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Author Topic: NBEMS and weak signal operators  (Read 777 times)
KV9U
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Posts: 166




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« on: March 11, 2008, 08:13:34 AM »

As many of you probably know, the NBEMS (Narrow Band Emergency Message System which some pronounce "En-beams"), is a new digital system that is primarily (but not exclusively) intended by the developers to operate on VHF. They have targeted 2 meters as the best combination of distance, with easier to handle antennas at portable sites, lowest noise, etc. The digital modes used are mostly PSK at the higher baud rates up to PSK250, but can be other modes as well.

The system requires manual (human) operators at each end of the circuit and enables the sending and receiving of messages between the operators using ARQ (error correcting) modes for accurate messaging. It can also handle e-mail, particularly outgoing, with the assisting operator forwarding the traffic into the internet.

The intent is to be able to bridge across disaster areas at least up to 100 miles, but can be more if the operators have the right equipment. I think you would be hard pressed to find any other terrestrial communications that can operate consistently 24/7/365 for short to moderate distances as is possible with 2 meter SSB/digital.

NBEMS modulates an SSB rig with tones from a computer sound card, just like is done on HF. The development team believes that there are many more VHF SSB operators than first thought. My understanding has been that there are fewer weak signal operators than we once had and a significant number of them only operate during contests. Considering the substantial numbers of Technician Class hams who could (but do not) purchase a multiband/multimode rig and then those who do but decide not to operate on SSB or digital VHF. I suspect one of the main impediments is the need for a horizontal antenna.

The NBEMS Development Team believes that horizontal polarization is necessary to be able to be able to bridge these distances to stations that work VHF SSB/digital and they want to draw upon the capable operators who have weak signal VHF capability.

If they are working WSJT modes they probably already have the necessary computer to rig interfacing, but is this getting to be a large percentage of weak signal operators?

Most importantly, do you think that a significant number of weak signal VHF operators will be interested in working emergency traffic into a disaster area?



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N9DG
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Posts: 317




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« Reply #1 on: March 11, 2008, 10:50:01 AM »

"Most importantly, do you think that a significant number of weak signal VHF operators will be interested in working emergency traffic into a disaster area?"

I seriously doubt that there will be much interest by the VHF weak signal community in doing this. The typical VHF weak signal op is more driven by technical achievements and the intricacies of propagation challenges on VHF+. They like playing on the edges of what they can get their equipment to do. They also like finding and working propagation events that often go completely unnoticed on the FM end of the VHF bands. So they as a whole are not particularly interested in the more utilitarian end goal coms like the EMCOMM crowd is. Then throw in the probable need for an endless array of structured test drills and the like and they will then be even less interested.

It stands a better chance of appealing to those already in EMCOMM and who do also have SSB capable 2M radios like the IC-706's, FT-8x7's, TS-2000's etc. But there again it will come down to *antenna systems*. If they are not able, or willing to build a good antenna system, then they will not be able to achieve what 2M SSB and programs like NBEMS have to offer. But then those of us already in the VHF+ weak signal world have seen this same "antenna problem" already before because we know that a lot of those radios are out there, but yet so few of them are ever heard on SSB or CW on the VHF/UHF bands.

FWIW using decent sized beam antennas and feedlines comparable to that of the typical VHF signal op on FM will also achieve those same 100 mile distances reliably too.
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WB2WIK
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« Reply #2 on: March 11, 2008, 07:09:30 PM »

NBEMS and weak signal operators  Reply  
by KV9U on March 11, 2008  Mail this to a friend!  
Most importantly, do you think that a significant number of weak signal VHF operators will be interested in working emergency traffic into a disaster area?<

::Unless the world changes a lot in the next few years, I really doubt it.  For one thing, weak signal VHF operators are mostly interested in working new countries, states and grid squares.  They have limited time to operate, which is exactly what you DON'T want in an emergency traffic operator, who should be available to operate any time there's an emergency.  Best thing for local traffic in an emergency is a mode that thousands can easily work with no new investment in hardware or software, and that's FM.  For working emergency traffic outside the local area, best thing is to take advantage of the existing infrastructure on HF, using SSB, CW or digital modes to work stuff far outside the local area.

The infrastructure is already in place in all 50 states.

WB2WIK/6
 
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W3LK
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« Reply #3 on: March 12, 2008, 07:29:03 AM »

In my opinion, NBEMS is a solution in search of a problem.

<< The intent is to be able to bridge across disaster areas at least up to 100 miles, but can be more if the operators have the right equipment.>>

It can already be done with two 50w FM 2m rigs and decent antennas at a decent height. As has already been mentioned, HF does the same thing without worrying about a line-of-sight issue.

