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Antenna Range Testing.
Hi all.
This may seem like a fairly basic question. But here we go! I want to performance test a 436MHz high gain antenna. My plan is to construct a simple dipole with a 1:1 balun for 436MHz as a reference antenna and construct another dipole with a 1:1 balun to receive the test signal, measure it with a diode detector and a milli-amp meter (field strength meter) at the shack. Do the calculation and have the antenna gain. This seems to me to be fairly straight forward, but has anyone carried out similar measurements and concur with the approach or are there are there traps and pit falls that I need to be aware of. Or is their simply a better way? Cheers -- Peter Miles VK3YSF Melbourne, Australia |
This may seem like a fairly basic question. But here we go! I want to performance test a 436MHz high gain antenna. My plan is to construct a simple dipole with a 1:1 balun for 436MHz as a reference antenna and construct another dipole with a 1:1 balun to receive the test signal, measure it with a diode detector and a milli-amp meter (field strength meter) at the shack. Do the calculation and have the antenna gain. This seems to me to be fairly straight forward, but has anyone carried out similar measurements and concur with the approach or are there are there traps and pit falls that I need to be aware of. Or is their simply a better way? You may want to use a small directional antenna on both ends. The ARRL handbook gives a standard refferance gain antenna that you can use on the end that you are going to replace with the antenna you are building. The antenna is suspose to have a certain ammount of gain if constructed exectally as given. The directiona antennas will help eliminate some reflections. Also make sure they are far enough apart to be out of the near field. |
This may seem like a fairly basic question. But here we go! I want to performance test a 436MHz high gain antenna. My plan is to construct a simple dipole with a 1:1 balun for 436MHz as a reference antenna and construct another dipole with a 1:1 balun to receive the test signal, measure it with a diode detector and a milli-amp meter (field strength meter) at the shack. Do the calculation and have the antenna gain. This seems to me to be fairly straight forward, but has anyone carried out similar measurements and concur with the approach or are there are there traps and pit falls that I need to be aware of. Or is their simply a better way? You may want to use a small directional antenna on both ends. The ARRL handbook gives a standard refferance gain antenna that you can use on the end that you are going to replace with the antenna you are building. The antenna is suspose to have a certain ammount of gain if constructed exectally as given. The directiona antennas will help eliminate some reflections. Also make sure they are far enough apart to be out of the near field. |
We just made a range dipole for 900 MHz. The balun we ordered from
Minicircuits (pay careful attention to pinouts) was a 1:1. It resonated well once we took into account that the polyethelene mounting block imparted a velocity factor which shortened the rods slightly. Peter wrote: Hi all. This may seem like a fairly basic question. But here we go! I want to performance test a 436MHz high gain antenna. My plan is to construct a simple dipole with a 1:1 balun for 436MHz as a reference antenna and construct another dipole with a 1:1 balun to receive the test signal, measure it with a diode detector and a milli-amp meter (field strength meter) at the shack. Do the calculation and have the antenna gain. This seems to me to be fairly straight forward, but has anyone carried out similar measurements and concur with the approach or are there are there traps and pit falls that I need to be aware of. Or is their simply a better way? Cheers -- Peter Miles VK3YSF Melbourne, Australia -- Joe Leikhim K4SAT "Jazz is not dead. It just smells funny." -F.Z. |
We just made a range dipole for 900 MHz. The balun we ordered from
Minicircuits (pay careful attention to pinouts) was a 1:1. It resonated well once we took into account that the polyethelene mounting block imparted a velocity factor which shortened the rods slightly. Peter wrote: Hi all. This may seem like a fairly basic question. But here we go! I want to performance test a 436MHz high gain antenna. My plan is to construct a simple dipole with a 1:1 balun for 436MHz as a reference antenna and construct another dipole with a 1:1 balun to receive the test signal, measure it with a diode detector and a milli-amp meter (field strength meter) at the shack. Do the calculation and have the antenna gain. This seems to me to be fairly straight forward, but has anyone carried out similar measurements and concur with the approach or are there are there traps and pit falls that I need to be aware of. Or is their simply a better way? Cheers -- Peter Miles VK3YSF Melbourne, Australia -- Joe Leikhim K4SAT "Jazz is not dead. It just smells funny." -F.Z. |
In message , Peter
