drewdownkali
Member
All I can think is the fact that its shorter coupled with the ground strap that wasn't there before with a whip at this length.
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Mounting a CB antenna on a modern hatchback without drilling?
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drewdownkali
Member
Writing down #'s in driveway: in actuality were Ch.1=1.3 Ch.19=1.55 Ch40=1.9
If these numbers hold true in an open area then I figure I should probably use a file to trim. Lol. Very very small amounts.
If these numbers hold true in an open area then I figure I should probably use a file to trim. Lol. Very very small amounts.
mmckenna
I ♥ Ø
No, higher SWR on the higher channel means it's a bit to short. Don't trim anymore off. Back the whip out a bit and tighten the set screw and check again. If it isn't long enough, take the other whip and trim it about 1 inch longer and start testing again.
drewdownkali
Member
Umm not according to the videos and info on web. lower on 1 and higher on 40 need to trim. Higher on 1 and lower on 40, need to make longer.
Tuning a CB Radio Antenna - YouTube
Tuning a CB Radio Antenna - YouTube
drewdownkali
Member
Firestick website says the same thing.
mmckenna
I ♥ Ø
" Writing down #'s in driveway: in actuality were Ch.1=1.3 Ch.19=1.55 Ch40=1.9
If these numbers hold true in an open area then I figure I should probably use a file to trim. Lol. Very very small amounts."
Longer antenna will resonate at a lower frequency. Shorter antennas will resonate at a higher frequency.
So, if your SWR is better on channel 1 than it is on channel 40, you need to move the resonance up, by shortening the antenna.
So, yeah, you are right, and this is one area where I always get confused. I can do it when I'm actually there at the antenna, but trying to type it out on the web just confuses the heck out of me. This is why the antenna analyzer systems are so much nicer to use. They will tell you at what frequency your antenna is working best, and you can adjust accordingly.
If these numbers hold true in an open area then I figure I should probably use a file to trim. Lol. Very very small amounts."
Longer antenna will resonate at a lower frequency. Shorter antennas will resonate at a higher frequency.
So, if your SWR is better on channel 1 than it is on channel 40, you need to move the resonance up, by shortening the antenna.
So, yeah, you are right, and this is one area where I always get confused. I can do it when I'm actually there at the antenna, but trying to type it out on the web just confuses the heck out of me. This is why the antenna analyzer systems are so much nicer to use. They will tell you at what frequency your antenna is working best, and you can adjust accordingly.
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drewdownkali
Member
Yea. I check it like 4 times to make sure before I will touch it. Lol
drewdownkali
Member
So, if my calculations are correct, lol and these numbers are true. Would you think that I should be able to get an even 1.6 across the band? 1.3+1.9=3.2 3.2/2=1.6
mmckenna
I ♥ Ø
You should probably get somewhere around 1.6:1 on channel 1 and 40, and something much lower on 19. Remember, it's a bell curve, and you are trying to get the antenna to be resonate at a point as close to the center of the bell curve as you can.
If you knew for sure that you were primarily going to use just one channel, you could tune it to be lowest at that channel, but since you likely want it good across the band, then getting it lowest at the center of the band is the best thing to do.
If you knew for sure that you were primarily going to use just one channel, you could tune it to be lowest at that channel, but since you likely want it good across the band, then getting it lowest at the center of the band is the best thing to do.
drewdownkali
Member
That makes a lot of sense. Just pictured the curve. Awesome. Thanks man.
mmckenna
I ♥ Ø
Yeah, no problem. I'm one of those people that learn visually. I can and do read the manuals and take a lot of courses, but give me something and let me take it apart and I'll master it. I've always had that issue with trying to type out the rules about SWR and when to trim. I can do it right in the shop, but when I try to reason it out in writing, I fail and fail miserably. That, and its the time of year when I have to write the performance evaluations for my staff, and it totally fries my brain for about 3 weeks. Sometimes I really wish I was back in the field doing this stuff full time. I really miss it. Getting to hop on here and help out is enjoyable. It at least holds me through until the weekend when I can get out in my own garage and start tinkering. I can't wait to retire.......
drewdownkali
Member
Oh gawd performance evals. Glad I haven't had to deal with that in my lifetime, yet... LOL. The union kept that crap out even though company tried. That trade (newspaper pressman) has been dying for a while now. Student now. Medical field here I come
drewdownkali
Member
Update
So far I have cut it down to 46 1/4 in. and have readings of CH.1=1.2 Ch.19=1.33 or so and CH. 40=1.63
So far I have cut it down to 46 1/4 in. and have readings of CH.1=1.2 Ch.19=1.33 or so and CH. 40=1.63
jhooten
Member
Are you allowing for the effects of the curvature of the whip cause by wind resistance at highway speed?
mmckenna
I ♥ Ø
Slippery slope......
drewdownkali
Member
Do you mean leaning the antenna fwd a bit so that its straight at highway speeds?
drewdownkali
Member
???
jhooten
Member
Even if you tilt the mount the rod will still bend. If the rod bends the SWR will change. The more it bends the more it will change. You can spend hours getting it just perfect sitting still in the middle of an open field and still have a very high SWR at speed and never know because nobody leaves their meter in line after they make the initial adjustments.
drewdownkali
Member
Think some of my pronlems may have been due to the nmo mount within the mount being a bit loose. Had intermitant high swr again today.
Don't have a proper size wrench to tighten. Any idea what size wrench the little flats inbetween the thread take?
Guessing you probably need a special tool to hold the center part?
Don't have a proper size wrench to tighten. Any idea what size wrench the little flats inbetween the thread take?
Guessing you probably need a special tool to hold the center part?
mmckenna
I ♥ Ø
15/16th's
My 6 inch Craftsman adjustable wrench will fit that. A pair of channel locks will work, too. Just be careful, it's soft and you can mess up the threads.
If that ring is loose, it can affect the grounding of the antenna coil, and that would certainly cause an intermittent high SWR.
As for tuning for the bent whip... Do that as soon as you get back from the snipe hunt. Like I said, slippery slope. Do you tune it for the flex at 25mph, 45mph, or interstate speeds? What if there is a headwind, or a tail wind? highly flexible whips will move a lot, and if they bend over too far, or get too close to an adjacent antenna, you could see the SWR change, but I wouldn't worry about it. I never had an issue with it, and your average CB will tolerate some high SWR. Most CB users can't even spell SWR, never mind know how to adjust an antenna. If the radios were that touchy, they'd all fry themselves in a couple of days.
My 6 inch Craftsman adjustable wrench will fit that. A pair of channel locks will work, too. Just be careful, it's soft and you can mess up the threads.
If that ring is loose, it can affect the grounding of the antenna coil, and that would certainly cause an intermittent high SWR.
As for tuning for the bent whip... Do that as soon as you get back from the snipe hunt. Like I said, slippery slope. Do you tune it for the flex at 25mph, 45mph, or interstate speeds? What if there is a headwind, or a tail wind? highly flexible whips will move a lot, and if they bend over too far, or get too close to an adjacent antenna, you could see the SWR change, but I wouldn't worry about it. I never had an issue with it, and your average CB will tolerate some high SWR. Most CB users can't even spell SWR, never mind know how to adjust an antenna. If the radios were that touchy, they'd all fry themselves in a couple of days.
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