Posted: 5/14/2016 8:34:44 AM EDT
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I've had this SWR meter laying around for years and have never used it. I have no idea how to use it.
I have concerns that the SWR of my mobile antenna is high, or at least can rule it out as causing other issues with my install. Can anyone give me some basic instructions on this?https://m.imgur.com/gallery/sLiJnmG |
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I believe you need to connect it, set the rotary switch on the left to "FWD", apply RF (key down) and rotate the knob on the right until the meter points to "set" on the far right of the scale. Then, rotate the rotary switch back to "REF" to read SWR
Edit: had it backwards initially. Actually found a manual, I was a little sketched out by this site but the manual downloaded just fine http://www.eserviceinfo.com/downloadsm/13632/SWAN_wm2000.html |
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Plot your SWR for every 100 kHz across each band and it'll give you the information needed to calculate whether to lengthen or shorten your antenna and by how much.
If the SWR rises as you go from the low end to the high end, the antenna is cut too long. If it goes down the antenna is too short. Calculating how much requires a bit more work. Using the formula L=468/f where L is the length in feet and f is the frequency in MHz, calculate the theoretical length at two different frequencies around the middle of the band in question. The difference in the lengths divided by the difference in MHz will tell you how much to lengthen or shorten the antenna in feet per Megahertz of the desired shift to move the SWR to where you want it. I generally use a difference of 100 MHz, and then convert the difference in length to inches. This is for the entire dipole, so each half of the antenna will be changed by half that much, which is your case for a quarter wave verticle. The results are approximate, but pretty darn close. |
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Quoted:
Plot your SWR for every 100 kHz across each band and it'll give you the information needed to calculate whether to lengthen or shorten your antenna and by how much. If the SWR rises as you go from the low end to the high end, the antenna is cut too long. If it goes down the antenna is too short. Calculating how much requires a bit more work. Using the formula L=468/f where L is the length in feet and f is the frequency in MHz, calculate the theoretical length at two different frequencies around the middle of the band in question. The difference in the lengths divided by the difference in MHz will tell you how much to lengthen or shorten the antenna in feet per Megahertz of the desired shift to move the SWR to where you want it. I generally use a difference of 100 MHz, and then convert the difference in length to inches. This is for the entire dipole, so each half of the antenna will be changed by half that much, which is your case for a quarter wave verticle. The results are approximate, but pretty darn close. Good info FrankB, thanks. I've got a Larsen NMO150 antenna on the roof on the Toyota, but I've been having some weird issues with the install. I don't think it's the antenna that's the problem directly. One issue was that when I tried to plug the Kenwood into the car audio system for sound I got bad feedback. The second issue was that even with the car audio and my Kenwood mobile disconnected, when I keyed up the mic I still got feedback. Third, when I turned off the car audio, occasionally when keying up the Kenwood the car audio system would turn itself on. Also, I'd previously had a two week old mobile radio go deaf and sent it back to the retailer. But with its replacement I thought I'd do some more investigating and see if I was having antenna issues that might have caused the previous radio to go dead so it didn't happen a second time. So I thought I'd start with the SWR and move on from there. I'm going to take a look at the NMO mount next and see if it has a good connection to the sheet metal on the roof. |
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I'm an ignorant fellow, but doesn't that sound like an RFI / common mode current issue?
LOTS of really good info on mobile radio here: http://www.k0bg.com but I believe most of it is directed to mobile HF. Given your antenna, are you running a 2 meter / 440 radio? Good luck with your issues, I've had LOTS of fun fighting RFI with my mobile HF installation. Cheers... Jim... |
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To be honest, it sounds like it may well be two separate issues.
On the SWR, make sure you check for the presence of water where it shouldn't be. On the RFI, how are you powering the radio? Do you have a dedicated power cable run to the battery, or some other configuration? |
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It does sound like you have two issues. One is RF interference to the auto electronics. Reroute coax away from vehicle electronics, and some ferrite beads would not be a bad idea... put ferrites on the coax as close to the antenna as possible, and also near where it encounters the stereo system or other vehicle wiring.
The radio should be grounded to the vehicle body at the radio if possible. I would try to find/borrow an antenna analyzer if at all possible. From your description one of the possibilities is an intermittent connection, which would be a lot easier to trace with an analyzer. One thing to watch out for with the Larsen base coils is intermittent or nonexistant contact on the center pins if the base-to-coil relationship is not just right. If the nut on the NMO mount isn't tightened down enough the center pin won't make good contact. |
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To start with many SWR meters are frequency sensitive, i.e. those that are accurate at HF may not be accurate at VHF or UHF and vice versa. So, be certain the SWR meter you are using is for the frequency range that you are testing.
