WTF SWR

[roadrage]

In my 35 years of radio I have never really found the internal SWR meters to be that far off really so apparently I am in the minority. One thing to consider when looking at an internal and external meter at the same time and seeing two different values of SWR is that if the antenna is not a pure 50 ohms then the SWR will appear to be different values at different points along the transmission line. Since the external meter is not located at the same point as the internal meter they will read different values. You will see the same thing if you simply insert an extra couple feet of coax cable.I suspect that the internal meter is fine and is simply measuring the SWR at whatever point it is in the circuit. If you insert another meter inline then the point where the internal meter is gets changed and thus the SWR reading will change.

My problem is that hooking up the external meter changes what the internal meter is showing. I have many radios and I consistanty see a slight variation between the external and an internal meter. This particular system is the first time I've seen the radio's internal meter change its reading by adding the external meter into the system. If the radio's meter shows 1.6 with the absence of the external meter; then when I add the external meter, the radio's should still read 1.6. But the radio meter changes to a 1.4. I see the radio's internal power meter change its result as well, going from showing a 20W DK with no external meter hooked up; to the radio's internal showing a 30W DK with the external meter hooked up. It doesn't make sense.

 

[psycho]

In my 35 years of radio I have never really found the internal SWR meters to be that far off really so apparently I am in the minority. One thing to consider when looking at an internal and external meter at the same time and seeing two different values of SWR is that if the antenna is not a pure 50 ohms then the SWR will appear to be different values at different points along the transmission line. Since the external meter is not located at the same point as the internal meter they will read different values. You will see the same thing if you simply insert an extra couple feet of coax cable.I suspect that the internal meter is fine and is simply measuring the SWR at whatever point it is in the circuit. If you insert another meter inline then the point where the internal meter is gets changed and thus the SWR reading will change.

I only use cross needle watt meters in the truck so problems can be found before 10 ohm smoke starts a blowing.
I never found a radio with a built in swr function that was that terribly inaccurate enough to be troublesome........they are close enough for government work.

 

[BOOTY MONSTER]

ignore the radios built in meter and go by what the external one says . you'll need less aspirin too .

 

[Captain Kilowatt]

ignore the radios built in meter and go by what the external one says . you'll need less aspirin too .

Ignore Booty Monster and you won't need any aspirin. Period.

 

[Mudfoot]

My 2950 with Wilson 1000 roof mount in my Cherokee would show 1 bar when my analyzer showed > 1.9.

I was wanting to use my little travel tuner and adjust my SWR using the built in meter, but couldn't trust it. My 2970 was flaky as well.

 

[Zman]

Buying an antenna analyzer isn't all that practical for most people. If you do more than casual antenna work, then it's certainly worth it. If not, don't waste your money for a 'one shot' thingy.
If it were black/white with no shades of grey, then the best device for tuning an antenna is the one that tells you the most pertinent information. There's so much gray in antennas that unless you are really serious about tune them, an analyzer is just too expensive.
I like playing with antennas and have played with enough so I think an analyzer is worth having. If I didn't do that much 'playing', I certainly wouldn't buy one (borrow one instead!). You have to decide for your self.
- 'Doc

Yeah i have one. Its worth every penny to me.

 

[BOOTY MONSTER]

Ignore Booty Monster and you won't need any aspirin. Period.

you know you love me

and you have my permission to use this pic in your siggy

 

[Captain Kilowatt]

My 2950 with Wilson 1000 roof mount in my Cherokee would show 1 bar when my analyzer showed > 1.9.

I was wanting to use my little travel tuner and adjust my SWR using the built in meter, but couldn't trust it. My 2970 was flaky as well.

I should have stated that my feelings and observations towards built in meters does not carry over to digital meters. Not for SWR,power, or signal. They are crap IMHO. The analog meters is what I was referring too.

 

[roadrage]

Got my mount for my 102" antenna today, so up it went. Things seem well again. I was going to mount the 102 on the front center of the bed, as high as i could get it. Next thing I know the headliner is coming down and holes are being drilled in my roof. I am going to hit everything, lol. I better get something to tie it down when I'm driving.

Who knows what went wrong with the Wilson, but I'll look into it one of these days.

