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High SWR Problem
- Thread starter 530
- Start date
I have no easy way to solve it for you because I would have to go over all the things to try getting a match.
Bottom line here is half the system is out of limits so far you can't get the match accounted for by simple adjustments.
You might try different lengths of add-on coax trying to find an impedance point that is close to a 50 ohm match for the radio.
Said another way, in a large mismatch condition the "reflected" impedance along the transmission line changes with distance along the line.
If you arrive at the right length, a match will appear to work.
The reason this happens is the mismatch at the antenna reflects voltage and currents out of phase.
The results of this is the voltage and current will be different along the line.
Finding the length that offers 50 ohm from that combination point will provide a match your looking for.
When you use this trick to find a match, it makes the match narrow banded because it's now "frequency sensitive" to changes in physical length because the phase changes with frequency along the line.
This is the major reason to get the antenna to match the feedline if at all possible then the feedline length has little effect because it's at the correct impedance to start with all along it's length.
Tuning the system by feedline length is only providing the radio the impedance it was designed to work into and does not solve the original mismatch issue.
Another reason to have the whole system in match is the high SWR on the feedline increases the losses because every time power is reflected either way the loss in the line is added to the total.
This also can cause a funny thing to happen with a power meter in that the meter can show more power than the radio is outputting because the 'vector sum' of the currents and voltage add making the meter read higher since the meter does not know any difference, only what it detects.
For example is if a coax has 2 db loss under matched conditions the loss will be higher under mismatched conditions from the way is has to work in that condition.
Let us know how you make out.
Good luck.
Bottom line here is half the system is out of limits so far you can't get the match accounted for by simple adjustments.
You might try different lengths of add-on coax trying to find an impedance point that is close to a 50 ohm match for the radio.
Said another way, in a large mismatch condition the "reflected" impedance along the transmission line changes with distance along the line.
If you arrive at the right length, a match will appear to work.
The reason this happens is the mismatch at the antenna reflects voltage and currents out of phase.
The results of this is the voltage and current will be different along the line.
Finding the length that offers 50 ohm from that combination point will provide a match your looking for.
When you use this trick to find a match, it makes the match narrow banded because it's now "frequency sensitive" to changes in physical length because the phase changes with frequency along the line.
This is the major reason to get the antenna to match the feedline if at all possible then the feedline length has little effect because it's at the correct impedance to start with all along it's length.
Tuning the system by feedline length is only providing the radio the impedance it was designed to work into and does not solve the original mismatch issue.
Another reason to have the whole system in match is the high SWR on the feedline increases the losses because every time power is reflected either way the loss in the line is added to the total.
This also can cause a funny thing to happen with a power meter in that the meter can show more power than the radio is outputting because the 'vector sum' of the currents and voltage add making the meter read higher since the meter does not know any difference, only what it detects.
For example is if a coax has 2 db loss under matched conditions the loss will be higher under mismatched conditions from the way is has to work in that condition.
Let us know how you make out.
Good luck.
Ok so today. I took off all the 3ft ground straps i posted i had i did a shorter setup for the ground to trunk, picture attached (not my picture, but i did the same thing with a piece of my straps). also i went and got some plastic washers and "upgraded" the plastic washer that came with the mount, and i was able to add a large washer at the ground side of the mount for sturdiness and contact surface. I CAN NOW TUNE MY ANTENNA! LOL! my swr's between 24mhz 2ishswr and 29mhz is 1:3swr and channel 1 is 2-ish and channel 40 is 1:5 so my antenna needs to be longer, which suuuuuuuuuuuuuuuux because my whip is all the way up on my 12 inch adjuster. iam going to adjust it from all the down into my adjuster tomorrow and work from there. i know some people say coax length doesn't mean anything but then i read it does so i'm going to try a couple different longer lengths. my coax set up right now is 3ft/meter/9ft. tomorrow after i try the whip adjuster thing and if it doesn't work i am going to try a 3ft/meter/12ft coax set up and then i can try a 3ft/meter/21ft to see if it does or doesn't make a difference. My only option i can think of after a that is to buy the 36 inch antenna adjuster like my 12 inch one and continue from there.
You won't get low SWR across 5MHz. Below 2:1 is OK so don't panic if one end is that and its low elsewhere. "Near enough" is good enough and there's no benefit other than a meter reading to having it lower. You won't get any further, you won't hear any more so don't get too obsessed about it.
It only matters if you don't have sufficient grounding and its using the coax as part of the antenna ground.
Trying to think out of the box when I say this.
But some cars that have the defroster lines in the rear window can interfere with the ground plane, I think.
And when you open the trunk your fooling the radio into thinking it's legit while it it not. Kinda like truckers leaning their antenna to get better swr.
Maybe not the case here but something to think about.
But some cars that have the defroster lines in the rear window can interfere with the ground plane, I think.
And when you open the trunk your fooling the radio into thinking it's legit while it it not. Kinda like truckers leaning their antenna to get better swr.
Maybe not the case here but something to think about.