Whelp..i put the external meter on the mobile and it showed good on 1 n 40..the radio is a 2950dx.this radio has digital display and has a built in swr meter and dosnt require calibration..the radio meter agreed perfectly with the extenal meter as i turned it on the same time that i was checking with the external one..both meters showed channel 40 just a smidgin high..the cauce for my alarm is that when i take the external meter off the internal meter now shows that channel one is now 2 bars high..now its not only showing a higher reading than with used in concert with the external meter,its showing channel 1 is higher than 40 just the oppisite of when used with the external..aint radios fun....
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Dueling swr meters..
- Thread starter Splash1
- Start date
LMAO 2 of our vehicles do that aswell I most of the time just leave the meters in line. I actually just went through that again when hooking meters back up ther can be a number of reasons for this bad coax ETC I swear my Wilson antennas were the worst with this I actually quit running them on those 2 vehicles with that problem. Its something with those antennas of mine because I actually switched the antennas around and it was the same effect touch the meter and watch SWR meter needle jump around.
You will see this anytime you use two SWR meters, doesn't matter who they were made by. That's because SWR meters are really dumb 'beasts', they can only tell you what they 'think' they see, not what's actually there. They only measure one thing and have no idea why that 'thing' is the way it is. Sort of like measuring the air pressure in a tire, but not knowing how it gets into that tire to start with, or what can affect that air once it's inside that tire. That's up to the guy doing the measuring.
The only time an SWR meter is actually telling the 'whole truth' is when there is no Standing Wave Ratio, when there's a 1:1 match, typically 50 ohms from one end of the system to the other. The rest of the time, what makes up that characteristic impedance can be very variable and the meter still thinks it's 'good'.
Why are there SWR meters if they are so 'wrong'? Cuz they are relatively simple and easy to make. They can provide an indication that something is/isn't right. And because unless it's really not even close to being 'right', SWR, by it's self, just doesn't make that much difference in the overall scheme of things. (Oh boy, is that gonna raise a stink!) There are 'better' ways of determining if the antenna system is usable. The key word there is, usable, which is really all that you are likely to ever have. The really important thing is that the user knows enough about what he/she is doing to know that there's something 'not right'. And how to 'cure' that condition... maybe. The learning how to do that isn't easy, but, it certainly pays off in the long run.
'Nuff of all that. Been up to long, going for breakfast! Delux-breakfastmeal, biscuts-n-gravy, whatever Macky-D calls their potato patties. Dump it all into one bowl, mix well, sprinkle with enough salt/pepper/hot sauce to kill the taste, shovel till it's gone! Makes you wanna slap your granny, don't it?
- 'Doc
The only time an SWR meter is actually telling the 'whole truth' is when there is no Standing Wave Ratio, when there's a 1:1 match, typically 50 ohms from one end of the system to the other. The rest of the time, what makes up that characteristic impedance can be very variable and the meter still thinks it's 'good'.
Why are there SWR meters if they are so 'wrong'? Cuz they are relatively simple and easy to make. They can provide an indication that something is/isn't right. And because unless it's really not even close to being 'right', SWR, by it's self, just doesn't make that much difference in the overall scheme of things. (Oh boy, is that gonna raise a stink!) There are 'better' ways of determining if the antenna system is usable. The key word there is, usable, which is really all that you are likely to ever have. The really important thing is that the user knows enough about what he/she is doing to know that there's something 'not right'. And how to 'cure' that condition... maybe. The learning how to do that isn't easy, but, it certainly pays off in the long run.
'Nuff of all that. Been up to long, going for breakfast! Delux-breakfastmeal, biscuts-n-gravy, whatever Macky-D calls their potato patties. Dump it all into one bowl, mix well, sprinkle with enough salt/pepper/hot sauce to kill the taste, shovel till it's gone! Makes you wanna slap your granny, don't it?
- 'Doc
If you inserted a length of coax the same length as you used to connect the external SWR meter I'll bet the SWR would be pretty much the same as when you have the external meter connected. The problem is caused by changing the length of cable from radio connector to antenna connector by inserting the external meter.
No,that's placing the SWR meter in a differant point along the cable. Unless the antenna is a pure and perfect 50 ohms at the feedpoint the SWR will vary all over the place at differant points along the line.
Wikipedia shows how vswr changes along a transmission line:
Image:Swr.png - Wikipedia, the free encyclopedia
Your vswr meter could be placed anywhere along that curve.
If its at a low spot, then it will read better than it really is.
Or if vswr meter is at a high spot then you would read worse.
The solution to the problem is to test your antenna with an antenna analyzer, because it measures phase so it knows how far away it is from the load. Or in other words, the length of coax between itself and the other end of the coax.
Image:Swr.png - Wikipedia, the free encyclopedia
Your vswr meter could be placed anywhere along that curve.
If its at a low spot, then it will read better than it really is.
Or if vswr meter is at a high spot then you would read worse.
The solution to the problem is to test your antenna with an antenna analyzer, because it measures phase so it knows how far away it is from the load. Or in other words, the length of coax between itself and the other end of the coax.
something else to take a look at is where in line you are placing the meter,I have had several people tell me for the ' most accurate ' reading the swr meter should be placed at the antenna end.
Now wether that is right or not I couldnt tell you,but that is what I have heard
*shrugs*
Now wether that is right or not I couldnt tell you,but that is what I have heard
*shrugs*
You can always use an exact multiple of 1/2 electrical wavelengths of coax between the meter and the antenna. That will cause the same impedance as the antenna to be presented to the meter. I tune all my antennas using a 1/2 wavelength of coax between my MFJ-269 and the antenna.When I am finished I install whatever length of feedline I need at the SWR is always the same as when I tuned it.I have differant cables made up from cheap coax that I use on 80,40,20,15,10, and 6m.