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Need Ideas for HF Antenna at Fire Station
Our local fire station would like us to provide an HF station to be
operated by hams during an emergencies. They have offered to pay the cost of this. We already have an VHF station there. The problem is the antenna. It cannot be visible (or at least not be at all obvious; they are allowing the VHF antenna on the roof now.). The most likely needed band is 75/80 meters, for in-state communications. So we need high-angle radiation, and a vertical does not seem to be a good choice. The roof is metal, so putting an antenna in the attic will not work. The building is a fairly large 2 or 3 story structure, and in the country with no other buildings nearby. Here are some ideas I have: 1, A horizontal loop, running all around the building up near the top, but somewhat below the metal roof. Would likely be non-resonant, although perhaps we could choose the length. Mount it on stand-off insulators just off the wooden siding. Use white insulated wire and paint all hardware white, to blend in with the white siding. Feed it at some convenient point, perhaps with a 4:1 balun and then coax into the building. Open wire feed would be better, but we cannot get that into the building and down to the station. Use a coax antenna tuner in the station. The SWR would not be good, but the losses of RG/8 at 75M are not that high. Maybe we could use some kind of outdoor automatic tuner directly connected to the antenna, but I don't know of any offhand. 2. Use the rain gutters as an antenna. I did this long ago in a house and it worked fairly well on 40M. Bridge all the joints with copper braid, painted white, to endure reliable connections. At one of the corner downspouts near the ground, connect the center conductor of a coax cable to the downspout. Bury radials extending out from the building an appropriate length, in a 270 degree sector, and connect to the shield. I don't know if the gutters are connected to the metal roof, but if so that might or might not rule out this approach. Use a coax antenna tuner in the station. I know this is basically a top-loaded vertical antenna, but the choices are limited. Comments on both these ideas, and other alternative suggestions, would be greatly appreciated. 73, Bob W8ERD |
Need Ideas for HF Antenna at Fire Station
Do they have a flagpole?
"Bob Dixon" wrote in message ... Our local fire station would like us to provide an HF station to be operated by hams during an emergencies. They have offered to pay the cost of this. We already have an VHF station there. The problem is the antenna. It cannot be visible (or at least not be at all obvious; they are allowing the VHF antenna on the roof now.). The most likely needed band is 75/80 meters, for in-state communications. So we need high-angle radiation, and a vertical does not seem to be a good choice. The roof is metal, so putting an antenna in the attic will not work. The building is a fairly large 2 or 3 story structure, and in the country with no other buildings nearby. Here are some ideas I have: 1, A horizontal loop, running all around the building up near the top, but somewhat below the metal roof. Would likely be non-resonant, although perhaps we could choose the length. Mount it on stand-off insulators just off the wooden siding. Use white insulated wire and paint all hardware white, to blend in with the white siding. Feed it at some convenient point, perhaps with a 4:1 balun and then coax into the building. Open wire feed would be better, but we cannot get that into the building and down to the station. Use a coax antenna tuner in the station. The SWR would not be good, but the losses of RG/8 at 75M are not that high. Maybe we could use some kind of outdoor automatic tuner directly connected to the antenna, but I don't know of any offhand. 2. Use the rain gutters as an antenna. I did this long ago in a house and it worked fairly well on 40M. Bridge all the joints with copper braid, painted white, to endure reliable connections. At one of the corner downspouts near the ground, connect the center conductor of a coax cable to the downspout. Bury radials extending out from the building an appropriate length, in a 270 degree sector, and connect to the shield. I don't know if the gutters are connected to the metal roof, but if so that might or might not rule out this approach. Use a coax antenna tuner in the station. I know this is basically a top-loaded vertical antenna, but the choices are limited. Comments on both these ideas, and other alternative suggestions, would be greatly appreciated. 73, Bob W8ERD |
Need Ideas for HF Antenna at Fire Station
"Bob Dixon" wrote in message ... Our local fire station would like us to provide an HF station to be operated by hams during an emergencies. They have offered to pay the cost of this. We already have an VHF station there. The problem is the antenna. It cannot be visible (or at least not be at all obvious; they are allowing the VHF antenna on the roof now.). The most likely needed band is 75/80 meters, for in-state communications. So we need high-angle radiation, and a vertical does not seem to be a good choice. The roof is metal, so putting an antenna in the attic will not work. The building is a fairly large 2 or 3 story structure, and in the country with no other buildings nearby. ********************** How about a 1/4 wave radiator, sloping down from the roof, with the shield of the coax connected to the metal roof. It would take some trimming. If you use black insulated wire, it will be almost invisible. Tam |
