GROL License

[AM909]

There was one where an answer was a bad Evinrude circuit.

I hear people say 'a minus 3 dB loss', I don't know how they can lose negative 3 dB.

The same folks that justify "irregardless" as a more emphatic term than "regardless".

 

[bot]

Considering putting together a list of videos for the exams. I found some more videos just haven't had a chance to review them all yet. May list them in their own thread. Should make it easier to find and so others can add links to resources on it.

 

[bot]

Or how bout someone stating antenna gain in dBm? That drives me nuts.

This is the first time I've heard this. And just saw it in one of the videos I am reviewing. The narrator states that it is "decibels relative to one milliwatt. "

 

[Token]

This is the first time I've heard this. And just saw it in one of the videos I am reviewing. The narrator states that it is "decibels relative to one milliwatt. "

For the folks who do not know the difference and are wondering what the big deal in this splintered section of the thread is:

That is, indeed, the definition of dBm (dBm = decibels refenced to one milliwatt). But, antenna gains, or gains in general, are not expressed in dBm, rather more typically dBi (referenced to isotropic radiator) or dBd (referenced to dipole). A number in dBm is a specific power level, while dBi or dBd are gain ratios based on specific references. dB alone is a ratio with no specific reference.

You can reference anything in dB. For example, 0 dBhuman would be one person, while 6 dBhuman would be 4 people. Would you rather have $20, or 20 dB$?

Related note, I get a tad perturbed when I see someone insist that their antenna is something like "4.5 DB's" and so it must be better than the other guys antenna that is 4.3 dBd, but having no idea if his antenna gain is rated in dBi or dBd, or the fact those different standards exist. Never mind that in the real world that 0.2 dB may not be present at all (depending on so many variables), or that without knowing the stated refence (i or d) you cannot know the relationships of the two antenna gains.

Oh, and and the other part of my peeve above, plural dB is dB, not dB's ;-) And the d is always lower case (SI prefix deci = small d) and the B is always capital (a persons name, Bell).

So many things wrapped up in such a such a little letter count.

T!

 

[dickie757]

This is the first time I've heard this. And just saw it in one of the videos I am reviewing. The narrator states that it is "decibels relative to one milliwatt. "

Good, now let's see if you learned anything....how much power is 0 dBm?

 

[prcguy]

Good, now let's see if you learned anything....how much power is 0 dBm?

One milliwatt of course. But the load impedance is just as important like is it 50 ohms or 600 ohms? There will be a huge difference in the voltage between 50 ohms and 600 ohms for the same power level.

 

[Token]

Good, now let's see if you learned anything....how much power is 0 dBm?

The part that often messes with new people to the concept is negatives in this application. How much power is -6 dBm?

The fact that -6 dBm is still a positive number can mess with folks that did not get the basics of, anything in dB is always a ratio.

T!

 

[speedway_navigator]

I don't see dBc, decibels below carrier, in 2 way much, more used in the cell world.
These are from Tom Dover's GCT books.

 

[Echo4Thirty]

Antenna manufacturers love to rate things in dBi since it gives them an extra 2.15 dB to add to their numbers compared to ones who use dBd.

 

[prcguy]

Antenna manufacturers love to rate things in dBi since it gives them an extra 2.15 dB to add to their numbers compared to ones who use dBd.

dBc is very common in the satellite/satcom industry and dBi is a legitimate reference and used throughout the satellite industry and even some FCC test specs are referenced to dBi. The problem is when antenna mfrs toss out a dB gain with no reference to anything.

 

[Echo4Thirty]

I dont disagree with that. I can do the math to compare if i know what reference they used.

 

[merlin]

Came a long way since class1 with broadcast.