| Author |
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Marconi
| | Posted on Wednesday, November 28, 2001 - 9:04 am: | 
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I would like to have a little discussion regarding the use of one of these units. Do you find them useful in your radio work? Explain please.
Marconi |
Hamcber
| | Posted on Wednesday, November 28, 2001 - 12:51 pm: |
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I use an MFJ for non-critical stuff. For critical calculations, I use a service monitor with tracking generator and a return loss bridge to do a DC-daylight sweep and print it out for the client.
Sweeping an antenna/feedline/system is the only way to get an accurate picture. However, the MFJ is quick to set up and use, and if it breaks, I am only out $350 instead of $30,000 for my other apparatus.
With the sweep method, I can tell if all elements of a multiple element array are tuned together, if there is a mismatch in cable, elements, or connectors, etc. With the MFJ, I can tell only if the radio will like the load or not at any given freq. |
Marconi
| | Posted on Wednesday, November 28, 2001 - 10:42 pm: |
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Hamcber, I have one of those what-jama-callits laying around here somewhere too. Problem is it has a three prong plug on the wire and my wall jack thingie only has two holes in it. So, I can't use it. I tried sweeping my antenna one time and I just made a big mess. Of course my wife just had to try and show me what I was doing wrong. What to do? Darn! Shoot! Shucks!
Does the MFJ read R and X equally well at either end, the TX end or at the antenna feed point? In other words does the presence of the line make a difference?
If it does not make a difference, then that is good.
But, if it does make a difference, how does one compensate for that? I cannot always get close to the feed point if the antenna is installed and I would like to know if these meters can handle that.
Marconi |
Hamcber
| | Posted on Thursday, November 29, 2001 - 12:40 pm: |
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Wha? What were you trying to use to do your sweep? I use an IFR service monitor w/tracking generator option (I think it's option 5) and a return loss bridge.
The MFJ does read R and X pretty well. As you should already know, feedline does make a difference. If you are doing a sweep using a return loss bridge as I referenced above, it is referenced to 50 ohms all the time, so feedline makes no difference.
Technical discussions having to do with equipment most hams and CBers have never heard of is never understood on a CB forum and always leads to questions asking me to explain EVERYTHING, and as such, these discussions always stress me out.
Best bet, give me a call. The forum master has all my contact info., I give permission for you (Marconi only) to have it. I'm 10-7 from this one. |
Marconi
| | Posted on Thursday, November 29, 2001 - 9:23 pm: |
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Hamcber, my remarks about doing the sweep thing was made in jest.
I have never heard of an IRF service monitor w/tracking generator option. I am curious about the MFJ meter and what it will do. I do not own any of this expensive stuff but have considered getting an analyzer.
I was curious about if and how these things are able to overcome the line problems we are told about when we simply read the SWR using a random line.
I assume that a lot of Hams and some CB'ers use these analyzers, but when it comes to a discussion about how they are used and what they do, things get real quite all of a sudden???
What you do for your clients sounds very technical. Do they really understand the results you print out for them. I don't think I will be looking around for any of that high-a-dollar equipment any time soon, but I would like to see an example of what that report might look like. Are you able to actually tune a single passive element with that setup?
I appreciate your offer to talk about this on the phone, but if I couldn't understand it on the forum then I sure wouldn't understand it on the phone.
I am forced to speak in general terms about all this antenna business because I am not technically trained. I do have a little common sense, but even that won't permit me to go very far into a technical discussion with a well trained Ham operator when it gets off into the really technical aspects of antenna design, tune, and performance.
Marconi |
Hamcber
| | Posted on Thursday, November 29, 2001 - 10:42 pm: |
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Not all hams are very technical either. In fact, most hams are 'plug and play' operators these days. If something breaks, they send it out for repair. Sad, sad thing....
I am much less of a ham than I am a tech. |
Hydro
| | Posted on Thursday, November 29, 2001 - 11:38 pm: |
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I use the Anritsu Site Master. I can send a sample of the printout file but you would have to download the software to open it from their site to open the file.
