Questions about AMPS

proroc · 03-03-2003

I have a question about amps, I want to buy a amp but see they come in 250mW, 500mW, 1WATT. I dont want to spend $300 to find out they do nothing. Right now I am using a orinoco gold card with a 5dBI omni. If I were to buy an amp what would be the right wattage, and what kind of dBI gains can I expect. Thanks for all your help...

blackwave · 03-03-2003

Quote:

Originally posted by proroc
I have a question about amps, I want to buy a amp but see they come in 250mW, 500mW, 1WATT. I dont want to spend $300 to find out they do nothing. Right now I am using a orinoco gold card with a 5dBI omni. If I were to buy an amp what would be the right wattage, and what kind of dBI gains can I expect. Thanks for all your help...

what is it that you plan to do with an amp?... if you were just using it with netstumbler you would probably be better off with a pre-amp (Rx)... either way check your local laws to make sure the amp isn't violating any laws.

proroc · 03-03-2003

Yeah, i only want to use it for netstumbler, i dont want to TX with it only RX. Are there any links or suggestions of what i should buy ???? thanks.

Thorn · 03-03-2003

Generally, RF amps are a bad idea unless you have a real need, and know what you are doing with them. If you're just wardriving, the card and antenna alone is more than sufficient. If you really have to have something, Blackwave is right. Get a RX only amp.

The is no such thing as the "right wattage." Right wattage for what? That depends on what your SOM works out to be.

deciBels are logorithmic reference, where the basic unit is 1.0 mW. Therefore a 3dB increase is a doubling in power. The examples you cited work out to:
24dB = 250 mW
27dB = 500 mW
30dB = 1.0 W

A couple of things to remember:
1) Amps increase the noise level along with the signal level.
2) A TX only amp will not help with reception. Many amps are TX only. Two way amps cost more.
3) Know what antenna and amp combinations are legal. YOU as the operator are responsible for the ERP. If you violate the applicable laws because you don't know how correctly compute the output, the FCC will still make you pay the fines.

proroc · 03-03-2003

Ok I am starting to understand and see things much clearer, thanks to you guys. Last question, can you post a link to a site that sells a RX only amp?

Also when you say:

deciBels are logorithmic reference, where the basic unit is 1.0 mW. Therefore a 3dB increase is a doubling in power. The examples you cited work out to:
24dB = 250 mW
27dB = 500 mW
30dB = 1.0 W

Do you mean if I currently receive my AP at 60dBI signal strenght using my orinoco gold card and a 5dBI omni, I can expect to gain 24dB in signal strenght using a amp, making it 36dB final signal strenght??

Thorn · 03-03-2003

Search around for the amp various dealers. There a plenty out there. I'd start with Fab-Corp and YDI. Wireless Central also has a link above.

Most amps on the TX side will take any input within a certain range. That input put has no effect on the output level which is fixed. So you add only the amp output to the antenna gain. So assuming a 250mW amp and a 5dB antenna: 24dB + 5db = 29dB final output. Some amps output is added to the card or AP output, but those usually have limited upper end which they cannot exceed.

As far as seeing a 24dB increase in received signal strength, you may, but you can't count on it. Remember, the noise will increase too, and may drowned out any increase. For a good explanation of this, look at this FAQ at YDI's site.

BTW, you might want to check around regarding dB v. dBi v. dBd v. dBm. You're mixing some terms, and while it's hardly a big deal, there are differences. A purist would already have been flaming you.

If you don't know the difference, just stick with dB. It's safe generic term.

proroc · 03-03-2003

Thanx thorn.. you have been a real help.... Yeah, yeah there are differences between db terms, and one day i'm sure I will know those differences. As for now I am a newbie to certain terms, and I will admit that I do not know all the answers...

BTW: Don't flame me for being a st00pid n00b, it's not nice

03-03-2003	#1 (permalink)
proroc Registered Member Join Date: Jan 2003 Posts: 7	Questions about AMPS I have a question about amps, I want to buy a amp but see they come in 250mW, 500mW, 1WATT. I dont want to spend $300 to find out they do nothing. Right now I am using a orinoco gold card with a 5dBI omni. If I were to buy an amp what would be the right wattage, and what kind of dBI gains can I expect. Thanks for all your help...

03-03-2003	#4 (permalink)
Thorn Did you do the math? Join Date: Apr 2002 Location: Villa Straylight Posts: 10,358	Generally, RF amps are a bad idea unless you have a real need, and know what you are doing with them. If you're just wardriving, the card and antenna alone is more than sufficient. If you really have to have something, Blackwave is right. Get a RX only amp. The is no such thing as the "right wattage." Right wattage for what? That depends on what your SOM works out to be. deciBels are logorithmic reference, where the basic unit is 1.0 mW. Therefore a 3dB increase is a doubling in power. The examples you cited work out to: 24dB = 250 mW 27dB = 500 mW 30dB = 1.0 W A couple of things to remember: 1) Amps increase the noise level along with the signal level. 2) A TX only amp will not help with reception. Many amps are TX only. Two way amps cost more. 3) Know what antenna and amp combinations are legal. *YOU* as the operator are responsible for the ERP. If you violate the applicable laws because you don't know how correctly compute the output, the FCC will still make you pay the fines. __________________ Thorn "Read Altas Shrugged. Compare it to today. Repeat as necessary"

03-03-2003	#6 (permalink)
Thorn Did you do the math? Join Date: Apr 2002 Location: Villa Straylight Posts: 10,358	Search around for the amp various dealers. There a plenty out there. I'd start with Fab-Corp and YDI. Wireless Central also has a link above. Most amps on the TX side will take any input within a certain range. That input put has no effect on the output level which is fixed. So you add only the amp output to the antenna gain. So assuming a 250mW amp and a 5dB antenna: 24dB + 5db = 29dB final output. Some amps output is added to the card or AP output, but those usually have limited upper end which they cannot exceed. As far as seeing a 24dB increase in received signal strength, you may, but you can't count on it. Remember, the noise will increase too, and may drowned out any increase. For a good explanation of this, look at this FAQ at YDI's site. BTW, you might want to check around regarding dB v. dBi v. dBd v. dBm. You're mixing some terms, and while it's hardly a big deal, there are differences. A purist would already have been flaming you. If you don't know the difference, just stick with dB. It's safe generic term. __________________ Thorn "Read Altas Shrugged. Compare it to today. Repeat as necessary"

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03-03-2003	#3 (permalink)
proroc Registered Member Join Date: Jan 2003 Posts: 7	Yeah, i only want to use it for netstumbler, i dont want to TX with it only RX. Are there any links or suggestions of what i should buy ???? thanks.

03-03-2003	#5 (permalink)
proroc Registered Member Join Date: Jan 2003 Posts: 7	Ok I am starting to understand and see things much clearer, thanks to you guys. Last question, can you post a link to a site that sells a RX only amp? Also when you say: deciBels are logorithmic reference, where the basic unit is 1.0 mW. Therefore a 3dB increase is a doubling in power. The examples you cited work out to: 24dB = 250 mW 27dB = 500 mW 30dB = 1.0 W Do you mean if I currently receive my AP at 60dBI signal strenght using my orinoco gold card and a 5dBI omni, I can expect to gain 24dB in signal strenght using a amp, making it 36dB final signal strenght??

03-03-2003	#7 (permalink)
proroc Registered Member Join Date: Jan 2003 Posts: 7	Thanx thorn.. you have been a real help.... Yeah, yeah there are differences between db terms, and one day i'm sure I will know those differences. As for now I am a newbie to certain terms, and I will admit that I do not know all the answers... BTW: Don't flame me for being a st00pid n00b, it's not nice