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Is it possible to ask questions here?
Is it possible to ask questions here without triggering an arcane debate
about competing views of theory. I'm about to find out. I asked earlier in another thread what measuring instruments I would need to have the use of in order to compare the effective radiated power of different antennas. As near as I can tell there was no answer. I built a collinear J pole using copper tubing. I'd like to know if it is more or less effective at radiating whatever works to the stations I'd like to be able to talk to under conditions of emergency operation then say a collinear ground plane or any other omni directional antenna. I would like to deploy the most effective practical antennas that field testing can devise and not have to wait until the next breakthrough in physics to be able to get my local governments Email out to my county's government, the state government and the responding relief forces. My question, again, is what measuring instruments can be effectively applied to the comparison to provide results that will be born out by real world performance. I have to admit that I find the endless theoretical debate wearying. As long as it continuous then the newsgroup will be useless to newer licensees, like my self, who would like to get some "patient council to the beginner" from those of you who have been there and done that. Before I have to go there and do that would be soon enough. -- Tom Horne, W3TDH |
Is it possible to ask questions here?
Tom Horne wrote:
Is it possible to ask questions here without triggering an arcane debate about competing views of theory. I'm about to find out. I asked earlier in another thread what measuring instruments I would need to have the use of in order to compare the effective radiated power of different antennas. As near as I can tell there was no answer. I built a collinear J pole using copper tubing. I'd like to know if it is more or less effective at radiating whatever works to the stations I'd like to be able to talk to under conditions of emergency operation then say a collinear ground plane or any other omni directional antenna. I would like to deploy the most effective practical antennas that field testing can devise and not have to wait until the next breakthrough in physics to be able to get my local governments Email out to my county's government, the state government and the responding relief forces. My question, again, is what measuring instruments can be effectively applied to the comparison to provide results that will be born out by real world performance. In order to answer your question, one would need to know... How accurately do you want to measure? If you want to know to tenths of a dB, that's a very different matter from, say, to the nearest 3 dB. In most practical field antenna installations, local conditions and installation can result in field strength variations of +/- 3dB without needing to come up with absurd scenarios. This is why most commercial emergency HF comm systems rely on fairly simple antennas which are fairly insensitive to surroundings (e.g. loaded folded dipoles, or wires with autotuners at the feedpoint, and so forth) and having enough RF power to accomodate the inevitable variations in performance. Note that this is a VERY different scenario than the typical ham setup, where the ham wants to get the very best performance from limited power. So, maybe your testing might be to work out the deployment details (what's easy to put up), and just do simple RF testing to make sure that your easy to deply scheme isn't "terrible" and is "good enough". OTOH, if you're looking to do antenna shootouts with cases of beer riding on the results, a whole nother measurement methodology would be called for. Now to practicalities... Something like a Icom PCR1000 computer controlled HF receiver has a pretty accurate signal strength measuring feature, certainly, it's pretty good over small variations (10-20dB) in signal strength. You could put it at some distance (a mile away?) with a short whip (so the receiving antenna is nondirectional) and make your measurements. You'd put a fixed amount of power into the test antenna (i.e. set up your rig for, say, 10W out, and "put a brick on the key"..) Actually, almost any receiver will do, if it has a reasonably stable way to check if the received signal is at the same level. You put a variable attenuator on the input, and just adjust it until the audio output voltage is the same, or the S-meter hits the same tick mark on the scale, etc. Since the receiver is always seeing the same level, things like nonlinear AGC or uncalibrated meters don't make any difference. It's all in the variable attenuator. What's also important is making sure the transmitter power is really the same each time. You don't much care exactly what it is, just that it's the same. Almost any power meter can do this, as long as the system isn't too horribly mismatched. Remember, you're looking to hit the same mark, not have some absolute value. Big changes in mismatch mean that the quality of the forward and reverse balance in the meter will have an effect. Easy way is to have transmitter: power meter: tuner: feedline: antenna system. Adjust the tuner for no reverse power on the meter, and there you go. (Of course, feedline and tuner losses are now part of your measurement) People literally spend their entire lives doing this kind of thing professionally, so you need to take a step back and decide what level of measurement you need. For all you know, just doing some A/B comparisons when receiving WWV might be good enough. |
Is it possible to ask questions here?
Tom,
I tried to reply to you directly but you posted a bogus email address the email bounced. Larry, W0QE Tom Horne wrote: Is it possible to ask questions here without triggering an arcane debate about competing views of theory. I'm about to find out. I asked earlier in another thread what measuring instruments I would need to have the use of in order to compare the effective radiated power of different antennas. As near as I can tell there was no answer. I built a collinear J pole using copper tubing. I'd like to know if it is more or less effective at radiating whatever works to the stations I'd like to be able to talk to under conditions of emergency operation then say a collinear ground plane or any other omni directional antenna. I would like to deploy the most effective practical antennas that field testing can devise and not have to wait until the next breakthrough in physics to be able to get my local governments Email out to my county's government, the state government and the responding relief forces. My question, again, is what measuring instruments can be effectively applied to the comparison to provide results that will be born out by real world performance. I have to admit that I find the endless theoretical debate wearying. As long as it continuous then the newsgroup will be useless to newer licensees, like my self, who would like to get some "patient council to the beginner" from those of you who have been there and done that. Before I have to go there and do that would be soon enough. -- Tom Horne, W3TDH |
Is it possible to ask questions here?
On Nov 9, 1:23 pm, Tom Horne wrote:
Is it possible to ask questions here without triggering an arcane debate about competing views of theory. I'm about to find out. I asked earlier in another thread what measuring instruments I would need to have the use of in order to compare the effective radiated power of different antennas. As near as I can tell there was no answer. I built a collinear J pole using copper tubing. I'd like to know if it is more or less effective at radiating whatever works to the stations I'd like to be able to talk to under conditions of emergency operation then say a collinear ground plane or any other omni directional antenna. I would like to deploy the most effective practical antennas that field testing can devise and not have to wait until the next breakthrough in physics to be able to get my local governments Email out to my county's government, the state government and the responding relief forces. My question, again, is what measuring instruments can be effectively applied to the comparison to provide results that will be born out by real world performance. I have to admit that I find the endless theoretical debate wearying. As long as it continuous then the newsgroup will be useless to newer licensees, like my self, who would like to get some "patient council to the beginner" from those of you who have been there and done that. Before I have to go there and do that would be soon enough. -- Tom Horne, W3TDH All things being equal, a simple field strength meter will let you compare different antennas. Those things needing to be equal a all the test antennas are all vertical or all are horizontal. The distance from the radiating element to the pickup antenna on the FSM is always the same, the power to the antenna is the same, perhaps others, as well. Any help? Paul, KD7HB |
Is it possible to ask questions here?
