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SWR, which one to believe?

mb91w126

mb91w126

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Jul 24, 2013
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I have an Autec swr/power meter in line w/ radios.
AL is Maco y-quad, boom is about 15' above the roof, 38' above ground, heading 55*.
optima mk3 am dead key barely moves the Autek swer meter 27.385 am, same with a Galaxy 949.
switch to lsb and xmit with both radios, same thing, swr 1.125:1.
mk3 does not have an swr meter but the dx-949 swr meter was agreeing with the Autek.

enter the ranger 2970 n2. Set to 27.385 am. dead key about 10W swr bearley moves. switch to lsb and xmit , boom swr swings out to 4:1, yikes!

power was set down to just above minimum with mike gain 50%. Switched on the swr meter on the radio and nothing! not a single bar. I removed the meter and the swr meter on the radio registered nothing.

I'm apprehensive about using it with these meter readings.

your thoughts?
 

Since SSB is simply another mode on the same frequency SWR will not change. Also you cannot reliability check SWR onSSB because there is no steady carrier. Whatever the SWR is on AM is what it will ne on SSB. The difference you are seing is due to more power out on SSB and the fact you are not recalibrating the meter to compensate for that. Bottom line is use AM or FM to check SWR.
 
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What is the length of coax between the radio and the meter? Since coax transmission line is unbalanced, there is a need for proper length and depends on many factors beginning with the power out of the transmitter. SSB needs to be modulated with a continuous tone of a set level to have an accurate balance for SWR reading. The radio's meter has no coax before it's sample point.
If all transmitters are showing a good SWR where the 2970 does not and on SSB the radio may not be in balance of it's alignment. Over modulation can 'flat top' and may cause errorful readings on the Autek meter. Remember that SWR is the ratio of power out to power back and should be close to 1:1 balance as possible. As the Captain said, all SWR checks should be done in AM or FM mode as the carrier is constant. Modulating SSB is not consistent and will show on the meter as out of balance.

73 mechanic
 
mechanic said:
What is the length of coax between the radio and the meter? Since coax transmission line is unbalanced, there is a need for proper length and depends on many factors beginning with the power out of the transmitter. SSB needs to be modulated with a continuous tone of a set level to have an accurate balance for SWR reading. The radio's meter has no coax before it's sample point.
Click to expand...

Actually the fact that coax cable is unbalanced has no bearing whatsoever regarding the need for a proper length. There is no "proper length" of coaxial cable except in phasing lines. Also the power of the transmitter has absolutely no bearing whatsoever on the length of cable between the transmitter and meter or between the meter and the antenna.


If all transmitters are showing a good SWR where the 2970 does not and on SSB the radio may not be in balance of it's alignment. Over modulation can 'flat top' and may cause errorful readings on the Autek meter. Remember that SWR is the ratio of power out to power back and should be close to 1:1 balance as possible. As the Captain said, all SWR checks should be done in AM or FM mode as the carrier is constant. Modulating SSB is not consistent and will show on the meter as out of balance.

73 mechanic
Click to expand...


I fail to even understand what you mean or are thinking by this. No alignment issues will affect SWR as read on an external meter. The meter responds to reflections from the antenna and displays that as SWR.

The fact that the 2970, which has much higher power output, shows higher SWR on SSB than on AM is because of the much higher power output and failure to recalibrate the meter when switching modes. He went from 10 watts carrier to what 50? 75? 100 watts?
 
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the 2970 could be osciilating, a jump to 4:1 is more than i would expect from just turning up the power plus that is an automatic meter.
 
The only problem I can see with the Autek meter is that the mechanical zero is off on both meters. I have never even heard of somebody checking SWR on SSB. I normally turn the power down on any radio while I'm tuning the antennas. There is less chance of damage to the finals if it takes a little longer than normal for tuning. Most often I use a junker radio to test and tune. Checking the SWR on SSB is possible if you have a dual tone signal generator modulating the radio. But I have not heard of anyone doing that either,
 
mb91w126 said:
this model doesn't appear to have a calibrate knob, rats


View attachment 14239
Click to expand...


Ooooops....I guess the joke's on me then. If the SWR meter did have a calibrate knob then i would stand by what I said until proven otherwise however in this case you did just prove otherwise. (y)I have to wonder if the meter is able to self calibrate fast enough to respond to voice peaks. Got another SSB radio to try on it or did I miss that too?
 
Tallman said:
The only problem I can see with the Autek meter is that the mechanical zero is off on both meters. I have never even heard of somebody checking SWR on SSB. I normally turn the power down on any radio while I'm tuning the antennas. There is less chance of damage to the finals if it takes a little longer than normal for tuning. Most often I use a junker radio to test and tune. Checking the SWR on SSB is possible if you have a dual tone signal generator modulating the radio. But I have not heard of anyone doing that either,
Click to expand...

those are not my meters, I just grabbed a representative photo.

I checked the swr with both the mk3 and dx-949 on AM, I am quite aware that SSB lacks carrier. I don't check swr on SSB, I monitor it while xmiting.

I agree with your practice of antenna tuning and follow the same regiment myself.

I was alarmed when It jumped so high, ergo the the original post.
 

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