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Dbu

 

Hi. Is it possible to make a choice in the generator not in dbm but in dbu?
 

"dBu" simply means "dB unspecified" where the load impedance is not the same as the system impedance.?
0 dBm is 1mW into a 50 ohm load and defines an actual power level in watts.
Any measurement where the load impedance is something other than 50 ohms is automatically in dBu and is useful only for relative measurements such as adjusting for min/max.
dBu is often used to describe signal voltage levels (technically incorrect) by ignoring the impedance and relating the voltage levels that would be present as if the impedance was 50 ohms.? 0dBu is 0.224v at any impedance. 10 dBu is 0.707v at any impedance.
 

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Isn't 0 dBu equal to 0.775 volts???

On 8/14/2024 5:44 AM, Neil Preston W0NRP via groups.io wrote:

"dBu" simply means "dB unspecified" where the load impedance is not the same as the system impedance.?
0 dBm is 1mW into a 50 ohm load and defines an actual power level in watts.
Any measurement where the load impedance is something other than 50 ohms is automatically in dBu and is useful only for relative measurements such as adjusting for min/max.
dBu is often used to describe signal voltage levels (technically incorrect) by ignoring the impedance and relating the voltage levels that would be present as if the impedance was 50 ohms.? 0dBu is 0.224v at any impedance. 10 dBu is 0.707v at any impedance.
 

what value should be in dbm??
0dbu=? dbm
6dbu=? dbm
9dbu=? dbm
thanks for the help.

Screenshot_20240814-124227.jpg

 

I understood correctly.?
0dbu = -107dbm
6dbu= -101dbm
9dbu= -98dbm
 

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Yes. 0 dBu = 0.775 vac. It was originally defined that way by the phone company to represent 1 mW ?in a 600 Ω system.

p = v?/R
v = √pR
v = √1 mW * 600 Ω
? ?= √600 mW?
? ?= 0.775 vac

DaveD
KC0WJN

Thanks for all the fish.
==============================
All spelling mistakes are the responsibilty of the reader (Rick Renz, STK, ca. 1994)
==============================

On Aug 14, 2024, at 09:36, Geoff Peters - AB6BT via groups.io <AB6BT@...> wrote:

?

Isn't 0 dBu equal to 0.775 volts???

On 8/14/2024 5:44 AM, Neil Preston W0NRP via groups.io wrote:
"dBu" simply means "dB unspecified" where the load impedance is not the same as the system impedance.?
0 dBm is 1mW into a 50 ohm load and defines an actual power level in watts.
Any measurement where the load impedance is something other than 50 ohms is automatically in dBu and is useful only for relative measurements such as adjusting for min/max.
dBu is often used to describe signal voltage levels (technically incorrect) by ignoring the impedance and relating the voltage levels that would be present as if the impedance was 50 ohms.? 0dBu is 0.224v at any impedance. 10 dBu is 0.707v at any impedance.
 
Edited

Have a look at this calculator to understand the relation between dBm and dBu
.
?
--
Designer of the tinySA
For more info go to

 

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Also, just to be entirely correct, the unit is "dB"something (m, u, Vu, W, V, f, etc.), where:

d is for "deci" (1/10th)
B is for "Bel", named after Alexander Graham Bell, known as the inventor of rhe telephone.

Also, the secret ingredient is the assumed impedance (50Ω, 75Ω, 600Ω, etc.).

IIRC, the dBu unit, today, is used in audio production equipment and *does not* imply any particular impedance. If I'm mis-remembering that, someone who knows better can correct me.

DaveD
KC0WJN

Thanks for all the fish.
==============================
All spelling mistakes are the responsibilty of the reader (Rick Renz, STK, ca. 1994)
==============================

On Aug 14, 2024, at 10:03, Erik Kaashoek via groups.io <erik@...> wrote:

?
Have a look at this calculator to understand the relation between dBm and dBu
https://www.analog.com/en/resources/interactive-design-tools/dbconvert.html#:~:text=dBm%20is%20a%20power%20ratio,0.775V%20and%201V%2C%20respectively.
--
Designer of the tinySA
For more info go to

 

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I believe the "dBu" referred to in the attached document should be written as "dBuV".
0dBuV = 1uV into any impedance, similar to 0dBm = 1mW (into 50 Ohms)
In that case, the figures you state elsewhere are correct. See below (rounded to whole dBm).

There are numerous calculators online.
Here is one:

On 14/08/2024 11:53 pm, Святослав Маханьков wrote:

what value should be in dbm??
0dbuV=? dbm?? = -107dBm
6dbuV=? dbm?? = -101dBm
9dbuV=? dbm?? = -98dBm
thanks for the help.
 

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"dBu" and "dBVU" are different.

DaveD
KC0WJN

Thanks for all the fish.
==============================
All spelling mistakes are the responsibilty of the reader (Rick Renz, STK, ca. 1994)
==============================

On Aug 14, 2024, at 10:39, Bob Ecclestone via groups.io <becclest@...> wrote:

? I believe the "dBu" referred to in the attached document should be written as "dBuV".
0dBuV = 1uV into any impedance, similar to 0dBm = 1mW (into 50 Ohms)
In that case, the figures you state elsewhere are correct. See below (rounded to whole dBm).