There is a polarity issue with most SWR meters. Make certain that the side marked TRANSMITTER is going to the transmitter and the side marked ANTENNA is going to the antenna. As a general rule SWR reading of over 2,5 to 1 will increase the plate or collector current which will shorten the life of you final amplifier, sometimes suddeny. Keeping the SWR under 1.5 to 1 or better is desirable. When testing your SWR use the lowest power setting that will still give you full deflection of the needle in the forward reading position. High SWR and elevated power can and will SMOKE your finals! While the resonant frequency of the antenna being different than the transmitting frequency is one cause of high swr readings, shorted or open coaxial cables are also a cause and in my 40+ years in the hobby the more frequent problem in previously installed and properly operating antenna installations that have gone bad over time or suddenly is the coaxial cable or it's connections. Free advice from an old ham ... W9ALD |
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I'll start another thread tonight.
I've got a diamond SWR meter suitable for 2 meters. I keep hearing about antenna analyzers and don't really know the difference. I use 10, 20, 40and 2m with occasional 70cm. I need to know more and need to know what analyzer I might need. Don't know what's out there and what's the most bang for my buck. |
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Quoted:
I keep hearing about antenna analyzers and don't really know the difference. I use 10, 20, 40and 2m with occasional 70cm. Quoted:
I keep hearing about antenna analyzers and don't really know the difference. I use 10, 20, 40and 2m with occasional 70cm. An SWR meter is a device you put between a transmitter and a load, which measure the amount of power going each direction so as to give you a computed SWR reading. An antenna analyzer is it's own minuscule transmitter, which sweeps across a defined swath of radio frequencies, and typically shows you a graphic display of SWR over that frequency range. The better meters will also display resistance & reactance, some can find cable faults or other sometimes useful functions. It's one thing to measure and say your SWR is 2:1 at for example 146.520 MHz. It's somewhat more informative to connect a single device and in moments be able to see that your SWR is 2:1 at 146.520, that your antenna's lowest SWR is at 139.500, and 2:1 SWR bandwidth is approximately 14 MHz. And that's just the beginning of things you can experiment with, tune and adjust. Want to know if the ferrites you bought at a hamfest are actually good for HF? Test them and see. I need to know more and need to know what analyzer I might need. Don't know what's out there and what's the most bang for my buck. Depends on what you do with antennas, filters etc, and what frequency bands you need it to cover. |
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Quoted:
Good info FrankB, thanks. I've got a Larsen NMO150 antenna on the roof on the Toyota, but I've been having some weird issues with the install. I don't think it's the antenna that's the problem directly. One issue was that when I tried to plug the Kenwood into the car audio system for sound I got bad feedback. The second issue was that even with the car audio and my Kenwood mobile disconnected, when I keyed up the mic I still got feedback. Third, when I turned off the car audio, occasionally when keying up the Kenwood the car audio system would turn itself on. Also, I'd previously had a two week old mobile radio go deaf and sent it back to the retailer. But with its replacement I thought I'd do some more investigating and see if I was having antenna issues that might have caused the previous radio to go dead so it didn't happen a second time. So I thought I'd start with the SWR and move on from there. I'm going to take a look at the NMO mount next and see if it has a good connection to the sheet metal on the roof. Quoted:
Quoted:
Plot your SWR for every 100 kHz across each band and it'll give you the information needed to calculate whether to lengthen or shorten your antenna and by how much. If the SWR rises as you go from the low end to the high end, the antenna is cut too long. If it goes down the antenna is too short. Calculating how much requires a bit more work. Using the formula L=468/f where L is the length in feet and f is the frequency in MHz, calculate the theoretical length at two different frequencies around the middle of the band in question. The difference in the lengths divided by the difference in MHz will tell you how much to lengthen or shorten the antenna in feet per Megahertz of the desired shift to move the SWR to where you want it. I generally use a difference of 100 MHz, and then convert the difference in length to inches. This is for the entire dipole, so each half of the antenna will be changed by half that much, which is your case for a quarter wave verticle. The results are approximate, but pretty darn close. Good info FrankB, thanks. I've got a Larsen NMO150 antenna on the roof on the Toyota, but I've been having some weird issues with the install. I don't think it's the antenna that's the problem directly. One issue was