I would like some help for creating wireless ethernet network using
VHF radio with frequency range of 130MHz-18MHz (for SCADA
application). The distance supported shall be upto 100km LOS.
can be added as necessary. Kindly advise on industry products
available for such option.
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
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
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.
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
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:
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
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
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.
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.
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
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.
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
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
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
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.
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?