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Author Topic: emcomm freq's  (Read 1119 times)
KJ4SKP
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Posts: 69




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« on: January 14, 2013, 12:20:22 PM »

Lately I've seen many vids of hams w/ emcomm boxes equipped w/ 2meter rigs.  Just curious about the range of 2 meters. If the emergency situation disabled repeaters, how effective would 2 meters be then?
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VA3GUY
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Posts: 177




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« Reply #1 on: January 14, 2013, 01:08:01 PM »

Years ago, when I was involved in 2 meters, I lived in a 15 story apartment building and had access to the roof. I had an 11 element beam up there and using 25 watts, I was able to have a conversation with a friend in Montreal (120 miles away), SIMPLEX.

All that to say that 2 meters is often line-of-sight so the higher the better, with no obstructions and obviously, power will also be a large determining factor.
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KE3WD
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Posts: 5694




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« Reply #2 on: January 14, 2013, 02:03:18 PM »

It is also a very good drill for the ham interested in emcomm to find out ahead of time what their particular setup can accomplish Simplex as well as with repeaters. 

Monitoring the repeater's Input Freq when it is being operated by other hams can often give you an idea of who and where you can work Simplex.  That alone may surprise you, you may find out how many QSOs can be carried out without the repeater at all. 

A simple home made three element beam for 2 mtrs, one for 440 as well, mounted at rooftop levels, can change things dramatically along these lines.  A plus is that beams of this size can use a simple mast mount -- and old Television rotators, often available for the asking. 


73
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WB6BYU
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Posts: 13152




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« Reply #3 on: January 14, 2013, 02:16:42 PM »

That depends on the required coverage area.

I cover our whole county (except for some canyons in among the hills) on 2m
from my house using 5 watts to an antenna up about 30', and I can get into
parts of 3 surrounding counties as well.   I'm on a bit of a hill (perhaps 100'+
above much of the surrounding area) but most hams in the county can check
into the simplex net if they are running 5+ watts to an antenna at roof-top
height.  If we have problems with coverage to specific areas and the repeaters
are down, then we can send a relay team to the top of a convenient hill at 1000+
feet above the valley floor.  With a reasonable antenna and 25+ watts output,
distances of 30 to 50 miles can be covered over relatively flat ground.

Of course, knowing which stations have good coverage, and which hills cover
what parts of the county (along with how to get to them and who has the
key to the gate if needed) is part of training and preparation beforehand, as
is providing good antennas for the sites that need them.  I always recommend
that all ARES members have some sort of portable mast that will get their
antenna up 12' to 20' in the air, because height makes so much difference in
the range that can be covered.
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K2YO
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Posts: 436




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« Reply #4 on: January 14, 2013, 05:50:38 PM »

You also have to consider they type of disaster. Here in the NYC area, all five of our repeaters stayed on the air during and after the hurricane. My past experience in CA also showed that may repeaters stayed on the air after the earthquakes. Your question is an important one that most repeater operators take seriously. Here in the NE where we get a couple of days notice of a storm coming, we make it a point to take precautions to make sure the repeaters stay on the air. We also have backup equipment that can be deployed in the case of the lose of one or more machines.

That being said, some repeaters were knocked off the air by the storm. So it was dependent on those that survived to pick up the slack.

Worse case solution, the Ecomm people have portable repeaters, generators, and towers and can set up new repeaters if needed.

Last but not least, if all else fails, there's HF.

Bernie
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K5LXP
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Posts: 4474


WWW

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« Reply #5 on: January 15, 2013, 07:52:59 AM »

Just curious about the range of 2 meters.

Direct answer - line of sight.  Put the antenna in a basement and your lucky to get a fraction of a mile.  Put it on a mountaintop and you can go a hundred miles.  Testing out potential sites before a "disaster" is key to understanding what a given systems' capabilities are.