writes Hi all. This may seem like a fairly basic question. But here we go! I want to performance test a 436MHz high gain antenna. My plan is to construct a simple dipole with a 1:1 balun for 436MHz as a reference antenna and construct another dipole with a 1:1 balun to receive the test signal, measure it with a diode detector and a milli-amp meter (field strength meter) at the shack. Do the calculation and have the antenna gain. This seems to me to be fairly straight forward, but has anyone carried out similar measurements and concur with the approach or are there are there traps and pit falls that I need to be aware of. Or is their simply a better way? I've done it on 1296MHz in a similar way. However I borrowed a calibrated step attenuator and took the difference in readings between the reference dipole and the antenna under test as the gain for the same detector reading to avoid nonlinearities. You can also measure antenna gain using sun noise on 70cm, but that's a bit trickier. Brian GM4DIJ -- Brian Howie |
In message , Peter
writes Hi all. This may seem like a fairly basic question. But here we go! I want to performance test a 436MHz high gain antenna. My plan is to construct a simple dipole with a 1:1 balun for 436MHz as a reference antenna and construct another dipole with a 1:1 balun to receive the test signal, measure it with a diode detector and a milli-amp meter (field strength meter) at the shack. Do the calculation and have the antenna gain. This seems to me to be fairly straight forward, but has anyone carried out similar measurements and concur with the approach or are there are there traps and pit falls that I need to be aware of. Or is their simply a better way? I've done it on 1296MHz in a similar way. However I borrowed a calibrated step attenuator and took the difference in readings between the reference dipole and the antenna under test as the gain for the same detector reading to avoid nonlinearities. You can also measure antenna gain using sun noise on 70cm, but that's a bit trickier. Brian GM4DIJ -- Brian Howie |
There are a lot of factors that can potentially affect measurements. The
first and most obvious is impedance matching, which has to be done to extract the maximum possible power from the antennas (assuming that this is what you'll be doing when actually using the antenna) and delivering a known amount of power to each. Another is to make sure the feedlines aren't radiating or picking up signals, by using proper baluns, which you've mentioned. Move the feedlines around and change their lengths, making sure the results don't change. If they do, your baluns aren't adequate. If you want quantitative measurements, you'll have to carefully calibrate your signal strength meter at the power level involved. Don't make assumptions about its linearity. Better yet would be to carefully match the antennas to 50 ohms, then insert a step attenuator in series with the Yagi in the 50 ohm environment and increase the attenuation until it reads the same as the dipole. That way, the FS meter linearity is immaterial (although the attenuator accuracy is important). Then there's the possibility of signals radiated off the back of the dipole being reflected from near or distant objects which would affect the dipole's measured field strength more than it would the Yagi's. The different widths of the forward lobes can also cause unequal reflections. Although reflections can affect the forward gain up to several dB, their impact on nulls or front/back measurements is likely to be greater. I'd do a couple of things. One is to build an NBS reference Yagi which is easy to construct and has a well known and documented gain. It's also easy to model. Modern modeling programs do very well with full size Yagis. Measure this on your range and verify that the measurements agree with its known properties. Another check would be to rotate the dipole and see if its pattern is what it should be. And rotate the NBS Yagi and verify that its pattern matches modeled results. Only after doing those tests would I have reasonable confidence in other measurements made with similar types of antennas. Roy Lewallen, W7EL Peter wrote: Hi all. This may seem like a fairly basic question. But here we go! I want to performance test a 436MHz high gain antenna. My plan is to construct a simple dipole with a 1:1 balun for 436MHz as a reference antenna and construct another dipole with a 1:1 balun to receive the test signal, measure it with a diode detector and a milli-amp meter (field strength meter) at the shack. Do the calculation and have the antenna gain. This seems to me to be fairly straight forward, but has anyone carried out similar measurements and concur with the approach or are there are there traps and pit falls that I need to be aware of. Or is their simply a better way? Cheers -- Peter Miles VK3YSF Melbourne, Australia |
There are a lot of factors that can potentially affect measurements. The
