a volt, watt, amp, or any other
reference. Disregard it.

Think in terms of recording data as suggested from 100kHz to 3GHz every
25MHz into a spreadsheet. That's about 120 data points. Now find the
highest and lowest. What is the difference between the two? The spec
says not more than 1dB. It doesn't matter whether it is dBV, dBW, dBI,
or any other reference.

I'm not all that educated about all the dbxx things, but, as I see it
you can have a relative difference in db, but if you are measuring the
level (which he is) then the measurement is with reference to one of
those references listed.
Mikek

 

[mpm]

On Friday, February 7, 2020 at 12:02:37 AM UTC-5, Jasen Betts wrote:

I'm guessing they mean difference between consecutive readings, but
they may mean difference between any two readings (ie between max and
min)

My read of this is +/- 1.0 dB across the entire range and not from any two adjacent measurements in 25 MHz steps.

I get here by realizing there are around 120 such measurement steps in the specified range. If 1.0 dB variance were allowed with each step, that spec quickly becomes meaningless.

But either way, poorly worded spec.

 

[Phil Hobbs]

On 2020-02-09 10:22, amdx wrote:

On 2/9/2020 8:22 AM, John S wrote:
On 2/8/2020 6:01 PM, amdx wrote:
On 2/8/2020 5:58 PM, amdx wrote:
On 2/6/2020 4:31 PM, Cursitor Doom wrote:
Gentlemen,

I came across this instruction in a service manual and for some reason
find it hard to understand its meaning. It's probably my fault, but
I'd appreciate confirmation of that.

The wording is:

13.  "Adjust output dBm until the power meter indicates +9dBm.
14.  "Adjust tuning slowly through the range 100kHz to 3Ghz and note
the meter readings at 25Mhz intervals. The difference between the
readings should not be greater than 1.0dB."

Are they trying to say all the readings should lie between 7.74dBw and
10.26dBw?? It's far from clear - to me at any rate!

Thanks,

CD

I see it as,

The spread between you highest and your lowest measurement should
not have more than 1db difference.
  It could be a lowest reading of 8.5db and highest of 9.5db or a
low of 8db and high of 9db or a low of 9db and a high of 10db.

  But I don't even know what you are working on.

                                           Mikek

OK, add m to all those db.


  It could be a lowest reading of 8.5dbm and highest of 9.5dbm or a
low of
  8dbm and high of 9dbm or a low of 9dbm and a high of 10dbm.

                             Mikek

I don't think you need to add m to your statement. The m is simply the
reference. It could be anything such a volt, watt, amp, or any other
reference. Disregard it.

Think in terms of recording data as suggested from 100kHz to 3GHz
every 25MHz into a spreadsheet. That's about 120 data points. Now find
the highest and lowest. What is the difference between the two? The
spec says not more than 1dB. It doesn't matter whether it is dBV, dBW,
dBI, or any other reference.


 I'm not all that educated about all the dbxx things, but, as I see it
you can have a relative difference in db, but if you are measuring the
level (which he is) then the measurement is with reference to one of
those references listed.
                            Mikek

For us old-timey analogue voice/datacom types, there's also dBA, dBC,
dBm0, and dBrnC0 ("dibrinco").

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[John S]

On 2/9/2020 9:00 AM, mpm wrote:

On Friday, February 7, 2020 at 12:02:37 AM UTC-5, Jasen Betts wrote:

I'm guessing they mean difference between consecutive readings, but
they may mean difference between any two readings (ie between max and
min)

My read of this is +/- 1.0 dB across the entire range and not from any two adjacent measurements in 25 MHz steps.

I get here by realizing there are around 120 such measurement steps in the specified range. If 1.0 dB variance were allowed with each step, that spec quickly becomes meaningless.

But either way, poorly worded spec.

It does not mention +/- 1dB.

 

[John S]

On 2/9/2020 9:22 AM, amdx wrote:

On 2/9/2020 8:22 AM, John S wrote:
On 2/8/2020 6:01 PM, amdx wrote:
On 2/8/2020 5:58 PM, amdx wrote:
On 2/6/2020 4:31 PM, Cursitor Doom wrote:
Gentlemen,

I came across this instruction in a service manual and for some reason
find it hard to understand its meaning. It's probably my fault, but
I'd appreciate confirmation of that.

The wording is:

13.  "Adjust output dBm until the power meter indicates +9dBm.
14.  "Adjust tuning slowly through the range 100kHz to 3Ghz and note
the meter readings at 25Mhz intervals. The difference between the
readings should not be greater than 1.0dB."

Are they trying to say all the readings should lie between 7.74dBw and
10.26dBw?? It's far from clear - to me at any rate!