Mark K5LXP
Albuquerque, NM
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KJ4SKP
Member

Posts: 69




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« Reply #6 on: January 15, 2013, 08:08:10 AM »

thanks gentlemen. Seems like 6m might give a little better range?
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WB2WIK
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Posts: 20574




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« Reply #7 on: January 15, 2013, 11:32:29 AM »

thanks gentlemen. Seems like 6m might give a little better range?

It might, but only if the antennas are three times larger to accommodate the lower operating frequency.
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WB6BYU
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Posts: 13152




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« Reply #8 on: January 15, 2013, 12:25:05 PM »

6m has some advantages for simplex coverage, particularly in rolling hills.

But in any analysis the first step is to identify the required communications, and then
the resources you have available to accomplish it.

For our ARES group, most of our communications will be relatively local, from
the County EOC to shelters, hospitals, fire stations, etc.  As long as you can put
up an antenna at a reasonable height, 2m simplex is quite adequate for that,
and if repeaters are up then we can cover a much wider area.

The other critical path is to the State Office of Emergency Management:  we're
close enough that we can hit them on VHF simplex, but other counties that are
hundreds of miles away with some 8,000' hills in between have a harder time of it.

So 2m and 440 easily cover our local traffic.  If we need coverage into the
remote parts of the county and the repeaters are down, we send a relay team.
Several hams also have portable HF capability if needed.

Another argument for using 2m is because that is what most operators are
familiar with and have equipment for.  One of my mantras is, "if you don't
use it regularly, it won't work in an emergency."  (This applies to equipment,
people, procedures, etc.)  There are relatively few hams in the county who
have 6m equipment, and even fewer who use it regularly.  If I need to maintain
a radio link from, say, Testament Creek to Springbrook, and the repeaters aren't
working, then I'm more likely to get the link operational by sending mobile teams
to act as relays on 2m, even if it takes 2 of them, than trying to find the 6m
or HF equipment to cover the path, just because we have more 2m operators
available.  That's not to say that we don't encourage our members to upgrade
and develop a portable HF capability, but that we still have a lot of hams in the
county who only operate 2m and perhaps 440, so the pool of resources (both
equipment and operators) is much larger.

Even if we need to use HF, having a 2m rig may allow the operator to contact
a local ham with HF capability to act as a relay from their home, so a portable
HF station might not be required.  (At least at Springbrook - there aren't any
local hams living near Testament Creek.)


So, for a single radio in a go kit, a 2m radio isn't a bad choice, as that is where
a lot of the emergency response activity will be.  From most places in our county
we can reach the County EOC on simplex if necessary with a reasonable antenna,
and we can use any repeaters still functioning.  That doesn't mean that we aren't
prepared to use HF in those situations that require it, but it isn't the first thing
that we grab for most activations.

What works best for you depends on who you need to talk to in an emergency,
what frequencies they use, and what will cover the path.  For relatively local
emergencies, VHF may easily reach outside the affected area.  In other cases
(earthquake or hurricane perhaps) where a large area is affected, other bands
and/or modes may be needed, depending on your local communications plan.
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AA4HA
Member

Posts: 1389




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« Reply #9 on: January 15, 2013, 10:20:50 PM »

Barring conditions like sub or super-refraction VHF and up frequencies are usually limited to the radio horizon between two antennas. That is a function of the height of the antennas. There is a handy calculator at http://www.qsl.net/w4sat/horizon.htm

Other factors are;

Terrain
Vegetation losses (attenuation based on vegetation type)
Fresnel zone losses/obstructions
Free Space Loss (function of distance)
Reflection and refraction of signal (this may be beneficial or harmful)
Refraction may be modeled with a 2/3, 1 or 3/4 Earth and is usually connected to atmospheric effects
To a lesser extent, temperature and precipitation (unless you are in the microwave band
Polarization

You may get much greater range than a simple calculation for radio horizon, you may also get something significantly less. Usually for EMCOMM type work you want to have the most reliable link possible so you try to be reasonable in factoring in the worst case (but not being ridiculous)
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
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