Hello all my name is Tom and I was hoping for some input/advice on antenna type and placement. I have a very limited back ground with communications as I work for the FAA. I know just enough as they say. At any rate I am part of an all-volunteer non profit ski patrol on MT Spokane. We currently have a 50W UHF repeater system in place. All lifts are on one face/side of the mountain. We have had issues the last several years with getting coverage at the bottom of 1 chair lift that is border line LOS to the antenna located at the top of the mountain. Basically we have to try and find a sweet spot to get good communications when calling for equipment or working. We currently have a single folded dipole antenna on the repeater. I want to get it up higher but am limited in my ability. I was wondering do any of you have any input on another type of antenna say any an omni directional? 2 element dipole? Does it matter what bearing the single element dipole is pointed? Thanks for any advice you may have….
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UHF Mountian top Antenna Question
- Thread starter tommyt37
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UHF Mountain Top Antenna Question
Hello Tom and welcome to RadioReference. I will try and help. I have owned and maintained repeaters for over 25 years.
First, to answer your question about the bearing of the single element, yes it does make a difference. The leading edge is where you get the most gain from the dipole so point it towards the coverage area you need.
The antenna and coax is the most important part of any radio system. Spending the money on good hardline coax and antenna will make any repeater system work well. Depending on the length needed, I would suggest running Andrew Helix LDF5-50A 7/8 Hardline coax. If the repeater is close to the antenna (50 feet or less) you could use the Andrew Helix LDF4-50a 1/2 Hardline coax. Stay away from LMR400, and any RG type coax for any repeater operations.
Adding more elements is more than likely going to help. I would suggest to stay with the dipole antennas. They are very durable and can hold up against the weather especially in the mountains. I will add links to some antennas and the hardline coax I mentioned before.
The Commscope DB411 would work well for your application. It is a 4 bay dipole in the elliptical pattern (all elements pointed in one direction). If you do use this type of antenna, be sure to point all the elements towards the area were you would like the most coverage.
Here is the link to the antennas: https://www.theantennafarm.com/cata...nas-1098/uhf-406-512mhz-dipole-antennas-1099/
Commscope DB411: http://www.theantennafarm.com/catalog/commscope-db411-4269.html
Andrews Hardline Coax: Product Categories Andrew® Helix HardLine Coax Cable & Connectors
If you have any other questions, please feel free to ask.
Hello Tom and welcome to RadioReference. I will try and help. I have owned and maintained repeaters for over 25 years.
First, to answer your question about the bearing of the single element, yes it does make a difference. The leading edge is where you get the most gain from the dipole so point it towards the coverage area you need.
The antenna and coax is the most important part of any radio system. Spending the money on good hardline coax and antenna will make any repeater system work well. Depending on the length needed, I would suggest running Andrew Helix LDF5-50A 7/8 Hardline coax. If the repeater is close to the antenna (50 feet or less) you could use the Andrew Helix LDF4-50a 1/2 Hardline coax. Stay away from LMR400, and any RG type coax for any repeater operations.
Adding more elements is more than likely going to help. I would suggest to stay with the dipole antennas. They are very durable and can hold up against the weather especially in the mountains. I will add links to some antennas and the hardline coax I mentioned before.
The Commscope DB411 would work well for your application. It is a 4 bay dipole in the elliptical pattern (all elements pointed in one direction). If you do use this type of antenna, be sure to point all the elements towards the area were you would like the most coverage.
Here is the link to the antennas: https://www.theantennafarm.com/cata...nas-1098/uhf-406-512mhz-dipole-antennas-1099/
Commscope DB411: http://www.theantennafarm.com/catalog/commscope-db411-4269.html
Andrews Hardline Coax: Product Categories Andrew® Helix HardLine Coax Cable & Connectors
If you have any other questions, please feel free to ask.
ks4ui
Member
Sounds like you might need an antenna with electrical or mechanical down tilt. If the antenna is at the top of the mountain and you are trying to talk down to all areas around the mountain a unity gain antenna is a good place to start, if that does not provide the coverage you need in your desired coverage area procure an antenna with electrical down tilt. Your local radio shop should have an idea of what I am talking about.
If your current antenna is not in a position where it can look down into the desired coverage area then you need to raise or move the antenna to the edge of the mountain so it can see the coverage area. Might also try putting a preamp on the receive side of the of base station.
Ensure that your base station heliax is suitable for the length of the cable. For UHF frequencies use 1/2 " line for runs under 100 but since you are having problems you might want use 7/8" . Do not increase the gain of your antenna! That will only squeeze the RF signal more towards the horizon. You want the signal (transmit and receive) to be improved downhill not out in the horizon.