Joe |
Vernonott
| | Posted on Friday, November 30, 2001 - 12:21 am: |
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Marconi: I have one of the MFJ 259 models and have really enjoyed using it.The radio is not used at all.The MFJ test the coax and antenna. |
Marconi
| | Posted on Friday, November 30, 2001 - 6:59 am: |
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There you go Vernon, you are the guy I wanted to talk to. I understand that the radio is not used when using this device. I have questions about use and results.
I am talking base antennas here if that makes any difference. We all hear the statement, "...tune your antenna at the antenna." When possible, I do that myself. I do it simply because things simply are never the same when you tune in one place, move and install at another. I didn't get that out of a book either, I don't think.
Question is, do these analyzers compensate somehow for line effects or is it still advisable to tune at the antenna?
I don't think I really need to know what the actual feed point impedance relative to SWR is, in order to tune or match a radiating element. So assuming these meters likely serve other purposes, is the information derived in this regard of any great benefit when tuning?
If you made SWR checks along with your tuning efforts while using this meter, would you get similar results that are relative to how well you were doing with your tune and matching?
Hydro, I would only be interested in looking at what the actual printout. What does it show, how does it show it? If it is like looking at an X-ray of a tumor, then I would not be interested. Is the report just a bunch of numbers or is it a graph or a graphic similar to what we might see when using antenna design software?
If it takes a trained eye with years of interpretive skills to understand, then no thanks.
Marconi |
Hamcber
| | Posted on Friday, November 30, 2001 - 12:34 pm: |
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The MFJ will be best used at the antenna on a grounded type antenna. In other words, an antenna which shows a DC 'short' when checked using an ohmmeter. An antenna that shows an 'open' should be checked at the radio end of the cable using an MFJ meter. Why is complicated.
A printout of a sweep looks like a larger tic-tac-toe board. Along the bottom of the display shows frequency. Let's say the left most line is 26 MHz. Then you could set it up so there is a line every 10 kc. all the way up to 28 MHz. O.K., now along the left side of the chart would be numbers relating to dB of return loss. The more return loss, the more 'signal' the antenna is either absorbing or radiating. What you would see on a good CB antenna is a 'U' shape line on the chart with the center around 27.0 MHz. Let's say the edges are at about 26 dB return loss (an SWR of about 1.5:1 at 50 ohms) and the center is at about 35 dB return loss (an SWR below what an SWR meter can accurately read, CBers would say it is 'FLAT'). However, you can accurately read return loss down to better than 90 dB. Some professional antennas will actually show return loss down into the 60 or 70 dB range! You could convince some CBers that the antenna is 'sucking' the signal out of the radio for some fun....
When sweeping business band antennas with multiple elements, you would see some 'bobbles' in the sweep line. With a single element like a CB antenna, it will usually just be a 'U' shape plot. |
Vernonott
| | Posted on Friday, November 30, 2001 - 9:08 pm: |
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Thanks for jumping in Hamcber.All contributions appreciated.Marconi,the 259 will do about twenty test that I'm not educated enough to operate.The 259 can be used to adjust or test the following-
Antennas
Antenna tuners
Ampliers
Coaxial transmission lines
Filters
Matching or tuning stubs
Traps
Tuned circuits
Small capacitors
RF chokes & inductors
Transmitters & oscillators
and the list goes on.Not enough room on here to post it all.Hamcber has forgotten more about this stuff than I will ever know.I'm assuming that he will be glad to give you a helping hand.73's |
Marconi
| | Posted on Saturday, December 01, 2001 - 6:03 am: |
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Vernon, you are correct about Hamcber. I fit into your category as well. I note the list of functions you provide, but I am only interested in the tuning and matching functions that this meter can provide. In my case it will be multi-element beams.
Hamcber, it is always a revolting development when the complexity of an issue seems to get in the way of a good description and/or thorough understanding. For me however, it is great just to be aware of the distinction you make between grounded and non-ground radiators when using these devices. You are fortunate that your understanding and experience in the use of this technology gives you a minds-eye view of this complicated subject. Of course I would like to know why, but maybe another time.
