Radio Frequencies for Passing Through Walls

[Bignutsami]

What radio frequencies pass through walls the best? I thought it was long waves but i just read that UHF CB's are better for indoor use, as opposed to the 27mhz band radios. How effective would a 2.5ghz TV transmitter be when transmiting through walls.

[10fingers]

2.5 ghz would not pass through much. The higher the frequency the more the radio waves have the tendency to reflect.

[J]

Lower frequencies are better. What are you trying to do? The 2.4GHz commercial video senders will transmit through a couple of walls or so in a house.

[Zambosan]

Unfortunately, the Shannon limit for useful bandwidth scales linearly with the frequency, so low frequencies can carry less information. Real-time video is a bandwidth hog, particularly hi-res video, so you're stuck with a frequency & modulation/FEC scheme capable of carrying the required rate of data. High frequencies are also much more directional, so with a focused antenna and aligned receiver, you lose a much lower percentage of the radiated power due to spreading (diffraction). And of course, if you radiate more power, you'll get better range & penetration.

[Jack Ruby]

At Radio Shack they sell Transmitters for Tele signal. I belive these are UHF.

[Jumala]

There is no doubt, VLF frequencies are best to pass through solids like water or rock. Submarines use VLF to contact their bases while under water operation. The problem is that the antennas are extreme long. The land-stations have their km long antennas buried in the ground. For example Seattle (W7) works at 24,8 KHz with more than 500 KW.
I think for practical use is CB the best because the cheapest.

If you intend to transmit a video signal you need a big band-width of some MHz. (no chance for CB)

[PYRO500]

VLF would never be able to carry a video signal, at such low frequencyes you can carry much less data without using several MHz worth of banwith at huge powers to radiate that energy in fact I remember hearing about planes that communicated with submerged subs that had to fly in a circle to drag the antenna trailing wire in a loop and could take something like 3 min to send 1 alpha charachter

[Fl4PP4W0k]

If you want a radio to have good penetration, look for something around the UHF mid band. Like 400-600 or so.
In applications that require the use of radios indoors, and thru obstructions Eg: Steel hulls of ships, then usually ~450MHz are used.

I know for sure that many warehouses \ container storage areas use UHF radios, for the fact that VHF (~150MHz) is TERRIBLE in these conditions.

For your application... I would go with either 450MHz for long range... or 800MHz for shorter ranges. 800MHz has OK penetration... though not as much as 450. Its used in many cell-phones...and they operate indoors <img border="0" title="" alt="[Wink]" src="wink.gif" /> mostly

Oh..is this analog video or digital?
Digital needs way less than the 5MHz or so that analog uses.
I think 1MHz would be more than adequate for low-ish res.

l8r,
rob

[Fl4PP4W0k]

Oh... 3 minutes to send one alphanumeric character :|

Nope.

I would guess that the VLF military use could handle a data rate of about 150bps or so.
Its mostly used for telemetry based applications, so thats perfectly adequate.

What about submarine voice \ data ???
Is that broad band VLF?

[Zambosan]

If I'm not mistaken, subs must surface or float an antenna buoy before making voice communications. It's difficult to do any kind of spread-spectrum communication at low frequencies because of the low bandwidth of each freq & the large degree of spreading & inter-symbol interference you get from the very directionless LF signals. But then again, the (US) military may have solved many of these problems already; and we won't know about it for another 30 years. :)

[PYRO500]

most subs can float a bouy for some communications but when in enemy territory the last thing you want to do is launch a big bouy that will leap out of the water drawing attention to the subs location.

[James]

Ah, slightly off topic, but. I just finished reading 'The hunt for Red October'. I think that the very low bandwidth technology mentioned earlier is called ELF. '...the ELF radio passed on data slowly about one character every thirty seconds.' It also mentioned the use of '...new, a laser transmitter. This rotated and locked onto the carrier wave...without giving away the subs position'

[PYRO500]

Yes, ELF, that's what I was talkng about. As for 1 charachter every 30 seconds, thats in the best of circumstances. You have to allow for error corection.

<small>[ July 04, 2002, 06:42 PM: Message edited by: PYRO500 ]</small>

[Fl4PP4W0k]

Hrmph... I have been proved wrong <img border="0" title="" alt="[Wink]" src="wink.gif" />
The extremely long wavelengths would mean any sort of data transfer wouldnt exactly be speedy....

[AmonDin]

What would you even use it for? A home network is easier and cheaper to set up using Cat 5 standard. Just buy a cheap 10/100 hub and a few lengths of cable, if you're smart you'll invest 70 bucks tops.