"Tom Horne" wrote in message
news:Md4Zi.36$WN2.29@trnddc08... Is it possible to ask questions here without triggering an arcane debate about competing views of theory. I'm about to find out. I asked earlier in another thread what measuring instruments I would need to have the use of in order to compare the effective radiated power of different antennas. As near as I can tell there was no answer. I built a collinear J pole using copper tubing. I'd like to know if it is more or less effective at radiating whatever works to the stations I'd like to be able to talk to under conditions of emergency operation then say a collinear ground plane or any other omni directional antenna. I would like to deploy the most effective practical antennas that field testing can devise and not have to wait until the next breakthrough in physics to be able to get my local governments Email out to my county's government, the state government and the responding relief forces. My question, again, is what measuring instruments can be effectively applied to the comparison to provide results that will be born out by real world performance. I have to admit that I find the endless theoretical debate wearying. As long as it continuous then the newsgroup will be useless to newer licensees, like my self, who would like to get some "patient council to the beginner" from those of you who have been there and done that. Before I have to go there and do that would be soon enough. -- Tom Horne, W3TDH Tom Get together with some friends and have them drive out and assess your signal under real life conditions. Make a day of it and all get together in the evening for a social gathering and to compare notes. You really need to know whether it works okay or not, not what the 'S' meter is reading. Mike G0ULI |
Is it possible to ask questions here?
"Tom Horne" wrote in message news:Md4Zi.36$WN2.29@trnddc08... Is it possible to ask questions here without triggering an arcane debate about competing views of theory. I'm about to find out. I asked earlier in another thread what measuring instruments I would need to have the use of in order to compare the effective radiated power of different antennas. As near as I can tell there was no answer. Tom Horne, W3TDH A Field strength meter can be used to compare relative output of antennas. |
Is it possible to ask questions here?
"Tom Horne" wrote in message news:Md4Zi.36$WN2.29@trnddc08... Is it possible to ask questions here without triggering an arcane debate about competing views of theory. I'm about to find out. I asked earlier in another thread what measuring instruments I would need to have the use of in order to compare the effective radiated power of different antennas. As near as I can tell there was no answer. I built a collinear J pole using copper tubing. I'd like to know if it is more or less effective at radiating whatever works to the stations I'd like to be able to talk to under conditions of emergency operation then say a collinear ground plane or any other omni directional antenna. There is no exect answer to the question. If you are only transmitting to one fixed station , the better types of antennas can be determined. If transmitting to several differant stations, there is usually no one antenna that will be the best. Several times I and some of the local hams have been together and had mobile rigs with the same mounts and differant antennas. Swapping antennas from car to car, the results were differant depending on where the distance stations are. Sometimes the 1/4 wave would be beter and on the same mount a 5/8 or longer colinear would be beter on other stations. While we could not use it on the same mount, one ham had a 40 meter antenna on the bumper of his car and it had a beter receive signal on one repeater than the antennas cut for 2 meters we tried on the same car. It is not so much as the effective radiatred power, but having both stations in the same lobe of the power. Antennas do not really give any gain to the signal, they just redirect the ammount you have to a differant direction. Just as a beam will have lots of gain, if it is not pointed at or near the desired station, they will not be heard. |
Is it possible to ask questions here?
On 9 Nov, 14:29, Larry Benko wrote:
Tom, I tried to reply to you directly but you posted a bogus email address the email bounced. Larry, W0QE Tom Horne wrote: Is it possible to ask questions here without triggering an arcane debate about competing views of theory. I'm about to find out. I asked earlier in another thread what measuring instruments I would need to have the use of in order to compare the effective radiated power of different antennas. As near as I can tell there was no answer. I built a collinear J pole using copper tubing. I'd like to know if it is more or less effective at radiating whatever works to the stations I'd like to be able to talk to under conditions of emergency operation then say a collinear ground plane or any other omni directional antenna. I would like to deploy the most effective practical antennas that field testing can devise and not have to wait until the next breakthrough in physics to be able to get my local governments Email out to my county's government, the state government and the responding relief forces. My question, again, is what measuring instruments can be effectively applied to the comparison to provide results that will be born out by real world performance. I have to admit that I find the endless theoretical debate wearying. As long as it continuous then the newsgroup will be useless to newer licensees, like my self, who would like to get some "patient council to the beginner" from those of you who have been there and done that. Before I have to go there and do that would be soon enough. -- Tom Horne, W3TDH- Hide quoted text - - Show quoted text - He would be better off going to E ham for basic questions |
Is it possible to ask questions here?
Would a simple field strength meter do the trick?
Scott N0EDV Tom Horne wrote: Is it possible to ask questions here without triggering an arcane debate about competing views of theory. I'm about to find out. I asked earlier in another thread what measuring instruments I would need to have the use of in order to compare the effective radiated power of different antennas. As near as I can tell there was no answer. I built a collinear J pole using copper tubing. I'd like to know if it is more or less effective at radiating whatever works to the stations I'd like to be able to talk to under conditions of emergency operation then say a collinear ground plane or any other omni directional antenna. I would like to deploy the most effective practical antennas that field testing can devise and not have to wait until the next breakthrough in physics to be able to get my local governments Email out to my county's government, the state government and the responding relief forces. My question, again, is what measuring instruments can be effectively applied to the comparison to provide results that will be born out by real world performance. I have to admit that I find the endless theoretical debate wearying. As long as it continuous then the newsgroup will be useless to newer licensees, like my self, who would like to get some "patient council to the beginner" from those of you who have been there and done that. Before I have to go there and do that would be soon enough. -- Tom Horne, W3TDH -- Scott http://corbenflyer.tripod.com/ Gotta Fly or Gonna Die Building RV-4 (Super Slow Build Version) |
Is it possible to ask questions here?
On Nov 9, 1:23 pm, Tom Horne wrote:
Is it possible to ask questions here without triggering an arcane debate about competing views of theory. I'm about to find out. I asked earlier in another thread what measuring instruments I would need to have the use of in order to compare the effective radiated power of different antennas. As near as I can tell there was no answer. I built a collinear J pole using copper tubing. I'd like to know if it is more or less effective at radiating whatever works to the stations I'd like to be able to talk to under conditions of emergency operation then say a collinear ground plane or any other omni directional antenna. I would like to deploy the most effective practical antennas that field testing can devise and not have to wait until the next breakthrough in physics to be able to get my local governments Email out to my county's government, the state government and the responding relief forces. My question, again, is what measuring instruments can be effectively applied to the comparison to provide results that will be born out by real world performance. I have to admit that I find the endless theoretical debate wearying. As long as it continuous then the newsgroup will be useless to newer licensees, like my self, who would like to get some "patient council to the beginner" from those of you who have been there and done that. Before I have to go there and do that would be soon enough. -- Tom Horne, W3TDH So, given that you want an omnidirectional antenna ("flat pancake" radiation pattern), if I were in your shoes, I'd place a field strength meter far enough away from the point at which I'm placing each antenna I'll test that it's well into the far field, and then install the antennas I want to test, feed them power from the transmitter I'll be using, and see which gives the highest indicated field strength. Note that you can take a liberal interpretation of "field strength meter." It might well simply be the received signal strength indication on a receiver at one of the remote sites you want to communicate with. Note that this is getting really close to testing exactly the condition you want to optimize. Why do otherwise unless you have to? Why not try to optimize the communications on the path that's giving you the most trouble now, and then verify that all the others still work at least that well? You asked what instruments can be effectively applied to provide results that will be borne out by actual performance--to me, the best is a test of the performance itself. Implicit in this, to me, in the name of efficiency, is that you can try modelling some candidate antennas before building/buying physical versions to try out. Also, you're not the first person to have this problem, and others have solved it various ways. You very well may be able to get recommendations from people who have. You may be able to borrow some of the common commercially available antennas to try, too. Since the antenna itself is only one component of the overall communications channel, it seems to me that it would be good for you to step back and look too at other aspects of the channel. If you have limited resources to put into the project, it may well do more good to get a modest antenna up high at each site, than to put a "high gain" antenna in a bad location (e.g. too low). I suppose there will be several people who will disagree with this and get into theoretical debates about why it can't be so, just as you say. But don't let that keep you from trying real antennas and finding out what really solves your particular problem. |
Is it possible to ask questions here?
