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#1
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Tom Horne wrote:
I am interested in having a rapid set up multi-band vertical for Field Day and EMCOMM. If I use the Hy-Gain sixty four foot (64') push up mast as the radiator and an ICOM AH-4 as the automatic antenna tuner is this likely to be an effective approach to having a rapid set up multi band vertical? Yes.. You don't need that much height, though.. the loss in radiation effectiveness going from 1/4 wavelength (20m long) to 1/8 wavelength (10m) isn't all that big a deal. It's when you get down to the 1/20th wavelength and the feedpoint Z gets very wild that you have problems with loss in the matching network. Will I need radials? Should they be elevated or can they lie on the ground? Yes.. you do need radials. Laying on the ground is just fine. Get some very flexible stranded insulated wire (the kind with lots of fine strands is better.) and figure a way to rapidly throw it out and store without tangling. I've thought about spring return reels. 3 or 4 makes a huge difference over 1 or 2. after that, it's a bit of diminishing returns.. You'd be better off just doing what the people who do this for a living (rapid deploy HF comms) do.. jack up the Tx power. BTW, a better approach than a vertical might be a inverted V dipole from the top of your 60 foot pole. MUCH better radiation effectiveness because of H polarization.. Since the total length of the radiator is less than a 1/4 wave on eighty meters at say 3.6 MHz will that make the antenna ineffective on eighty meters? Nope.. it's the loss in the tuning network that's the thing to worry about.. you could make a lumped matching network to feed with your autotuner if you're worried.. Second question would four of those sixty four foot masts make an effective forty meter four square. Yes I realize that it would cost eight hundred dollars for the masts alone before the cost of controller, remote, phasing coax, and control cable. Once again would radials be required for forty meters. Radials are (almost) always required for verticals. even if you don't install them, your feedline shield will act as a radial with unpredictable and usually undesirable effects. Running a 4 square with autotuners at each element is VERY difficult (if not impossible).. the tuner changes the phase shift, and the interaction from the other antennas will screw up the auto adjustment algorithm. I've only been back in radio for a few years after very long gap so I'm starting over and finding the learning curve a little steeper than I remember. -- Tom Horne, W3TDH |
#2
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On Apr 8, 1:16*pm, Jim Lux wrote:
BTW, a better approach than a vertical might be a inverted V dipole from the top of your 60 foot pole. * MUCH better radiation effectiveness because of H polarization.. Much easier to deal with. You really don't want to have to deal with radials at a field day. And using an antenna tuner to match a vertical is not the greatest way to go about it. Then you have the radiator height issue.. A 64 foot mast is too tall for most of the higher HF bands. So it's not going to be too practical for multi band use unless it's only for the lower bands. Heck, it's slightly tall even to be a 5/8 wave on 30m... It's going to be fairly useless as a vertical on 20m and up.. High angle lobes.. If it were me, I'd use the mast to support dipoles for each band to be used. I feed them all with a single coax and spread the legs apart at right angles to minimize interaction. Or one could use a multi band dipole of some type. One method I used to use camping was the "jumper" dipole. IE: I'd run a 80m length dipole, but have insulators breaking it up into higher band dipoles. For 80m, they would all have jumpers across them. For higher bands, you would use remove the jumper across the insulator to shorten the length. But I prefer the parallel dipoles for FD use, and I almost always have enough room to do it. That way I have instant band changing with no retuning, fiddling, etc.. If I were to use a vertical for all bands, I'd probably go with some type of elevated 1/2 wave design that didn't require radials. But except for far off DX, I would prefer the dipoles. The bulk of FD contacts are not going to be DX on the lower bands. You would be better served with the NVIS pattern of a dipole on 40, 80 meters. An 80 or 40 meter dipole will work quite well if supported at 60 ft at the apex. Really doesn't have to be that high, but if you can get them up to 60 ft, they will work well. Even to most DX. |
#3
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On Apr 8, 2:16*pm, Jim Lux wrote:
Tom Horne wrote: I am interested in having a rapid set up multi-band vertical for Field Day and EMCOMM. *If I use the Hy-Gain sixty four foot (64') push up mast as the radiator and an ICOM AH-4 as the automatic antenna tuner is this likely to be an effective approach to having a rapid set up multi band vertical? Yes.. You don't need that much height, though.. the loss in radiation effectiveness going from 1/4 wavelength (20m long) to 1/8 wavelength (10m) isn't all that big a deal. *It's when you get down to the 1/20th wavelength and the feedpoint Z gets very wild that you have problems with loss in the matching network. * Will I need radials? *Should they be elevated or can they lie on the ground? * Yes.. you do need radials. *Laying on the ground is just fine. *Get some very flexible stranded insulated wire (the kind with lots of fine strands is better.) and figure a way to rapidly throw it out and store without tangling. I've thought about spring return reels. 