73,

Lon - W3LK
Naugatuck, Connecticut
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KV9U
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« Reply #4 on: March 13, 2008, 02:39:30 PM »

The comments are pretty much in line with what I think most weak signal operators will be interested in, or in this case not interested in.

Using FM for at least a 100 mile distance seems very unlikely to me without some pretty good antennas. In most cases, you would have one station with reasonably good fixed station antennas, but the emergency station may have very modest portable antennas and may need to operate with reduced power. As we found this past summer during the flood, even areas less than 20 miles from our main repeater which has about as good a location and antenna as you could get was not usable to a specifically needed location to coordinate ARESMAT. Since we did not have a full blown communications emergency, the operator resorted to cellphone which was working. But this is not always an option. The operator, like many hams who actually are active with emergency communications holds a Technician class license so is limited with HF capability.

HF NVIS operation is not 24/7/365 since the FoF2 often goes below 80 meters, in fact it can go below 2 MHz at night and communication is nearly impossible for NVIS distances on 80. Not to mention QRN from storms or other sources. While 160 may still work, I have never been able to get others to consider it for emergency operation in my area, primarily due to perceived antenna size. Maybe other areas have had more success?

As most of us are aware, severe disturbances can take out the HF bands for an extended period. VHF tends to be avoid much of this. And NBEMS can be used on HF or VHF but the higher speeds tend to work better on VHF. The system is fairly simple to master for moderately technical hams. I have used it for short daytime NVIS at the 250 baud speed and it has worked well.

Unlike packet, it can work well below the noise, while packet needs a much stronger signal. In fact, it was recently pointed out to me that using FM with NBEMS was unnecessary because if you can make a connection with FM, you don't really need an ARQ mode. Of course FM just can not compete with SSB digital modes due to the drastically different S/N ratio, perhaps by as much as 20 dB?

The pool of hams with vertically polarized gain antennas seem much larger than those with horizontal ones because no matter what, you still need a vertical antenna for FM local use.

It may be possible to convince a few hams that VHF SSB has practical use now that more of them have the multiband/multmode rigs ... even though they rarely use SSB on VHF and up. But the difficulty may be convincing them that they must go horizontal and add yet another antenna.
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KB1GMX
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Posts: 815




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« Reply #5 on: March 15, 2008, 06:07:21 AM »

Several of us and myself have been experimenting with
the various digital modes for FM and SSB use here in
the Eastern MA area (EMA).

Our results are good.  PSK/FSK and other modes work
through repeaters well and give hard copy text.  For
SSB 5-10W into a square loop at ~20ft seems to have
a working radius of some 15-20mi and kicking in a beam
or more power extends that greatly.  When I say range
in this case I'm talking solid contacts with few if any
errors even with PSK31. Modes that are error correcting
or have the ability to work closer to the noise floor
extend the effective range.  We found 6M very effective
for this and 2M also works well.  The advantage with
2M is 3-6 element beams are easily made and small
making it easy to get them in the air 15FT with a
painters pole.  The only other bands that has good low
power local coverage we have checked out is 10M and
440 via repeater is also a candidate.  The 440 FM is
good as antennas are small and a beam of 6-11 elements
is still very small which can truly extract all
possible range from local repeaters.

Around here the regional repeaters do have a primary
working range of exceeding 15miles radius some are
better but this is a range where a 5W HT with a 19"
whip can hit the repeater well enough and with a
simple ground plane at 10-15FT make solid contacts
at that range or further.  Mobiles with 20-50W often
make solid contacts out to 30mi. Since we are near
NH, RI and CT a 50mile hop can easily make the
adjacent state and there are repeaters that have
that kind of coverage.  For local (15-30mi radius) coverage VHF and low UHF can make for a compact
portable station.  When combined with HF for long
haul it's a powerful combination.

The advantage for digimodes is that ops that are not
familiar or proficient with tactical or other
structured comms such as NTS can copy and forward a
message in plain text with fewer errors and possibly
at a faster rate. It doesn't hurt if you have on line
copy of messages sent as well afterwards.

From where I sit NBEMS is a tool and like all tools
a saw will not hammer a nail but it's really handy
on a fallen tree.  The bigger you tool kit the more
resources for dealing with problems are available.
Software (digimodes) has the adavantage that storage
space on computers or the USB pen drives is entirely
portable be it one program or hundreds.  So why not
have a big arsenal of free software.

FYI, PSK31 makes a fair and fun moderately weak signal
mode on 6&2m and is great for local ragchews.
 

Allison
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