Hi Tom
Direct field strength measurement at the "normal" coverage distances, calibrated and compared against a known/real world system is IMO the best choice. I was involved in a VHF paging project that used a laptop, GPS and measuring receiver for the job. The laptop had a A/D converter attached to the parallel port. This gave coverage results that were compared against a modeled prediction, but there is no reason you couldn't set it up to compare a "new" system to an existing/real one. One of the beauties of sampling over some time/distance is that small positional errors with nulls/peaks evident on VHF/UHF can be averaged or even studied as a distribution. The system I worked with you could even see Raleigh fading on, but for us it wasn't a useful output! Biggest hurdle is the RX. You need some kind of Volts per dBm signal output. You could of course take an S meter output and calibrate it. If you want a rough answer it may even be worthwhile attaching a laptop line input to an RX audio out and doing a visual/waterfall analysis of the level of (FM) quieting present with different antenna systems. You could of course also calibrate this system. If you don't want to travel to the limits of the coverage area you can always do the tests at a lesser distance and then extrapolate with some RF coverage software. Hope you find this helpful. Your comments on theoretical debates are noted, but the best you can do is to just not read them. Bob VK2YQA Tom Horne wrote: My question, again, is what measuring instruments can be effectively applied to the comparison to provide results that will be born out by real world performance. |
Is it possible to ask questions here?
"Hal Rosser" wrote in message ... "Tom Horne" wrote in message news:Md4Zi.36$WN2.29@trnddc08... Is it possible to ask questions here without triggering an arcane debate about competing views of theory. I'm about to find out. I asked earlier in another thread what measuring instruments I would need to have the use of in order to compare the effective radiated power of different antennas. As near as I can tell there was no answer. Tom Horne, W3TDH A Field strength meter can be used to compare relative output of antennas. Well, in addition to a field strength meter, some low low power source hooked onto to your antenna may help so you don't have to drive all over the country side. I used an MFJ antenna Analyzer, some string, and a tape measure, to 'map-out' on a graph locations of equal field strength. Just have to watch out for your body affecting the signal pattern. |
Is it possible to ask questions here?
Tom Horne wrote:
Is it possible to ask questions here without triggering an arcane debate about competing views of theory. I'm about to find out. I asked earlier in another thread what measuring instruments I would need to have the use of in order to compare the effective radiated power of different antennas. As near as I can tell there was no answer. I built a collinear J pole using copper tubing. I'd like to know if it is more or less effective at radiating whatever works to the stations I'd like to be able to talk to under conditions of emergency operation then say a collinear ground plane or any other omni directional antenna. I would like to deploy the most effective practical antennas that field testing can devise and not have to wait until the next breakthrough in physics to be able to get my local governments Email out to my county's government, the state government and the responding relief forces. My question, again, is what measuring instruments can be effectively applied to the comparison to provide results that will be born out by real world performance. I have to admit that I find the endless theoretical debate wearying. As long as it continuous then the newsgroup will be useless to newer licensees, like my self, who would like to get some "patient council to the beginner" from those of you who have been there and done that. Before I have to go there and do that would be soon enough. -- Tom Horne, W3TDH Larry Benko wrote: Tom, I tried to reply to you directly but you posted a bogus email address the email bounced. Larry, W0QE Larry I apologize for not checking the Verizon default newsgroup settings. Try hornetd via gmail com. And thank you for taking that time to try to answer. -- Tom Horne, W3TDH |
Is it possible to ask questions here?
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Is it possible to ask questions here?
Mike Kaliski wrote:
"Tom Horne" wrote in message news:Md4Zi.36$WN2.29@trnddc08... Is it possible to ask questions here without triggering an arcane debate about competing views of theory. I'm about to find out. I asked earlier in another thread what measuring instruments I would need to have the use of in order to compare the effective radiated power of different antennas. As near as I can tell there was no answer. I built a collinear J pole using copper tubing. I'd like to know if it is more or less effective at radiating whatever works to the stations I'd like to be able to talk to under conditions of emergency operation then say a collinear ground plane or any other omni directional antenna. I would like to deploy the most effective practical antennas that field testing can devise and not have to wait until the next breakthrough in physics to be able to get my local governments Email out to my county's government, the state government and the responding relief forces. My question, again, is what measuring instruments can be effectively applied to the comparison to provide results that will be born out by real world performance. I have to admit that I find the endless theoretical debate wearying. As long as it continuous then the newsgroup will be useless to newer licensees, like my self, who would like to get some "patient council to the beginner" from those of you who have been there and done that. Before I have to go there and do that would be soon enough. -- Tom Horne, W3TDH Tom Get together with some friends and have them drive out and assess your signal under real life conditions. Make a day of it and all get together in the evening for a social gathering and to compare notes. You really need to know whether it works okay or not, not what the 'S' meter is reading. Mike G0ULI Mike I already own the J pole I mentioned and an Isopole for two meters. I expect to have a third two meter omni to cover APRS, Packet, and voice. I can see me throwing up each of these antennas in turn in a shopping center parking lot on a Saturday night when all the cars are gone and doing some measurements. I cannot see me rigging each in turn to the eve brackets on my house while my victims, I er mean buddies or at least they would be at first, cool their collective heals waiting for each successive test. Then there is the possibility that we may need to pre-install some sort of dual or mono band antenna at each of thirty plus fire stations and you can see why we might want to know which of the designs we can build or buy will put out the strongest signal. If I test at my home I will know which antenna works here but I'm unlikely to be called on to provide emergency communications from my home. I'd like to find out in as objective way as possible which antenna has the best chance in terms of power out to get the signal through in conditions that cannot be known in advance. -- Tom Horne -- Tom |
Is it possible to ask questions here?
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Is it possible to ask questions here?
Hal Rosser wrote:
"Hal Rosser" wrote in message ... "Tom Horne" wrote in message news:Md4Zi.36$WN2.29@trnddc08... Is it possible to ask questions here without triggering an arcane debate about competing views of theory. I'm about to find out. I asked earlier in another thread what measuring instruments I would need to have the use of in order to compare the effective radiated power of different antennas. As near as I can tell there was no answer. Tom Horne, W3TDH A Field strength meter can be used to compare relative output of antennas. Well, in addition to a field strength meter, some low low power source hooked onto to your antenna may help so you don't have to drive all over the country side. I used an MFJ antenna Analyzer, some string, and a tape measure, to 'map-out' on a graph locations of equal field strength. Just have to watch out for your body affecting the signal pattern. Please guys Without going to war with each other over the answer and leaving me not knowing who to believe, is an MFJ analyzer a good choice in the under five hundred dollar range? Would using one of the one watt HTs do for a signal source or is that still to high. -- Tom Horne |
Is it possible to ask questions here?
