Alligators and mw

Hi, John, Jeff and list,

So, I'm about to get a new bridge, g-enabled. Several choices seem to
fit.

Some of them appear to be what I've come to be cautioned about -
alligators. At least one of them allows me to set the size of his
mouth, so that's helpful to me and my neighbors when I get it going
wherever I am, though I'm not certain he can be muzzled sufficiently to
avoid yelling a bit.

However, one of them is fixed at 16dBm, with no comment about mw
amplification. mw amplification I understand at least enough to be
dangerous, but this and some others have no comment on their
amplification mw level.

It's my presumption that every bridge made has *some* level of
amplification. However, they don't seem to talk about it until one
gets to at least 100mw. Given that 100 to 200 is only 3dBm in those
I've seen, 16 infers something on the order of 40mw.

At what point does a bridge become an alligator? And since I'm
clueless, other than what I read, and manufacturers and marketers have
widely herein been chastised for inaccuracies or outright deception,
what does 16dBm translate to in mw amplification? And, for that
matter, can I take what I see in the specifications with any degree of
seriousness, or should I, as in the case of the prior antenna
discussion, just assume that whatever I read is either inaccurate or
intentionally misrepresented, and buy on price and warranty?

Thanks for any assistance.

L8R

Skip, back to replumbing the engine room

Morgan 461 #2
SV Flying Pig KI4MPC
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On 1 Sep 2006 08:09:21 -0700, "Skip - Working on the boat"
<(E-Mail Removed)> wrote in
<(E-Mail Removed) om>:

>So, I'm about to get a new bridge, g-enabled. Several choices seem to
>fit.
>
>Some of them appear to be what I've come to be cautioned about -
>alligators. At least one of them allows me to set the size of his
>mouth, so that's helpful to me and my neighbors when I get it going
>wherever I am, though I'm not certain he can be muzzled sufficiently to
>avoid yelling a bit.
>
>However, one of them is fixed at 16dBm, with no comment about mw
>amplification.

Not necessary, since that's a direct statement of output power.
Amplification is irrelevant.

>mw amplification I understand at least enough to be
>dangerous,

No and yes,

>but this and some others have no comment on their
>amplification mw level.

dBm is output power, _not_ amplification.
<http://en.wikipedia.org/wiki/Decibel#Electronics>

In radio electronics, the decibel is used to describe the ratio
between two measurements of electrical power. It can also be combined
with a suffix to create an absolute unit of electrical power. For
example, it can be combined with "m" for "milliwatt" to produce the
"dBm". Zero dBm is one milliwatt, and 1 dBm is one decibel greater
than 0 dBm, or about 1.259 mW.

dBm to Watt Conversion Calculator
<http://www.moonblinkwifi.com/dbm_to_watt_conversion.cfm>
16 dBm is 40 mW, typical of standard consumer Wi-Fi gear.

>It's my presumption that every bridge made has *some* level of
>amplification.

Essentially all radios have output amplifiers.

>However, they don't seem to talk about it until one
>gets to at least 100mw.

Look for data/spec sheets and in user manuals.

>Given that 100 to 200 is only 3dBm in those
>I've seen,

In _all_ units that's a difference of 3 dBm.

>16 infers something on the order of 40mw.

More than infers -- 16 dBm is 40 mW.

>At what point does a bridge become an alligator?

It becomes an alligator when its transmit range significantly exceeds
its receive range. That's of course a function of the transmitter at
the other end. With a high-power transmitter at the other end, it can
put out more power without becoming an alligator (and operate at greater
range). With a typical Wi-Fi transmitter at the other end it becomes an
alligator when it has much more than typical output power (e.g., an
alligator at [say] 20 dBm or more).

>And since I'm
>clueless, other than what I read, and manufacturers and marketers have
>widely herein been chastised for inaccuracies or outright deception,

I prefer to call it optimism. Variations in real world implementations
tend to result in somewhat less output power then the spec, but since
that applies to both ends, it's not terribly important.

