First time posting to these forums, so greets.
? : Our EMS is just getting ready to buy a new unit with a fibreglass mod body, and I've suggested an NGP (nogroundplane) antenna for the new comms install. As it happens, we are located in an area known for it's comms problems in-extremus. No cell coverage whatsoever, (even though we can see the tower at times !). Besides that, when we get just outside the community we usually have to rely on a HAM to maintain contact, and even he's hard pressed at 75W/OP.
Whats your take on these ant types?
No Ground Plane antennae
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Tom in D.C.
- Posts: 3859
- Joined: Tue Sep 04, 2001 4:00 pm
- What radios do you own?: Progreso soup can with CRT
Re: No Ground Plane antennae
What antenna types are you thinking of? The only NGP antenna in common
use is what we call a coaxial which has the same gain as a quarter-wave
ground plane which has no gain at all. It sounds to me as if you need help from
an engineer or radio technician who can make some recommendations as to your
system and the continuing problems, probably starting with how much clearance
you have in your quarters for a longer roof antenna. There's no reason you couldn't
also put an aluminum plate inside the cab roof to serve as the antenna's
groundplane; it's done all the time and works very well.
And I, probably like many others reading this Board, am curious about your reference to using a "ham" in your emergency communications, unless the person also happens to be member of your organization.
use is what we call a coaxial which has the same gain as a quarter-wave
ground plane which has no gain at all. It sounds to me as if you need help from
an engineer or radio technician who can make some recommendations as to your
system and the continuing problems, probably starting with how much clearance
you have in your quarters for a longer roof antenna. There's no reason you couldn't
also put an aluminum plate inside the cab roof to serve as the antenna's
groundplane; it's done all the time and works very well.
And I, probably like many others reading this Board, am curious about your reference to using a "ham" in your emergency communications, unless the person also happens to be member of your organization.
Tom in D.C.
In 1920, the U.S. Post Office Department ruled
that children may not be sent by parcel post.
In 1920, the U.S. Post Office Department ruled
that children may not be sent by parcel post.
Re: No Ground Plane antennae
A coaxial NGP was what I suggested in hopes of saving further mods to the unit's body, and I'm wondering if this type of antenna would offer any advantage. We use only Moto gear, and our tech is very thorough. He has assessed the issue and deemed a repeater would be necessary atop a hill to help solve some of the problem. Even then comms wuld still be spotty in some areas. We run vhf in the 150 Mhz band before switching to uhf for comms with med facilities; but only when we have ascended a 900 ft hill! We are even berefit of cell comms in a broad area. We do use a 50 ft tower for local comms, and cp200's for portable comms when available. We're just located in a uniquely rough spot for good comms, and the telco is slow to step up to the plate to improve cell comms.
The HAM op who assists us is indeed part of our service, and a very valuable part at that. He has maintained comms on more that one occassion when we were stuck on the wrong side of 15 ft snow banks awaiting emergency xfers to another transport during major storms. Our comms info never breaches privacy laws for it's content; as info passed is quite specific, and generic, with no identifying data.
As I stated, we are a well seasoned service in a very unique situation when it comes to weather, operations, distance to ER services, pre-hospital care. Funds are very limited for the next couple of years, and the comms system needs to be tweaked.
I do apologize for straying off-issue; but being an optimist I see us as having a two year lead on creating solutions to problems with the comms issues.
Thanks/Merci
The HAM op who assists us is indeed part of our service, and a very valuable part at that. He has maintained comms on more that one occassion when we were stuck on the wrong side of 15 ft snow banks awaiting emergency xfers to another transport during major storms. Our comms info never breaches privacy laws for it's content; as info passed is quite specific, and generic, with no identifying data.
As I stated, we are a well seasoned service in a very unique situation when it comes to weather, operations, distance to ER services, pre-hospital care. Funds are very limited for the next couple of years, and the comms system needs to be tweaked.
