It didn't take a 259b or VNA to see there was a problem with that antenna, the SWR showed it was acting more like a dummy load than an antenna.
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High Swr??
- Thread starter undertaker
- Start date
To support your POV DB, the inverted L I used for contesting as a multiband antenna when modelled presented a SWR of >85:1 on some bands. Didn't stop it working exceptionally well because although it had high SWR it also had lobes with quite considerable gain. It was fed with an antenna coupler at the feedpoint which presented a 50 Ohm impedance to the coax feeder and radio thus ensuring that the maximum amount of power possible entered the tuner and was fed into the radiating element.
There is a very good article on the internet entitled "SWR Meters make you stupid" and it is worth a read.
http://www.eham.net/articles/23317
As for low SWR, I've seen on my antenna analyser quite a few times where I'd see a very low SWR but an impedance you'd really not want. The reactance and the feeder losses were the things which resulted in a low SWR reading.
There's actually a very good example of why SWR doesn't matter and that can be seen when you use a tuner. Say you use an antenna with a high SWR, a random length of wire. When you plug it into your radio you don't hear much. You use a tuner to get the impedance seen by the radio down to 50Ohms or thereabouts and magically lots of signals appear. The tuner doesn't physically alter the antenna, merely corrects the mismatch between the impedance of the antenna and what the radio wants to see....
There is a very good article on the internet entitled "SWR Meters make you stupid" and it is worth a read.
http://www.eham.net/articles/23317
As for low SWR, I've seen on my antenna analyser quite a few times where I'd see a very low SWR but an impedance you'd really not want. The reactance and the feeder losses were the things which resulted in a low SWR reading.
There's actually a very good example of why SWR doesn't matter and that can be seen when you use a tuner. Say you use an antenna with a high SWR, a random length of wire. When you plug it into your radio you don't hear much. You use a tuner to get the impedance seen by the radio down to 50Ohms or thereabouts and magically lots of signals appear. The tuner doesn't physically alter the antenna, merely corrects the mismatch between the impedance of the antenna and what the radio wants to see....
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People could go on and on about antenna SWR, antenna Gain, what type Coax and how many feet of it ect.
I myself like to see a low SWR with as close to 50 ohms as possible when using 50 ohm coax. Like said above sometimes 50 ohms and the lowest SWR reading don't agree.
The antenna system is the most important factor in radio communication.
No radio modification or external amplifier will ever make the antenna perform passed what is was designed for.
I myself like to see a low SWR with as close to 50 ohms as possible when using 50 ohm coax. Like said above sometimes 50 ohms and the lowest SWR reading don't agree.
The antenna system is the most important factor in radio communication.
No radio modification or external amplifier will ever make the antenna perform passed what is was designed for.
Technically you would be correct, assuming the guy in question had more than a 40 channel CB radio which gives him a whopping 0.44 MHz of tuning bandwidth to check SWR over. So how, with just that radio and an SWR meter, was he supposed to see the issue that showed up with SWR over a much larger bandwidth? The only way to test the antenna over a larger bandwidth is to put something else in place of the radio that has more bandwicdth. I suppose we could put an export radio or ham radio in there, or I could go through even less of a hassle and hook up my VNA and in the process get far more data in far less time than using said export or ham radio with only an SWR meter... So the VNA actually ended up saving time in this case... Go figure...
Assuming your single band mobile antenna is working as intended you would be absolutely correct, SWR will get you close. The problem is you have to assume certain things, such as all single band mobile antennas are fine out of the box. Good luck with that...
The DB
I've read that article before, it is a good article, although it goes beyond what most people on the CB band will ever use.
If a low SWR is all you are looking at when tuning an antenna then you are looking at the wrong data. One of the best written series of books on the subject has an entire chapter called "Low SWR for the Wrong Reasons". The books were written my M. Walter Maxwell, W2DU, and called "Reflections Transmission Lines and Antennas". There is a freely available .pdf file called "Another Look at Reflections" that includes chapters 1 through 7 from that book, which includes said chapter. Look it up.
Look, all I was trying to say is SWR doesn't tell you nearly as much as most people seem to think it does. To many people treat it like its the King of antenna tuning when in reality it barely qualifies as the lowliest of peasants... At best all it will ever be is a pretender to the throne.
The DB
I would expect to see a curve even at .44MHz honestly. The last mobile I owned was a hard mounted Wilson on the top of a quad cab dually. From my notes it showed a 2:1 curve of 1.3MHz which is pretty flat, and 3-4 tenths of a point curve within .44MHz. An antenna that's flat from 2m to 20m wouldn't exhibit even that much of a curve I wouldn't think, it would appear to be dead. I think someone as yourself would be suspect of that antenna using an SWR meter and a 40 channel CB. Plus the owner was undoubtedly complaining that he couldn't talk across the street
If you sweep an 80m dipole from 2-30MHz you'll see the SWR/REF has a direct relationship to the impedance/phase, even though it may never approach anything as good as even a 10:1 SWR, and be resonant at several points. You can't see all of that with an SWR meter, and I'm not suggesting that you can.
