A question on whips...

[Wire Weasel]

the swr on the feedline has nothing to do with the fact that @ 102" your antenna is operating in the 10 meter amateur band. you've allowed your education by antenna manufacturers to interfere with your learning.

feedline swr indicates whether or not the antenna is matched to the feedline. it never has been, isn't now and never will be an indication that the antenna is operating at any particular frequency.

246 ÷ (102") 8.5' = 28.941 mhz., 246 ÷ (108.588") 9.049' = 27.185 mhz..

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Wha ??? always thought it was like this. 1/4 wave is 234, 1/2 is 468
234 / 27.550(mhz) = 8.49 (feet) - X 12 (inches) = 101.9 inches > and there is your 102" whip. Done this way ..... the 102 comes in at around 27.550mhz.
At any rate, many times the 102 comes in with an elevated SWR & resonance on the CB channels and has to be lengthened some. Other times it's not necessary as the 1/4 Wave design tends also to be very broad-banded in performance and wherever the whip achieves Center Frequency on a particular installation it is wide enough to cover a big chunk of 10/11 meters. 1/4 Wave Verticals often achieve a 1:1 SWR over a whopping 2mhz of bandwidth.

 

[Recon]

Must admit my 102 whip with the spring works great on the back of my toolbox it is in the center.

I also have a 102" stainless whip with a spring. Right or wrong, I did the following "science fair".
Using a Breedlove Quick-Disconnect Mount installed on a Breedlove Stake Pocket Mount located on the forward left (driver's side) stake pocket on my "aluminum" 2019 F-350.
Total length of the Breedlove Quick-Disconnect Mount from top to bottom: 4.490"
Length of spring without the 3/8" stud: 4.275"
Length of whip: 102".
Total length = 110.765"
I loosened the set-screw on the feral at the base of the whip, removed the whip and trimmed-off (Dremel Cutting Wheel) just enough material to obtain a total of 108" from the bottom of the Breedlove mount where the coax connects to the top of the whip.
Right or wrong......it works and the average SWR is 1.3:1.
I also have a (trimmed) 6' Firestick Fiberglass Antenna and have an acceptable SWR with the spring. The diameter of the fiberglass antenna is considerably larger than the stainless whip and at highway speeds, the fiberglass whip with the spring bends-over much more than the stainless whip and the transmit and receive decreases.
I removed the spring from the fiberglass antenna and trimmed the antenna and have an acceptable SWR.

 

[redbeast]

Aaahhhh yes!! The age old discussion about 102" vs 108". I'm no expert and certainly no tech, BUT, I have decades of whip experience! ( sounds kinky)

I've installed at least 100 whips in my days, and have NEVER had 102" load up like 108". This is the one time where all that math fails, terribly. I've mounted whips on bumpers, side panels, special brackets, tool boxes, and many more. Yes, had one on my own vehicle in the middle of the roof. In EVERY case 108" loaded much better than 102". AND, I ALWAYS use the shortest length of coax I need to get the job done. None of this crap about 3', 18' or any of the other wives tales.
I've asked numerous good, established technicians to explain this to me, but, no joy. My very good friend was a chief engineer and RF specialist working for the local radio and TV stations, doing maintenance, repairs, and transmitter installs. He knew his stuff. Can't explain why 108" is the magic number. The math doesn't work.

Aaahhhh yes!! The age old discussion about 102" vs 108". I'm no expert and certainly no tech, BUT, I have decades of whip experience! ( sounds kinky)

I've installed at least 100 whips in my days, and have NEVER had 102" load up like 108". This is the one time where all that math fails, terribly. I've mounted whips on bumpers, side panels, special brackets, tool boxes, and many more. Yes, had one on my own vehicle in the middle of the roof. In EVERY case 108" loaded much better than 102". AND, I ALWAYS use the shortest length of coax I need to get the job done. None of this crap about 3', 18' or any of the other wives tales.
I've asked numerous good, established technicians to explain this to me, but, no joy. My very good friend was a chief engineer and RF specialist working for the local radio and TV stations, doing maintenance, repairs, and transmitter installs. He knew his stuff. Can't explain why 108" is the magic number. The math doesn't work.

Kind of have to agree with Greg here, have had my 102 whip since the seventies on many different vehicles, always with swivel base and spring. Swr almost always about 1.4-5:1, setup on my ram with breedlove mount and an extender.......102 plus 4 for spring plus about 2 for extender.....swr came in about 1.05-1.1:1 on 40 and 1, almost dead flat on 20. No expert here but good results. See pic attached

 

[Greg T]

Kind of have to agree with Greg here, have had my 102 whip since the seventies on many different vehicles, always with swivel base and spring. Swr almost always about 1.4-5:1, setup on my ram with breedlove mount and an extender.......102 plus 4 for spring plus about 2 for extender.....swr came in about 1.05-1.1:1 on 40 and 1, almost dead flat on 20. No expert here but good results. See pic attachedView attachment 49118

Yup. I've always used the ball mount and pot belly spring. Even when mounted on a bumper or bed rail of a truck. Ball mount and pot belly spring will load perfectly every time. And, coax length is NOT a factor. Had a whip in the middle of my roof on a Chevy Celebrity, back in the day, radio mounted on the headliner and the coax was about 8" or 10" long.