Need Ideas for HF Antenna at Fire Station
Hi Bob
I guess one should ask how big the roof is... Be handy for modeling the thing. Since you probably want a set and forget installation with no tuning needed across the 80m (or other) bands, it may be worthwhile looking to a resistive terminated antenna rather than trying to make it resonant/low Z by its size. Kind of like a TFDP but maybe a loop construction using very thin (say) stainless steel wire. I would guess that a balun would still be needed but by playing with a terminating resistor you may be able to make it multiband. Perhaps running around the edges of the roof above the gutter line wont be very visible. Does the fire station have one of those hose drying towers? I realize you want NVIS rather than vertical pol low angle but it may be worth considering that avenue. I guess a roof mounted DDRR would be too visible.. A magloop can be small but there might be an efficiency issue there. A balloon lifted antenna only for use during emergencies or exercises? If the building is indeed way out in the country are there any trees within a few 100 yards? Perhaps some underground coax to an antenna structure would do it. Cecil has this interesting design at http://www.w5dxp.com/notuner.htm that uses ribbon cable switched in and out for the bands you want to use. This switching could be remoted with the use of relays. Apologies for not being too specific.. Cheers Bob W5/VK2YQA Bob Dixon wrote: Our local fire station would like us to provide an HF station to be operated by hams during an emergencies. |
Need Ideas for HF Antenna at Fire Station
How about running a `Zep out to the flagpole or telephone pole? All
but invisible and if it's seen, not too many people would even think twice about it. FFF On Fri, 09 Feb 2007 15:59:46 -0500, Bob Dixon wrote: Our local fire station would like us to provide an HF station to be operated by hams during an emergencies. They have offered to pay the cost of this. We already have an VHF station there. The problem is the antenna. It cannot be visible (or at least not be at all obvious; they are allowing the VHF antenna on the roof now.). The most likely needed band is 75/80 meters, for in-state communications. So we need high-angle radiation, and a vertical does not seem to be a good choice. The roof is metal, so putting an antenna in the attic will not work. The building is a fairly large 2 or 3 story structure, and in the country with no other buildings nearby. Here are some ideas I have: 1, A horizontal loop, running all around the building up near the top, but somewhat below the metal roof. Would likely be non-resonant, although perhaps we could choose the length. Mount it on stand-off insulators just off the wooden siding. Use white insulated wire and paint all hardware white, to blend in with the white siding. Feed it at some convenient point, perhaps with a 4:1 balun and then coax into the building. Open wire feed would be better, but we cannot get that into the building and down to the station. Use a coax antenna tuner in the station. The SWR would not be good, but the losses of RG/8 at 75M are not that high. Maybe we could use some kind of outdoor automatic tuner directly connected to the antenna, but I don't know of any offhand. 2. Use the rain gutters as an antenna. I did this long ago in a house and it worked fairly well on 40M. Bridge all the joints with copper braid, painted white, to endure reliable connections. At one of the corner downspouts near the ground, connect the center conductor of a coax cable to the downspout. Bury radials extending out from the building an appropriate length, in a 270 degree sector, and connect to the shield. I don't know if the gutters are connected to the metal roof, but if so that might or might not rule out this approach. Use a coax antenna tuner in the station. I know this is basically a top-loaded vertical antenna, but the choices are limited. Comments on both these ideas, and other alternative suggestions, would be greatly appreciated. 73, Bob W8ERD |
Need Ideas for HF Antenna at Fire Station
It seems to me that a simple dipole would work fine or an inverted V. All
the fire stations I know of already have a tower of some kind to place the feed point. All you would need is about 66' of wire off each side slopeing toward the ground at the ends (to make it more omnidirectional ) Black stealth wire comes to mind. The wireman sells it online (just google thewireman) It is very hard to see. Or you could buy a pre-made dipole for 75 / 80 meters. My 2 cents. Joe |
Need Ideas for HF Antenna at Fire Station