I know you are passionate about antennas and are more knowledgeable than myself on antenna theory, and I would never tell a person to ditch an analyser for an SWR meter. But I don't think either of the articles linked here said to completely disregard SWR readings either (it's been a couple years since I read either of them). Some Working knowledge or access to information, some troubleshooting skills and some common sense make an SWR meter a decent little tool for the average CB user. Since since this is the CB antenna forum section and the topic was a video posted by a guy who sells CB antennas, I think it has relevance and answers the OP. The guy in the video either didn't know what he was trying to say, or just couldn't express himself. He almost made it sound like a higher SWR was better, but you had to keep it low for the sole purpose of making the radio happy. And that's not true.
In my example, it wasn't a single curve, SWR did peak in a few spots, it just didn't peak higher then 2:1 SWR in the frequency range. Also, there are some mobile antennas that I've seen the in that narrow frequency range never make it above 1.2:1 SWR. Could you have made the determination with just an SWR meter in that case? I would only go so far as a maybe at best, and the person using the SWR meter would need to really know what they are looking at.
Speaking of knowledge of using an SWR meter, if you are skilled at using the tool, and/or don't mind thinking outside the box a little, then you can find out quite a bit about an antenna system with one. You can get even more info if you add in a simple power meter and some ingenuity. I wouldn't put the info in the same league as an equally (or even lesser) skilled user using even a low end antenna analyzer, but there is useful information to be had. I could easily get actual loss characteristics of the feedline for example, and make sure it is in (or within reason of) spec. There is all kinds of stuff that can be done with just a simple SWR/power meter and some knowledge/creativity. Unfortunately SWR/Power meters are rarely used for such uses.
The DB
Speaking of knowledge of using an SWR meter, if you are skilled at using the tool, and/or don't mind thinking outside the box a little, then you can find out quite a bit about an antenna system with one. You can get even more info if you add in a simple power meter and some ingenuity. I wouldn't put the info in the same league as an equally (or even lesser) skilled user using even a low end antenna analyzer, but there is useful information to be had. I could easily get actual loss characteristics of the feedline for example, and make sure it is in (or within reason of) spec. There is all kinds of stuff that can be done with just a simple SWR/power meter and some knowledge/creativity. Unfortunately SWR/Power meters are rarely used for such uses.
The DB
DB, I would like to hear more details about this Wilson 1000 story that you claim showed you a flat SWR as noted above.
No Wilson 1000 is going to do what you claim in the first place...without extenuating circumstances.
What are you really trying to tell us about the 259b?
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When you say above, "...In my example...", what expample are you talking about?
Are you still talking about the Wilson 1000 experience?
Flat was a bit off, it had a few points that peaked between 1.3:1 to 1.5:1 or so SWR. Bad wording on my part admittedly, but looking at the plot the SWR line did appear to be flat.
I simply said someone used an MFJ 259b and said the antenna was good. I was not the guy that used the MFJ, nor am I aware of exactly the process that he used, I just know what I was told about it.
I wish I saved the plot to post, but as I recommended that the antenna be returned/replaced, and that is what the guy did, I didn't figure I would need it... I likely have a copy of it laying around somewhere, but I'm not sure where it would be offhand. I'll look around for it, no guarantees though.
And yes I was still talking about the Wilson 1000 example above.
Extenuating circumstances... I'de have been the first in line to take it apart and see what was up, but I wan't going to recommend the guy not get his money back on a new antenna that wasn't working for him... Would you be willing to risk breaking the guys warranty not knowing for sure what the problem was to begin with just to figure it out? I would also say that any antenna with that wide of an SWR bandwidth has extenuating circumstances, and its not the only one of those I've seen...
I posted a 102" whip plot that had similar type bandwidth a while back, but that one was caused by water damage inside the mount, and likely the coax as well. I did replace it about a month later with a new mount/coax, and he hasn't reported a problem since. The link to that thread is here.
The DB
It's been about four years since I played with mine, but I remember the complex number not being +/- indicating an inductive or capacitive circuit. If I changed modes to check Xl or Xc individually, it called X, Xl and Xc all the same number and did read out the inductance and capacitance, but you were still left with manual calculations. I also remember converting the complex numbers to polar form only to find that while the magnitude of Z matched, the phase angle was off.
It's been awhile, and maybe it needs calibrated, but I can dig it out next week and play with it more for a memory refresher.
DB, I didn't think for one minute that your really had anthing to do with the BS part of the story, but you did tell us you tested it with your VNA.
I'm curious why didn't you just tell us the real results you saw with your VNA, rather than just leave us thinking the 1000 was likely bad, and the 259b was wrong. Am I wrong?
MFJ now sells an add on device that can be used with their analyzers that can tell you if the phase (or reactance) is positive or negative. It just became available this year I think, or last year at the earliest.
Link
All you should have to do if it is wrong is invert the sign. Knowing if you need to invert said sign, however, that is where the difficulty comes into play. I have some ideas on that, however, with all the methods I came up with that would work, they would only work effectively in a limited set of circumstances, say being near specific electrical lengths of antennas, as an example. Other methods required you to be at least so far away from resonance to get an accurate result. I'de be happy to look up my data on said topic if you would like, however, I think it would be worthy of its own thread...
The DB
In my opinion based on my results the 1000 was bad, and in my opinion the guy with the 259b, assuming it happened as I was told, was not doing something right. When it comes to the shop in question and what I know of it, I'll leave that at no comment as I don't have anything good to say about them...
The DB