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I have never seen as SWR curve anything like this...
- Thread starter The DB
- Start date
RatsoW8
Supporting Member, W9WDX ARC Member - WD8T
If you use the color code key on the right hand side it makes sense 
It's data you don't often see in a SWR curve graph but it's always there.
It's data you don't often see in a SWR curve graph but it's always there.With all due respect, I am well aware of the color coding of the lines and what they mean and how they relate to each other. This isn't the first time I have used this analyzer.
What I was referring to was the fact that the SWR, as it goes back up after the first low impedance point, never again went above 2:1 SWR. I have never seen this before, in pretty much every case before now it has gone much higher, and generally off the chart.
Just so you know that data you are referring to is a specific frequency, not the whole range, namely the blue line near the left edge of the graph. You actually get most of the color coding from the top right corner.
I don't like the fact that the SWR stays below 2:1 SWR for such a long time, (over 150Mhz measured, actually more). I know, make it long enough to include the 12 meter band and there are people on here that would call this a widebanded dream, I am not one of them. I also don't like how much return loss is the antenna has between the resonant points as that usually goes down much lower level than 10db.
The antenna has been installed on that car for a few years. Next time we meet we are going to take his antenna apart to make sure it doesn't have an internal issue somewhere.
Maybe I can talk him into RF Bonding as well...
Actually now that I looked at it again, that seems to also be higher cable loss than I would expect for such a ½λ run of RG8-X coax. I would have calibrated that out had the mount been easier to get to.
The DB
What I was referring to was the fact that the SWR, as it goes back up after the first low impedance point, never again went above 2:1 SWR. I have never seen this before, in pretty much every case before now it has gone much higher, and generally off the chart.
Just so you know that data you are referring to is a specific frequency, not the whole range, namely the blue line near the left edge of the graph. You actually get most of the color coding from the top right corner.
I don't like the fact that the SWR stays below 2:1 SWR for such a long time, (over 150Mhz measured, actually more). I know, make it long enough to include the 12 meter band and there are people on here that would call this a widebanded dream, I am not one of them. I also don't like how much return loss is the antenna has between the resonant points as that usually goes down much lower level than 10db.
The antenna has been installed on that car for a few years. Next time we meet we are going to take his antenna apart to make sure it doesn't have an internal issue somewhere.
Maybe I can talk him into RF Bonding as well...
Actually now that I looked at it again, that seems to also be higher cable loss than I would expect for such a ½λ run of RG8-X coax. I would have calibrated that out had the mount been easier to get to.
The DB
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DB,
Everything looks fine to me. Looking at what you have though, the whip is 102" + 6" +2" = 110" = 9.1666667'. 234/9.1666667 = 25.5273 MHz or so. Stray capacitance from the cable has shifted the resonance point to 29.66655 MHz. You will notice that resonance is where the phase = 0 (where the purple line crosses the 0 line). There are 15 points of resonance shown on your graph. But your system is primarily resonant at 29.66655 MHz as eveident by the Return Loss curve. Your RL = 26.44 dB for a value that's near to 1.1:1 VSWR. (Note: As a reference, a VSWR of 1.01:1 = a Return Loss (RL) of 45.8 dB). The fact that the antenna never exceeds 100 ohms is most likely due to the cable losses of your RG-8X cable, or the lack of bonding, or both. You would have to measure the antenna with a short 6" cable to get a better answer. I don't know where you want the antenna to work best at? But it works great at 29.66655 MHz the way it is.