If your current antenna is not in a position where it can look down into the desired coverage area then you need to raise or move the antenna to the edge of the mountain so it can see the coverage area. Might also try putting a preamp on the receive side of the of base station.
Ensure that your base station heliax is suitable for the length of the cable. For UHF frequencies use 1/2 " line for runs under 100 but since you are having problems you might want use 7/8" . Do not increase the gain of your antenna! That will only squeeze the RF signal more towards the horizon. You want the signal (transmit and receive) to be improved downhill not out in the horizon.
ks4ui
Member
One more thing, if you are only trying to communicate down one face of the mountain then gain will work for you if you can direct the signal down the path you want it to go. Park Service radio systems frequently use a gain antenna such as a yagi that will favor one direction. Without more details its hard to say what you need.
I would hesitate to recommend a specific antenna with no knowledge of the local terrain and layout of the ski area. But in general, if the desired area of coverage is all in one direction relative to the repeater location, then a directional antenna is in order, not an omni.
One thing that could be considered is locating the repeater at the bottom of the slope looking upward, if coverage of the ski area is all that is needed. The high mountain top is great for wider area coverage, and that might be what you need.
The problem we have, here in the forum, is insufficient data to make a good recommendation. My suggestion would be to take a map of your area, and draw a circle (or square or elipse or bugsplat) of the desired coverage, and show where the repeater is located. Then see if you can find an antenna with a pattern that will compliment the required coverage area. And the previously mentioned downtilt could be important.
Based on your comments, I'm visualizing the repeater at one end of the coverage area, and the area of interest itself all down hill from there, with several runs. A small corner reflector with a broad unidirectional pattern might be good in that sort of situation. But without better data, all we can do is guess.
One thing that could be considered is locating the repeater at the bottom of the slope looking upward, if coverage of the ski area is all that is needed. The high mountain top is great for wider area coverage, and that might be what you need.
The problem we have, here in the forum, is insufficient data to make a good recommendation. My suggestion would be to take a map of your area, and draw a circle (or square or elipse or bugsplat) of the desired coverage, and show where the repeater is located. Then see if you can find an antenna with a pattern that will compliment the required coverage area. And the previously mentioned downtilt could be important.
Based on your comments, I'm visualizing the repeater at one end of the coverage area, and the area of interest itself all down hill from there, with several runs. A small corner reflector with a broad unidirectional pattern might be good in that sort of situation. But without better data, all we can do is guess.
n5ims
Member
- Joined
- Jul 25, 2004
- Messages
- 3,993
The answers above are good ones, but haven't answered all of your questions.
First off, like others have indicated, the folded dipole antenna is most likely the design you should stay with. They're rugged and work well in rough climates. I also agree that getting one with more than just a single element would be helpful. Probably one with 4 or 8 elements would be my recommendation. As others have said, you'll need commercial grade coax like the LDFx-50A type. What number replaces the "x" would be based on the length of your coax run (the longer the run, the higher the number). You can safely go larger than you may need, but going smaller will affect your range so error on the side of a thicker coax.
The elements can be placed on a single side if you want your signal to favor that side, but for a more even coverage, they should be placed around the support pole (e.g., for a 2 element array place them on opposite sides of the pole; for a 4 element array place them evenly around the pole; for an 8 element array, place them around the pole in 90 degree increments so you'll end up with two rotations around the pole - N E S W N E S W as an example).
With a mountain top location where snow is the norm and ice is common, you may also want a design that has some weather protection as well. This can be in the form of "deicers" (where the elements include a heater of some sort to thaw the snow and ice buildup) or some type of radome to protect that antenna from buildup of snow and ice.
Don't know what he can do regarding placing the repeater and antenna but, what if it was located mid-point or at the point where the terrain is blocking the signal toward the bottom? The 4-bay dipole could be set in a bi-directional configuration to cover both up and down.
DisasterGuy
Member
It sounds like the most likely situation here is relative to the site location overshooting. As mentioned, the two methods to fix this are to either provide downtilt to the antenna or (likely easier and cheaper) simply relocate the repeater to the base of the mountain (assuming that coverage is only needed on the single slope of the mountain).
In order to more fully understand the effect here, you should realize that every antenna has a vertical and horizontal beam width measured in degrees. The horizontal beamwidth determines how directional the antenna is from side to side and the vertical determines how directional the antenna is up and down. In general, with folded dipole antennas, the more elements that you add the tighter the vertical beamwidth becomes. For example Sinclair's 1 bay dipole has a vertical beamwidth of 60 degrees whereas their 8 bay dipole has a vertical beamwidth of only 9 degrees. The higher the antenna and less vertical beamwidth it has the more that the signal will be shooting over the top of the terrain. The effect is the same as an umbrella.
