| Author |
Message |
    
Cbblackbeard
Member
Username: Cbblackbeard
Post Number: 68
Registered: 12-2003
| | Posted on Monday, August 02, 2004 - 10:22 pm: | 
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I mounted a 102" whip on the rear bumper of my Dad's conversion van and have an SWR of 2.0
I thought triming off some of the antenna would lower it, but it went UP instead. What can I do?
I realize that I'll have to buy another whip. |
Viking
Intermediate Member
Username: Viking
Post Number: 148
Registered: 2-2002
| | Posted on Tuesday, August 03, 2004 - 10:32 am: |
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I've seen most installations with a 102 needing the 4" (+/-) spring added in to lower the SWR's. From what you said, shortening the antenna raised them, so lengthening it will lower them. Also, make sure you have the plastic/rubber insulators installed at the mount. Since the SWR's are only 2.0, you probably have them in.
Also, to determine if the antenna need lengthening or shortening, check the SWR on channel 1 and 40. If the SWR is higher on 1 than on 40, the antenna needs shortening. If the SWR is higher on 40 than on 1, the antenna needs lengthening. |
Crackerjack
Intermediate Member
Username: Crackerjack
Post Number: 187
Registered: 7-2004
| | Posted on Tuesday, August 03, 2004 - 1:36 pm: |
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Viking:
Don't you have that (1/40) backwards? |
Cbblackbeard
Member
Username: Cbblackbeard
Post Number: 70
Registered: 12-2003
| | Posted on Wednesday, August 04, 2004 - 12:27 am: |
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Thanks Viking.
I bought the spring like you suggested and a brand new whip and now my SWR is at 1.5
I can live with that, but all my other antennas are darn near flat. Is there anything else I can try? |
Crackerjack
Intermediate Member
Username: Crackerjack
Post Number: 199
Registered: 7-2004
| | Posted on Wednesday, August 04, 2004 - 1:19 am: |
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How much and what kind of cable are you running? Any loops in the run, kinks, hard corners? |
Simpleman
Junior Member
Username: Simpleman
Post Number: 28
Registered: 2-2004
| | Posted on Wednesday, August 04, 2004 - 6:00 am: |
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Cbblackbeard , I have a shed full of 102" whip that Ive tried to get the SWR down below 2. If you have a SWR of 1.5 , leave it alone . Thats great for the 102" whip. You can try more grounding , or different springs , But at 1.5 I'd leave it alone. |
Viking
Intermediate Member
Username: Viking
Post Number: 149
Registered: 2-2002
| | Posted on Wednesday, August 04, 2004 - 10:34 am: |
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Crackerjack, You're right! You know I sat and thought to get it right... well, brain-fart's cleared now.
From: http://www.alpharubicon.com/elect/tuningantennaeli.htm
****Moderator558 Note****
Viking
great link,,, because of the copyright I had to edit your post but the full detail can be found at the link you provided.
Thanks
|
Nightcrawler
New member
Username: Nightcrawler
Post Number: 2
Registered: 8-2003
| | Posted on Wednesday, August 04, 2004 - 12:32 pm: |
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cbblackbeard,you may be getting some reflect off the back door of the van,how much of the antenna is above the roof of the van. to get the swr below 1.5 you might try adding a quick disconnect to add more length to the antenna, Ive used the 102in whip for 12 years and have always had to use the spring and quick disconnect to get the swr around 1.1. |
Crackerjack
Intermediate Member
Username: Crackerjack
Post Number: 200
Registered: 7-2004
| | Posted on Wednesday, August 04, 2004 - 3:15 pm: |
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Just curious, you are not checking it -inside the garrage, Just being humorous here! LOL
Do you have 18 feet of cable? Not coiled up? |
Cbblackbeard
Member
Username: Cbblackbeard
Post Number: 71
Registered: 12-2003
| | Posted on Wednesday, August 04, 2004 - 10:52 pm: |
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Thanks for all of your comments.
Most of the whip IS behind the rear door.
