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so just because..................i tried a SS 102 on the roof of my montero and it wouldnt go below 2.5 for the swr . i did swap out my older coax for a new section of belden 9913F7 14 foot 8 1/2 inches long per this formula . "468/27.195=17.21 ft X .85 = 14.63 feet or 14 feet 7.5 inches"

the 10k tuned fine just like it did b4 but the 102 was really high . i know a 6 inch spring or spacer is needed to be a true 108 1/4 wave whip , but i was expecting a acceptable swr reading without it . we double and tripple tested the coax for proper assembly and i have contiunity between my roof and vehicle frame and the negative on the battery . i also resanded the area around the mounting hole to be sure i had shiny clean metal underneath for optimum grounding . the mounting stud was taken apart and reassembled with no visual dammage and very careful reinstallation . its a lug mount stud , CATALOG Main Page (Frame Setup) .

i was really suprised . i expected the 102 to kinda be plug and play . i have absolutely no problem with the 10k . it works just fine , i just wanted to play with something different and the 102 was a "good excuse" (cough cough) to upgrade the coax too . what would cause this ? ive got good ground , good coax and a good mounting stud .

oh yea , we used 3 different meters he had a electronic MFJ and a 3 window dosy and i had my astatic 700 . the 10k would barely move the needels on the dosy and 700 but the MFJ showed 1.3 to 1.4 from channels 1 though 40 . on the 102 both needles were in the red and the MFJ was almost 3 to over 3 from channel 1 through 40 .


sooooooooooooooooooooooooooooo..............whatsg oingon??????

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"468/27.195=17.21 ft X .85 = 14.63 feet or 14 feet 7.5 inches"

wrong formula, wrong vf. vf is 84%, not 85. 15' 2.3" for thw @ 27.195.
102" closer to resonance @ 28.6....whip was capacitively reactive @ 27.195 which explains the high swr, not plug n' play if wrong length for resonance.

if your purpose in using a thw line was to make accurate measurements at the transmitter input you didn't get any because the length was wrong. check the swr on the whip @ 28.6 Mhz. if you're looking for a lower swr. don't forget the hd spring and ball mount next time. have fun.

thanks for replying jack , hope youre doing well .
i got the velocity factor from belden https://edeskv2.belden.com/Products/...il&partid=2906 .
what is the right formula ?

i originally learned here that coax length doesnt matter . then i learned that different coax lengths can affect THE METERS reading or the swr . then i find that a ELECTRICAL half wave (or multiple) of coax gives the truest reading . i wonder if i read too much , or , maybe im just not as bright as i think i am . lol

so would a spring or some other 6 inch spacer (all thread) make the antenna the right length for resonance ?

if the formula i used is wrong care to share the correct one ?

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thanks for replying jack , hope youre doing well .

i got the velocity factor from belden https://edeskv2.belden.com/Products/...il&partid=2906 .

one point one way or the other in terms of vf doesn't have that much effect on the overall length but when you use a formula designed to cut dipoles that suffer from end effect to calculate the length of a thw line that really screws things up, as you can see.

what is the right formula ?

the correct formula is: 492/fmhz. X %vf = length in feet, multiply everything to the right of the decimal point by 12 to convert to inches.

i originally learned here that coax length doesnt matter . then i learned that different coax lengths can affect THE METERS reading or the swr . then i find that a ELECTRICAL half wave (or multiple) of coax gives the truest reading . i wonder if i read too much , or , maybe im just not as bright as i think i am . lol

feedline length can and does matter, the secret is understanding when it does and when it doesn't and being able to tell the difference.

a thw line only works for measurement accuracy (translating feedpoint values) when the measurement is made directly at the transmitter output. best accuracy is obtained with a thw line cut and terminated at the proper length less the additional length added by a double male barrel connector that guarantees that the measurement is made as closely to the transmitter as possible. if the radio includes a built-in swr meter then you can skip the barrel connector and add back the length to the thw line.

so would a spring or some other 6 inch spacer (all thread) make the antenna the right length for resonance ?

the missing 5.5 inches caused the resonant frequency of the whip to actually end up somewhere plus or minus 28.6 Mhz. according to calculations.

if the formula i used is wrong care to share the correct one ?

see above:

Hey Bootymonster,Jack's right about that formula I gave you. I had a brain fart and gave you that info just after having read a few antenna articles I plan to experiment with and my brain was still stuck in halfwave dipole mode. Yep,492 is the correct figure to use and that is what I used when I cut all my cables for testing. I'll make the corrections "over there" in my posts where we discussed this on the other forum. Sorry for the mistake but like I said my brain was still stuck in dipole mode after reading a lot about various antennas.

in the 'old days', when your 102" whip went from 'perfect' swr to 3:1 or worse, you checked the spring & almost guaranteed the connecting braid had broken.....

Booty Monster, if you will just use a longer coax from the meter to the 102" whip (like 18 to 20') your problems will be solved for the 102" whip...But if your going to later replace the whip, back to the 10K, you'll need to fine tune the 10K again...

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