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

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Reply to
Skip - Working on the boat
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On 1 Sep 2006 08:09:21 -0700, "Skip - Working on the boat" wrote in :

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

No and yes,

dBm is output power, _not_ amplification.

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

16 dBm is 40 mW, typical of standard consumer Wi-Fi gear.

Essentially all radios have output amplifiers.

Look for data/spec sheets and in user manuals.

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

More than infers -- 16 dBm is 40 mW.

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).

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.

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

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.

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.)

Reply to
John Navas

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

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Reply to
Skip - Working on the boat

"Skip - Working on the boat" hath wroth:

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.
Reply to
Jeff Liebermann

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