I think I will try a quick disconnect and see what happens. I'm using 18' of Belden coax( with the gray jacket ) no kinks or loops. I test my SWR in a vacant lot away from any other cars or structures. I would LOVE to have 1.1. |
Gijoe
Junior Member
Username: Gijoe
Post Number: 36
Registered: 4-2002
| | Posted on Wednesday, August 04, 2004 - 11:23 pm: |
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My SWR is flat. The needle doesn't even move. I have a 102" steel whip with the base of it cut off and slid into a pole. I adjust the SWR by moving the whip up and down. |
Crackerjack
Intermediate Member
Username: Crackerjack
Post Number: 208
Registered: 7-2004
| | Posted on Thursday, August 05, 2004 - 1:22 am: |
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Cbblackbeard:
You haven't answered on the coax yet. RG8Mini will improve the performance, and 18' is the magic number -not less/not more. |
Crackerjack
Intermediate Member
Username: Crackerjack
Post Number: 210
Registered: 7-2004
| | Posted on Thursday, August 05, 2004 - 4:13 pm: |
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GI-Joe:
That is one fine looking installation.
I wonder if I cound do that on my Jeep? |
Cbblackbeard
Member
Username: Cbblackbeard
Post Number: 73
Registered: 12-2003
| | Posted on Thursday, August 05, 2004 - 6:25 pm: |
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Thanks everyone.
This is my first experience with a 102" whip and I wanted to see how it would perform. I guess I would do better if it were mounted differently on another type of vehicle. Thanks for all the input. |
Simpleman
Junior Member
Username: Simpleman
Post Number: 29
Registered: 2-2004
| | Posted on Thursday, August 05, 2004 - 7:30 pm: |
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Hey Gijoe, Where did you find the Pole ?? |
Hollowpoint445
Intermediate Member
Username: Hollowpoint445
Post Number: 203
Registered: 6-2004
| | Posted on Thursday, August 05, 2004 - 8:53 pm: |
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Crackerjack - RG-8X is a better grade of coax than RG-58, but it's also got foam dielectric and will degrade much easier than a solid dielectric. Good quality RG-58 will work just fine in a mobile installation unless you are using insane amounts of power - which I'd advise against anyway.
I suspect in your situation that there was a major problem with impedance matching and the change to a coax with foam dielectric changed the impedance that the radio saw because of the change in the velocity factor, and allowed it to transmit more power. In this case it would really be beneficial to use 1/2 wavelength of coax regardless of type, so you can get a good VSWR at the radio. |
485
Junior Member
Username: 485
Post Number: 22
Registered: 8-2006
| | Posted on Sunday, August 27, 2006 - 8:02 am: |
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I wish I had a penny for every hour spent on finding that perfect swr spot the last 35 years. This is terrific conversation as I sit here nodding my head at everyone's comment's, ya'll are great. I see some good "Reflective Comments" but didn't see mention of door's being open while checking swr's. I had a 102 on the roof of a van for years and noticed if the front doors were open the swr would go up about 1/2 point while checking it. |
Tech808
Moderator
Username: Tech808
Post Number: 10956
Registered: 8-2002
| | Posted on Sunday, August 27, 2006 - 8:14 am: |
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485,
Choose a clear location to adjust the SWR.
Antennas are very sensitive to objects close to them.
Go to an open area to tune your antenna, such as a parking lot.
This can be done at home, providing you are not close to the house.
Do not try to tune inside a building, under trees, near or under power lines, nor with someone standing next to the antenna.
This distorts the signal and causes a reflection back into the antenna giving false readings.
Also, close all doors, the hood and trunk lid.
WILSON ANTENNA TECH SUPPORT ~ General SWR Notes
NOTE!
The above information applies to ALL MOBILE ANTENNA's even if is not a WILSON Antenna.
