Since you're not getting any answers, it sounds like nobody really knows[1]. If they're selling you an antenna, they probably use voltage gain, which would be "marketing dB," much like marketing watts output.
As long as you're consistent throughout, it probably doesn't matter that much anyway.
Hope This Helps! Rich [1] I had a boss once who was looking at some HTML, and wanted me to explain it to him. He pointed to an
Pawihte, (listen to Phil if you want to learn something.) dB's are a measure of power.
George H.
Get the money back to your teacher.
Thanks for the lessons, Phyllis. It's always good to learn from the master.
Power. A broadcast station is licensed for 'Effective Radiated Power' which is the transmitter power times the antenna system's gain, or loss in dB.
Her latest record, 'Onik off, You pig!!!' is due to be relased on Febuary first. Look for it at your local feed store.
Is that why an OpAmp's gain (CMRR, PSRR, ...) is expressed in dB?
No, and the 'voltage ratio' isn't any kind of possibility for an antenna. The antenna output, after all, is an electromagnetic field, measured in watts/sq. meter, or volts/meter. Until you find some way to specify a receiving antenna, you CANNOT extract a 'volts' value for the output.
The gain of an antenna is a ratio of the peak power/steradian to the total power/ (4*pi ). There was an advertisement for a surface mount antenna, meant to solder a millimeter or two above the ground plane of a printed wiring board. The antenna, according to its proud marketer, 'features 3 dB of gain'. I giggled a LOT about that: if you block half the radiation with a ground plane, ANY antenna must have at least 3 dB of gain.
I knew that. But dB is a much abused term, almost as much as Watts in audio. Knowing or stating its correct usage is no guarantee that it's used universally. There are many cases where the incorrect is used as much as, if not more than, the correct one. For example, although I'm not a native user of English, I know that your insertion of an apostrophe in "dB's" is incorrect. Just an illustration, no offence meant.
For example, although I'm not a native user of English, I know that your insertion of an apostrophe in "dB's" is incorrect. Just an illustration, no offence meant.
It may me incorrect as to English grammar, the apostrophe in this example would lead one to assume possession, but it is often used in this context to make clear that one it not using a term called "dBs". I, for one, fully accept this nomenclature.
OK, Back to electronics please.
"George Herold"
Pawihte, (listen to Phil if you want to learn something.) dB's are a measure of power.
** Phil did not say that - he did say this:" There is only one kind of dB and it always relates to power."
Sometimes, the relationship can get a bit thin - as when a voltage ratio is expressed in dB but the two voltage are not taken at the same point. The context will make it clear when this is the case - egs:
Amplifier voltage gain = 60dB, CMRR = 45 dB, PSRR = 70 dB
Electronics engineers are so used to thinking about *ratios* in dBs they contrive to use them whenever ordinary numbers get a bit awkward.
.... Phil
It's power. P1/P2 = 10^(dB/10)
6dB is a power gain of 4 10 dB is a power gain of 10However, since power is proportional to voltage squared, you can get straight to the voltage ratio with V1/V2 = = 10^(dB/20).
POWER.. always..
You can't use voltage gains with antennas because different impedance's yield different voltages and you need to use a matching network to transfer this level properly into and from your antenna and transmission line to get the most out of it..RF transformer, balun, ect..
Isotropic antennas are the level of reference ( 0 dB/ 0dBi)
Any antenna that can move the wasted RF into the useable area's is gain.. the amount of power over the power of a isotropic..
Jamie
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I'm not sure why opamp specs are like that. (I'm always converting to volts.) You can always convert dB to amplitude, but dB's are the logarithim of a power ratio, with a decimal shift. At least that's my understanding. (Am I missing something?)
George H.
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Yeah, I think it may be sometimes used just to confuse people. It might have been easier if a straight logarithim had been used. 1 is a gain of ten, 2 a gain 100, etc.
George H.
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Sorry Phil, I didn't mean to put words in your mouth. I should have said 'relates' to power.
George H.
No, it's not always a power ratio or there wouldn't be units like dBV. The dB is just as useful for calculating voltage gains (and noise, CMRR, dynamic range...) as it is for power gains. With antennas it's always power ratios since voltage gain is pretty meaningless, at least by itself.
Yes, John. I saw it was capitalized just as I hit send.
If I say, thanks for a well-reasoned answer without any profanity, will you cuss me out like Phil did on that other thread?
Thanks, Rich
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