Tom Horne wrote:
My question, again, is what measuring instruments can be effectively applied to the comparison to provide results that will be born out by real world performance. Bob Bob wrote: Hi Tom Direct field strength measurement at the "normal" coverage distances, calibrated and compared against a known/real world system is IMO the best choice. I was involved in a VHF paging project that used a laptop, GPS and measuring receiver for the job. The laptop had a A/D converter attached to the parallel port. This gave coverage results that were compared against a modeled prediction, but there is no reason you couldn't set it up to compare a "new" system to an existing/real one. One of the beauties of sampling over some time/distance is that small positional errors with nulls/peaks evident on VHF/UHF can be averaged or even studied as a distribution. The system I worked with you could even see Raleigh fading on, but for us it wasn't a useful output! Biggest hurdle is the RX. You need some kind of Volts per dBm signal output. You could of course take an S meter output and calibrate it. If you want a rough answer it may even be worthwhile attaching a laptop line input to an RX audio out and doing a visual/waterfall analysis of the level of (FM) quieting present with different antenna systems. You could of course also calibrate this system. If you don't want to travel to the limits of the coverage area you can always do the tests at a lesser distance and then extrapolate with some RF coverage software. Hope you find this helpful. Your comments on theoretical debates are noted, but the best you can do is to just not read them. Bob VK2YQA Bob As you can see from some of the replies I gave to others I'm trying to devise a way of practically comparing antennas available because in emergency service communications support we have no way of knowing were we will need to set up. Hence the desire to set up some sort of antenna experiment that will allow us to compare the antennas against each other. Just for the sake of my education is it likely to be true that the antenna that puts out the most effective radiated power will be a bad choice in a large percentage of possible sites? -- Tom Horne, W3TDH |
Is it possible to ask questions here?
"Tom Horne" wrote in message news:0Z9Zi.79$Y32.0@trnddc04... Mike Kaliski wrote: "Tom Horne" wrote in message news:Md4Zi.36$WN2.29@trnddc08... Is it possible to ask questions here without triggering an arcane debate about competing views of theory. I'm about to find out. I asked earlier in another thread what measuring instruments I would need to have the use of in order to compare the effective radiated power of different antennas. As near as I can tell there was no answer. I built a collinear J pole using copper tubing. I'd like to know if it is more or less effective at radiating whatever works to the stations I'd like to be able to talk to under conditions of emergency operation then say a collinear ground plane or any other omni directional antenna. I would like to deploy the most effective practical antennas that field testing can devise and not have to wait until the next breakthrough in physics to be able to get my local governments Email out to my county's government, the state government and the responding relief forces. My question, again, is what measuring instruments can be effectively applied to the comparison to provide results that will be born out by real world performance. I have to admit that I find the endless theoretical debate wearying. As long as it continuous then the newsgroup will be useless to newer licensees, like my self, who would like to get some "patient council to the beginner" from those of you who have been there and done that. Before I have to go there and do that would be soon enough. -- Tom Horne, W3TDH Tom Get together with some friends and have them drive out and assess your signal under real life conditions. Make a day of it and all get together in the evening for a social gathering and to compare notes. You really need to know whether it works okay or not, not what the 'S' meter is reading. Mike G0ULI Mike I already own the J pole I mentioned and an Isopole for two meters. I expect to have a third two meter omni to cover APRS, Packet, and voice. I can see me throwing up each of these antennas in turn in a shopping center parking lot on a Saturday night when all the cars are gone and doing some measurements. I cannot see me rigging each in turn to the eve brackets on my house while my victims, I er mean buddies or at least they would be at first, cool their collective heals waiting for each successive test. Then there is the possibility that we may need to pre-install some sort of dual or mono band antenna at each of thirty plus fire stations and you can see why we might want to know which of the designs we can build or buy will put out the strongest signal. If I test at my home I will know which antenna works here but I'm unlikely to be called on to provide emergency communications from my home. I'd like to find out in as objective way as possible which antenna has the best chance in terms of power out to get the signal through in conditions that cannot be known in advance. -- Tom Horne -- Tom Hi Tom That's a very fair comment under the circumstances. That sounds like a pretty big project you are planning. Setting up an antenna farm in a big field or car park and plotting the antenna patterns with a field strength meter, or hooking up an Icom scanner to a PC and recording the results seem like the best suggestions so far. Do remember that each site where you eventually install the antennas will have it's own characteristics. One design may not be suitable for everywhere. I personally have had very good results with a semi commercial 5/8 over 5/8 co-linear design with 6 x 24" horizontal radials at the base. The antenna is cut and tuned for the 2 metre band, but also works well on 70 Cm. Range fully quietening around 40 miles on only 5W on 2m across flat terrain with the base of the antenna 20 feet above ground. This is the most effective design I have come across for omni-directional working. The whole thing is built in a seamless fibre glass tube with the radials screwed into a ring bonded at the base of the antenna. Good luck with the project Mike G0ULI |
Is it possible to ask questions here?
