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#1
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![]() "Dale Parfitt" wrote in message ... "Peter" wrote in message ... "Owen Duffy" wrote in message ... "Peter" wrote in . au: ... I must admit I had assumed that the 269 analyzer display the sign of the reactance, I will have to reread the ad. Ah, you were looking for honesty in advertising! The online guff on the MFJ259B says: "Read Complex Impedance as series resistance and reactance (R+jX) or as magnitude (Z) and phase (degrees)." The MFJ259B definitely does *not* show phase angle or reactance as negative for cases where X is actually negative. The same words appear in the MFJ269 online page, so it may also be a misrepresentation. I see in the MFJ269 manual, the same pretence over the sign of phase and reactance. It contains the words "Besides Z, an angle between zero and 90 degrees is shown. This angle represents the phase difference between current and voltage at the terminals of the analyzer." Of course, a phase angle between "zero and 90 degrees" does not represent "phase difference between current and voltage at the terminals of the analyzer" in the case of a capacitive impedance. Honesty in advertising... think again. Owen What was I thinking! I was impressed with what was being claimed. I will continue with my product research and you can expect me to float some other manufactures device on this group soon for comments. Peter VK6YSF Again- look at the RigExpert A-200A. Batteries seem to last forever, it's USB upgradable and it DOES resolve the sign of R +/-JX. Dale W4OP Thanks Dale I have just had a look at the RigExpert site. Look impressive, but the MFJ269 at about $400US was about my limit. I think I will take a step back and conduct a more scientific review of all of the antenna analyzers on offer, there for you should get sick of my postings over the next couple of weeks/months. I must say that the ability to save and analyze data on the lap top is an appealing feature. Regards Peter VK6YSF http://members.optushome.com.au/vk6ysf/vk6ysf/main.htm |
#2
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Peter wrote:
I have just had a look at the RigExpert site. Look impressive, but the MFJ269 at about $400US was about my limit. I think I will take a step back and conduct a more scientific review of all of the antenna analyzers on offer, there for you should get sick of my postings over the next couple of weeks/months. I must say that the ability to save and analyze data on the lap top is an appealing feature. Regards Peter VK6YSF http://members.optushome.com.au/vk6ysf/vk6ysf/main.htm Have a look at the AIM 4170 at http://www.arraysolutions.com/ I have that and a MFJ analyzer. For a quick antenna adjustment, the MFJ is easier to use. For in depth analysis, the AIM can't be beat. If I had only one, I would prefer to have the AIM. -- Jim Pennino Remove .spam.sux to reply. |
#4
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Ian Wade G3NRW wrote:
The other nice thing about the 4170 is the ability to control it remotely. With the 4170 connected to the antenna system in the shack and controlled by a local PC, it's then possible to remotely access the PC from a cheapy notebook in the backyard. You can make antenna adjustments out in the yard and see the effects of the changes immediately, without having to repeatedly walk back indoors to look at the 4170 PC. This feature alone has saved me a *lot* of time: I tend to make my SWR readings right at the antenna, whenever possible. That length of coax to the xceiver will only make it look better in most cases. - 73 de Mike N3LI - |
#5
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Michael Coslo wrote:
Ian Wade G3NRW wrote: The other nice thing about the 4170 is the ability to control it remotely. With the 4170 connected to the antenna system in the shack and controlled by a local PC, it's then possible to remotely access the PC from a cheapy notebook in the backyard. You can make antenna adjustments out in the yard and see the effects of the changes immediately, without having to repeatedly walk back indoors to look at the 4170 PC. This feature alone has saved me a *lot* of time: I tend to make my SWR readings right at the antenna, whenever possible. That length of coax to the xceiver will only make it look better in most cases. - 73 de Mike N3LI - One of the advantages of the 4170 is the ability to calibrate out the effects of the feedline. -- Jim Pennino Remove .spam.sux to reply. |
#6
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From: Michael Coslo
Date: Fri, 21 Aug 2009 Time: 09:51:05 I tend to make my SWR readings right at the antenna, whenever possible. That length of coax to the xceiver will only make it look better in most cases. - 73 de Mike N3LI - Mike, With the 4170 I can calibrate the instrument to compensate for the feeder impedance. After calibration, the indicated impedance at the TX end of the feeder is actually the antenna feedpoint impedance. This makes life a *lot* easier. -- 73 Ian, G3NRW |
