Wrap your head around this stuff

Discussion in 'CB Radio Forum' started by craig_sez, Feb 1, 2021.

  1. craig_sez

    craig_sez Road Train Member

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    I have often wondered and never understood the phase angle concept....Been searching for a good explanaition for it to help me wrap my head around it and i think now i have a half a clue..
    If im getting this right in my head this can help with antenna issues some have but to see it your gonna need an analyzer....

    Anyways,enjoy..

    Antenna Terminology Defined | MobileMark
     
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  3. Night Stalker10

    Night Stalker10 Heavy Load Member

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    Good article. I wouldn't get too hung up on the physics of how an antenna works. To me the phase angle comes into play with the coax length due to velocity factor. This causes a problem, because 12 to 14 feet (depending on VF of the coax), is probably too short for most mobile installations. Or it can be way too long if you cut it to the next 1/2 wavelength. I don't think I've ever seen a manufacturer say to install their antennas a certain distance from a metal object. Like the 1 inch that was recommended in the article. Of course that wouldn't apply to the 11 meter HF band. Unfortunately the biggest problem with 1/4 wavelength antennas, is the location on the vehicle. I've always summed up mobile antennas in one word.... compromise. You just have to do whatever it takes to make it work. If every vehicle's ground plane was like a big suburban or van, the antenna system would be so much better. Mobile antennas are a constant learning experience as you have mentioned a time or two. Thank goodness for the antenna analyzer. It sure does help.
     
  4. craig_sez

    craig_sez Road Train Member

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    Im jjst tryin to understand it in general...I see my phase on my analyzer way up one min and down another...
    Lookin to see how it helps and or hinders....Just such a pain on the low mount mirrors on some trucks to get whats required....
    Yeah we gotta lean kt a good bit foward for reflect but we loose ground plain which in turn drops range....Then a long antenna flex so much with the wind that it changes ant tune.......Im just pickin away tryin to learn....
     
  5. Night Stalker10

    Night Stalker10 Heavy Load Member

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    Ya, I hear what your saying. You just made a great reason for not tilting a cb antenna forward. Sure it may show a lower swr reading, but low swr reading doesn't necessarily mean the antenna is resanant. From what I understand, a 1/4 wave mobile antenna's impeadance is around 25 to 36 ohms. So if an antenna mounted on a mirror is 36 ohms. Then according to the math.... a 50 ohm radio/coax divided by 36 ohm antenna equals around 1.4 for swr. 50/36=1.39, or about 1.4 for swr. I wish I had my rig expert analyzer when I was still driving that old Pete. Since I had a 2 foot coax jumper cable, I used the vna calibration kit to calibrate the analyzer with the jumper cable attached. This would have made it real easy to attach the analyzer to the antenna mount, and verified what was the impeadance of that hustler antenna I was using. Then compared that reading according to what the math says the antenna should be, without the radio and coax hooked up. I believe that would be the ideal way to adjust the antenna. That's another good reason to have an analyzer too.
     
  6. craig_sez

    craig_sez Road Train Member

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    I had the same idea about tuneing ant directly and takeing out the coax in the mix but not enoigh room to do so..
    I know on my rig expert there is a way to do so while still hooked up but i dont understand that chart(forget the name)that looks like a bunch of circles inside one another..
    I also dont have the proper tools to calibrate it other than whats in the software..
    Saw a expensive 3 way tool made for that but its a lil expensive,so i gotta find out how to make one..
    Re keeping ant str8 up well in my case with a cascadia i dont have any option..
    1 the whip will need securement to keep it from waveing and slapping up against the cab and the issue of reflect..
    Like to pick up another 7ft skip shooter and work with one of those again..
     
  7. craig_sez

    craig_sez Road Train Member

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    SMITH CHART!!!!!! Just woke up and had to mention it before i forgot again..
     
  8. Night Stalker10

    Night Stalker10 Heavy Load Member

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    Lol... Ya that's easy to do. Sometimes I can't think of a word either when I'm trying to explain something. Anyway, I just bought a simple open/short test kit off of fleebay. Something like this kit.

    SMA-Type 50Ohm NanoVNA Vector Network Analyzer Calibration Kit Load&Short&Open | eBay

    You can make these kits if you have the time. But it seemed that after you buy all the parts, it didn't cost much more than to just buy the kit that's already made.
     
  9. Night Stalker10

    Night Stalker10 Heavy Load Member

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  10. craig_sez

    craig_sez Road Train Member

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    Good price..They work with the pl259 style connector correct?? Way more of a reasonal price..Ill have to grab one..

    Here is the vid where i saw the o/s/l
     
  11. Night Stalker10

    Night Stalker10 Heavy Load Member

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    If you are referring to the mfj kit, they look like female uhf connectors. You will still need the male to male pl259 adapter. I think I paid $11 for the sma o/s/l kit. I bought the female uhf to sma adapter for $6. I already had the male to male pl259 adapter. That's a good video about making your own calibration kit. Here's a picture of what I have.
    20210204_182913.jpg
     
    craig_sez Thanks this.
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