booster questions US

The FCC only allows 36dB. If I use a 100 mW booster (20 dB), does it matter
what the radio power is? If the transmit power of the radio is 15dbm, does
the booster simply "absorb" it? Or is the booster 20 dB + the 15dbm? - -
And, BTW, what is the difference between dbm and dB and dBi?

To stay within the FCC unlicensed band regulations, I want to use a 100 mW
outdoor booster (20dB) and a 15 dBi antenna (or I'll have another example
below). Will I actually be within the regulations just considering those,
or do I have to think about the transmit power of the radio itself?

Also, from my reading, I understand that some 802.11 boosters do not play
well with 54G. I don't really understand why that is, but some retailers
like Fleeman Anderson and Bird say that the only 54G boosters they have are
from RF Linx in the L series. RF Linx lists a 200 mW indoor "antennafier"
booster at 23 dB and a 100 mW "antennafier" booster at 20 dB. 50 feet of
LMR 400 should typically have a loss of about about 3.3 dB (I think). So,
if my booster is indoors and my antenna is at the end of 50 feet of LMR-400
and has lightening protection installed (for an additional .3 dB loss), -
Well, can I count on that sort of loss to actually be evident? - I'm
hoping to be able to safely stay within the regulations while using the 200
mW booster and a 15.4 dBi antenna.

On Mon, 24 Nov 2003, i'm_tired wrote:
> The FCC only allows 36dB. If I use a 100 mW booster (20 dB), does it matter
> what the radio power is? If the transmit power of the radio is 15dbm, does
> the booster simply "absorb" it? Or is the booster 20 dB + the 15dbm? - -
> And, BTW, what is the difference between dbm and dB and dBi?

dB = 1000 * dBm. dBi is not comparable in that context. You should get a book
on electronics theory (or physics that includes E&M) to properly understand
these terms.

The "booster" (really, an amplifier) is usually designed for a set maximum
output power and an input power range over which the output may vary or may be
fixed. One doesn't simply add these values together for transmit power.

> To stay within the FCC unlicensed band regulations, I want to use a 100 mW
> outdoor booster (20dB) and a 15 dBi antenna (or I'll have another example
> below). Will I actually be within the regulations just considering those,
> or do I have to think about the transmit power of the radio itself?

Not a problem. It could be a problem if the amplifier put out a higher
powered transmit signal.

> Also, from my reading, I understand that some 802.11 boosters do not play
> well with 54G. I don't really understand why that is, ...

Because the signal that is output is modulated differently - in a way that the
design for 802.11b (or b+ = 22Mbps) works but not that g works (or works well).

> ... but some retailers
> like Fleeman Anderson and Bird say that the only 54G boosters they have are
> from RF Linx in the L series. RF Linx lists a 200 mW indoor "antennafier"
> booster at 23 dB and a 100 mW "antennafier" booster at 20 dB. 50 feet of
> LMR 400 should typically have a loss of about about 3.3 dB (I think).

Times Microwave (who makes "LMR" cables) has a data sheet available so anyone
can compute the actual loss.

> So, if my booster is indoors and my antenna is at the end of 50 feet of
> LMR-400 and has lightening protection installed (for an additional .3 dB
> loss), - Well, can I count on that sort of loss to actually be evident? - I'm
> hoping to be able to safely stay within the regulations while using the 200 mW
> booster and a 15.4 dBi antenna.

200mW into a 15.4dBi antenna will be 38.4 dBm before cable losses, and the
overall system should be under 36dBm (~34.8). However, you didn't say if you
were using a directional antenna - which doesn't have the 1-for-1 reduction rule
(but has a 1-for-3 rule and no cap on the ERP other than physical size).

D. Stussy wrote:
> On Mon, 24 Nov 2003, i'm_tired wrote:
>> The FCC only allows 36dB. If I use a 100 mW booster (20 dB), does
>> it matter what the radio power is? If the transmit power of the
>> radio is 15dbm, does the booster simply "absorb" it? Or is the
>> booster 20 dB + the 15dbm? - - And, BTW, what is the difference
>> between dbm and dB and dBi?
>
> dB = 1000 * dBm. dBi is not comparable in that context. You should
> get a book on electronics theory (or physics that includes E&M) to
> properly understand these terms.

Can you recommend a book that will describe the basics?

>
> The "booster" (really, an amplifier) is usually designed for a set
> maximum output power and an input power range over which the output
> may vary or may be fixed. One doesn't simply add these values
> together for transmit power.

This is good news. I've been looking over some charts like these
http://www.rflinx.com/Calculations.htm and I assumed that's how it worked,
but I just wasn't sure.

<snip>
> Times Microwave (who makes "LMR" cables) has a data sheet available
> so anyone can compute the actual loss.

I found it. It looks like I'll have to be able to identify if my cable is
SuperFlex or not, but otherwise, I was right. 6.6 dB loss over 100 feet and
thus 3.3 over 50 feet. At least that is my assumption. It seems like loss
is progressive, though, so perhaps 3.3 might be somewhat of a high estimate.
Hopefully, the lightening protection, pigtail, and related connectors will
keep it near 3.3 or so.