"Tom Horne" wrote in message news:j1aZi.80$Y32.72@trnddc04... Hal Rosser wrote: "Hal Rosser" wrote in message ... "Tom Horne" wrote in message news:Md4Zi.36$WN2.29@trnddc08... Is it possible to ask questions here without triggering an arcane debate about competing views of theory. I'm about to find out. I asked earlier in another thread what measuring instruments I would need to have the use of in order to compare the effective radiated power of different antennas. As near as I can tell there was no answer. Tom Horne, W3TDH A Field strength meter can be used to compare relative output of antennas. Well, in addition to a field strength meter, some low low power source hooked onto to your antenna may help so you don't have to drive all over the country side. I used an MFJ antenna Analyzer, some string, and a tape measure, to 'map-out' on a graph locations of equal field strength. Just have to watch out for your body affecting the signal pattern. Please guys Without going to war with each other over the answer and leaving me not knowing who to believe, is an MFJ analyzer a good choice in the under five hundred dollar range? Would using one of the one watt HTs do for a signal source or is that still to high. -- Tom Horne Tom, A one watt HT will do fine, but the signal will still be too strong close in to work with. You need to get the power down to perhaps one milliwatt or less to plot the antenna pattern in a field or car park. You can make up an attenuator to reduce the power from the HT. Just making up a patch lead between the HT and the antenna with a 50 ohm, 1 watt resistor shorting the core and outer will probably reduce the signal to something you can work with while still giving the transmitter a load to work into. (You can make up exactly 50 ohms using two 100 ohm, 1/2 watt resistors). Or make up a simple single transistor 'bug' transmitter from a handful of components. Plenty of designs available through Google No need to spend more than a couple of dollars. The 9v battery is likely to be the most expensive bit. Mike G0ULI |
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On Nov 9, 1:23 pm, Tom Horne wrote:
Is it possible to ask questions here without triggering an arcane debate about competing views of theory. I'm about to find out. I asked earlier in another thread what measuring instruments I would need to have the use of in order to compare the effective radiated power of different antennas. As near as I can tell there was no answer. I built a collinear J pole using copper tubing. I'd like to know if it is more or less effective at radiating whatever works to the stations I'd like to be able to talk to under conditions of emergency operation then say a collinear ground plane or any other omni directional antenna. I would like to deploy the most effective practical antennas that field testing can devise and not have to wait until the next breakthrough in physics to be able to get my local governments Email out to my county's government, the state government and the responding relief forces. My question, again, is what measuring instruments can be effectively applied to the comparison to provide results that will be born out by real world performance. I have to admit that I find the endless theoretical debate wearying. As long as it continuous then the newsgroup will be useless to newer licensees, like my self, who would like to get some "patient council to the beginner" from those of you who have been there and done that. Before I have to go there and do that would be soon enough. -- Tom Horne, W3TDH Tom, I feel that the best results are achieved when measuring the field strength/receiving effectiveness at a distance far enough away to avoid near-field effects. I have used a spectrum analyzer connected directly to the antenna to make the measurements. Most units can read out directly in dB. First, I had a friend that was about 2 miles away transmit and I measured the amplitude of his signal at my home using my different antennas. I was comparing a 1/4 wave ground plane to a homebrew 5 element beam. We then reversed the setup, where he took the analyzer to his house and measured the amplitudes of me transmitting using the different antennas (same power output, of course) Antenna gain difference and front/back ratio if it is a beam, are easily measured. In my case, measurements were very close to theoretical. This is an expensive piece of test equipment, but someone in the area may have access to one. On the other hand, if you are only looking for seat-of-pants measurements, find a few hams in the area with analog s-meters and have them give you relative signal strength readings for your different antennas. No cost, and the real test is whether you can communicate effectively. We often send out a rover in a car and do signal strength comparisons throughout the valley so we know where our signal needs improvement. Good luck. Gary WA7MLK |
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Please guys Without going to war with each other over the answer and leaving me not knowing who to believe, is an MFJ analyzer a good choice in the under five hundred dollar range? Would using one of the one watt HTs do for a signal source or is that still to high. -- Tom Horne Tom, A one watt HT will do fine, but the signal will still be too strong close in to work with. You need to get the power down to perhaps one milliwatt or less to plot the antenna pattern in a field or car park. You can make up an attenuator to reduce the power from the HT. Just making up a patch lead between the HT and the antenna with a 50 ohm, 1 watt resistor shorting the core and outer will probably reduce the signal to something you can work with while still giving the transmitter a load to work into. (You can make up exactly 50 ohms using two 100 ohm, 1/2 watt resistors). Or make up a simple single transistor 'bug' transmitter from a handful of components. Plenty of designs available through Google No need to spend more than a couple of dollars. The 9v battery is likely to be the most expensive bit. Mike G0ULI Mike's right - but if you don't have an MFJ 259 antenna analyzer yet, this would be a good excuse to go ahead and get one. Its just great when working with antennas. You can get one for about half of your $500 budget. |
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Tom Horne wrote:
I asked earlier in another thread what measuring instruments I would need to have the use of in order to compare the effective radiated power of different antennas. As near as I can tell there was no answer. A Palomar PFS-1 will do what you need done. Unfortunately, they are out of production. -- 73, Cecil http://www.w5dxp.com |
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"Hal Rosser" wrote in message ... Please guys Without going to war with each other over the answer and leaving me not knowing who to believe, is an MFJ analyzer a good choice in the under five hundred dollar range? Would using one of the one watt HTs do for a signal source or is that still to high. -- Tom Horne Tom, A one watt HT will do fine, but the signal will still be too strong close in to work with. You need to get the power down to perhaps one milliwatt or less to plot the antenna pattern in a field or car park. You can make up an attenuator to reduce the power from the HT. Just making up a patch lead between the HT and the antenna with a 50 ohm, 1 watt resistor shorting the core and outer will probably reduce the signal to something you can work with while still giving the transmitter a load to work into. (You can make up exactly 50 ohms using two 100 ohm, 1/2 watt resistors). Or make up a simple single transistor 'bug' transmitter from a handful of components. Plenty of designs available through Google No need to spend more than a couple of dollars. The 9v battery is likely to be the most expensive bit. Mike G0ULI Mike's right - but if you don't have an MFJ 259 antenna analyzer yet, this would be a good excuse to go ahead and get one. Its just great when working with antennas. You can get one for about half of your $500 budget. Tom It has just occurred to me that if you can make or get hold of a switched attenuator to stick in between the antenna and the input socket of your remote receiver, you can make very accurate measurements indeed. I am thinking of the type with 8 or 10 switches. The first switch gives 1dB of attenuation, the next 2dB, 4dB, 8dB, and so on. So long as you have some sort of signal strength meter you can monitor on the receiver, you just switch in enough attenuation to give the same meter reading at each test location and record how much attenuation you have switched in at that point. The more attenuation, the better the received signal. That will allow you to determine relative signal strength to within 1dB which is going to be good enough for your purposes. The attenuator can be used for all kinds of projects, so it might be worth taking the time to build one irrespective of what you end up using for a signal source. The usual Google search will turn up construction details, just resistors and switches in a screened box with some PCB offcuts or copper foil to provide internal screening between each section. I agree with Hal, the MFJ kit is jolly good for the price. It does what it says on the box, just don't expect miracles. Mike G0ULI |
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I agree with Hal, the MFJ kit is jolly good for the price. It does what
it says on the box, just don't expect miracles. =================== Endorse that. Using the MFJ259B I have learned a lot about antennas and matching units (ATUs) ,not just antenna gain ,but also antenna bandwidth and (for HF freqs) dial settings for matching units. Whereas the quality and uncertainty figures of the analyser might be frowned upon by 'professionals', it an excellent device for any radio amateur climbing the knowledge ladder. Frank GM0CSZ / KN6WH |
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On 10 Nov, 04:17, Highland Ham
wrote: I agree with Hal, the MFJ kit is jolly good for the price. It does what it says on the box, just don't expect miracles. =================== Endorse that. Using the MFJ259B I have learned a lot about antennas and matching units (ATUs) ,not just antenna gain ,but also antenna bandwidth and (for HF freqs) dial settings for matching units. Whereas the quality and uncertainty figures of the analyser might be frowned upon by 'professionals', it an excellent device for any radio amateur climbing the knowledge ladder. Frank GM0CSZ / KN6WH Why not compare in the real world Only the poster knows the conditions that he is likely to operate in and it appears that it is in a very mixed environment. In such a case I would compare antennas at home or some place and move the frequency generator around to desired situations. The generater can be a hand held or anything for that matter. Now the real world does not care for "s" meters so one would switch off the limitor in the radio and use a db counter at the speaker.These results can be graphically recorded for direct antenna comparison and for the record. A sound DB counter can be obtained very cheaply on E bay and the mechanics of comparison are in situations that only the poster can determine. Lets face it , communication is measured from what comes out of the speaker. It is not rocket science! Art |
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Now spouting way too much theory to support my suggestions...
