102" Whip problems...

[plutonium233]

Hey yall,
I've been a member of the forum for a while but I havn't posted much mainly because I usually find out what I need to know just from reading threads on here. I have been looking at several 102" whip/SWR threads, but I am still confused. Here's what I have: cobra 25 in a ford ranger, two 9' lengths of coax to the antenna which is mounted on the bedrail at the front of the bed on the driver's side. The original antenna is a cheapo truckstop 4' fiberglass antenna, but it has performed really well and we've had low SWR on it all along (below 1.5). I few days ago a buzzard flew into the antenna at 60 MPH the SWR is still pretty low and it works fine, but we wanted to put the 102 on there for a while. So I screw it in and the SWR is around 2.8. So I add a spring, SWR only goes down slightly. I think it could be grounding so I get my brother to hold a piece of wire from the antenna base to a screw behind the gas cap door which didn't help much if any. I also tried lengthening the antenna with tin foil wrapped around it, but it just made it worse. I suspected the spring so i ran a wire from the top of the spring to the bottom and it seemed to get worse. I finally put the old antenna back on and check the SWR, and it was way high on low channels and way low on high channels so I took the antenna off and played with the mount some and got it to come back down some, but its not exactly where it was to start with... I am beginning to suspect the mount now, but I don't have another one to try. It is a basic L shaped mount/antenna holder.

Thanks,
Kyle

[Grump]

First I would ground everything to the frame works best. Then I would check the coax to see if it maybe shorted out. you said you are using two nine foot sections of coax try only one if you can do it then check the lug they usually only have a plastic sleeve in them which after hitting the buzzard might have damaged the lug. once again ground it to the frame clean off any paint or rust get it down to shiny metal

[Texas Mobil 219]

Sounds to me like you got a shorted mount. They only have a plastic insulator the will crack and brake on the inside and it really hard to tell if they are broke except for the swrs.

<----------<<<<< The best place i think a whip should be. No kick back from the cab and 360 deg of radiation.

Firestick puts out a good one. Ive been running it on my truck now for about 6 months and it takes the abuse of the 102 '' whip hitting alot of stuff. I would also run a external ground to the frame itself.

As for the two 9' pieces of coax with the barrel connector. I was told that you will loss alot of the RF. One solid piece is the best way im told and from what ive learned of the year. If your using RG58 or the like and you are running power. It wears out fast. Ive replace a few string in my truck before i figured it out.

Good luck.

[Texas Mobil 219]

Sounds to me like you got a shorted mount. They only have a plastic insulator the will crack and brake on the inside and it really hard to tell if they are broke except for the swrs.

<----------<<<<< The best place i think a whip should be. No kick back from the cab and 360 deg of radiation. Flat SWRs

Firestick puts out a good one. Ive been running it on my truck now for about 6 months and it takes the abuse of the 102 '' whip hitting alot of stuff. I would also run a external ground to the frame itself.

As for the two 9' pieces of coax with the barrel connector. I was told that you will loss alot of the RF. One solid piece is the best way im told and from what ive learned of the year. If your using RG58 or the like and you are running power. It wears out fast. Ive replace a few string in my truck before i figured it out.

Good luck.

['Doc]

I think your problem may be in the mounting bracket too, at least partially. Why? Cuz' you said after the old antenna didn't work right either, and it had before, that you 'messed' with the 'L' bracket and got it at least close to where it used to be. A typical 'L' bracket can work just fine, but they do have limits depending on how they are mounted to the car/truck, scews, bolts, welded. A typical 'L' bracket just isn't made to support a 'large' antenna. Medium to small ones, sure, just not big ones with a lot of wind force applied to them, or that just wiggle a lot. Really 'cranking' the thing down tight (with out stripping the screws) is one 'cure'. Welding the thing on is another 'cure', but sort of 'drastic', kind'a. The 'hint' about the insulator in that mount is a good one too!
Once you make sure of your mount, then you can try that 102" whip again. It wouldn't surprise me if you do hear a difference. It also wouldn't surprise me if you don't. One'a those 'maybe' thingys. A "full sized" antenna will always do better than one that's been shortened by some means. May not be a huge difference, but always some. Will that difference be worth the time/trouble/$$$? Beats me, you have to answer that one.
Those 'double-female' connectors do work if done correctly. If you have to use them, do so. If you don't have to, then don't. It's a good idea to weather proof them cuz they will get water in them (so will the typical PL-259 connectors).
There is no benefit in using a 9 foot section of coax, or 18 feet. The 'best' length is whatever will reach from one place to another with a little slack to play with. There are exceptions to that, but those exceptions are few and far between, never with a single antenna.
Where you mount an antenna can make a difference on how well it performs. There are also practical aspects that make that 'best' place just too much of a P.I.T.A. to live with conveniently/comfortably. Wish I had a penny for every truck bedrail mounted antenna in the world that worked just fine! (And if wishes were fishes I wouldn't be eating newspaper soup quite as often, right?) Oh well...
- 'Doc

[plutonium233]

Thanks for all your suggestions. I'm gonna try out some of these ideas today, and I'll let yall know what happens.

[Storm/413]

If when adding length via aluminum foil things got worse,SWR wise,Id think shortening the stinger may work for lowering the SWR if the mount isnt the problem.
Just thinkin out loud,I'll shut up now.