Our local fire station would like us to provide an HF station to be operated by hams during an emergencies. Emergencies? You mean like in the case of a disaster such as a tornado in your community , you might be called upon to provide communications that could save peoples lives and property? You mean, you may be able to provide a communications link to other government agencies in your state when all other ones fail? This is impressive, and this is a great responsibility and you are to be commended for accepting such a responsibility, and providing such a service to your fellow citizens. Now you need to lay the law down to your fellow citizens/politicians/firefighters. You need an antenna. It requires a support, such as a 30-40 ft tower, one that will survive whatever disasters you forsee, such as wind storms, floods, snow/ice storms (no, it will not survive a direct tornado hit, we all know that). It needs to be vandal-proof, not climbable by kids, etc. You can tell them it will have 2 simple wires running off of it and will look like an letter vee upside down. You can tell them not to waste your time because they are not serious about saving peoples lives if they expect you to do such Mickey Mouse things as loading up the rain gutters, disguising wire antennas around the roof of the building, or any other such foolishness. An antenna that will do what they expect is 2 simple pieces of wire 65 feet long connected to some coax cable suspended 30-40 feet in the air. Tell them if they handcuff you into doing anything else they really weren't serious in the first place. Aesthetics have no place when we are talking about saving peoples lives. Imagine if you were ever called to put into action your ham station, and firefighters were standing behind you looking over your shoulder, and you couldn't be heard because the the friggin rain gutter wouldn't load up. Give me a break. Rick K2XT |
Need Ideas for HF Antenna at Fire Station
"Rick" wrote in message ... Our local fire station would like us to provide an HF station to be operated by hams during an emergencies. Emergencies? You mean like in the case of a disaster such as a tornado in your community , you might be called upon to provide communications that could save peoples lives and property? You mean, you may be able to provide a communications link to other government agencies in your state when all other ones fail? This is impressive, and this is a great responsibility and you are to be commended for accepting such a responsibility, and providing such a service to your fellow citizens. Now you need to lay the law down to your fellow citizens/politicians/firefighters. You need an antenna. It requires a support, such as a 30-40 ft tower, one that will survive whatever disasters you forsee, such as wind storms, floods, snow/ice storms (no, it will not survive a direct tornado hit, we all know that). It needs to be vandal-proof, not climbable by kids, etc. You can tell them it will have 2 simple wires running off of it and will look like an letter vee upside down. You can tell them not to waste your time because they are not serious about saving peoples lives if they expect you to do such Mickey Mouse things as loading up the rain gutters, disguising wire antennas around the roof of the building, or any other such foolishness. An antenna that will do what they expect is 2 simple pieces of wire 65 feet long connected to some coax cable suspended 30-40 feet in the air. Tell them if they handcuff you into doing anything else they really weren't serious in the first place. Aesthetics have no place when we are talking about saving peoples lives. Imagine if you were ever called to put into action your ham station, and firefighters were standing behind you looking over your shoulder, and you couldn't be heard because the the friggin rain gutter wouldn't load up. Give me a break. Rick K2XT That was my exect thoughts. If they want to save lives and be prepared for an emergency thye should provide a way to support a wire abotu 130 feet long fed in the middle with a piece of rg-8 type coax. If not tell them to forget it and take your VHF antenna and equipment with you. Someone mentioned a DDRR on the roof. That may work ok, but the bandwidth is very narrow on 75 meters and can cause problems when you may need to change frequencies. What type of antenna system are they using for the fire trucks ? It may be like it is here, there is not much communications gear at the station, but a central dispatch point for several stations. You may need to do something like that and put the HF station at another location. |
Need Ideas for HF Antenna at Fire Station
On Fri, 09 Feb 2007 15:59:46 -0500, Bob Dixon wrote:
The problem is the antenna. Not ready for prime-time. Mission defines the requirements, unless this is to be designed to the standards of Homeland Insecurity. If push comes to shove, the troops of Desert Storm used wire on the ground (sand actually). It had the form of a capital H, fed in the middle of the cross bar. 73's Richard Clark, KB7QHC |
Need Ideas for HF Antenna at Fire Station
You could mount a SCREWDRIVER antenna either to the roof or maybe on a leg