Thanks,

CD

I see it as,

The spread between you highest and your lowest measurement should
not have more than 1db difference.
  It could be a lowest reading of 8.5db and highest of 9.5db or a
low of 8db and high of 9db or a low of 9db and a high of 10db.

  But I don't even know what you are working on.

                                           Mikek

OK, add m to all those db.


  It could be a lowest reading of 8.5dbm and highest of 9.5dbm or a
low of
  8dbm and high of 9dbm or a low of 9dbm and a high of 10dbm.

                             Mikek

I don't think you need to add m to your statement. The m is simply the
reference. It could be anything such a volt, watt, amp, or any other
reference. Disregard it.

Think in terms of recording data as suggested from 100kHz to 3GHz
every 25MHz into a spreadsheet. That's about 120 data points. Now find
the highest and lowest. What is the difference between the two? The
spec says not more than 1dB. It doesn't matter whether it is dBV, dBW,
dBI, or any other reference.


 I'm not all that educated about all the dbxx things, but, as I see it
you can have a relative difference in db, but if you are measuring the
level (which he is) then the measurement is with reference to one of
those references listed.
                            Mikek

How do you know what the meter's reference is? It is measuring *some*
level. The meter may be calibrated such that it reads volts across a
known resistance and reads dBm printed on the face. Should it be reading
volts and refer to a resistor reference? Forget the dBm until the end of
the final analysis is done.

 

[Tom Gardner]

On 09/02/20 10:29, Martin James Smith wrote:

On Sat, 08 Feb 2020 21:15:18 +0000, Cursitor Doom
curd@notformail.com> wrote:

On Sat, 08 Feb 2020 19:17:55 +0200, Mikko OH2HVJ
mikko.syrjalahti@nospam.fi> wrote:

Nope, it works exactly like that. 1dB is relation (multiply) and 1dBm is
absolute power.

Agreed.

If you increase power from 9dBm by 1dB, that equals 10^(0.1)=1.25
multiplication, i.e. 9dBm + 1dB = 8mW * 1.25 = 10mW = 10dBm.

Agreed. But that's just the "cumbersome method" I used myself earlier
up the thread.

But if you combine 9dBm and 1dBm, you get 8mW+1mW=9mW=9.6dBm.

Which differs from your own answer further up the thread! And I have
no idea what you mean by "combine" either.

Decibels are great for calculating the overall gain of an amplifier,
you just add together the individual stage gains in dB and Bob's your
uncle. Unfortunately, however, whenever you see something like "10dBm
plus or minus 1dB" there's no alternative to translating the figures
back to absolute quantities, performing the multiplication (x1.26 in
the case of 1dB) then translating the answer back into dB again.

Er. You could go back to basic definitions...
P = 10^(PdB / 10), (i.e antilog10(PdB/10) )

10dBM + 1dB = 11dBm.
so 11dBm = 1mW * antilog10(1.1)
= 1mw * 1.258

9dBm is left as an exercise for the student - or just use
an online calculator!

 

[Cursitor Doom]

On Sun, 9 Feb 2020 11:45:37 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

For us old-timey analogue voice/datacom types, there's also dBA, dBC,
dBm0, and dBrnC0 ("dibrinco").

And dBM for movies. For example, I was watching some biopic on Whitney
Houston last night and IMO it was 3dBM longer than it needed to be.
--

"We are with Europe, but not of it. We are linked, but not comprised. We are interested and associated, but not absorbed. And should European statesmen address us with the question, 'Will you join us in this undertaking?' we should reply, “Nay Sir, for we are an island race and we dwell among our own.”

- Winston Spencer Churchill

 

[Cursitor Doom]

On Sun, 9 Feb 2020 11:21:08 -0600, John S <Sophi.2@invalid.org> wrote:

On 2/9/2020 9:00 AM, mpm wrote:
On Friday, February 7, 2020 at 12:02:37 AM UTC-5, Jasen Betts wrote:

I'm guessing they mean difference between consecutive readings, but
they may mean difference between any two readings (ie between max and
min)

My read of this is +/- 1.0 dB across the entire range and not from any two adjacent measurements in 25 MHz steps.

I get here by realizing there are around 120 such measurement steps in the specified range. If 1.0 dB variance were allowed with each step, that spec quickly becomes meaningless.

But either way, poorly worded spec.


It does not mention +/- 1dB.

"The difference between the
readings should not be greater than 1.0dB."

Which I take to mean the same thing. But the wording's not entirely
unambiguous. It would have been better to say, "the difference in
readings should be within 1.0dB [either way]" which more clearly
implies +/- 1dB.

