Calculating "Total" Power for RF Meter

[JohnnyB]

Calculating "Total" Power for attenuation needed for the rf meter... A few of us needs to know this and I need to know if I'm on the right track. I'll use my set-up for an example.
What I have and want to test:
P4 controller - .303W
Sunhan booster - 3W
Maxxrange antenna - 14db or .025W (?)
Total watts = 3.328 or 35.22dBm (actual attenuation needed)
So, 40dB worth of attenuation would suffice? Am I on the right track? If not, could you explain as simple as possible? I understand now it's all Log scale and not linear, but wanted to check with you guys about adding controller and antenna being used to the equation.
Thanks in Advance.
JB

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[NM_Quad]

I don't understand what you are trying to do. Apply attenuation to what and why? Why would you want to attenuate either the RC or AC signals? That would certainly reduce your range, especially 40dB. Also, adding attenuation to the antennas will increase the noise figure. Not criticizing, just lost as to your intent.

 

[JohnnyB]

Adding attenuators to rf meter.. sorry. I tried to be clear.

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[N017RW]

Simply put: If your meter has a 10db max input and you want to measure something expected to output 45db you should insert 40db or so attenuation. Then add the 40db to the actual meter reading.

 

[JohnnyB]

Back to #1 post talking about calculating "total" power.. and the question was, am I on the right track the way I got my total power? Knowing the expected total power should tell me how much to attenuate. The meter itself don't want to see nothing over 0dBm.

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[JohnnyB]

Immersion rf meter BTW

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[N017RW]

I don't have mw to dbm conversion handy but IGNORE antenna gain. You cannot measure that. It is derived at manufacture.

I do not have any of your equipment so I can only address the use of attenuation to drop to levels compatable with equipment specs.

 

[JohnnyB]

I don't have mw to dbm conversion handy but IGNORE antenna gain. You cannot measure that. It is derived at manufacture.

I do not have any of your equipment so I can only address the use of attenuation to drop to levels compatable with equipment specs.

Thanks for trying to help me out. Appreciated. Really. I know when your trying to decide how much attenuation you need to use on a meter, you have to come up with a base number to go by. That's all I'm trying to do.

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[Rich C.]

Calculating "Total" Power for attenuation needed... A few of us needs to know this and I need to know if I'm on the right track. I'll use my set-up for an example.
What I have and want to test:
P4 controller - .303W
Sunhan booster - 3W
Maxxrange antenna - 14db or .025W (?)
Total watts = 3.328 or 35.22dBm (actual attenuation needed)
So, 40dB worth of attenuation would suffice? Am I on the right track? If not, could you explain as simple as possible? I understand now it's all Log scale and not linear, but wanted to check with you guys about adding controller and antenna being used to the equation.
Thanks in Advance.
JB

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There is a bit more to it. It's more involved than a direct measurement of RF power....

ERP, or effective radiated power, is a more relevant measurement of system output power. Example: a bare light bulb radiates evenly in all directions (I know, it doesn't radiate where the electrical connection is made). Put a reflector behind the bulb and the reflector concentrates the light in a single direction. If you wanted to measure the light output of a flashlight you wouldn't be particularly interested in how bright the bulb is. You would be more interested in how bright the flashlight is in the direction it's pointed in.

It's the same thing with RF. Transmitter power is a single component of RF measurement. ERP is a combination of transmitter power, and how the antenna concentrates radiated energy in the intended direction. This how an antenna system can have gain.

Example: an antenna with, say, 5dB of gain gets that gain by concentrating RF power in the intended direction(s). The ERP will be a combination of RF power output at the transmitter, and the gain the antenna system concentrates in the intended direction. Other factors come into play, such as antenna HAAT (Height Above Average Terrain), but for most of us, HAAT doesn't factor in.

The reflector of a flashlight concentrates light in the direction the flashlight is pointed. The bulb only gets so bright, there is only so much radiated light to work with, so the flashlight concentrates light in a single direction at the expense reduced light emitted at the rear of the flashlight. It works exactly the same with RF power measurements.

My P4 RC has a pair of antennas. Assuming that both antennas radiate energy (which makes sense) and if the spacing between antennas is correct, an unmodified RC will radiate more energy in the forward direction, and in the direction behind me. Because of this, if both antennas are radiating, the resulting antenna array will have some gain. I'll assume this is the rationale for DJI using a pair of antennas.

For all I know, only a single antenna radiates. The other antenna may be there just for show.

I could be wrong about this, but I doubt that one antenna is used for transmission, and the other antenna is used for reception, as I have heard out here. It's because transmission and reception don't occur at the same time. Instructions go from the RC to the bird, then it's the bird's time to transmit. It's a back-and-forth type of communication.

The most honest way to measure ERP is either by use of a field strength meter, or by implementation of some truly gnarly math. Me, I'll use the field strength meter...

So there, that's my $.02

Cheers

 

[N017RW]

No actual ERP measurement can be done in the field or with consumer hand-held meters. You need a calibrated range with lots of characterization data.
Using signal input level to antenna plus antenna dBi gain will yield a far more accurate estimation than using consumer grade field strength meter(s).

 

[Rich C.]

No actual ERP measurement can be done in the field or with consumer hand-held meters. You need a calibrated range with lots of characterization data.
Using signal input level to antenna plus antenna dBi gain will yield a far more accurate estimation than using consumer grade field strength meter(s).