of the antenna support structure if they have one for the regular FD antenna! "Bob Dixon" wrote in message ... Our local fire station would like us to provide an HF station to be operated by hams during an emergencies. They have offered to pay the cost of this. We already have an VHF station there. The problem is the antenna. It cannot be visible (or at least not be at all obvious; they are allowing the VHF antenna on the roof now.). The most likely needed band is 75/80 meters, for in-state communications. So we need high-angle radiation, and a vertical does not seem to be a good choice. The roof is metal, so putting an antenna in the attic will not work. The building is a fairly large 2 or 3 story structure, and in the country with no other buildings nearby. Here are some ideas I have: 1, A horizontal loop, running all around the building up near the top, but somewhat below the metal roof. Would likely be non-resonant, although perhaps we could choose the length. Mount it on stand-off insulators just off the wooden siding. Use white insulated wire and paint all hardware white, to blend in with the white siding. Feed it at some convenient point, perhaps with a 4:1 balun and then coax into the building. Open wire feed would be better, but we cannot get that into the building and down to the station. Use a coax antenna tuner in the station. The SWR would not be good, but the losses of RG/8 at 75M are not that high. Maybe we could use some kind of outdoor automatic tuner directly connected to the antenna, but I don't know of any offhand. 2. Use the rain gutters as an antenna. I did this long ago in a house and it worked fairly well on 40M. Bridge all the joints with copper braid, painted white, to endure reliable connections. At one of the corner downspouts near the ground, connect the center conductor of a coax cable to the downspout. Bury radials extending out from the building an appropriate length, in a 270 degree sector, and connect to the shield. I don't know if the gutters are connected to the metal roof, but if so that might or might not rule out this approach. Use a coax antenna tuner in the station. I know this is basically a top-loaded vertical antenna, but the choices are limited. Comments on both these ideas, and other alternative suggestions, would be greatly appreciated. 73, Bob W8ERD |
Need Ideas for HF Antenna at Fire Station
A local fire dept will probably want regional communications within a
few hundred miles rather than DX and this would usually be on 80/60/40m bands. Since the roof is metal, an ideal NVIS antenna for regional communications would be a dipole type suspended 20-30ft above the metal roof. To keep it simple, a T2FD type antenna would not require any tuning or thought, just plug in and talk. B&W makes a commercial T2FD style, model BWD-90. I know someone will chime in and say these are crap but they work just fine and I believe a slight trade off in performance for ease of use is paramount for the situation you describe. Bob Bob Dixon wrote: Our local fire station would like us to provide an HF station to be operated by hams during an emergencies. They have offered to pay the cost of this. We already have an VHF station there. The problem is the antenna. It cannot be visible (or at least not be at all obvious; they are allowing the VHF antenna on the roof now.). The most likely needed band is 75/80 meters, for in-state communications. So we need high-angle radiation, and a vertical does not seem to be a good choice. The roof is metal, so putting an antenna in the attic will not work. The building is a fairly large 2 or 3 story structure, and in the country with no other buildings nearby. Here are some ideas I have: 1, A horizontal loop, running all around the building up near the top, but somewhat below the metal roof. Would likely be non-resonant, although perhaps we could choose the length. Mount it on stand-off insulators just off the wooden siding. Use white insulated wire and paint all hardware white, to blend in with the white siding. Feed it at some convenient point, perhaps with a 4:1 balun and then coax into the building. Open wire feed would be better, but we cannot get that into the building and down to the station. Use a coax antenna tuner in the station. The SWR would not be good, but the losses of RG/8 at 75M are not that high. Maybe we could use some kind of outdoor automatic tuner directly connected to the antenna, but I don't know of any offhand. 2. Use the rain gutters as an antenna. I did this long ago in a house and it worked fairly well on 40M. Bridge all the joints with copper braid, painted white, to endure reliable connections. At one of the corner downspouts near the ground, connect the center conductor of a coax cable to the downspout. Bury radials extending out from the building an appropriate length, in a 270 degree sector, and connect to the shield. I don't know if the gutters are connected to the metal roof, but if so that might or might not rule out this approach. Use a coax antenna tuner in the station. I know this is basically a top-loaded vertical antenna, but the choices are limited. Comments on both these ideas, and other alternative suggestions, would be greatly appreciated. 73, Bob W8ERD |
Need Ideas for HF Antenna at Fire Station
On Sat, 10 Feb 2007 08:35:55 -0800, Bob wrote:
To keep it simple, a T2FD type antenna would not require any tuning or thought, just plug in and talk. B&W makes a commercial T2FD style, model BWD-90. I know someone will chime in and say these are crap but they work just fine and I believe a slight trade off in performance for ease of use is paramount for the situation you describe. Good morning, Bob. Yeah, good luck with that. T2FD antennas can exhibit as much as 17 db of loss while maintaining a decent VSWR. I have run communications tests with another amateur who lives one town away. We have similar grounds, similar HAAT, and similar height AMSL. He uses a B&W T2FD antenna (I believe it's the B&W-90) and I use a cut dipole for 75 meters, at comparable heights (mine is 17 feet high and his is something like 25 feet I think). He runs 100 watts and I run a grand total of FIVE (5) watts with a Yaesu FT-817. I often get BETTER signal reports on 75 meters than he does, from stations within about a 100 mile radius of here. I certainly wouldn't want a T2FD antenna for mission-critical use, especially since for the price of a B&W, you could buy an auto-tuner from LDG and have just about enough money left over to cover the materials for a cut dipole. |
Need Ideas for HF Antenna at Fire Station
The B&W BWD90 is about 5-6dB down from a dipole on 40m and up and 80m
and down does suffer more loss that’s true. If there is room for the 180ft version it should have consistent performance down to 80m. If you try to feed a mono band dipole with coax and an LDG tuner it will probably have more loss on some bands than a T2FD and using a 4:1 balun and balanced line is better with an LDG but it will not tune everywhere. What’s worse, an antenna that will not reliably tune where you need it or an antenna that will always work with some loss? You have to consider the user in this case as someone who may not have the experience to diddle with tuners or recognize when something is not working properly. Not everyone can make reliable contacts with an FT-817, it requires knowledge, patience and higher efficiency antennas. If it were up to me to set up a fire station for regional comms, I would consider the 180ft B&W, a simple to use HF rig and a solid state 500w amp which will make up for the 5-6dB loss of the antenna over a dipole when necessary. And that is assuming a resonant dipole at low height is my design goal. Also, 1000’s of B&W T2FD type antennas in use right now working just fine in military and government use for there intended purpose, which is push the button and get the message through without messing around. Bob Eric wrote: On Sat, 10 Feb 2007 08:35:55 -0800, Bob wrote: To keep it simple, a T2FD type antenna would not require any tuning or thought, just plug in and talk. B&W makes a commercial T2FD style, model BWD-90. I know someone will chime in and say these are crap but they work just fine and I believe a slight trade off in performance for ease of use is paramount for the situation you describe. Good morning, Bob. Yeah, good luck with that. T2FD antennas can exhibit as much as 17 db of loss while maintaining a decent VSWR. I have run communications tests with another amateur who lives one town away. We have similar grounds, similar HAAT, and similar height AMSL. He uses a B&W T2FD antenna (I believe it's the B&W-90) and I use a cut dipole for 75 meters, at comparable heights (mine is 17 feet high and his is something like 25 feet I think). He runs 100 watts and I run a grand total of FIVE (5) watts with a Yaesu FT-817. I often get BETTER signal reports on 75 meters than he does, from stations within about a 100 mile radius of here. I certainly wouldn't want a T2FD antenna for mission-critical use, especially since for the price of a B&W, you could buy an auto-tuner from LDG and have just about enough money left over to cover the materials for a cut dipole. |
Need Ideas for HF Antenna at Fire Station
I remain puzzled why you guys are discussing compromise antennas in an
emergency communications system. I wonder if the fire department guys built a compromise VHF/UHF communications system when they spec'd out their requirements and performance. Did they hide their 154 MHz antennas under the roof? Did they look for a means to "just get by?" Did they mount a rubber ducky, with a gutter clip on the backside of the firehouse under the rain gutter, and connect it with RG-58 to their radio? If this is a for-real emergency communications solution that the community desires, and they have asked amateur radio operators to be prepared (that is truly an honor) then don't we hams owe it to the community and our own reputation to build them a station, with antenna, that WORKS, that puts out a solid, dependable signal? Rick K2XT |
Need Ideas for HF Antenna at Fire Station
After re-reading the original post I see the fire dept system will be
manned by experienced hams and that would allow for more complex but efficient equipment like antenna tuners and antennas fed with balanced line, etc. Even a G5RV with a tuner might be something to consider. One thing I will point out would be the compromise if someone installed a vertical like an R-7 or GAP Titan or Butternut, etc for regional or statewide comms. The difference between a T2FD and resonant dipole would seem like nothing compared to a T2FD over a vertical for this type use. Bob Rick wrote: I remain puzzled why you guys are discussing compromise antennas in an emergency communications system. I wonder if the fire department guys built a compromise VHF/UHF communications system when they spec'd out their requirements and performance. Did they hide their 154 MHz antennas under the roof? Did they look for a means to "just get by?" Did they mount a rubber ducky, with a gutter clip on the backside of the firehouse under the rain gutter, and connect it with RG-58 to their radio? If this is a for-real emergency communications solution that the community desires, and they have asked amateur radio operators to be prepared (that is truly an honor) then don't we hams owe it to the community and our own reputation to build them a station, with antenna, that WORKS, that puts out a solid, dependable signal? Rick K2XT |