3 or 4 makes a huge difference over 1 or 2. *after that, it's a bit of diminishing returns.. You'd be better off just doing what the people who do this for a living (rapid deploy HF comms) do.. jack up the Tx power. BTW, a better approach than a vertical might be a inverted V dipole from the top of your 60 foot pole. * MUCH better radiation effectiveness because of H polarization.. Since the total length of the radiator is less than a 1/4 wave on eighty meters at say 3.6 MHz will that make the antenna ineffective on eighty meters? Nope.. it's the loss in the tuning network that's the thing to worry about.. you could make a lumped matching network to feed with your autotuner if you're worried.. Second question would four of those sixty four foot masts make an effective forty meter four square. *Yes I realize that it would cost eight hundred dollars for the masts alone before the cost of controller, remote, phasing coax, and control cable. *Once again would radials be required for forty meters. Radials are (almost) always required for verticals. even if you don't install them, your feedline shield will act as a radial with unpredictable and usually undesirable effects. Running a 4 square with autotuners at each element is VERY difficult (if not impossible).. the tuner changes the phase shift, and the interaction from the other antennas will screw up the auto adjustment algorithm. I've only been back in radio for a few years after very long gap so I'm starting over and finding the learning curve a little steeper than I remember. -- Tom Horne, W3TDH Jim I had no intention of running a four square with four auto tuners. Perhaps I should have put that inquiry into a separate posting for the sake of clarity. We built a four square for field day two years ago. Because the masts that we had then were only thirty feet high a kind of capacitance hat was built into the guy lines. We had very good performance from that four square until a severe thunderstorm destroyed it. I was wondering if having sixty four foot masts would allow us to adjust the height to resonance on forty meters so that the four masts themselves could serve as the elements of the four square. Since a half wave at 7150 kHz is nearly sixty seven feet I would have to add three feet worth of additional tubing in order to get a resonant half wave antenna. I had thought that half wave verticals did not require a counterpoise was I misinformed? If a counterpoise is needed it wouldn't be too hard to throw out four radials for each mast. I was just looking for a quick way to put up a four square and these aluminum masts seemed like they might fill the bill. -- Tom Horne |
#4
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Tom Horne wrote:
On Apr 8, 2:16 pm, Jim Lux wrote: Tom Horne wrote: I am interested in having a rapid set up multi-band vertical for Field Day and EMCOMM. If I use the Hy-Gain sixty four foot (64') push up mast as the radiator and an ICOM AH-4 as the automatic antenna tuner is this likely to be an effective approach to having a rapid set up multi band vertical? Yes.. You don't need that much height, though.. the loss in radiation effectiveness going from 1/4 wavelength (20m long) to 1/8 wavelength (10m) isn't all that big a deal. It's when you get down to the 1/20th wavelength and the feedpoint Z gets very wild that you have problems with loss in the matching network. Will I need radials? Should they be elevated or can they lie on the ground? Yes.. you do need radials. Laying on the ground is just fine. Get some very flexible stranded insulated wire (the kind with lots of fine strands is better.) and figure a way to rapidly throw it out and store without tangling. I've thought about spring return reels. 3 or 4 makes a huge difference over 1 or 2. after that, it's a bit of diminishing returns.. You'd be better off just doing what the people who do this for a living (rapid deploy HF comms) do.. jack up the Tx power. BTW, a better approach than a vertical might be a inverted V dipole from the top of your 60 foot pole. MUCH better radiation effectiveness because of H polarization.. Since the total length of the radiator is less than a 1/4 wave on eighty meters at say 3.6 MHz will that make the antenna ineffective on eighty meters? Nope.. it's the loss in the tuning network that's the thing to worry about.. you could make a lumped matching network to feed with your autotuner if you're worried.. Second question would four of those sixty four foot masts make an effective forty meter four square. Yes I realize that it would cost eight hundred dollars for the masts alone before the cost of controller, remote, phasing coax, and control cable. Once again would radials be required for forty meters. Radials are (almost) always required for verticals. even if you don't install them, your feedline shield will act as a radial with unpredictable and usually undesirable effects. Running a 4 square with autotuners at each element is VERY difficult (if not impossible).. the tuner changes the phase shift, and the interaction from the other antennas will screw up the auto adjustment algorithm. I've only been back in radio for a few years after very long gap so I'm starting over and finding the learning curve a little steeper than I remember. -- Tom Horne, W3TDH Jim I had no intention of running a four square with four auto tuners. Perhaps I should have put that inquiry into a separate posting for the sake of clarity. We built a four square for field day two years ago. Because the masts that we had then were only thirty feet high a kind of capacitance hat was built into the guy lines. We had very good performance from that four square until a severe thunderstorm destroyed it. I was wondering if having sixty four foot masts would allow us to adjust the height to resonance on forty meters so that the four masts themselves could serve as the elements of the four square. Since a half wave at 7150 kHz is nearly sixty seven feet I would have to add three feet worth of additional tubing in order to get a resonant half wave antenna. I had thought that half wave verticals did not require a counterpoise was I misinformed? If a counterpoise is needed it wouldn't be too hard to throw out four radials for each mast. I was just looking for a quick way to put up a four square and these aluminum masts seemed like they might fill the bill. Tom, is this a serious exercise here? This is just way too much trouble for a 40 meter antenna. Some antennas like the half wave verticals, don't require radials. But I see a vacillating back and forth between high performance and well, these verticals, which really aren't High performance. As for several 64 foot masts, Why not go to one mast and put up a 40 meter beam beam? Add an Amp, and you will rule the air. Although I wouldn't do that personally, because I would imagine that the idea of emergency ops is getting set up and running ASAP. It could be a matter of temperament I guess. You can get most of your needed performance out of a simple dipole. But if you want to wring the last drop of performance, I'd have to think the beam would take less time to set up and perform better than a 4-square. You don't want to finish installing and tuning just at the time they send everyone home. - 73 de Mike N3LI - |