 

[Martin James Smith]

On Sun, 9 Feb 2020 03:09:57 -0800 (PST), pcdhobbs@gmail.com wrote:

Unfortunately, however, whenever you see something like "10dBm
plus or minus 1dB" there's no alternative to translating the figures
back to absolute quantities, performing the multiplication (x1.26 in
the case of 1dB) then translating the answer back into dB again.

Why? It's not as though ą1 dB is a precision instrument. 'Plus or minus 25%' is close enough.

Yes, but the point I was trying to make is that in the case of the
original question, you can't just add 1dB to 9dBm as some here were
trying to suggest. You have to convert these figures into what they
really mean then convert the answer back into dBm again. There's no
shortcut - except for the case of 1, 3, 4, 6dB and whatnot,, the
commonly encountered values that we just know off the top of our heads
after years and years of dealing with this stuff. If the question had
been ' what's xdBm +/- 17dB, even some big shot like you would have to
convert back to absolute values and work it out the long way.

 

[mpm]

On Sunday, February 9, 2020 at 11:45:47 AM UTC-5, Phil Hobbs wrote:

For us old-timey analogue voice/datacom types, there's also dBA, dBC,
dBm0, and dBrnC0 ("dibrinco").

For us RF guys, there's always dBu.

 

[Phil Hobbs]

On 2020-02-09 13:02, Cursitor Doom wrote:

On Sun, 9 Feb 2020 11:21:08 -0600, John S <Sophi.2@invalid.org> wrote:

On 2/9/2020 9:00 AM, mpm wrote:
On Friday, February 7, 2020 at 12:02:37 AM UTC-5, Jasen Betts wrote:

I'm guessing they mean difference between consecutive readings, but
they may mean difference between any two readings (ie between max and
min)

My read of this is +/- 1.0 dB across the entire range and not from any two adjacent measurements in 25 MHz steps.

I get here by realizing there are around 120 such measurement steps in the specified range. If 1.0 dB variance were allowed with each step, that spec quickly becomes meaningless.

But either way, poorly worded spec.


It does not mention +/- 1dB.

"The difference between the
readings should not be greater than 1.0dB."

Which I take to mean the same thing. But the wording's not entirely
unambiguous. It would have been better to say, "the difference in
readings should be within 1.0dB [either way]" which more clearly
implies +/- 1dB.

I'd be inclined to read it as 1 dB p-p, i.e. +-0.5 dB.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Jeroen Belleman]

On 2020-02-09 19:30, Martin James Smith wrote:

On Sun, 9 Feb 2020 03:09:57 -0800 (PST), pcdhobbs@gmail.com wrote:

Unfortunately, however, whenever you see something like "10dBm
plus or minus 1dB" there's no alternative to translating the figures
back to absolute quantities, performing the multiplication (x1.26 in
the case of 1dB) then translating the answer back into dB again.

Why? It's not as though ą1 dB is a precision instrument. 'Plus or minus 25%' is close enough.

Yes, but the point I was trying to make is that in the case of the
original question, you can't just add 1dB to 9dBm as some here were
trying to suggest.

But you can! That's precisely why deciBells are so useful!

You have to convert these figures into what they
really mean then convert the answer back into dBm again. There's no
shortcut - except for the case of 1, 3, 4, 6dB and whatnot,, the
commonly encountered values that we just know off the top of our heads
after years and years of dealing with this stuff. If the question had
been ' what's xdBm +/- 17dB, even some big shot like you would have to
convert back to absolute values and work it out the long way.

Not at all. xdBm +/- 17dB = (x +/- 17) dBm. Work it out the long way,
if you have to, but you'll find it's spot-on.

Jeroen Belleman

 

[amdx]

On 2/9/2020 11:36 AM, John S wrote:

On 2/9/2020 9:22 AM, amdx wrote:
On 2/9/2020 8:22 AM, John S wrote:
On 2/8/2020 6:01 PM, amdx wrote:
On 2/8/2020 5:58 PM, amdx wrote:
On 2/6/2020 4:31 PM, Cursitor Doom wrote:
Gentlemen,

I came across this instruction in a service manual and for some
reason
find it hard to understand its meaning. It's probably my fault, but
I'd appreciate confirmation of that.

The wording is:

13.  "Adjust output dBm until the power meter indicates +9dBm.
14.  "Adjust tuning slowly through the range 100kHz to 3Ghz and note
the meter readings at 25Mhz intervals. The difference between the
readings should not be greater than 1.0dB."

Are they trying to say all the readings should lie between 7.74dBw
and
10.26dBw?? It's far from clear - to me at any rate!

Thanks,

CD

I see it as,

The spread between you highest and your lowest measurement should
not have more than 1db difference.
  It could be a lowest reading of 8.5db and highest of 9.5db or a
low of 8db and high of 9db or a low of 9db and a high of 10db.