Mike
Everything looks fine to me. Looking at what you have though, the whip is 102" + 6" +2" = 110" = 9.1666667'. 234/9.1666667 = 25.5273 MHz or so. Stray capacitance from the cable has shifted the resonance point to 29.66655 MHz. You will notice that resonance is where the phase = 0 (where the purple line crosses the 0 line). There are 15 points of resonance shown on your graph. But your system is primarily resonant at 29.66655 MHz as eveident by the Return Loss curve. Your RL = 26.44 dB for a value that's near to 1.1:1 VSWR. (Note: As a reference, a VSWR of 1.01:1 = a Return Loss (RL) of 45.8 dB). The fact that the antenna never exceeds 100 ohms is most likely due to the cable losses of your RG-8X cable, or the lack of bonding, or both. You would have to measure the antenna with a short 6" cable to get a better answer. I don't know where you want the antenna to work best at? But it works great at 29.66655 MHz the way it is.
Mike
DB it looks like you have the bandwidth scan set to cover 1 - 180 mhz. At best the scan should be limited to about 2 or 3 mhz at best. It doesn't look to bad down a little below 31 mhz.
If so, what would you expect the meter to show scanning near 180 mhz of bandwidth.
If so, what would you expect the meter to show scanning near 180 mhz of bandwidth.
KC9Q, I'm sure there is some damage somewhere in there. He says he set it up himself and he is not the most mechanically inclined person there is. After it warms up some we will take it apart and see what is up.
Marconi, I started that way, and kept adding more and more. As I said above, I have never seen an SWR curve not go above 2:1 SWR on both sides of a dip (bumps not included). The lowest I've seen SWR plateau at between ¼λ and ½λ before was 5:1, that was an A99. In this case I was looking to see if it ever went back up above 2:1 SWR, and it never did, at least within the range I am able to scan.
The DB
Marconi, I started that way, and kept adding more and more. As I said above, I have never seen an SWR curve not go above 2:1 SWR on both sides of a dip (bumps not included). The lowest I've seen SWR plateau at between ¼λ and ½λ before was 5:1, that was an A99. In this case I was looking to see if it ever went back up above 2:1 SWR, and it never did, at least within the range I am able to scan.
The DB
I'm not familiar with this analyzer, but I suspected the 180 mhz might be the default bandwidth for its scan range.
If you limit the scan to a CB frequency, or a range in the CB band, and don't use the default, then I think you will see a much better curve without all that garbage. No antenna is going to report good with the scan set to a 180 mhz range...when the antenna at best might only effectively work a 1 to 3 mhz bandwidth. Why would you want to scan a CB antenna at a frequency for 2 or 80 meters? You ought to know such results would be off the charts and riddled with losses.
You need to talk to Bob how to set the scan range, and then I think you will see some results close to 27 mhz for a 102" - 108" whip.
Man, I may be the one that is all corn'fused, but what is in a 102" whip antenna to take apart and check?
Are you having a bad day?
If you limit the scan to a CB frequency, or a range in the CB band, and don't use the default, then I think you will see a much better curve without all that garbage. No antenna is going to report good with the scan set to a 180 mhz range...when the antenna at best might only effectively work a 1 to 3 mhz bandwidth. Why would you want to scan a CB antenna at a frequency for 2 or 80 meters? You ought to know such results would be off the charts and riddled with losses.
You need to talk to Bob how to set the scan range, and then I think you will see some results close to 27 mhz for a 102" - 108" whip.
Man, I may be the one that is all corn'fused, but what is in a 102" whip antenna to take apart and check?
Are you having a bad day?
Marconi,
It's an Array Solutions AIM Antenna Analyzer, either the 4170 or the UHF model. Cannot tell since the header has been stripped from view. There are tabs at the bottom: one is called LIMIT, and that is where you set the bandwidth measurement limits. Going to setup menu at the top, and that's where you select what parameter (graph) you would like to display. This display is showing almost all parameters: It looks confusing, but if you know what you're looking for you can see the forest for the trees.
It's an Array Solutions AIM Antenna Analyzer, either the 4170 or the UHF model. Cannot tell since the header has been stripped from view. There are tabs at the bottom: one is called LIMIT, and that is where you set the bandwidth measurement limits. Going to setup menu at the top, and that's where you select what parameter (graph) you would like to display. This display is showing almost all parameters: It looks confusing, but if you know what you're looking for you can see the forest for the trees.