#5
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Tom Horne wrote:
Jim I had no intention of running a four square with four auto tuners. Perhaps I should have put that inquiry into a separate posting for the sake of clarity. We built a four square for field day two years ago. Because the masts that we had then were only thirty feet high a kind of capacitance hat was built into the guy lines. We had very good performance from that four square until a severe thunderstorm destroyed it. I was wondering if having sixty four foot masts would allow us to adjust the height to resonance on forty meters so that the four masts themselves could serve as the elements of the four square. Since a half wave at 7150 kHz is nearly sixty seven feet I would have to add three feet worth of additional tubing in order to get a resonant half wave antenna. I had thought that half wave verticals did not require a counterpoise was I misinformed? If a counterpoise is needed it wouldn't be too hard to throw out four radials for each mast. I was just looking for a quick way to put up a four square and these aluminum masts seemed like they might fill the bill. -- Tom Horne If you put the feedpoint in the middle of the antenna and run the coax up the middle of the bottom, and have a really good choke, it might work. (basically, an elevated half wave dipole) There was such an antenna scheme for a 4 square in one of the ARRL antenna compendiums (I think they were doing it for 160m, and had a matching network (mostly inductance) at the feedpoint to deal with the "electrically short" radiator. Making it actually work is another story entirely. You've got to have a pretty good choke, or the feedline starts to be a big part of the system, and since it's laying on the ground, it's a pretty lossy part of the system. The bottom half of the antenna is closer to the ground than the top half, so there's those effects too. SO, even if you sat at the bottom of the antenna with your antenna tuning meter and carefully adjusted the matching network at the feed to get 50 ohms, I don't know that when you set it all up, the phasing will be right. It might be close enough.. but the odds of not getting as good a F/B as you want (e.g. null depth) are pretty good. The phasing isn't so critical for forward gain (you can be tens of degrees off and not lose much in forward gain, but that will completely kill your 10dB null) But just feeding the end of a 1/2 wave wire sticking in the air is asking for difficulties. Your coax is nominally 50 ohm sort of impedance, and you'd be end feeding a dipole at a high Z point (a thousand ohms, maybe). |
#6
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On Apr 16, 6:16*pm, Jim Lux wrote:
But just feeding the end of a 1/2 wave wire sticking in the air is asking for difficulties. *Your coax is nominally 50 ohm sort of impedance, and you'd be end feeding a dipole at a high Z point (a thousand ohms, maybe). Feeding it would be fairly easy.. But.. Just because it's a half wave will not mean that there will be low ground losses if ground mounted. You would see less ground loss than a ground mount quarter wave, but it could still be an issue. Note that most broadcasters who run half waves, also use a set of half wave radials. I'd probably rather use 32 ft masts supporting self supporting 32 ft radiators, and use a few sloping radials as radials, and also to double as guy wires. That will work fairly well with as few as three radials. More to be optimum, but this is field day.. :/ |
#7
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#8
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On Apr 29, 1:03*pm, Jim Lux wrote:
wrote: On Apr 16, 6:16 pm, Jim Lux wrote: But just feeding the end of a 1/2 wave wire sticking in the air is asking for difficulties. *Your coax is nominally 50 ohm sort of impedance, and you'd be end feeding a dipole at a high Z point (a thousand ohms, maybe). Feeding it would be fairly easy.. But.. Just because it's a half wave will not mean that there will be low ground losses if ground mounted. You would see less ground loss than a ground mount quarter wave, but it could still be an issue. Note that most broadcasters who run half waves, also use a set of half wave radials. I'd probably rather use 32 ft masts supporting self supporting 32 ft radiators, and use a few sloping radials as radials, and also to double as guy wires. That will work fairly well with as few as three radials. More to be optimum, but this is field day.. * :/ And would strongly resemble the radiators at WWV... If you do this, you'd put the AH4 at the join point too. *For FD, you might want to have the bottom 8-10 feet of the guy/radial be an insulator, so that nobody touches the HV part of the antenna. It would be above ground level with a 32 ft mast. So that would be no problem. I've used that antenna here at the house, except I had the 32 ft radiator on a 36 ft mast. I used four radials and sloped them down and tied off to trees, fences, whatever.. I would not use the AH4 tuner. No need.. The antenna would be resonant. It would work pretty well on longer paths at night. The same antenna can also be used for 17m if you add a matching coil to use it as a 5/8 wave. I had a 24 volt relay rigged up at the feed point of mine, and could switch from the shack. |
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