I do apologize for straying off-issue; but being an optimist I see us as having a two year lead on creating solutions to problems with the comms issues.
Thanks/Merci
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Tom in D.C.
- Posts: 3859
- Joined: Tue Sep 04, 2001 4:00 pm
- What radios do you own?: Progreso soup can with CRT
Re: No Ground Plane antennae
The coaxial antenna won't improve anything so don't waste your money on it.
Probably the best short-term improvement you could make would be to use
gain antennas on all of your vehicles. A typical 5/8-wave antenna has a gain
of about 3db which means you double the effective radiated power on transmit
and on receive the radio is somewhat more sensitive. These antennas are about
36 inches tall and need a ground plane.
Since your present comms are all simplex you could probably make good use of
mobiles rated at 100 watts output. Question is whether you're licensed for
that power level.
Long-term you obviously could make very good use of a repeater. New VHF repeater
licenses are hard to come by these days, but a good advisory service can tell you
what's available in your area. The FCC also wants everyone to switch over to
narrowband radios eventually, but enforcement/actual requirements are still not
really in effect. Applying for a new license, though, you might run into some walls
involved with the new standards. UHF is another possibility, and if your local med
channels are working for you it's possible to get licensed in that general range and
the UHF may work better than the VHF.
You'll also find that, in general, any kind of reliance on cellphone service for emergency
comms will not serve your interests. In any large-scale emergency, cell service will
overload almost immediately and you will have no priority to use it over anyone else.
Probably the best short-term improvement you could make would be to use
gain antennas on all of your vehicles. A typical 5/8-wave antenna has a gain
of about 3db which means you double the effective radiated power on transmit
and on receive the radio is somewhat more sensitive. These antennas are about
36 inches tall and need a ground plane.
Since your present comms are all simplex you could probably make good use of
mobiles rated at 100 watts output. Question is whether you're licensed for
that power level.
Long-term you obviously could make very good use of a repeater. New VHF repeater
licenses are hard to come by these days, but a good advisory service can tell you
what's available in your area. The FCC also wants everyone to switch over to
narrowband radios eventually, but enforcement/actual requirements are still not
really in effect. Applying for a new license, though, you might run into some walls
involved with the new standards. UHF is another possibility, and if your local med
channels are working for you it's possible to get licensed in that general range and
the UHF may work better than the VHF.
You'll also find that, in general, any kind of reliance on cellphone service for emergency
comms will not serve your interests. In any large-scale emergency, cell service will
overload almost immediately and you will have no priority to use it over anyone else.
Tom in D.C.
In 1920, the U.S. Post Office Department ruled
that children may not be sent by parcel post.
In 1920, the U.S. Post Office Department ruled
that children may not be sent by parcel post.
Re: No Ground Plane antennae
I suspected the NGP antennae would not offer much advantage other than less modding of the new unit. Thanks for the clarity. Our tech has been informed, and will be sending specs for the new install while the unit is being built. The present ant is modified to work both the vhf and uhf channels, and I'm wondering if we might specify a separate ant for each band. That would allow us a 5/8 wave for vhf, and a suitable ant for uhf comms. I expect that might require a switching relay of some sort; but would offer a dedicated radiator to each band?? Should I be looking at issues such as phasing etc? Our tech is a busy fella and we meet on a regular basis to stay in the know.
Given our region (Newfoundland), we are waaaay behind when it comes to rural comms, and everythings an effort. I can see the future of our system needing a complete upgrade and redo when it comes to inter-communications with all of the public services.
WRT cell srvc, it quite a chuckle when locals can see the tower less than 2K distance and can't get srvc! Quite a chuckle till they're in the business end of the unit, and we're in a dead-comms zone. There oughta' be a law. Experience has it that GMRS works better here; but alas, Canada has regulated a max of 2W O/P on those bands! Not that we use them for business; but they do well for maintaining contact with fellow volunteers.