  But I don't even know what you are working on.

                                           Mikek

OK, add m to all those db.


  It could be a lowest reading of 8.5dbm and highest of 9.5dbm or a
low of
  8dbm and high of 9dbm or a low of 9dbm and a high of 10dbm.

                             Mikek

I don't think you need to add m to your statement. The m is simply
the reference. It could be anything such a volt, watt, amp, or any
other reference. Disregard it.

Think in terms of recording data as suggested from 100kHz to 3GHz
every 25MHz into a spreadsheet. That's about 120 data points. Now
find the highest and lowest. What is the difference between the two?
The spec says not more than 1dB. It doesn't matter whether it is dBV,
dBW, dBI, or any other reference.


  I'm not all that educated about all the dbxx things, but, as I see
it you can have a relative difference in db, but if you are measuring
the level (which he is) then the measurement is with reference to one
of those references listed.
                             Mikek

How do you know what the meter's reference is?

He said so in a follow up post.

It is measuring *some*

level. The meter may be calibrated such that it reads volts across a
known resistance and reads dBm printed on the face. Should it be reading
volts and refer to a resistor reference? Forget the dBm until the end of
the final analysis is done.

In his original post the OP said he set the original value to 9db.
Then came back and corrected that to 9dbm, which is one scale on 4 of my
meters. When I saw his correction, I also corrected my db to dbm, in my
followup post. So yes he set the original value to 9dm as in, reference
to a milliwatt, as far as I know setting a level to 9db, without
reference to something, is meaningless and useless.
But I would need a 3rd or 4th opinion, as we have each side of the
argument and neither of us will be satisfied with input from the other.
Phil chimed in with some old timey references, but didn't add that I
was right, but he didn't say I was wrong either.
I'm waiting for others to confirm or explain.
Mikek

 

[Michael Terrell]

On Sunday, February 9, 2020 at 1:35:32 PM UTC-5, mpm wrote:

On Sunday, February 9, 2020 at 11:45:47 AM UTC-5, Phil Hobbs wrote:

For us old-timey analogue voice/datacom types, there's also dBA, dBC,
dBm0, and dBrnC0 ("dibrinco").


For us RF guys, there's always dBu.

And dBmv for CATV and other TV RF sources. Also the Reference Levels for Cable Modems.

0dBmv = 1mV across a 75 Ohm load.

 

[amdx]

On 2/9/2020 11:37 AM, Tom Gardner wrote:

On 09/02/20 10:29, Martin James Smith wrote:
On Sat, 08 Feb 2020 21:15:18 +0000, Cursitor Doom
curd@notformail.com> wrote:

On Sat, 08 Feb 2020 19:17:55 +0200, Mikko OH2HVJ
mikko.syrjalahti@nospam.fi> wrote:

Nope, it works exactly like that. 1dB is relation (multiply) and
1dBm is
absolute power.

Agreed.

If you increase power from 9dBm by 1dB, that equals 10^(0.1)=1.25
multiplication, i.e. 9dBm + 1dB = 8mW * 1.25 = 10mW = 10dBm.

Agreed. But that's just the "cumbersome method" I used myself earlier
up the thread.

But if you combine 9dBm and 1dBm, you get 8mW+1mW=9mW=9.6dBm.

Which differs from your own answer further up the thread! And I have
no idea what you mean by "combine" either.

Decibels are great for calculating the overall gain of an amplifier,
you just add together the individual stage gains in dB and Bob's your
uncle. Unfortunately, however, whenever you see something like "10dBm
plus or minus 1dB" there's no alternative to translating the figures
back to absolute quantities, performing the multiplication (x1.26 in
the case of 1dB) then translating the answer back into dB again.

Er. You could go back to basic definitions...
P = 10^(PdB / 10),  (i.e antilog10(PdB/10) )

10dBM + 1dB = 11dBm.
so 11dBm = 1mW * antilog10(1.1)
= 1mw * 1.258

9dBm is left as an exercise for the student - or just use
an online calculator!

I did use the calculators in my 2:48 post, and list them for any one
else to use to prove what Tom Gardner and a few others say is correct.

Repeated,

After using this calculator to convert dbm to watts
> https://www.rapidtables.com/convert/power/dBm_to_Watt.html

Convert 8 dbm and 9 dbm to watts, then do a division with those to
answers, take that answer and put it into the next calculator.

> http://www.satsig.net/lnb/db-calculator.htm
Lower left side,
dB calculator
Conversion Ratio to dB

The end result I get,is 0.998 db.(truncated input numbers) This holds
whether it is the ratio of 1dbm to 2 dbm or 50 to 51 dbm.

Try it and then you can convince yourself that it is as easy to make the
conversion as it seems.

Mikek