 

[jazzsinger]

ignore the radios built in meter and go by what the external one says . you'll need less aspirin too .

alternatively you could insert a 1/2 wave coaxial impedance repeater between the radio and swr meter and most likely you will see both meters read roughly the same,

which is basically the inverse of what Captain Kilowatt described as the meters reading differently due to being at different points in the transmission line of a reactive antenna,

alternatively keep the lead very very short, less than 6 inches if you don't want to see massively different readings on both meters.

like Captain Kilowatt i have also found radio swr meters reasonably accurate and even s/tx power meters reliable enough to indicate problems before they do damage.

when a tx power meter is calibrated to read s9 into a 50 ohm resistive load and all of sudden it starts read very low or off the scale it is indicating a mismatch to the transmitter,

you will notice on a properly set up tx/po meter small variations from s9 as you go away from the resonant point of the antenna (especially on multibanded export radios), thats normal, but large variations are not normal, so even a radio without a built in swr meter can indicate bad swr problems.

 

[Beetle]

alternatively you could insert a 1/2 wave coaxial impedance repeater between the radio and swr meter and most likely you will see both meters read roughly the same,

which is basically the inverse of what Captain Kilowatt described as the meters reading differently due to being at different points in the transmission line of a reactive antenna,

alternatively keep the lead very very short, less than 6 inches if you don't want to see massively different readings on both meters.

like Captain Kilowatt i have also found radio swr meters reasonably accurate and even s/tx power meters reliable enough to indicate problems before they do damage.

when a tx power meter is calibrated to read s9 into a 50 ohm resistive load and all of sudden it starts read very low or off the scale it is indicating a mismatch to the transmitter,

you will notice on a properly set up tx/po meter small variations from s9 as you go away from the resonant point of the antenna (especially on multibanded export radios), thats normal, but large variations are not normal, so even a radio without a built in swr meter can indicate bad swr problems.

How does a transmitting power meter get "calibrated to read S9"? S-meter function is only when receiving.

 

[jazzsinger]

How does a transmitting power meter get "calibrated to read S9"? S-meter function is only when receiving.

its generally set in the s9 region which is around the same position the proper power level is set at, most people are familiar with the s9 position but not as familiar with the power meter scale (on many radios it isn't numbered but merely a space between a green line and red line), which on most multimodes/cb's is roughly the same meter position as s9 on the s meter.

i'm sure most cb'ers knew what i meant, :sneaky2:funnily enough i'm sure you did too, but maybe not, it might not apply the same on the line of sight bands above HF

 

[Captain Kilowatt]

its generally set in the s9 region which is around the same position the proper power level is set at, most people are familiar with the s9 position but not as familiar with the power meter scale (on many radios it isn't numbered but merely a space between a green line and red line), which on most multimodes/cb's is roughly the same meter position as s9 on the s meter.

i'm sure most cb'ers knew what i meant, :sneaky2:funnily enough i'm sure you did too, but maybe not, it might not apply the same on the line of sight bands above HF

Actually it does not apply to pretty much any radio built for any other band than 11m including HF or VHF. HF radios have a calibrated RF power output scale and VHF radios usually do as well depending on whether the radio has a digital or analog meter.

 

[jazzsinger]

Actually it does not apply to pretty much any radio built for any other band than 11m including HF or VHF. HF radios have a calibrated RF power output scale and VHF radios usually do as well depending on whether the radio has a digital or analog meter.

i appreciate that, but this is the cb section, therefore what i said is relevant despite beetle's nitpicking, and i think you might have missed the point on "might not apply to all the line of sight bands"

as for vhf/hf radios being calibrated, either on s meter or power meter is a tad hit and miss, with most s meters being set for s9/r5 no matter what received signal strength is, unless of course those operating them talk crap (persish the thought), as for the power meters, i doubt any but the very best ham sets are properly calibrated, but then there's fantasy power and there's real power.

 

[Captain Kilowatt]

That fantasy power you reference is predominant on 11m mostly. As far as hf radios and the power meters I have slways found then to be as good ad any external meter of decent quality. Not a gigadollar meter mind you but an average decent meter.