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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?
|
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?
|
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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