Antenna effectiveness is always affected grossly by physical location, height above ground and nearby obstructions. If you don't know where you need to setup in advance I assume you want to take some measurements and thus coverage predict when you do. I'll stick to VHF/UHF systems only.. Antenna systems are relatively easy to predict performance of. Assuming you follow known gain figures, the only big problem (IMO) you will strike is excessive skying of radiation due to feedline etc radiation. This is commonly cured by "decoupling the line" through some means. - but I digress. (Its strange you are looking at emergency comms, that is what the pager service was I worked on!) I disagree that max ERP is undesirable. I assume of course you are talking omnidirectional antennas that tend to compress the vertical beamwidth. About the only time this isn't desirable is if you are in high mountainous country and need to either radiate into valleys or gain reflections from high angles. I can see the problem you are trying to resolve now. I think however you need to take a multi tier approach and not just rely on a one time measurement at a test site. There are just too many variables to allow for when you move to a "real" location. Do a number of basic field strength tests in variable topography at "normal" operating distances and maybe 3-4 locations with a calibrated measuring system. It doesn't have to be calibrated to an absolute figure but you need to be able to replicate the process from on test to the next. At some stage you will be able to create a table of -dBm vs whatever device you are using for measurement. If you want to be pedantic play around with likely base antenna mounting height and method. Make sure you do a distribution or at least minimally an average measurement over several wavelengths. When you come back and do the other antennas use the same measuring location. (A distribution will also give you an idea how "choppy" the signal will become for a mobile station) Weather conditions may also influence results so try and do them at close to the same time/day By variable topography I am talking a hill top, flat area and then a valley. You'll now have some operating distance parameters that you can plug into a RF coverage program (like RadioMobile). You should be able to work backwards from the figures you got in the field to establish the actual antenna gain and radiation angle/lobe etc characteristics. You will even see the slight bump in the horiz plane pattern of a jpole. The next step now in setting up for real world is to take the known antenna parameters and model actual locations that you need to cover for the emergency. IMO this will give you a much better idea of what your coverage will be without needing to do actual site measurements. In other words you have now characterized your antennas and used a PC to establish what the coverage will be. When you want to compare another antenna you'll need to go back to your test site for the greatest accuracy. I assume you have done coverage modeling. The link below is not a good representation but will give you an idea of what the output looks like. In this case it is a 25W base to mobile 2m setup with a 5/8 on the car and 6dB collinear at the base. The base is off to the upper right of the image, the map is about 25 miles square and dBm is the scale on the top left. It is Tyler TX. http://pages.suddenlink.net/vk2yqa/f...in%20Tyler.jpg I hope you find this useful. I believe it far more accurate and useful for your application than comparing antenna ERP by itself. Cheer Bob W5/VK2YQA Tom Horne wrote: As you can see from some of the replies I gave to others I'm trying to devise a way of practically comparing antennas available because in emergency service communications support we have no way of knowing were we will need to set up. Hence the desire to set up some sort of antenna experiment that will allow us to compare the antennas against each other. Just for the sake of my education is it likely to be true that the antenna that puts out the most effective radiated power will be a bad choice in a large percentage of possible sites? -- Tom Horne, W3TDH |
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On Sat, 10 Nov 2007 04:13:56 GMT, Tom Horne
wrote: I'm trying to devise a way of practically comparing antennas available because in emergency service communications support we have no way of knowing were we will need to set up. Hi Tom, There are one, two, three or four certainties about antenna performance. There are dozens of factors that are way beyond your control that degrade system performance. Emergencies rarely conform to optimization; instead you need to think of flexibility. Hence the desire to set up some sort of antenna experiment that will allow us to compare the antennas against each other. As has been offered by a multitude here, that is both very simple in description and complex in accomplishment. Just for the sake of my education is it likely to be true that the antenna that puts out the most effective radiated power will be a bad choice in a large percentage of possible sites? This question alone reveals a most curious idea. First, it presumes a fact that has never, or should have never grown in your mind from all the contributions here (or from external study): Effective = Bad is a non-starter. Communications performance is measured by link budgets, not antennas alone. The link budget is an accumulation of factors such as: 1. Applied Power; 2, Transmission line loss; 3. Antenna Gain (Effective Radiated Power); 4. Path Loss; 5. Receiver Sensitivity; 6. Multipath Sensitivity; 7. Noise in receive path. This list could be made longer, but as long as it is, in an emergency you really have no control over 4, 5, 6, and 7 (and you may be at some risk even with 2 and 3). Your task as an emergency operator would be to recognize and compensate for them as best as possible where it does not jeopardize mission. Often, mission will negate any opportunity to do anything about these last factors. This requires you to plan ahead so that you recognize where these factors could occur and avoid them first, rather than being distracted with them after their discovery. The difference between a J-Pole's performance measured on a range, and that of the standard ground plane is really negligible in comparison to putting either antenna into a Fresnel Zone where the multipath completely nulls the signal. They are BOTH dummy loads in that situation. So you carry a yagi to compensate and switch out the J-Pole or ground plane. Unfortunately, you may not know where your contact is and you point the "optimal" antenna in the wrong direction. The best antenna does not supply the best result - but that is not a function of the antenna, but rather the operator (pilot error). In a nutshell, the questions you are asking imply you are seeking assurance for managing risk, risk that is so variable that no assurance is possible. Links fail in the face of best efforts, that is why it is a hobby at our level of cash flow. $500 is not much of a premium payment for some emergencies. The emergency repeater systems I've worked on have represented many 10s of thousands of (1970s) dollars as built up from surplused (MASTR II and similar) equipment. We spent more like thousands of (2007) dollars to get there. 73's Richard Clark, KB7QHC |
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"Tom Horne" wrote in message news:8eaZi.83$Y32.5@trnddc04... Tom Horne wrote: My question, again, is what measuring instruments can be effectively applied to the comparison to provide results that will be born out by real world performance. Bob Bob wrote: Hi Tom Direct field strength measurement at the "normal" coverage distances, calibrated and compared against a known/real world system is IMO the best choice. I was involved in a VHF paging project that used a laptop, GPS and measuring receiver for the job. The laptop had a A/D converter attached to the parallel port. This gave coverage results that were compared against a modeled prediction, but there is no reason you couldn't set it up to compare a "new" system to an existing/real one. One of the beauties of sampling over some time/distance is that small positional errors with nulls/peaks evident on VHF/UHF can be averaged or even studied as a distribution. The system I worked with you could even see Raleigh fading on, but for us it wasn't a useful output! Biggest hurdle is the RX. You need some kind of Volts per dBm signal output. You could of course take an S meter output and calibrate it. If you want a rough answer it may even be worthwhile attaching a laptop line input to an RX audio out and doing a visual/waterfall analysis of the level of (FM) quieting present with different antenna systems. You could of course also calibrate this system. If you don't want to travel to the limits of the coverage area you can always do the tests at a lesser distance and then extrapolate with some RF coverage software. Hope you find this helpful. Your comments on theoretical debates are noted, but the best you can do is to just not read them. Bob VK2YQA Bob As you can see from some of the replies I gave to others I'm trying to devise a way of practically comparing antennas available because in emergency service communications support we have no way of knowing were we will need to set up. Hence the desire to set up some sort of antenna experiment that will allow us to compare the antennas against each other. Just for the sake of my education is it likely to be true that the antenna that puts out the most effective radiated power will be a bad choice in a large percentage of possible sites? -- Tom Horne, W3TDH Hi Tom My approach to the problem of comparing antennas to each other would involve using satellite signals as the illuminator and build as many test antennas as you have interest in. For 2 meter antennas, the 137 MHz from the NOAA satellites is probably close enough. That would require making some test antennas about 5% bigger than the 2meter antennas. If you E-mail me I can show you some radiation patterns I have plotted from NOAA satellites. My plots of actual measured signal strength make me more and more confident that EZNEC is accurate. Jerry |