Given our region (Newfoundland), we are waaaay behind when it comes to rural comms, and everythings an effort. I can see the future of our system needing a complete upgrade and redo when it comes to inter-communications with all of the public services.
WRT cell srvc, it quite a chuckle when locals can see the tower less than 2K distance and can't get srvc! Quite a chuckle till they're in the business end of the unit, and we're in a dead-comms zone. There oughta' be a law. Experience has it that GMRS works better here; but alas, Canada has regulated a max of 2W O/P on those bands! Not that we use them for business; but they do well for maintaining contact with fellow volunteers.
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Tom in D.C.
- Posts: 3859
- Joined: Tue Sep 04, 2001 4:00 pm
- What radios do you own?: Progreso soup can with CRT
Re: No Ground Plane antennae
With an aluminum plate installed in the truck's roof as a ground plane you should
have plenty of room for both types of antennas. Spacing should be minimum of
about 18 inches. With a 5/8 wave VHF antenna and a stacked UHF antenna (maybe
5db gain there if your license allows it) you'll be doing everything possible in the
antenna department to maximize your results. You don't want to be faced with any
kind of manual antenna switching in your type of work and there's no reason to do
so anyway if you put in the two antennas. Long range you could also consider going
the repeater route on VHF and taking advantage of your existing tower. In the field
on a call your truck would still have the choice of repeater vs. direct (simplex) operation
but I'd be willing to bet that with decent power levels the repeater would materially
improve your overall situation.
have plenty of room for both types of antennas. Spacing should be minimum of
about 18 inches. With a 5/8 wave VHF antenna and a stacked UHF antenna (maybe
5db gain there if your license allows it) you'll be doing everything possible in the
antenna department to maximize your results. You don't want to be faced with any
kind of manual antenna switching in your type of work and there's no reason to do
so anyway if you put in the two antennas. Long range you could also consider going
the repeater route on VHF and taking advantage of your existing tower. In the field
on a call your truck would still have the choice of repeater vs. direct (simplex) operation
but I'd be willing to bet that with decent power levels the repeater would materially
improve your overall situation.
Tom in D.C.
In 1920, the U.S. Post Office Department ruled
that children may not be sent by parcel post.
In 1920, the U.S. Post Office Department ruled
that children may not be sent by parcel post.
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afterimage84
- Posts: 151
- Joined: Mon Apr 14, 2003 5:09 pm
Re: No Ground Plane antennae
We use the Laird/Antennex NGP VHF with the below discs for good measure:
http://www.tessco.com/products/displayH ... ventPage=1
We use these discs under the roof grounded with UHF Elite Phantoms :
http://www.tessco.com/products/displayP ... ventPage=1
This is for the largest EMS provider in the country...no complaints.
http://www.tessco.com/products/displayH ... ventPage=1
We use these discs under the roof grounded with UHF Elite Phantoms :
http://www.tessco.com/products/displayP ... ventPage=1
This is for the largest EMS provider in the country...no complaints.
Suddenly You Were Gone
Re: No Ground Plane antennae
Thanks for the link. A similiar item was suggested by our auxilary control volunteer. I've scrapped the idea of using the NGP antenna, in favor of a solid ground ground plane. After looking over our base/mobile setup I've concluded the only way to tweak the comms system is to look at upgrading both equipment and power.
The piper hasn't been paid in quite a few years.
Theres a move from the telcos to improve coverage locally, so we just might see a new tower coming in with some rental space available for a repeater.
We bandied the idea of installing a 1/2 wave ant on the new units too. Wind load might affect it somewhat, considering it will run about 3 ft. It should be an enhancement though. I'd even consider a dual ant setup.
The piper hasn't been paid in quite a few years.
Theres a move from the telcos to improve coverage locally, so we just might see a new tower coming in with some rental space available for a repeater.
We bandied the idea of installing a 1/2 wave ant on the new units too. Wind load might affect it somewhat, considering it will run about 3 ft. It should be an enhancement though. I'd even consider a dual ant setup.