Hope this help's,
Lon
Tech808
CEF808
N9CEF
CVC#2 |
Vanillagorilla
Advanced Member
Username: Vanillagorilla
Post Number: 808
Registered: 4-2005
| | Posted on Monday, August 28, 2006 - 5:52 am: |
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The 102" whip is resonant out of the box. All the comments regarding the reflect are 100% true. You should never have to clip or adjust the 102 whip. If your in the clear and still having problems then you'll have to look a little harder at your counterpoise...that being where you have the antenna grounded and what it's grounded to. This, in a mobile application, IS the other half of your antenna! By adjusting your radiating element what your doing is trying to balance the two halves...radiating element(antenna) and counterpoise (grounding element...vehicle) to be resonant on 27MHz and keep a 50ohm impedance.
If I'm out of line here I'M SURE a tech will straighten me out but thats the way I see it.
Only thing cutting the coax will do is change the way your radio see's SWR. Check SWR between the antenna and feedline...at the antenna or as close as possible with a helper keying the mic for you. Go back and check it at the radio with a good external meter afterwards. If it does not match within reasonable specs THEN cutting the coax will change the way your radio see's it and NOT the actual SWR at the antenna.
The radios built in meter (where applicable) is generally not a good reference. I've seen TOO many give WAY false readings.
Best of luck!
Hank CEF559 |
Hotwire
Senior Member
Username: Hotwire
Post Number: 1695
Registered: 1-2005
| | Posted on Monday, August 28, 2006 - 11:05 am: |
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Hollowpoint is correct. You should NEVER mount a 102 inch whip or any antenna on the rear bumper of a van. It just does not work. The vehicle is blocking all the rf thats trying to escape! On top the van is the only correct way to do it. At least get 2 thirds of the whip above the vehicle so a little bit of signal can escape!
I like to explain to my friends to think of their antenna like its a long fluorescent tube. Where would you mount that lightbulb so that you get the most even spread of light all around the vehicle? Same for antennas! |
Ajm1571
Intermediate Member
Username: Ajm1571
Post Number: 282
Registered: 12-2004
| | Posted on Thursday, August 31, 2006 - 12:55 pm: |
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I ran a 102' ss whip on my light bar on the truck with just a stud mount an 21ft of coax an had a 1.2-1.3 match. If I put 18ft of coax on it it went up to a 1.4-1.8 on the match. I also have ran them on a beehive mount on the roof of a vehicle an got pretty much the same match. Now that I have a van I cant use the light bar an the wife refuses to let me drill a hole in the roof for the beehive mount . Looks like I have to find a decent mag mount to use  .But newayz, thats my experience with a 102.
Allen |
Captian_radio
Junior Member
Username: Captian_radio
Post Number: 33
Registered: 9-2004
| | Posted on Tuesday, September 05, 2006 - 8:56 am: |
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Well a very good discussion on the 102 inch whip, great reading.I have a 102 inch ss whip on the back of my 1992 tempo, its mounted in the center of the trunk lid just a bit above the trunk lock with a home made bracket, i also had to put an extension on the whip to make it resonant.As a further step i also installed grounding straps on the trunk lid , doors and hood to maximize as much ground plane IE metal of the car as i could get.This has improved the performance of the whip.Check with an ohm meter between the doors, trunk lid and hood to see if there is a good connection to the rest of the car.I my case the doors ,trunk and hood were not bonded very well RF wise to the rest of the car, try it , might make a difference. |
Hotwire
Senior Member
Username: Hotwire
Post Number: 1737
Registered: 1-2005
| | Posted on Tuesday, September 05, 2006 - 2:00 pm: |
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Captain Radio, I have my antenna on my trunk also. The way you described how you ground your vehicle sounds the same as what I have done. I agree thats how it should be done. I have noticed a major improvement in recieve qaulity as well as transmit since I "upgraded" my setup. |
Znut
Advanced Member
Username: Znut
Post Number: 717
Registered: 1-2002
| | Posted on Tuesday, September 05, 2006 - 8:54 pm: |
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A 1.5:1 VSWR doesn't sound bad. Theoretically a true 1/4 wave antenna is very effecient though in optimum situations it has approximately a 35 ohm feed point. With that said, how does it work on the air? Your SWR may not be perfect but it is pretty good. I would like to know how it is working for you. If it does well for you it must be working!
Take Care,
Randy |