[plutonium233]

We took some braided sheild from a piece of coax and grounded the mount to the frame today. When I checked the SWR with the 4' fiberglass antenna I couldn't even get needle swing in the FWD position, but I could get a little swing in the REF. This happened once before with this meter and I think there is a short/open somewhere in it. My next step is to get another meter. I also discovered that the spring I am using has a smaller corroded spring in the center of it that is obviously meant to provide a good electrical path through the spring. Well i also noticed that this spring is broken off in two places so This must be where some of my problems are coming from. I will also be getting a new spring for it. I'll let yall know how it turns out.

[plutonium233]

We got another SWR meter and an antenna stud. With the old 4' fiberglas antenna the swr ranged from 1.5 on ch1, to 1.75 on ch20, to around 3 on ch40. So we decided to tune it. We took off about 1/8" off the wire and tucked it back in. This is where it gets strange.. all of the readings reversed. Ch1 is around 3, ch 20 is still around 1.75 and ch 40 is about 1.5. I don't know what to think about this...

['Doc]

I hope that 'wire' was the 'whip' part of the antenna, not the feed line. Otherwise, you really haven't changed anything. And the 'quick-n-dirty' answer is, you cut off too much. There ought'a be a little 'play' in how far you can stick that whip into the ferrule (thing that holds it) before tightening it down.
- 'Doc

[Texas Mobil 219]

What wire did you cut and tucked back in. The Coax. Or the wire inside the spring. Its like Doc said . If you cut it of the coax you haven't really change nothing, Cuting the wire inside the spring is not the way to tune and antenna. Ive never heard of anyone doing that.

If you cut the ground wire and tuck it back in. You got something wrong with the coax itself. 1/8 should of the ground wire shouldn't change nothing.

If your running power and and swinging over 500 watts using RG 58, RG 8X or the such its wore plunb out. Or worn somewere on the ground side of the coax and sending rf all thru the truck. You might even get some coax and just run it to see if it straightens out. Try another radio too.

Hope this helps. Good luck.

219 quite in Texas.

[Grump]

i know this is a stupid question but are you calibrating the meter when you change channels to check swr

[Lost Sheep]

The type of antenna he is tuning is a fiberglass cheapo truck stop type.....WITHOUT a tuning tip!

The "wire" he is referring to is the loading coil at the top of the antenna that is underneath the plastic coating.
How on EARTH you guys got that he cut wire inside the spring, OR the coax, OR the feedline on an antenna with a tuning tip is BEYOND ME!! If you actually READ his post, he makes it QUITE CLEAR how he tuned the antenna.

WHEW The advice people give on this forum blows my mind sometimes!


HEY, Plutonimum...My best advice....as far as a 102" whip is concerned, is to use one "SINGLE" 18' length of good quality coax (not the skinny black stuff), a good HD antenna stud (not the Firestick stud, they SUCK) and a quality HD shock spring WITH THE BRAID INSIDE (not the one with a spring inside).
Also, make sure that the "mount" (not the antenna) is grounded very well to the body AND frame. Your best bet is to use old coax shield (because its braided) and ring connectors with NUTS & BOLTS for grounding (not self tapping screws..they dont stay tight).

Another BIG issue with SWR and 102" whips is to make sure that the majority of the antenna is above the vehicle body....preferably 2/3rds should be above the highest point of the vehicle.

If you stick to that TRIED & TRUE setup, your bound to get a low SWR....About a 1.3 thru 1.5 across the band. OF COURSE, Thats NO GAURANTEE considering that there are so many variables when it comes to tuning an antenna...BUT a 102" whip is usually an exception to the rule. There is practically NO TUNING needed.

Good luck and HAVE FUN!!!!

[Texas Mobil 219]

Hey Lost, Never mind i wont waste my time on ya.

[drdx]

18 feet? The length doesn't matter, and if you mention that length as a half wavelength, then that's off too. That length after the velocity factor is some odd length. The 18 was just a way for dealers to sell more coax, and some still listen to them and buy it. If the length meant anything then they would measure it more closely. I'm guessing that base stations need to subscribe to that too? Let's see, "coax lengths for a base should be 18,16,54,72,90 feet?" It doesn't apply on a base or a mobile. If you are seeing length swr variation in a mobile you have coax radiating and that's a bad deal. -drdx

[Grump]

lost sheep if you lower the swr by using coax length then you are just tricking the meter which means a loss of power. The longer the coax the more resistance the less power. If you don't believe me run a appliance which draws a fair amount of electricity plug it in with out an extention cord and run it 30 minutes. Then plug it in with a 50 foot extention cord and run it for 30 minutes. it will heat up the cord due to resistance. Not saying a cb would do that unless you are running ALOT of power but it is still the same princeable. Lenght = resistance =power loss. I hope the way i stated this made sense I'm just a mudduck with a little understanding of electricity

[Lost Sheep]

Did I say ANYTHING about coax length changing SWR???????????

NOPE.......sure didint!!!

I did say this.....

I would recommend using "One single 18' length of coax" INSTEAD OF two 9' lengths combined with an adapter............which is what he is using now.

I will also add this....

There are HUNDREDS of posts on THIS FORUM relating to 102" whip questions and I gaurantee you, if you look, you'll see the same combination working for many 102" antenna users right now.


Texas Mobil........WHATEVER .......If you'd read the posts a little better, you might be able to give some decent advice that makes some sense........but until then....dont "waste your time"!!!!

To all the MUD DUCKS and the ANTENNA ENGINEERS out there....ADIOS AMIGOS

992 Georgia.....GONE!