first and most obvious is impedance matching, which has to be done to extract the maximum possible power from the antennas (assuming that this is what you'll be doing when actually using the antenna) and delivering a known amount of power to each. Another is to make sure the feedlines aren't radiating or picking up signals, by using proper baluns, which you've mentioned. Move the feedlines around and change their lengths, making sure the results don't change. If they do, your baluns aren't adequate. If you want quantitative measurements, you'll have to carefully calibrate your signal strength meter at the power level involved. Don't make assumptions about its linearity. Better yet would be to carefully match the antennas to 50 ohms, then insert a step attenuator in series with the Yagi in the 50 ohm environment and increase the attenuation until it reads the same as the dipole. That way, the FS meter linearity is immaterial (although the attenuator accuracy is important). Then there's the possibility of signals radiated off the back of the dipole being reflected from near or distant objects which would affect the dipole's measured field strength more than it would the Yagi's. The different widths of the forward lobes can also cause unequal reflections. Although reflections can affect the forward gain up to several dB, their impact on nulls or front/back measurements is likely to be greater. I'd do a couple of things. One is to build an NBS reference Yagi which is easy to construct and has a well known and documented gain. It's also easy to model. Modern modeling programs do very well with full size Yagis. Measure this on your range and verify that the measurements agree with its known properties. Another check would be to rotate the dipole and see if its pattern is what it should be. And rotate the NBS Yagi and verify that its pattern matches modeled results. Only after doing those tests would I have reasonable confidence in other measurements made with similar types of antennas. Roy Lewallen, W7EL Peter wrote: Hi all. This may seem like a fairly basic question. But here we go! I want to performance test a 436MHz high gain antenna. My plan is to construct a simple dipole with a 1:1 balun for 436MHz as a reference antenna and construct another dipole with a 1:1 balun to receive the test signal, measure it with a diode detector and a milli-amp meter (field strength meter) at the shack. Do the calculation and have the antenna gain. This seems to me to be fairly straight forward, but has anyone carried out similar measurements and concur with the approach or are there are there traps and pit falls that I need to be aware of. Or is their simply a better way? Cheers -- Peter Miles VK3YSF Melbourne, Australia |
"Roy Lewallen" wrote in message ... There are a lot of factors that can potentially affect measurements. The first and most obvious is impedance matching, which has to be done to extract the maximum possible power from the antennas (assuming that this is what you'll be doing when actually using the antenna) and delivering a known amount of power to each. Another is to make sure the feedlines aren't radiating or picking up signals, by using proper baluns, which you've mentioned. Move the feedlines around and change their lengths, making sure the results don't change. If they do, your baluns aren't adequate. If you want quantitative measurements, you'll have to carefully calibrate your signal strength meter at the power level involved. Don't make assumptions about its linearity. Better yet would be to carefully match the antennas to 50 ohms, then insert a step attenuator in series with the Yagi in the 50 ohm environment and increase the attenuation until it reads the same as the dipole. That way, the FS meter linearity is immaterial (although the attenuator accuracy is important). Then there's the possibility of signals radiated off the back of the dipole being reflected from near or distant objects which would affect the dipole's measured field strength more than it would the Yagi's. The different widths of the forward lobes can also cause unequal reflections. Although reflections can affect the forward gain up to several dB, their impact on nulls or front/back measurements is likely to be greater. I'd do a couple of things. One is to build an NBS reference Yagi which is easy to construct and has a well known and documented gain. It's also easy to model. Modern modeling programs do very well with full size Yagis. Measure this on your range and verify that the measurements agree with its known properties. Another check would be to rotate the dipole and see if its pattern is what it should be. And rotate the NBS Yagi and verify that its pattern matches modeled results. Only after doing those tests would I have reasonable confidence in other measurements made with similar types of antennas. Roy Lewallen, W7EL I thought that NIST prefers a dipole antenna up to 1 GHz, and then a waveguide-fed horn beyond that. I would think that a pyramidal horn would be more predictable that a Yagi, and not unreasonably large, even for 400 MHz. Plus, the construction is simpler, and the design is more robust over time (i.e., it's easy to bend a Yagi element slightly, not enough to notice it, but enough to shift performance). Ed WB6WSN |
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