Marconi, I know how to set the scan range. I can choose set and custom bands from a list or enter my own high and low frequencies, as well as how far apart the individual scans can be (to few and the graph is points with lines, to many and it takes forever). I started with the frequency range set from 26.515 MHz to 27.855 MHz. I assume that is narrow enough of a scan range for you?
When I saw the point I was looking for was not in that frequency range itself I expanded the frequency range to include the 10 meter band and then some. The point I was looking for happens to be at 29.6665 MHz.
Then I noticed where the SWR curve plateaued at and continued expanding the bandwidth scanned as I was not expecting it to plateau so low. At some point I simply put in most of the scan range the device is capable of. I increased the scan range to such an extreme because I saw something I did not expect and have never seen before and wanted more information.
I was not asking for help using my analyzer, I was curious what people thought about the results of that scan, namely the SWR curve. I'm actually surprised that only one person actually said that they saw a problem with the antenna and what the cause of it may have been. Personally, that scan just doesn't look right to me, and usually when that happens there is something wrong somewhere. Unfortunately it will be a while before I get a look at the antenna mount and end of the coax.
Man, I may be the one that is all corn'fused, but what is in a 102" whip antenna to take apart and check?
The mount itself, as well as the end of the coax, all of which are behind a plate with a hole for the coax in it that and is bolted through the trunk lid to the mount itself. But, as you say, the whip itself does appear to be fine...
Nope, I felt fine yesterday and just as fine today, so far. Why?
The DB
This is correct. I'm guessing you have seen/used one of these before? It is a 4170C, one of the first C models sold (I talked to them before it came out, they told me it was coming so I waited for this model). The software allows you to save the plot as a .bmp image which I converted to .jpg and posted. When you save the plot as an image the program includes just the plot in the image, nothing else that is in the window.
The DB
I have never measured that wide. I have seen multiple peaks and dips, most well within the 2.0:1 SWR range - on my original Qv4k.
I do not know what is going on, but I think the trunk mount is a compromise location that begs for losses, but you see the graph.
My only question is more academic than diagnostic, but are you using a 1/2 wave jumper that is around 18', or is it an electrical 1/2 wve jumper cut for coax VF?
I do not know what is going on, but I think the trunk mount is a compromise location that begs for losses, but you see the graph.
My only question is more academic than diagnostic, but are you using a 1/2 wave jumper that is around 18', or is it an electrical 1/2 wve jumper cut for coax VF?
Marconi, I know how to set the scan range. I can choose set and custom bands from a list or enter my own high and low frequencies, as well as how far apart the individual scans can be (to few and the graph is points with lines, to many and it takes forever). I started with the frequency range set from 26.515 MHz to 27.855 MHz. I assume that is narrow enough of a scan range for you?
When I saw the point I was looking for was not in that frequency range itself I expanded the frequency range to include the 10 meter band and then some. The point I was looking for happens to be at 29.6665 MHz.
Then I noticed where the SWR curve plateaued at and continued expanding the bandwidth scanned as I was not expecting it to plateau so low. At some point I simply put in most of the scan range the device is capable of. I increased the scan range to such an extreme because I saw something I did not expect and have never seen before and wanted more information.
I was not asking for help using my analyzer, I was curious what people thought about the results of that scan, namely the SWR curve. I'm actually surprised that only one person actually said that they saw a problem with the antenna and what the cause of it may have been. Personally, that scan just doesn't look right to me, and usually when that happens there is something wrong somewhere. Unfortunately it will be a while before I get a look at the antenna mount and end of the coax.
The mount itself, as well as the end of the coax, all of which are behind a plate with a hole for the coax in it that and is bolted through the trunk lid to the mount itself. But, as you say, the whip itself does appear to be fine...
Nope, I felt fine yesterday and just as fine today, so far. Why?