Need Ideas for HF Antenna at Fire Station
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Need Ideas for HF Antenna at Fire Station
On Sat, 10 Feb 2007 18:50:54 +0000, Bob wrote:
If you try to feed a mono band dipole with coax and an LDG tuner it will probably have more loss on some bands than a T2FD Good morning, Bob. That's true, and that's why I wouldn't do that ... as you noted later, I'd use ladder line and a balun. What's worse, an antenna that will not reliably tune where you need it or an antenna that will always work with some loss? I don't know, depends on WHERE and to what extent the cut dipole would fail to reliably tune. Anyway, that should be handled in the design of the antenna, which of course needs to be done by somebody that knows what he/she is doing. I assume that the fire department that is the subject of this thread knows what frequency range(s) they need the HF station to cover. Design the antenna and autotumer combination so that it tunes efficiently across those frequency ranges You have to consider the user in this case as someone who may not have the experience to diddle with tuners That's why I suggest an autotuner. or recognize when something is not working properly. That's an issue with any installation. You could have any antenna you can imagine, and something could go wrong making it "not work properly". There needs to be someone around who has the skills and experience to recognize that. If it were up to me to set up a fire station for regional comms, I would consider the 180ft B&W, a simple to use HF rig and a solid state 500w amp which will make up for the 5-6dB loss of the antenna over a dipole when necessary. What if your emergency installation has to operate for extended periods of time on emergency power and you need to conserve power? That power-hungry 500-watt amplifier may not be especially welcome in that case. Anyway, I could put up at least three (or more) cut dipoles with ladder line and autotuners for the price of that amplifier. Also, 1000's of B&W T2FD type antennas in use right now working just fine in military and government use for there intended purpose, which is push the button and get the message through without messing around. They are working, somewhat, for the most part. I would argue whether they're working "just fine". They're doing the job because (a) the people that installed and use them don't know the difference; and/or (b) they have plenty of your tax dollars to spend on higher-power transmitters to compensate for the antenna inefficiency; and/or (c) they're operating ALE installations that jump around all over the spectrum and, really, the T2FD antennas are all they can use so they have to suck it up and live with the loss. |
Need Ideas for HF Antenna at Fire Station
On Sun, 11 Feb 2007 03:01:13 +0000, Bob wrote:
Even a G5RV with a tuner might be something to consider. One thing you need to keep in mind is whether even 75 meters will be sufficient for statewide communications around the clock. I can tell you that often it is not. Around here, in the wintertime the critical frequency (the maximum frequency at which a signal arriving straight up will bounce back) falls to well below the 80 meter band at night. Often the critical frequency will be around 2.5 MHz, or lower, by around 10 PM. During those times, your 75-meter NVIS signal will just go sailing off merrily into space. You have to be on 160 meters during those times, if you want reliable NVIS communications. I am a regular participant in a military traffic net (not MARS, but similar) that operates at 0730 each morning, on a frequency that's not so very far off the high end of the 75-meter band. The normal net control station is about 80 miles from here, and in the wintertime, the critical frequency is often right around our operating frequency and rising fast as the sun comes up. Very often, I can just barely hear the NCS (or can't hear it at all) at net starting time of 0730, but by 0745 to 0800 the NCS has come up in strength to where solid 100 percent copy is easy. Move the net start time to a half hour earlier and there'd be no way... we'd all be talking to ourselves. As for later in the daylight hours, 75 meter signals often get absorbed by the D and E layers so they never bounce back. During those times 40 meters is your only hope. So, for an emergency station that has a snowball's chance of being able to maintain communications 24x7, you need 160, 80, and 40 meter coverage from an antenna around 30 feet high if you can get it up that high. That would be the low end of the best height range for 160 meters and the high end of the best height range for 40 meters. |
Need Ideas for HF Antenna at Fire Station
I use a version of a fan dipole on HF.