that when I tried to plug the Kenwood into the car audio system for sound I got bad feedback. The second issue was that even with the car audio and my Kenwood mobile disconnected, when I keyed up the mic I still got feedback. Third, when I turned off the car audio, occasionally when keying up the Kenwood the car audio system would turn itself on. Also, I'd previously had a two week old mobile radio go deaf and sent it back to the retailer. But with its replacement I thought I'd do some more investigating and see if I was having antenna issues that might have caused the previous radio to go dead so it didn't happen a second time. So I thought I'd start with the SWR and move on from there. I'm going to take a look at the NMO mount next and see if it has a good connection to the sheet metal on the roof. Update: I basically started over with this install. I drilled a new 3/4 hole in the roof and reinstalled the nmo mount. The hole needed to be redone as the last one was bent from a previously ripped out antenna mount. I thought getting a better antenna install might help things. It didn't. Then I looked at my PL259 connector and cut it off. I went back and relearned how to install a new connector and realized I hadn't been soldering the shield properly. After resoldering a new connector I'm getting less than 1.5:1 SWR on multiple frequencies throughout the 2 meter band. A night and day difference from peaking out the meter. Thanks everyone for all your assistance. |
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Quoted:
Update: I basically started over with this install. I drilled a new 3/4 hole in the roof and reinstalled the nmo mount. The hole needed to be redone as the last one was bent from a previously ripped out antenna mount. I thought getting a better antenna install might help things. It didn't. Then I looked at my PL259 connector and cut it off. I went back and relearned how to install a new connector and realized I hadn't been soldering the shield properly. After resoldering a new connector I'm getting less than 1.5:1 SWR on multiple frequencies throughout the 2 meter band. A night and day difference from peaking out the meter. Thanks everyone for all your assistance. Quoted:
Quoted:
Quoted:
Plot your SWR for every 100 kHz across each band and it'll give you the information needed to calculate whether to lengthen or shorten your antenna and by how much. If the SWR rises as you go from the low end to the high end, the antenna is cut too long. If it goes down the antenna is too short. Calculating how much requires a bit more work. Using the formula L=468/f where L is the length in feet and f is the frequency in MHz, calculate the theoretical length at two different frequencies around the middle of the band in question. The difference in the lengths divided by the difference in MHz will tell you how much to lengthen or shorten the antenna in feet per Megahertz of the desired shift to move the SWR to where you want it. I generally use a difference of 100 MHz, and then convert the difference in length to inches. This is for the entire dipole, so each half of the antenna will be changed by half that much, which is your case for a quarter wave verticle. The results are approximate, but pretty darn close. Good info FrankB, thanks. I've got a Larsen NMO150 antenna on the roof on the Toyota, but I've been having some weird issues with the install. I don't think it's the antenna that's the problem directly. One issue was that when I tried to plug the Kenwood into the car audio system for sound I got bad feedback. The second issue was that even with the car audio and my Kenwood mobile disconnected, when I keyed up the mic I still got feedback. Third, when I turned off the car audio, occasionally when keying up the Kenwood the car audio system would turn itself on. Also, I'd previously had a two week old mobile radio go deaf and sent it back to the retailer. But with its replacement I thought I'd do some more investigating and see if I was having antenna issues that might have caused the previous radio to go dead so it didn't happen a second time. So I thought I'd start with the SWR and move on from there. I'm going to take a look at the NMO mount next and see if it has a good connection to the sheet metal on the roof. Update: I basically started over with this install. I drilled a new 3/4 hole in the roof and reinstalled the nmo mount. The hole needed to be redone as the last one was bent from a previously ripped out antenna mount. I thought getting a better antenna install might help things. It didn't. Then I looked at my PL259 connector and cut it off. I went back and relearned how to install a new connector and realized I hadn't been soldering the shield properly. After resoldering a new connector I'm getting less than 1.5:1 SWR on multiple frequencies throughout the 2 meter band. A night and day difference from peaking out the meter. Thanks everyone for all your assistance. If you have the crimping tool for .195" coax, look into the Larsen NMOHF mount. Crimp style mount and just requires crimping the center conductor using a Harbor Fugitive 2" C clamp with the base pulled off (exposing the joint) and a nickel. The braid is like regular connectors. |