Indoor vs Outdoor, directional or not?

I was considering a Yagi with these specs for indoor use:

looks like a sword with small nipples on each side of it.

Frequency range: 2400~2500MHz

- High quality wireless network booster antenna

- Gain: 15dBi~18dBi

- Bandwidth: 100MHz

- Interface: N female

- Vertical lobe width: 23°

- Horizon lobe width: 26°

- Input impedance: 50 Ohms

- Vertical Polarization

- Max power: 50W

Will use with a usb adapter.

Then I ran into these comments, which make me wonder if Yagis are any good indoors?

"I have great connections to hundreds(yes hundreds) of wifi hotspots and all this is without direct visibility!; I use it as an indoor antenna and it's not even pointed at the window but at a brick wall :)"

and from another user:

"Other Thoughts: The cable is a bit short, but this helps keeping the loss low. Directional antennas are not suited to be used indoor, walls reflections usually mess things up to the point that it will perform just as a normal omnidirectional antenna."

Is this true, that directional antennas are no good indoors?

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Directional antennas are great indoors, but a Yagi is not the best choice IMHO -- suggest a panel or dish antenna instead.

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John Navas

Any particular reason you left out he manufacturer and model number?

Umm... yeah, righ.

A 23 degree vertical beam width is not going to yield 18dBi of gain. My guess(tm) would be an optimistic 13-15dBi. Probably less. Kinda looks like the specs on the MFJ1800 yagi antenna.

I did an analysis on this antenna and declared it to be a piece of marginal junk:

Details and explanations if you need them. Some of the clone antennas found on eBay are somewhat better built.

Does this unspecified model USB adapter happen to have a coaxial connector for attaching the antenna?

No comment. Instead, kindly disclose what you're trying to accomplish and I'll pontificate on whether a yagi is appropriate. If you're trying to "drill" through a multitude of walls, any antenna with lots of gain will work. However, if you're trying to "illuminate" an area, room, or floor, a yagi is far to narrow beamwidth for the application.

Great connections are a good thing. Being able to use those connections is something else. If you have so much gain that you end up hearing more stations besides the desired one, you have the magic formula for maximizing interference. A really directional antenna will help you hear the desired station, but any other stations along the line of sight will also be heard. This is not a good thing.

The good news is that lots of gain implies a narrow beamwidth, which allows you eliminate interference coming in from the sides. You get get clobbered by anything along the line of sight, but little from the sides is a problem. The bad news is that the yagi is probably the worst antenna for side lobes and picking up crud from the back and sides. Consider a panel or parabolic dish if this is a problem.

Cable loss is the same, no matter what antenna you select. Yep, reflections cause problems indoors.

No comment. Disclose what you're trying to accomplish, and what you ahve to work with, and maybe a determination can be made. If you don't want to go through the exercise, I agree with John. Get a panel or maybe a dish.

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