>what does 16dBm translate to in mw amplification?

Output power of 40 mW (as explained above), _not_ amplification.

>And, for that
>matter, can I take what I see in the specifications with any degree of
>seriousness,

Take it as a rough guide. A device with a spec of 16 dBm might actually
deliver only (say) 15 dBm, but probably won't be as bad as (say) 12 dBm.

>or should I, as in the case of the prior antenna
>discussion, just assume that whatever I read is either inaccurate or
>intentionally misrepresented, and buy on price and warranty?

My advice is to stop worrying about output power. That's because you
have no control over the radios at the other end, which probably have
only standard power. Instead focus on how much antenna you need for the
range at which you want to operate with standard power output, and how
practical that will be on your boat. (A directional antenna can be
problematic on a moving boat, although I have seen [expensive]
auto-tracking setups.)

--
Best regards, FAQ for Wireless Internet: <http://Wireless.wikia.com>
John Navas FAQ for Wi-Fi: <http://wireless.wikia.com/wiki/Wi-Fi>
Wi-Fi How To: <http://wireless.wikia.com/wiki/Wi-Fi_HowTo>
Fixes to Wi-Fi Problems: <http://wireless.wikia.com/wiki/Wi-Fi_Fixes>

Hi, John, and thanks for the commentary. You've confirmed some things
and shed more light on areas previously dimly lit for me.

Just a couple of comments in followup. My observations and
presumptions:

1) Apparently my seat-of-the-pants estimation/calculation of mw at
16dBm was spot on - nowhere did I see mw discussions in manufacturer
data, other than at 100 or higher
2) The typical shore station, unless trying to do a widely distributed
subscription service, is likely to also be 16dBm/40mw, so if I were to
have that power level, I'd be matched, and not overwhelming my
neighbors

I've only gotten concerned about power levels after having been here -
before, 200mw was all I knew :{))

My antenna choice (disregarding the blatantly - per Jeff -
inaccurate/misrepresented polars) was an 8.5dBi omni stick, done long
before the discussion on prevaricating vendors. I saw that as the best
compromise between receptivity and narrow/wide band. Of course, I
also relied on the vendor (several, during my research) data, so who
knows what I *really* have? I'm still confused as to how a duck of
similar gain can have a donut, and a stick have a pizza, for a gain
pattern, however.

I might have been tempted to go higher, but that would have literally
meant higher, too (I haven't seen any higher gain antennae in the 20"
range) as I have an air draft of 62' already. Granted that in the
Caribbean I'll likely not have any issues with that, but there's no
guarantees I'll be there the rest of my life, and I also have to get
there, first :{))

Thanks again. I'll come back with the end result. Still haven't
hauled the current setup (which is doing fine, most of the time) up the
mast to see the differences, but expect they'd be better, not worse,
than at the deck level...

L8R

Skip

Morgan 461 #2
SV Flying Pig KI4MPC
See our galleries at www.justpickone.org/skip/gallery!
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"Skip - Working on the boat" <(E-Mail Removed)> hath wroth:

>I'm still confused as to how a duck of
>similar gain can have a donut, and a stick have a pizza, for a gain
>pattern, however.

dB is a ratio.
dBi is a ratio where the reference is an isotropic radiator (0dBm).

You can easily have different antennas with the same gain, but with
different radiation patterns. Some donuts will be flatter than
others. If you imagine a water balloon in the shape of the antenna
pattern, you can mold the pattern almost any way that does not change
the volume of water in the balloon. The volume of the water
represents the amount of xmit power[1]. Since antennas do NOT create
RF, the volume is always constant for a give transmitter or reference
level. Some patterns are quite bizarre. Many of them have identical
maximum gains. Some point the donut's maximum gain at the horizon,
while others point the donut somewhat above the horizon.

More details on you General Class license exam.

[1] For the hair splitters... The water balloon analogy only works
for antenna patterns with a linear scale, not a logarithmic scale.

--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558