>
>> So, if my booster is indoors and my antenna is at the end of 50 feet
>> of LMR-400 and has lightening protection installed (for an
>> additional .3 dB loss), - Well, can I count on that sort of loss to
>> actually be evident? - I'm hoping to be able to safely stay within
>> the regulations while using the 200 mW booster and a 15.4 dBi
>> antenna.
>
> 200mW into a 15.4dBi antenna will be 38.4 dBm before cable losses,
> and the overall system should be under 36dBm (~34.8). However, you
> didn't say if you were using a directional antenna - which doesn't
> have the 1-for-1 reduction rule (but has a 1-for-3 rule and no cap on
> the ERP other than physical size).

I can't pretend to know exactly what ERP stands for (In my line of work, it
stands for Enterprize Resource Planning <g>). I keep seeing it in the FCC
docs but it always seems to go along with a dB rating. - So, are you saying
that if I am using a Yagi, Panel, or Parabolic Grid directional antenna, it
is't governed by the 36 dB rule? I can amplify three times as much as for
an Omni?

Thanks for your time.

"D. Stussy" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) rg...
> On Mon, 24 Nov 2003, i'm_tired wrote:
> > The FCC only allows 36dB. If I use a 100 mW booster (20 dB), does it
matter
> > what the radio power is? If the transmit power of the radio is 15dbm,
does
> > the booster simply "absorb" it? Or is the booster 20 dB + the
15dbm? - -
> > And, BTW, what is the difference between dbm and dB and dBi?
>
> dB = 1000 * dBm. dBi is not comparable in that context. You should get a
book
> on electronics theory (or physics that includes E&M) to properly
understand
> these terms.
>

D.Stussy, You should brush up yourself!

dB = decibel, which is a logarithmic ratio between to power values.

dBm is the ratio between the power level being measured and a fixed
reference of 1 mW.

dBi is the ratio between the peak signal strength of a given antenna and a
theoretical (isotropic) antenna with absolutely no directionality at all.
So dBi can be added diectly to dBm to yield what the FCC calls EIRP.

Here is a handy primer: http://www.ydi.com/deployinfo/wp-decibels.php

On Mon, 24 Nov 2003, i'm_tired wrote:
> D. Stussy wrote:
> > On Mon, 24 Nov 2003, i'm_tired wrote:
> >> The FCC only allows 36dB. If I use a 100 mW booster (20 dB), does
> >> it matter what the radio power is? If the transmit power of the
> >> radio is 15dbm, does the booster simply "absorb" it? Or is the
> >> booster 20 dB + the 15dbm? - - And, BTW, what is the difference
> >> between dbm and dB and dBi?
> >
> > dB = 1000 * dBm. dBi is not comparable in that context. You should
> > get a book on electronics theory (or physics that includes E&M) to
> > properly understand these terms.
>
> Can you recommend a book that will describe the basics?

Not any specific book - sorry. I learned about these things decades ago, so I
don't know what books are currently in print. However, see also "Amateur Radio"
- these terms are quite common there too.

> > The "booster" (really, an amplifier) is usually designed for a set
> > maximum output power and an input power range over which the output
> > may vary or may be fixed. One doesn't simply add these values
> > together for transmit power.
>
> This is good news. I've been looking over some charts like these
> http://www.rflinx.com/Calculations.htm and I assumed that's how it worked,
> but I just wasn't sure.

There is usually a graph supplied that will show the output power for a given
input - that would come with the amp.

> <snip>
> > Times Microwave (who makes "LMR" cables) has a data sheet available
> > so anyone can compute the actual loss.
>
> I found it. It looks like I'll have to be able to identify if my cable is
> SuperFlex or not, but otherwise, I was right. 6.6 dB loss over 100 feet and
> thus 3.3 over 50 feet. At least that is my assumption. It seems like loss
> is progressive, though, so perhaps 3.3 might be somewhat of a high estimate.
> Hopefully, the lightening protection, pigtail, and related connectors will
> keep it near 3.3 or so.

Yes, the loss in dB is linear over the length of the cable. Note that dB is a
function of an exponential/logarithmic nature and is therefore itself not
linear.

> >> So, if my booster is indoors and my antenna is at the end of 50 feet
> >> of LMR-400 and has lightening protection installed (for an
> >> additional .3 dB loss), - Well, can I count on that sort of loss to
> >> actually be evident? - I'm hoping to be able to safely stay within
> >> the regulations while using the 200 mW booster and a 15.4 dBi
> >> antenna.
> >
> > 200mW into a 15.4dBi antenna will be 38.4 dBm before cable losses,
> > and the overall system should be under 36dBm (~34.8). However, you
> > didn't say if you were using a directional antenna - which doesn't
> > have the 1-for-1 reduction rule (but has a 1-for-3 rule and no cap on
> > the ERP other than physical size).
>
> I can't pretend to know exactly what ERP stands for (In my line of work, it
> stands for Enterprize Resource Planning <g>). I keep seeing it in the FCC
> docs but it always seems to go along with a dB rating. - So, are you saying
> that if I am using a Yagi, Panel, or Parabolic Grid directional antenna, it
> is't governed by the 36 dB rule? I can amplify three times as much as for
> an Omni?

In this context, ERP = Effective Radiated Power.