The printed results you describe, reminds me a little of my own efforts to tune. I use a procedure that I refer to as “Tuning using SWR Curves.” The procedure is a bit labor intensive, and I make judgments based on relative information using only an SWR meter. I think I posted something about this a while back, right here on this forum somewhere.
I have found in my experience that finding true resonance seems to be very important when tuning. I have also noted that simply getting a very low SWR does not always provide the best results. This is why I may go to the extra trouble. I figure that one of these analyzer meters might really come in handy for me. For sure, it may save a lot of steps or the need for an able co-worker at a transmitter.
Vernon, I asked the following question of you earlier. “If you made SWR checks along with your tuning efforts while using this meter, would you get similar results that are relative to how well you were doing with your tune and matching?” I am sorry. After reading my question over again I find it to be very vague. Of course you made SWR checks as you tuned. It would only make sense that you would take note of what the analyzer indicates your SWR is during that process? In fact, I think these meters provide several values that you may take note of when tuning. Which value do you concentrate on to make judgments, the SWR, the impedance, the reactance, or a combination of all values?
This is not a trick question. I am trying to determine if this device is providing exacting information or is it simply providing relative information like an inline SWR meter. If the analyzer only provides relative information, then they are for convenience only and are not unlike a good SWR meter. What do you think?
Maybe you did not take the time to develop an SWR curve along with your tuning efforts while using the analyzer, but without consideration for convenience, my question should have read as follows. If you had used a transmitter and your inline SWR meter to do your tune, do you think you could have come to a similar tuning and matching result?
I think Hamcber thought that I wanted to discuss the details of tuning using these meters. At this point I am only interested in an overview of their use and results while tuning.
Thanks to both for your help,
Marconi |
Hamcber
| | Posted on Saturday, December 01, 2001 - 11:18 am: |
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Oh, O.K. Sorry for the confusion.
Using the MFJ, you can see your resistance value along with your reactive component. The shortcoming of the MFJ is that it does not tell you whether the reactive component is inductive or capacitive. That is important! You see, a transmitter will run into a slightly reactive load with no ill effects, however, a capacitive load will cause the amplifier to overheat very quickly.
As far as tuning for efficiency, the MFJ falls short. It will only tell you what the load is. Now, if you are looking to get that perfect 50 ohm, j=0 load at your favorite frequency, then the MFJ is perfect. However, if you are looking to tune for useable bandwidth, the MFJ is not much help since you can't tell if or how badly you go capacitive at either side of resonance.
For that kind of money plus only a little more, I suggest you keep your eyes open for a used Operating Impedance Bridge (OIB). |
Pinger
| | Posted on Monday, January 27, 2003 - 5:55 pm: |
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I have one of the MFJs and it's been pretty useful with tuning antennas. I still have to learn more about antennas even before i can use all of the MFJs features. I would love to learn more about matching/tuning antennas, and i was wondering if there are any good books that would help. |
Tech833
| | Posted on Tuesday, January 28, 2003 - 11:12 am: |
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The ARRL Antenna book would be the place to start. From there, you get into fragment areas that only technical textbooks appear to cover. |
Gonzo
New member
Username: Gonzo
Post Number: 5
Registered: 9-2004
| | Posted on Saturday, September 04, 2004 - 12:15 pm: |
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Lenghten or shorten the antenna itself to get best SWR if needed, and use a field strenght meter to determine best results.
The less "stuff" you have in the line the better.
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I use my MFJ-969 for my ham units only, where you cannot always lenghten or shorten the antenna. |
Bob_p
Intermediate Member
Username: Bob_p
Post Number: 309
Registered: 7-2004
| | Posted on Saturday, September 04, 2004 - 4:34 pm: |
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But from what I am beginning to understand C.B SWR meters are not very reliable. You can have several say one thing, and another say something completely different, and the only way to determine which is correct is by something like an antenna analyzer. Rendering most of our fairly expensive SWR Watt meters useless. And as someone else said good for looks but not much else. So buy the one that makes you feel best and be happy. But don't rely on it as telling you much of anything. |
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