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"Jerry Martes" wrote in message news:ydoZi.102$RR1.77@trnddc02... "Tom Horne" wrote in message For 2 meter antennas, the 137 MHz from the NOAA satellites is probably close enough. That would require making some test antennas about 5% bigger than the 2meter antennas. If you E-mail me I can show you some radiation patterns I have plotted from NOAA satellites. My plots of actual measured signal strength make me more and more confident that EZNEC is accurate. Jerry With all the OSCAR satellites up there is no need to do go to the NOAA in the 137 mhz range. The two meter sats will do just fine. Just because an antenna works well on a sat is no reason to assume it will work well on signals from the ground. I have not used one , but the old Ringo antenna sent most of its signal up at an angle. It would probably make a good sat antenna, but a poor antenna for ground work. People in this thread are making way too much out of it. In most cases the longer/bigger the antenna is , the more gain it will have. Just put up the biggest one of good quality you can and don't worry about it. There will be enough differance in the lay of the land to make differant antennnas work beter in differant directions unless you are on a very flat land. |
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"Ralph Mowery" wrote in message ... "Jerry Martes" wrote in message news:ydoZi.102$RR1.77@trnddc02... "Tom Horne" wrote in message For 2 meter antennas, the 137 MHz from the NOAA satellites is probably close enough. That would require making some test antennas about 5% bigger than the 2meter antennas. If you E-mail me I can show you some radiation patterns I have plotted from NOAA satellites. My plots of actual measured signal strength make me more and more confident that EZNEC is accurate. Jerry With all the OSCAR satellites up there is no need to do go to the NOAA in the 137 mhz range. The two meter sats will do just fine. Just because an antenna works well on a sat is no reason to assume it will work well on signals from the ground. I have not used one , but the old Ringo antenna sent most of its signal up at an angle. It would probably make a good sat antenna, but a poor antenna for ground work. People in this thread are making way too much out of it. In most cases the longer/bigger the antenna is , the more gain it will have. Just put up the biggest one of good quality you can and don't worry about it. There will be enough differance in the lay of the land to make differant antennnas work beter in differant directions unless you are on a very flat land. Hi Ralph I missed being able to be clear in my "other" post. If there is a Beacon signal available from a POE satellite at 2meters there is an Excellent 2Meter source of signal with which a person can use to Very Accurately record the radiation pattern from horizon to horizon at all azimuth angles. That radiation pattern will be the pattern of the Ground antenna, not the satellite antenna. We have to assume the satellite radiates equal in all directions. The strength of the received signal is recorded into some program like Excel as a function of time. The actual Az-El to the satellite is published, or can be computed. So, it becomes fairly easy to record the actual (ground based) antenna's radiation pattern which includes all the environmental effects like trees and neighbors's houses. Jerry KD6JDJ |
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"Jerry Martes" wrote in message news:m4qZi.419$763.177@trnddc07... I missed being able to be clear in my "other" post. If there is a Beacon signal available from a POE satellite at 2meters there is an Excellent 2Meter source of signal with which a person can use to Very Accurately record the radiation pattern from horizon to horizon at all azimuth angles. That radiation pattern will be the pattern of the Ground antenna, not the satellite antenna. We have to assume the satellite radiates equal in all directions. The strength of the received signal is recorded into some program like Excel as a function of time. The actual Az-El to the satellite is published, or can be computed. So, it becomes fairly easy to record the actual (ground based) antenna's radiation pattern which includes all the environmental effects like trees and neighbors's houses. Jerry KD6JDJ Jerry you were clear to me. There are several things wrong trying to use the sat to determine the patern of the antenna on the ground at other than the specific pass. Low orbiting sats will start at a great distance as they come over the horizon and get to with in a few hundred miles as they go over head. The squnit angle of the sat antenna will change so the sat antenna is not always pointing at the ground antenna. The apparent polarity will change and that can make a big differance. I have the KLM circular beam pair for 2 meters and 435 mhz on an az/el setup and computer control. Also can switch from left to right circular and have monitored the sats go over and sometimes have to switch left to right as they pass for the best signal. I have not tried it on a sat but for the Icoms ( it might work on others) there is a program that will record the s-meter and draw a plot on the screen . I have done it looking at repeaters and it does seem to work ok for drawing paterns. |
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"Ralph Mowery" wrote in message ... "Jerry Martes" wrote in message news:m4qZi.419$763.177@trnddc07... I missed being able to be clear in my "other" post. If there is a Beacon signal available from a POE satellite at 2meters there is an Excellent 2Meter source of signal with which a person can use to Very Accurately record the radiation pattern from horizon to horizon at all azimuth angles. That radiation pattern will be the pattern of the Ground antenna, not the satellite antenna. We have to assume the satellite radiates equal in all directions. The strength of the received signal is recorded into some program like Excel as a function of time. The actual Az-El to the satellite is published, or can be computed. So, it becomes fairly easy to record the actual (ground based) antenna's radiation pattern which includes all the environmental effects like trees and neighbors's houses. Jerry KD6JDJ Jerry you were clear to me. There are several things wrong trying to use the sat to determine the patern of the antenna on the ground at other than the specific pass. Low orbiting sats will start at a great distance as they come over the horizon and get to with in a few hundred miles as they go over head. The squnit angle of the sat antenna will change so the sat antenna is not always pointing at the ground antenna. The apparent polarity will change and that can make a big differance. I have the KLM circular beam pair for 2 meters and 435 mhz on an az/el setup and computer control. Also can switch from left to right circular and have monitored the sats go over and sometimes have to switch left to right as they pass for the best signal. I have not tried it on a sat but for the Icoms ( it might work on others) there is a program that will record the s-meter and draw a plot on the screen . I have done it looking at repeaters and it does seem to work ok for drawing paterns. Hi Ralph Although I disagree with your premise about "great distance and a few hundred miles", I must admit that I lack knowledge of the satellites other than the few NOAA satellites. The NOAA satellites are about 4 time more distant at the horizon than overhead. That results about 12 dB less signal at the low elevation angle. The 12 dB is fairly easy to put back in the plot. The guys at NASA/NOAA did an excellent job of tailoring the NOAA satellite pattern shape so it is close to equal over the entire pass. I'd have expected the "OSCAR" guys to have done the same and shaped their satellite antenna beams to be essentially equal level over the angle at which the Earth intercepts the satellite beam. I'd like to know more about a 2Meter beacon satellite. Can you point me to a site where I can learn about 2Meter beacon satellites? I have a friend who will write me a program to plot signal strength as a function of angle on a polar plot. He made me one for the NOAA (137 MHz) satellites. I like modeling antennas at 2Meters and have an Icom PCR1000 that I'd like to get some use out of. Jerry KD6JDJ |