The DB
If a 102" whip is installed with a suitable ground plane you should easily see a 4.0> mhz bandwidth at <2.0:1 SWR at 27 mhz. So, your range setting noted above is a little shy still. I can't answer why your meter only shows up to 2.0:1 SWR out to 180 mhz, but I notice the SWR indication looks fine going below frequency.
I recall my Autek VA1 indicating an SWR of 5.0:1> before, but that would have been lower in frequency for me with my range limitations going higher.
As we go higher in frequency the losses become far more significant. My VA1 analyzer only goes up to 30 mhz, so I can't check high, but when I go low to 2.5 mhz using my Starduster, I do see an SWR of 7.9 - 8 similar to what your meter is showing.
Maybe your meter is working just fine and excessive losses are your problem going too high in frequency.
Like CB'rs like to claim, "...this is just fooling your meter."
A few observations
I don't think I've ever seen an SWR curve like that either, that's interesting. Or so many particular aspects/characteristics/parameters displayed at the same time.
I think that by displaying all of those 'aspects' on the same graph that there are some conclusions that can be drawn. The first conclusion I would make is that this display only pertains to one particular and specific antenna set up. It means that conclusions can only be drawn about this one specific instance.
Another conclusion is that all of the 'aspects' affect each others behavior. I think that's about as 'normal' as it gets. There are a number of general conclusions that can be drawn/inferred from all of this information, it depends only on how 'well' you can integrate particular aspects of each 'piece' of information and how it relates to other 'pieces' at some particular 'time'/'place' on the graph. All of those 'inferences' are only going to be 'true' for this one set up though. So if you want to come up with a really good set of 'rules' for some particular 'aspect'/measured quantity out of this, then there are going to have to be a large number of other graphs done for other 'set ups'. 'Mix' all of those measurements, strain for particular aspects of the mix, and you have the 'dead nutz', typical way of coming to a scientific theory of operation. All things considered, that ought'a keep you busy for the next day/week/month/year/century or two, you think?
- 'Doc
ooooo, that doesn't even touch on all the incorrect conclusions you'll come to because something else wasn't considered/added to that 'mix'. Glad it's you and not me!
I don't think I've ever seen an SWR curve like that either, that's interesting. Or so many particular aspects/characteristics/parameters displayed at the same time.
I think that by displaying all of those 'aspects' on the same graph that there are some conclusions that can be drawn. The first conclusion I would make is that this display only pertains to one particular and specific antenna set up. It means that conclusions can only be drawn about this one specific instance.
Another conclusion is that all of the 'aspects' affect each others behavior. I think that's about as 'normal' as it gets. There are a number of general conclusions that can be drawn/inferred from all of this information, it depends only on how 'well' you can integrate particular aspects of each 'piece' of information and how it relates to other 'pieces' at some particular 'time'/'place' on the graph. All of those 'inferences' are only going to be 'true' for this one set up though. So if you want to come up with a really good set of 'rules' for some particular 'aspect'/measured quantity out of this, then there are going to have to be a large number of other graphs done for other 'set ups'. 'Mix' all of those measurements, strain for particular aspects of the mix, and you have the 'dead nutz', typical way of coming to a scientific theory of operation. All things considered, that ought'a keep you busy for the next day/week/month/year/century or two, you think?
- 'Doc
ooooo, that doesn't even touch on all the incorrect conclusions you'll come to because something else wasn't considered/added to that 'mix'. Glad it's you and not me!
I have seen a SWR curve much like that at one time, although it was nowhere that wide it covered a impossible bandwidth with peaks and dips under 3:1 and it was a I10-K base antenna, when I plotted the Curve I called Jay and asked what he thought about it, his first thought was bad Coax.
Soon after I replaced the old Coax with LRM-400 and magically the SWR plot became normal.
The thing is that the antenna worked just fine throughout the 10/11 meter band with no apparent problem.
Just my 2 cents worth.
73
Jeff