VHF Ethernet

This is a joke, no?

...

Jerry

Try Anusol boy!

I think you need to understand some facts of radio technology: First, VHF refers to those frequencies from 30 MHz to about 300 MHz. Second,

18 MHz is not a good frequency for ethernet radios because you'll have a skywave to contend with, not just ground wave. Third, below 50 MHz, you're looking at some impressively large antennas. Fourth, most countries in the world adhere to a frequency plan which does not suggest using these frequencies for wideband communications like Ethernet.

To suggest a radio to you there would have to be demand for such a thing. Without some international agreements that suggest the use of such frequencies for an application like this, there won't be a market. And without a market, there won't be products. Even if the country you're posting from does have such uses defined for the spectrum, it won't matter because most other countries aren't using products for that band.

I suggest the use of 5.8 GHz spread spectrum microwave. If you use dishes and towers every 40 kM or so, it will get a decent bandwidth to the destination.

There is a lot more to know about this issue. I couldn't possibly summarize it in a single post here. Suffice it to say that you have an awful lot of study ahead of you.

Jake Brodsky

I've been wondering what part of the world affords a 100 Km line of sight. I have stood on the continental divide and seen Navajo Mountain some 350 Km away, but such sites are rare and unlikely to benefit from SCADA links.

Jerry

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range is 130MHz to 180MHz

On 25 Feb 2007 04:29:02 -0800, "ok" proclaimed to the world:

Try

I have communicated using these units at 20 miles distance and speeds of 2 Meg/sec.

These transducers work in the microwave range. Your requirements for using 130 MHz is not likely to be met.

range is 130MHz to 180Mhz

Simply repeating over again one element of a silly specification does not change the laws of physics to your advantage to make your desires possible.

Please come back when you have a clue or please ask for one. There are many people here who will help you. A few have tried already, but you don't seem to want to be helped?

Here's your starter for 10...

If you are UK based, then here is the spectrum plan:

Note

Annex A: there is an allocation at 167.992 to 168.008MHz for ISM devices.

Annex C: there are allocations at 173.2 to 173.35MHz, 10mW radiated power maximum.

Annex G: This lists how the remiander of the spectrum you are interested in is licensed already to land mobile radio. This means police, fire, ambulance as well as commercial licensees. They are clearly going to give this up for you!

Then from the Radiocommunications Agency:

6b General-purpose telemetry and telecommand The 27 MHz, 40 MHz, 173 MHz, 418 MHz (see section 11), 433 MHz, 868 MHz, 2400 MHz and 5800 MHz bands are appropriate for a wide range of uses. See IR2030 and the following paragraphs for further details. The 173.2 MHz band may be used as either 12.5 kHz or 25 kHz channel spacing where the channel centre frequency is 173.2 MHz + (channel spacing x channel number). For 12.5 kHz channel spacing, the channel numbers available are 1 and 3 to 11; for 25 kHz channel spacing, the channel numbers available are 2 to 5. The frequency 173.225 MHz is for fixed or short-range alarms only, not for general-purpose applications.

And...

The 173.2 to 173.35 MHz band may also be used, up to a maximum radiated power of 10 mW Section 6b (i) above describes the assigned frequencies applicable to channel spacings of 12.5 and 25 kHz respectively. Exceptionally, devices requiring channel assignments greater than 25 kHz may be acceptable, but these must never operate outside the limits of the band

173.2 to 173.35 MHz.

So take something like a Teledesign TS4000...

You might get 9600 baud if you are lucky on a single 12.5kHz channel, and at

10mW radiated power, you might push this a couple of kilometres with some big antennas at each end of the link on rooftops.

So you are interested in Ethernet protocols and speeds ...

Now go away and have a think what this means in your situation. By all means come back with some sensible questions.

David.

On Tue, 27 Feb 2007 12:58:09 -0000, "Dave Slee" proclaimed to the world:

Nice resource. It could be formatted a bit better.

Actually, there is another option, though it's not commonly used by civilian agencies. It's called Troposcatter communications. It requires a lot of power and some impressive antennas. Basically, you beam a lot of power at the troposphere, and it scatters. Some of this power arrives at the receiving site. It's a brute force method, but it works well.

With such systems you can reliably cover paths of up to 900 km. Military forces occasionally use systems because it doesn't need much infrastructure in between. However, the equipment required is not for the faint of heart.

Oh, and good luck trying to license a system like this.

Jake Brodsky

On Sat, 03 Mar 2007 08:31:42 -0500, Jake Brodsky proclaimed to the world:

This has been used by amateur radio operators and CB users for some time. CBers called it talking "skip". I have seen CBers here in eastern US talk to New Zealand sites via skip. This is only possible during times when the atmosphere is ionized properly by the sun's rays. The window for communicating this far is very small, maybe an hours sometime after sunset, depending on where you wanted to talk too. I read somewhere a few years ago that the US military had been launching rockets and using jets to seed the atmosphere so they could open this window when they wanted too. The idea was to have a backup communication system available should WWIII happen and all our satellites destroyed.

I think you're a bit mixed up here. "Skip" is what happens when you bounce a signal off the ionosphere. It is primarily a phenomenon of shortwave signals although during solar storms and the like it is not uncommon to find it on frequencies as high as 50 MHz and even 150 MHz is not unheard of.

Ionospheric skip is subject to the condition of the various ionospheric layers. One of the problems with ionospheric skip is called selective fading. This is where more than one signal arrives at the destination slightly out of phase. This can cause very selective cancellation of a single frequency of an incoming signal. It makes data transmission an interesting challenge.

With troposcatter, one relies upon the condition of the troposphere. This tends to be much more stable through the day. It is also a single path. This makes it possible to retrieve a wideband signal with no multipath distortion.

Jake Brodsky

Skip and scatter are different phenomena. Skip is always forward, but scatter goes everywhere, weakest straight back and strongest forward, but with a somewhat cardioid reflection pattern. Jake had it right. Optimum scatter paths are closer to vertical.

Skip is specular enough to support several bounces, especially when the earth bounces are over water or flat ground. I heard from New York a car stranded in the Rockies that was broadcasting on 30 meters from his car antenna using maybe 5 watts. (I notified the Colorado State Police by telephone.) The record I know of is Chicago to Australia CW 3 watts.

Jerry

On Sat, 03 Mar 2007 11:55:38 -0500, Jake Brodsky proclaimed to the world:

More not paying attention. Does anyone remember the projects I mentioned that the US Military was doing with strange ways of taking advantage of atmospheric conditions, both natural and contrived?