Hello,
What tx-power= -30 means? Why to use negative values? Also have you tried to choose +30 on cm9?
-30 means -30dB of signal. The Decibel(dB) represents a relative value, where "0" does not mean "no signal". What the Decibel is actually relative to is determined by the letter placed after the "B" in "dB", which is assumed to be an "m"(dBm) if no other letter is present. 1(one) "dB" or "dBm" represents one milliwatt, and every increase or decrease from that number by 10dB represents 10 times more or less power. 10dB means 1 milliwatt X 10, and -10dB means 1 milliwatt divided by 10, which is still more than "no signal"..... If I recall correctly, support for less-than-zero values was added a few Release Candidates ago, in order to allow an administrator to turn his radio down further than 0dB.
The CM-9 card is rated at 18dB of output power, which equals about 65mW. 30dB is about one watt(1000mW) of power, which means that the 30dB setting will require the radio to put out 935mW more than the 65mW it was designed to put out, and this could obviously severely damage your radio, and would also make it draw much more current from the Mini-PCI slot than it was originally designed to draw. Also, for other reasons, special considerations are required in the design of a circuit that produces more than about 26dB or 27dB, in order to keep from severely compromising the effectiveness of some of the newer modulation schemes. In other words, even if it does work, it could damage the quality of your radio signal.....
Hitek
The CM-9 card is rated at 18dB of output power, which equals about 65mW. 30dB is about one watt(1000mW) of power, which means that the 30dB setting will require the radio to put out 935mW more than the 65mW it was designed to put out, and this could obviously severely damage your radio, and would also make it draw much more current from the Mini-PCI slot than it was originally designed to draw. Also, for other reasons, special considerations are required in the design of a circuit that produces more than about 26dB or 27dB, in order to keep from severely compromising the effectiveness of some of the newer modulation schemes. In other words, even if it does work, it could damage the quality of your radio signal.....
Hitek
Having a radio background I am happy with neg dB (m) and pos dB (m). Or even dBW .... not that we play with whole WATTS here!
However I would like to know what the 'default ' power setting (especially for CM9) actually sets the card power to..
If you look in the TX power in the 'advanced status' tab of a card set in station mode, the power of various data rates varies - which is how it should be - but 6 thru 24 Mbits/s show 27 dBm - which is well above the card spec..
It works fine and I suspect a minor bug, with the card just operating at default power - but I would like this confirmed.. The CM9 CAN'T produce 27 dBm power (or why would the SR5 be available !!)
Cheers.
However I would like to know what the 'default ' power setting (especially for CM9) actually sets the card power to..
If you look in the TX power in the 'advanced status' tab of a card set in station mode, the power of various data rates varies - which is how it should be - but 6 thru 24 Mbits/s show 27 dBm - which is well above the card spec..
It works fine and I suspect a minor bug, with the card just operating at default power - but I would like this confirmed.. The CM9 CAN'T produce 27 dBm power (or why would the SR5 be available !!)
Cheers.
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wisp-equipment
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In our testing, the dBm tx power settings are actually relative, but not likely true dBm tx powers.
Setting tx power to default, with the advanced tab, we see that default is 24-27dBm in some configs, some other configs, it might be 17dBm.
Regardless, RSSI on the remote side does not increase on a dB per dB increase basis (ie, if you increase the tx power on one side, the RSSI on the remote doesn't always change by 1dB).
I think this comes down the card you are using. Tx powers are relative to the radios max output. CM9's can be turned up above their default power setting, we've used them that way just fine for a long time, often set at 24-27dBm and even sometimes set at 30dBm.
I don't have a meter but I've been told that they put out up to about 23dBm at max output. But, that may also be relative to how the power is measured.
OFDM measurements are different from DSSS measurements. OFDM is measured by "peak" power, where DSSS is measured more on an "average" power. When in OFDM mode (802.11a or g), peak power may actually hit some high levels, but only on some of the carriers within the OFDM channel and only some of the time.
Anyway, I'm no RF guru, but thats the way I understand it and thats what our testing has shown us.
0-30dBm means you might get 0-23 or 0-24dBm actual tx power from a CM9. From another radio, those numbers will be relatively different, but should be relatively the same from radio to radio while the model is the same.
Plus, radios generally have a +/- 2dB variance in power. This is because components and the manufacturing process can only give you tx power within a certain range, with a potential for higher or lower tx power on a radio by radio basis (each radio manufactured will generally be slightly stronger or weaker than another).
I tend to fine tune my links by setting the power up and down until I find the "sweet spot". Once I find that sweet spot, I generally keep it there and that "sweet spot" will vary depending on a number of different factors:
- Frequency
- Coax
- Antenna Make/Model and specifically VSWR
- Ampflier (if used, generally we turn the tx power on the radio WAY down to 10-20dBm, depending on what the amp is designed for).
Judd
Setting tx power to default, with the advanced tab, we see that default is 24-27dBm in some configs, some other configs, it might be 17dBm.
Regardless, RSSI on the remote side does not increase on a dB per dB increase basis (ie, if you increase the tx power on one side, the RSSI on the remote doesn't always change by 1dB).
I think this comes down the card you are using. Tx powers are relative to the radios max output. CM9's can be turned up above their default power setting, we've used them that way just fine for a long time, often set at 24-27dBm and even sometimes set at 30dBm.
I don't have a meter but I've been told that they put out up to about 23dBm at max output. But, that may also be relative to how the power is measured.
OFDM measurements are different from DSSS measurements. OFDM is measured by "peak" power, where DSSS is measured more on an "average" power. When in OFDM mode (802.11a or g), peak power may actually hit some high levels, but only on some of the carriers within the OFDM channel and only some of the time.
Anyway, I'm no RF guru, but thats the way I understand it and thats what our testing has shown us.
0-30dBm means you might get 0-23 or 0-24dBm actual tx power from a CM9. From another radio, those numbers will be relatively different, but should be relatively the same from radio to radio while the model is the same.
Plus, radios generally have a +/- 2dB variance in power. This is because components and the manufacturing process can only give you tx power within a certain range, with a potential for higher or lower tx power on a radio by radio basis (each radio manufactured will generally be slightly stronger or weaker than another).
I tend to fine tune my links by setting the power up and down until I find the "sweet spot". Once I find that sweet spot, I generally keep it there and that "sweet spot" will vary depending on a number of different factors:
- Frequency
- Coax
- Antenna Make/Model and specifically VSWR
- Ampflier (if used, generally we turn the tx power on the radio WAY down to 10-20dBm, depending on what the amp is designed for).
Judd