Agreed. Precise ERP measurements fall outside of what's possible with consumer grade equipment, but that wasn't my point. My point was that direct measurement of transmitter power only tells part of the story. Manufacturers of "Range Boosters" understand that a curious hobbyist lacks the means to measure ERP, so they exploit that by making ridiculous claims regarding the gain of their products.

That being said, the RC must also receive signal from the bird. Let's assume that a 3 watt RF amplifier is used to pump signal into an efficient antenna array. Using an RF amp won't help with receive, unless an RF preamp is used, which introduces all kinds of unintended consequences into the mix.

Assuming that DJI is using both antennas to radiate, there are nodes to the front and rear of the RC. That is honest, useful gain for both transmit and receive.

There are all kinds of "range boosters" out there. Some of them may work a bit, most will not. I don't think that the manufacturers of inexpensive, shiny copper reflectors employed RF engineers to design their products. It's possible I suppose, but I doubt it.

My personal belief is that, because the bird has more altitude than the RC, it should be the bird that gets a proper "range boost" treatment. Doing so would require the expertise of an RF engineer, or at the very least, the expertise of an RF enthusiast who really knows his or her stuff.

Bottom line for me, if you want a serious range boost you'll end up paying someone who really knows their stuff a whole bunch of $$ to get the job done.

\Cheers

 

[JohnnyB]

Well, I don't know **** evidently and my range out last my battery, and I didn't cost me a dime!

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[N017RW]

Agreed. Precise ERP measurements fall outside of what's possible with consumer grade equipment, but that wasn't my point. My point was that direct measurement of transmitter power only tells part of the story. Manufacturers of "Range Boosters" understand that a curious hobbyist lacks the means to measure ERP, so they exploit that by making ridiculous claims regarding the gain of their products.

That being said, the RC must also receive signal from the bird. Let's assume that a 3 watt RF amplifier is used to pump signal into an efficient antenna array. Using an RF amp won't help with receive, unless an RF preamp is used, which introduces all kinds of unintended consequences into the mix.

Assuming that DJI is using both antennas to radiate, there are nodes to the front and rear of the RC. That is honest, useful gain for both transmit and receive.

There are all kinds of "range boosters" out there. Some of them may work a bit, most will not. I don't think that the manufacturers of inexpensive, shiny copper reflectors employed RF engineers to design their products. It's possible I suppose, but I doubt it.

My personal belief is that, because the bird has more altitude than the RC, it should be the bird that gets a proper "range boost" treatment. Doing so would require the expertise of an RF engineer, or at the very least, the expertise of an RF enthusiast who really knows his or her stuff.

Bottom line for me, if you want a serious range boost you'll end up paying someone who really knows their stuff a whole bunch of $$ to get the job done.

\Cheers

You should look around here a bit. There's lots of examples of the improvements folks have achieved over the last 2-3 years which may contradict some of your assumptions.

 

[Rich C.]

You should look around here a bit. There's lots of examples of the improvements folks have achieved over the last 2-3 years which may contradict some of your assumptions.

I know there are guys out there who are running multiple batteries in the bird, spotters and serious RF being pumped out of the RC. I have followed with interest conversations among serious enthusiasts who live for extended range. Most of these folks really know their stuff, and it shows. That impresses me. Inflated claims about cheap parabolic thingies doesn't impress me. Even if the parabolic range extenders actually work, they must be precisely aligned to the antenna, and theantennas must be precisely aligned to each other. A 1/4 wavelength at 2.4gHz isn't very long. It doesn't take much misalignment to make matters worse than stock.

It comes down to what I've been saying all along, that serious passion, expertise and money are required to get the job done right.

Cheers again...

 

[JohnnyB]

Joking aside, my only purpose for metering is troubleshooting. It doesn't take a $30,000 meter to see that an amp that use to read -11 dBm, now reads -18 dBm, and may need to be checked out. Even with my "lacking" Immersion RF meter I could tell this.

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[JohnnyB]

This is all fun to experience.. the flying, modifying, and learning, don't matter what level you're at. It's a hobby, and I'm loving it!

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[N017RW]

Joking aside, my only purpose for metering is troubleshooting. It doesn't take a $30,000 meter to see that an amp that use to read -11 dBm, now reads -18 dBm, and may need to be checked out. Even with my "lacking" Immersion RF meter I could tell this.

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Cool. You can be very confident in your conducted measurements. Once you start to try measure radiated power and fields that's where it becomes much less certain.

 

[JohnnyB]

Cool. You can be very confident in your conducted measurements. Once you start to try measure radiated power and fields that's where it becomes much less certain.

I can understand this. I may never get to the level some guys are, but the passion can be matched. Learn something everyday here and I'm thankful for it. Thanks for all the input.

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[JohnnyB]

Simply put: If your meter has a 10db max input and you want to measure something expected to output 45db you should insert 40db or so attenuation. Then add the 40db to the actual meter reading.

"Expected output" Is the only step I was asking about to begin with. While appreciated, all the replies went beyond and still nobody has answered if I was going about it correctly, besides saying to leave the antenna out of the picture. Just coming out and asking, to get the expected output, is converting my amps wattage and controller wattage to dBm all I need to worry about then to give me how much needs to be attenuated?


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