It differs from the standard fan in that the wires are hanging under each other with the longest wire on top. There separated 12" apart, the first one being close to the feed point. The 3 wires are cut for 20m 40m and 80m. With a good tuner it will tune any band from 10m and even a bit of 160m close to 1.8mhz. One good thing about it is... After it was tuned, I measured everything. If a storm or such takes it down it can be replaced very quickly. It is also hard to see unless you are looking for it. My 2 cents KI4ILB solar powered ham radio 24/7 |
Need Ideas for HF Antenna at Fire Station
Dear Bob:
It is nice to hear from another of W8JK's boys. You have received some good ideas and discussion. Having dealt with the underlining need you described, the technical issues usually turn out to be minor as compared to the people issues. What you are likely most to need is a sharp people-person who can uncover what the real reasons are for the apparent need for invisibility. Once you know what the actual issue is, you can work to optimize the system. You must have the clout, once you understand the people issues, to convince the right people about an effective antenna system. My preference is a dipole with about 100 feet of wire on each side that is supported in the middle by a 40 foot tower. From the feed point to the base of the tower I would run a piece of solid-outer coax that is heavily choked with surrounding choking-material. At the base, I would attach a commercial auto-tuner and run its coax and control cables (well choked) underground to the station. An embellishment would be a second dipole at right angles (connected to the first dipole) that is resonant around 5.4 MHz. A good fence around the tower is desirable. Feel free to contact me. 73 Mac N8TT -- J. Mc Laughlin; Michigan U.S.A. Home: "Bob Dixon" wrote in message |
Need Ideas for HF Antenna at Fire Station
2 ideas poped into my my head
you could get a verticle antenna , burry the ground radials or hid them and use some sort of tilt mount like dx engineering has, perhaps if the building has say in the back a long side to it it can be mounted horizontal when not in use then fliped up when needed a variation of this might be a collapseable tower or mast if the roof is flat and the antenna lowered is near the roof it should be hard to see another idea might be to use a tuner like a sgc237 at the center or near center of a dipole a properly sized dipole would be somwhat visible thou i think the most hard to see off all antennas, you could mount the sgc on the lower part of a center supporting mast run ladder line to the dipole center up along a plastic/fiberglass support of course it would certainly tune more efficiently than a at the rig tuner but it's just my crazy ideas In article , Bob Dixon wrote: Our local fire station would like us to provide an HF station to be operated by hams during an emergencies. They have offered to pay the cost of this. We already have an VHF station there. The problem is the antenna. It cannot be visible (or at least not be at all obvious; they are allowing the VHF antenna on the roof now.). The most likely needed band is 75/80 meters, for in-state communications. So we need high-angle radiation, and a vertical does not seem to be a good choice. The roof is metal, so putting an antenna in the attic will not work. The building is a fairly large 2 or 3 story structure, and in the country with no other buildings nearby. Here are some ideas I have: 1, A horizontal loop, running all around the building up near the top, but somewhat below the metal roof. Would likely be non-resonant, although perhaps we could choose the length. Mount it on stand-off insulators just off the wooden siding. Use white insulated wire and paint all hardware white, to blend in with the white siding. Feed it at some convenient point, perhaps with a 4:1 balun and then coax into the building. Open wire feed would be better, but we cannot get that into the building and down to the station. Use a coax antenna tuner in the station. The SWR would not be good, but the losses of RG/8 at 75M are not that high. Maybe we could use some kind of outdoor automatic tuner directly connected to the antenna, but I don't know of any offhand. 2. Use the rain gutters as an antenna. I did this long ago in a house and it worked fairly well on 40M. Bridge all the joints with copper braid, painted white, to endure reliable connections. At one of the corner downspouts near the ground, connect the center conductor of a coax cable to the downspout. Bury radials extending out from the building an appropriate length, in a 270 degree sector, and connect to the shield. I don't know if the gutters are connected to the metal roof, but if so that might or might not rule out this approach. Use a coax antenna tuner in the station. I know this is basically a top-loaded vertical antenna, but the choices are limited. Comments on both these ideas, and other alternative suggestions, would be greatly appreciated. 73, Bob W8ERD |
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