#7
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Ian Wade G3NRW wrote:
From: Michael Coslo Date: Fri, 21 Aug 2009 Time: 09:51:05 I tend to make my SWR readings right at the antenna, whenever possible. That length of coax to the xceiver will only make it look better in most cases. - 73 de Mike N3LI - Mike, With the 4170 I can calibrate the instrument to compensate for the feeder impedance. After calibration, the indicated impedance at the TX end of the feeder is actually the antenna feedpoint impedance. This makes life a *lot* easier. Oaky, well good enough. My vertical uses a stub on the feedline, so I have to be out there anyhow.with a connector in the line. Seems like 6 of one, half dozen of the other situation. - 73 De Mike N3LI - |
#8
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From: Michael Coslo
Date: Fri, 21 Aug 2009 Time: 15:05:13 Oaky, well good enough. My vertical uses a stub on the feedline, so I have to be out there anyhow.with a connector in the line. Seems like 6 of one, half dozen of the other situation. - 73 De Mike N3LI - Agreed. But I guess your antenna feedpoint is more-or-less at ground level. That's a little different from peering through binoculars at an MFJ suspended at the feedpoint 50ft above ground .... grin -- 73 Ian, G3NRW |
#9
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Ian Wade G3NRW wrote:
Mike, With the 4170 I can calibrate the instrument to compensate for the feeder impedance. After calibration, the indicated impedance at the TX end of the feeder is actually the antenna feedpoint impedance. This makes life a *lot* easier. Easy, yes. But If you're not careful, this can be a great example of garbage in, garbage out. I frequently calculate out the feedline transformation when making antenna measurements. But it's essential that you realize a small error in estimating the feedline loss(*) or length can sometimes result in a very large error in calculated impedance. This is particularly true if there's a large impedance mismatch between the line and antenna. Transmission line impedance, which can vary a lot from the specified nominal value (I've seen +/-20% with coax, more with ladder line), also has an effect on the result. So whenever I need accurate results or whenever the line Z0 is quite different from the antenna impedance, I start by carefully measuring the properties of the actual transmission line I'll be using. If you're not convinced, spend a few minutes playing with something like N6BV's TLW calculator that comes with the ARRL Antenna Book. (*) Some simplified techniques ignore transmission line loss altogether. This can lead to very inaccurate results in some situations. And loss is often quite different than the specified value, so it really has to be measured if it makes a significant difference. Roy Lewallen, W7EL |
#10
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Roy Lewallen wrote:
Ian Wade G3NRW wrote: Mike, With the 4170 I can calibrate the instrument to compensate for the feeder impedance. After calibration, the indicated impedance at the TX end of the feeder is actually the antenna feedpoint impedance. This makes life a *lot* easier. Easy, yes. But If you're not careful, this can be a great example of garbage in, garbage out. I frequently calculate out the feedline transformation when making antenna measurements. But it's essential that you realize a small error in estimating the feedline loss(*) or length can sometimes result in a very large error in calculated impedance. This is particularly true if there's a large impedance mismatch between the line and antenna. Transmission line impedance, which can vary a lot from the specified nominal value (I've seen +/-20% with coax, more with ladder line), also has an effect on the result. So whenever I need accurate results or whenever the line Z0 is quite different from the antenna impedance, I start by carefully measuring the properties of the actual transmission line I'll be using. If you're not convinced, spend a few minutes playing with something like N6BV's TLW calculator that comes with the ARRL Antenna Book. (*) Some simplified techniques ignore transmission line loss altogether. This can lead to very inaccurate results in some situations. And loss is often quite different than the specified value, so it really has to be measured if it makes a significant difference. Roy Lewallen, W7EL The 4170 makes this a lot easier as you can measure the feedline actual parameters as well as calibrate out their effects. -- Jim Pennino Remove .spam.sux to reply. |
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