There are numerous calculators online.
Here is one:

On 14/08/2024 11:53 pm, Святослав Маханьков wrote:
what value should be in dbm??
0dbuV=? dbm?? = -107dBm
6dbuV=? dbm?? = -101dBm
9dbuV=? dbm?? = -98dBm
thanks for the help.
 

In audio, yes. That was based on a 600 ohm impedance for 0 dBm.
In a 50 ohm system, 1mW would be 0.224v to 50 ohms.?
 

dBm requires a specified load impedance.? dBu does not.
Therefore there can be no equivalence unless you know the load impedance and do the math.
 

DaveD? you are correct.
 

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I was responding to your statement "0dBu is 0.224v at any impedance."

I agree with you statement that 0dBm is 0.224v in a 50 Ohm system.

On 8/14/2024 10:45 AM, Neil Preston W0NRP via groups.io wrote:

In audio, yes. That was based on a 600 ohm impedance for 0 dBm.
In a 50 ohm system, 1mW would be 0.224v to 50 ohms.?
 

input resistance 50ohm


ср, 14 авг. 2024 г., 20:53 Geoff Peters - AB6BT via <AB6BT=[email protected]>:

I was responding to your statement "0dBu is 0.224v at any impedance."

I agree with you statement that 0dBm is 0.224v in a 50 Ohm system.

On 8/14/2024 10:45 AM, Neil Preston W0NRP via wrote:
In audio, yes. That was based on a 600 ohm impedance for 0 dBm.
In a 50 ohm system, 1mW would be 0.224v to 50 ohms.?
 

Agreed, "dBu" and "dBVU" are different, but looking at the scan of the alignment document, in this case I'm pretty sure it's a typo or an incorrect abbreviation, and they really intended it to mean dBuV.
?
Regards,
?
Martin
?
On Wed, Aug 14, 2024 at 02:44 PM, Dave Daniel wrote:

"dBu" and "dBVU" are different.
 

dBu and dB?V and several similar sounding things are apparently easily confused - although the context usually gives a clue..

To add to the confusion some companies and? authors say 0 dB?V refers to the potential? difference across a given load? while others believe it is (open circuit) EMF of the source.? ? ?=? ?6dB's of uncertainty?

For obvious reasons most authors and technicians have had enough and now prefer their instructions to be in dBm??
 

You are confusing dBu with dBuV, totally different things.
dBuV is dB relative to 1uV = -107dBm
dBu is are rather loosely specified measurement often taken to be 0.775 Vac.

73
Jeff G8HUL

-----Original Message-----
From: [email protected] <[email protected]> On Behalf Of ????????? ?????????
Sent: 14 August 2024 14:57
To: [email protected]
Subject: Re: [tinysa] Dbu

I understood correctly.
0dbu = -107dbm
6dbu= -101dbm
9dbu= -98dbm
 

Anyhow, we probably concur that the swell thing coming out of the logarithmic scale is getting rid of multiplication in favor of addition ;-)


to 15. elok. 2024 klo 11.22 G8HUL via <g8hul=[email protected]> kirjoitti:

You are confusing dBu with dBuV, totally different things.
dBuV is dB relative to 1uV = -107dBm
dBu is are rather loosely specified measurement often taken to? be 0.775 Vac.

73
Jeff G8HUL


-----Original Message-----
From: [email protected] <[email protected]> On Behalf Of ????????? ?????????
Sent: 14 August 2024 14:57
To: [email protected]
Subject: Re: [tinysa] Dbu

I understood correctly.
0dbu = -107dbm
6dbu= -101dbm
9dbu= -98dbm
 

dBu is an audio term, and is intended to stand for "Unloaded" i.e. with a high impedance termination.
?
Many items of audio kit use a low value of source impedance, and high value of termination impedance.
?
This allows many items to be fed from the same source, without worrying about the level changing due to loading effects. This is similar to the EMF value in the RF domain that was referred to earlier. As opposed to the more commonly used "loaded" or Potential Difference value.
?
I actually failed an interview in my early days of working, when I didn't realise that the German made signal generator (with German markings) during my practical test (in an English company), was for some reason calibrated in EMF, when I assumed it was PD. Fortunately, that saved me from accepting a very poor job, so there was a silver lining to it in the end.
?
However, once things are in the dB domain, it all becomes a lot easier as you only have to add and subtract.
?
As one of my former lecturers used to say as a mantra, "A dB is a dB is a dB", there may be other twists such as 10 x log 10 (power) or 20 x log 10 (voltage) to convert to dB, but once converted it is constant.
?
Personally, as a former RF engineer, I like dBm. With 0dBm referenced to 1mW in a 50 ohm system, you know where you stand, and it makes system gain / loss calculations very easy. I just wish amateur radio receivers were all calibrated in this way, rather than arbitrary S-Units, which mean nothing, and vary depending on how they have been implemented by the manufacturer.
?
Regards,
?
Martin
?
On Thu, Aug 15, 2024 at 08:22 AM, G8HUL wrote:

dBu is are rather loosely specified measurement often taken to be 0.775 Vac.

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