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"Jerry Martes" wrote in message news:%dsZi.2897$CI1.289@trnddc03... Although I disagree with your premise about "great distance and a few hundred miles", I must admit that I lack knowledge of the satellites other than the few NOAA satellites. The NOAA satellites are about 4 time more distant at the horizon than overhead. That results about 12 dB less signal at the low elevation angle. The 12 dB is fairly easy to put back in the plot. The guys at NASA/NOAA did an excellent job of tailoring the NOAA satellite pattern shape so it is close to equal over the entire pass. I'd have expected the "OSCAR" guys to have done the same and shaped their satellite antenna beams to be essentially equal level over the angle at which the Earth intercepts the satellite beam. I'd like to know more about a 2Meter beacon satellite. Can you point me to a site where I can learn about 2Meter beacon satellites? I have a Jerry you can find information on the ham sats at www.amsat.org. I guess the great distances I was thinking about was from about 200 miles to around 1000 or so. As you said that is getting close to 10 to 12 db differant. In one way that is not really that much differance in signal, but the types of antennas we have been talking about would have from 0 db to about 6 db of gain. Most would have just one or two db worth of differance in the best direction. |
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"Ralph Mowery" wrote in message ... "Jerry Martes" wrote in message news:%dsZi.2897$CI1.289@trnddc03... Although I disagree with your premise about "great distance and a few hundred miles", I must admit that I lack knowledge of the satellites other than the few NOAA satellites. The NOAA satellites are about 4 time more distant at the horizon than overhead. That results about 12 dB less signal at the low elevation angle. The 12 dB is fairly easy to put back in the plot. The guys at NASA/NOAA did an excellent job of tailoring the NOAA satellite pattern shape so it is close to equal over the entire pass. I'd have expected the "OSCAR" guys to have done the same and shaped their satellite antenna beams to be essentially equal level over the angle at which the Earth intercepts the satellite beam. I'd like to know more about a 2Meter beacon satellite. Can you point me to a site where I can learn about 2Meter beacon satellites? I have a Jerry you can find information on the ham sats at www.amsat.org. I guess the great distances I was thinking about was from about 200 miles to around 1000 or so. As you said that is getting close to 10 to 12 db differant. In one way that is not really that much differance in signal, but the types of antennas we have been talking about would have from 0 db to about 6 db of gain. Most would have just one or two db worth of differance in the best direction. Hi Ralph I would sincerely like to know where to find that 2Meter beacon from a satellite. I have searched a little. Since you have knowledge of the satellite with the 2Meter beacon, I'd appreciate any link to it. I have some AMSAT journals but I havent recognized which satellite transmits that 2 Meter beacon. Your posts show clearly that you question the accuracy of the radiation pattern measurement of an antenna when the satellite is used for the illuminator. I submit to you that you wont find a better way to record the actual radiation pattern. I can measure an antenna's pattern with close to 20 dB dynamic range. It is unclear to me why you doubt the accuracy of patterns I record. One of the benefits of using 137 MHz is the ease with which a person is able to find programs that tell the exact location (Az - El) to the satellite. You can se an example of the radiation pattern at Patrik Tast's site http://www.poes-weather.com/. The pattern is in the section "antennas". I sure will appreciate any information you can give me related to 2Meter beacon satellites. I'm trying to make a program (free) that amateurs can use to record 2Meter antenna radiation patterns. I am very pleased with the program Patrik made for me using the 137 MHz satellites. Thanks for your help Jerry |
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"Jerry Martes" wrote in message news:rDGZi.171$RR1.12@trnddc02... entire pass. I'd have expected the "OSCAR" guys to have done the same and shaped their satellite antenna beams to be essentially equal level over the angle at which the Earth intercepts the satellite beam. I'd like to know more about a 2Meter beacon satellite. Can you point me to a site where I can learn about 2Meter beacon satellites? I have a Most of the ham sats are simple as far as that can be. The antennas on them are not really made to point that accurate. Here are some sats that have beacons near 145 mhz. http://www.amsat.org/amsat-new/satel...tes/status.php |
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"Ralph Mowery" wrote in message ... "Jerry Martes" wrote in message news:rDGZi.171$RR1.12@trnddc02... entire pass. I'd have expected the "OSCAR" guys to have done the same and shaped their satellite antenna beams to be essentially equal level over the angle at which the Earth intercepts the satellite beam. I'd like to know more about a 2Meter beacon satellite. Can you point me to a site where I can learn about 2Meter beacon satellites? I have a Most of the ham sats are simple as far as that can be. The antennas on them are not really made to point that accurate. Here are some sats that have beacons near 145 mhz. http://www.amsat.org/amsat-new/satel...tes/status.php Thanks Ralph I found the staellite and will set up my receiver to learn more about that 2Meter beacon from VO-52. I sure appreciate your help. Jerry |
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What's the easiest method of determining which antenna works the best
for a particular situation? Simplest answer is to try it and see (experience). Then again, what happens when that 'situation' changes? Hmm, try something else? Great answer, isn't it? Very helpful, right? There is no 'best' answer for all situations unless you do some very comprehensive testing, with some very expensive equipment, done by people who know what they are doing. That 'best' answer is still a 'maybe'. So. A "Can you hear me now?" tends to work well. Accept the fact that there are always going to be times when everybody isn't gonna hear you. That's what relays are for (the 'INFO' line on a message header?). For almost any range, but especially for VHF/UHF, higher is usually better. Produces more usable range than the antenna design (within reason!). Everybody wants the 'best'! Very few, except in particular instances, ever get it. - 'Doc (Don't you just hate answers like that?) |
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Tom Horne wrote:
Mike I already own the J pole I mentioned and an Isopole for two meters. I expect to have a third two meter omni to cover APRS, Packet, and voice. I can see me throwing up each of these antennas in turn in a shopping center parking lot on a Saturday night when all the cars are gone and doing some measurements. I cannot see me rigging each in turn to the eve brackets on my house while my victims, I er mean buddies or at least they would be at first, cool their collective heals waiting for each successive test. Then there is the possibility that we may need to pre-install some sort of dual or mono band antenna at each of thirty plus fire stations and you can see why we might want to know which of the designs we can build or buy will put out the strongest signal. I would venture to guess that any of the popular designs will be within a dB or so of each other. Your bigger concern will be system issues like cost, feedline losses, construction time, etc. You might look into some form of collinear array (multiple half waves stacked on top of each other) because you'll get more gain at the horizon and still have an easy install. There's lots of these in all the commercial catalogs (e.g. Tessco), and there's a few in the ARRL antenna book if you want to build something. If I test at my home I will know which antenna works here but I'm unlikely to be called on to provide emergency communications from my home. I'd like to find out in as objective way as possible which antenna has the best chance in terms of power out to get the signal through in conditions that cannot be known in advance. -- Tom Horne -- Tom |
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