In order to more fully understand the effect here, you should realize that every antenna has a vertical and horizontal beam width measured in degrees. The horizontal beamwidth determines how directional the antenna is from side to side and the vertical determines how directional the antenna is up and down. In general, with folded dipole antennas, the more elements that you add the tighter the vertical beamwidth becomes. For example Sinclair's 1 bay dipole has a vertical beamwidth of 60 degrees whereas their 8 bay dipole has a vertical beamwidth of only 9 degrees. The higher the antenna and less vertical beamwidth it has the more that the signal will be shooting over the top of the terrain. The effect is the same as an umbrella.
Wow you guys are great! I just got back from a mountain top VOR site(MLP VOR)....finally started snowing over here lol I have patrol duty this weekend so will be up on the mountain and will read over and research what you all have suggested. Stay tuned!
I will also take pictures give equipment types and maps for a better explanation. Stand by for details..... thanks again all looking forward to getting this resolved. It really sucks having bad comms with an injured skier. I should have worked on it this summer but didn't. For a quick try I am going to rotate the antenna and get some radio checks done this weekend. But again stand by for details and more questions...... I have other questions on analog digital radios ect... ..
ks4ui
Member
One more thing, this guy is trying to improve communications at the top of a ski run. If they get a lot of snow up there he better use an antenna that can handle several inches of radial ice which can be expected in the wake of a big snow storm. Can tell some of you guys have been around but we just don't have enough to work with, what is the base station antenna AGL and HAAT, what is the farthest distance then need to communicate with portables to the base, what is the transmit power of the portable radios? So many more questions, he has gleaned a lot from us but really needs to call in the pros.
rfradioconsult
Member
If your antenna is readily accessable you may want to try changing it from vertical polarization to horizontal, might provide enough improvement to fill your spotty coverage areas.
I plan on doing that when I can. I can check power out, vswr, cable loss and run a DTF with an anritsu. The main problem we have with spotty coverage is hitting the repeater with the hand helds. At times the xmit won't hit the hand held but more often it is the other way around. I had planed on getting more details last weekend while I was up on duty but we had allot of codes (people needing medical attention) so I never got around to it. I plan on doing it next duty weekend or if I go up and free ski this weekend.
So I am starting to realize that per haps the repeater is doing it's job getting the hand held radios with it's 50 watt power but the icom hand helds can't get to the repeater.....I skiied over on chair 4 allot last weekend and was able to hear most repeater xmits but again hard to get my hand held to hit the repeater.....again I'll get equipment type and all kinds of stats on this thread soon. Sorry perhaps I should have waited to post when I got all the data. I was just sitting at work and thought.. hey they have a subaru tribeca forum, kawasaki versys forum, how to compress mkv video forums I bet there is a comm forum and up popped you guys! 
rapidcharger
Member
Which begs the question, where are all the stations/units that need to communicate with one another? Are you needing to talk from the bottom of the mountain to other units on other mountains? Are all the slopes on one side of one mountain?
Because a 50 watt repeater just to talk from the summit to the bottom of a chair lift at the base of a ski slope sounds like major overkill to say the least. A lot of places dont even use repeaters unless they've already got one for the resort.
Because a 50 watt repeater just to talk from the summit to the bottom of a chair lift at the base of a ski slope sounds like major overkill to say the least. A lot of places dont even use repeaters unless they've already got one for the resort.
12dbsinad
Member
- Joined
- Mar 15, 2010
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- 1,954
So I am starting to realize that per haps the repeater is doing it's job getting the hand held radios with it's 50 watt power but the icom hand helds can't get to the repeater.....I skiied over on chair 4 allot last weekend and was able to hear most repeater xmits but again hard to get my hand held to hit the repeater.....again I'll get equipment type and all kinds of stats on this thread soon. Sorry perhaps I should have waited to post when I got all the data. I was just sitting at work and thought.. hey they have a subaru tribeca forum, kawasaki versys forum, how to compress mkv video forums I bet there is a comm forum and up popped you guys!
Yes, get the repeater checked out.
And another thing I forgot to mention: Too much antenna gain will not be of any help in that situation.
Antenna gain is a result of focusing the radiation in one plane or direction. Picture all the repeater's signal going straight out over the area and not down the hill.
Antenna gain is a result of focusing the radiation in one plane or direction. Picture all the repeater's signal going straight out over the area and not down the hill.
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