klhutch
Sububan Chicago
Senior Member
Joined: 09/14/2005
View Profile
 Offline
|
Just a word of warning about the Firestik NGP antenna. Since it is a popular topic around here right now I have looked over their website. Potentially it could be a good antenna. It appears to be a variant of a "sleeve dipole" and like any other dipole antenna it should work well without a ground plane. Normally in a sleeve dipole one half of the antenna is a metal tube and the coaxial feedline runs up through this tube. It makes connection to the tube and the other half of the antenna, a metal whip that extends upwards from the tube, at their junction at the center of the antenna.
You can make a nice sleeve dipole from a length of coax. Measure from your radio to where you want to mount the antenna and add half a wavelength to this distance. Cut the coax to that length or better yet a few feet longer. Put a connector on the radio end of the coax. Cut a quarter wavelength of the outer insulating jacket off the free end of the coax to expose the braided shield. Fold the shield back over the insulated jacket of the coax. When you are done it will extend back over the coax by a quarter wave. If this is a permanent outdoor antenna you would wrap the exposed braid with duct tape or similar to weatherproof it. You are left with a quarter wave of insulated center conductor that forms one half of the dipole and the braid folded back over the coax forming the other half. This is not a self supporting antenna so you will have to mount it in PVC pipe or hang it from an insulating support at its tip to keep it vertical. If you did cut it long you want to wind the excess coax into a coil a foot or two from the bottom end of the folded back shield. This will make a "choke balun" that will keep RF currents off the outside of the shield of the coax running to the radio. It also addresses the balanced/unbalanced issue that I mentioned above so it is a very good thing to do.
If you read all the Firestik information you will note some similarities to the above. However Firestik does not use a folded back braid on their feed coax and they warn you away from making a choke balun from any excess coax. My guess is that they are using the normal shield on the coax as both the feedline shield and the sleeve of a traditional sleeve dipole. They are making the coax half a wavelength long and are apparently depending on the voltage null that would occur at that point. If you have excess coax they tell you not to cut it for this reason and they tell you how to bundle the excess in a non-inductive manner. They also tell you to add coax, if you need more, in multiples of 9 feet which is a little odd. Given all the rest that they say it seems additions should be in multiples of 18 feet.
The bottom line is that the Firestik NGP looks like a very odd antenna system design. I'm not going to say it won't work, I will say the same thing that they say: if you install one follow their instructions exactly. This antenna is an exception to what I said in my earlier post and if it is to have a prayer of working you must follow the directions. Don't cut the coax and don't coil any excess, bundle it as they suggest. In this case the coax is part of the antenna and must only be modified as they suggest! If I needed to add coax to one of these antennas I would add it in multiples of 18 feet, not 9, and that is the only thing I would do different from what they say. Of course since 18 is a multiple of 9 that is not violating anything they say, just putting a different constraint on it.
Ken
|
DAS26miles
San Fernando Valley, California
Senior Member
Joined: 10/11/2003
View Profile
Offline
|
time to go now-I called the CB shop you recommended. The first thing they said was the NGP don't work well. They then asked if I tried a regular ground plane antenna. Of course I said no, assuming the fiberglass siding and top would not work. They said you don't know until you try. There is plenty of metal on the chassis and cab. They said to bring it in for a FREE evaluation, and that they could greatly improve my range of RX and TX. Going to the beach tomorrow for the weekend, but will try to go next Saturday. It will cost $70 in gas to drive the MH the 65 miles each way. But there are no CBshops closer.
2004 Class C Winnebago Minnie 22E
|
DAS26miles
San Fernando Valley, California
Senior Member
Joined: 10/11/2003
View Profile
Offline
|
Just a little update on installation. Gave up on the NGP antenna. I mounted a regular ground plane antenna (3ft Firestik, Firefly) on my rear ladder. I tried grounding the mount to the ladder, bumper and frame. the best turned out to be two #10 wires running to the awning gutter at the rear of the MH. I currently have a good match all under 2.0 and the channels I use like 15-19 are at 1.1-1.3. So I'm a happy camper. I am going to get my older (1 year old) Cobra 29 LTD CLassic tuned and see if it makes a difference over the Cobra 18ST WX II. I really like the Cobra 18.
|
donee
Simi Valley, Ca. 93063
Senior Member
Joined: 03/05/2006
View Profile
Offline
|
Iv been thinking about installing one in our 05 Monaco.
I dont want to drill holes in the side.
Thought about an antenna mount but dont think it would clear the side very well.
Could some of you email me the pics of your installs so I can get a better idea of whaich antenna to go with?
Thanks.
05 Monaco Esquire 29PBD
05 Silver Dodge Cummins w/3.73 gears 4 spd auto.
|
DAS26miles
San Fernando Valley, California
Senior Member
Joined: 10/11/2003
View Profile
Offline
|
I finally got around to going to a CB shop and have my radio tuned. I am seeing a big difference. As for my antenna mounted on the ladder, I am getting 1.1:1 on channels 15 to 20. But I am going to have to buy a shorter antenna. The 3 foot Firestik Firefly with a spring mounted on the ladder near the top hits 13'8". That's 4 inches below the CA DMV max. I think I will be hitting too much stuff. I tried lowering the mount down about 10 inches and the match goes way off. The ladder is interfering with the signal. So to mount an antenna high enough to clear the ladder I will have to get a 2 foot.
Donee did you do anything yet?
|
|
|
SoCalDesertRider
SanDiego, CA, USA
Senior Member
Joined: 12/14/2003
View Profile
|
Max height is 13'6". You're only 2" over. The antenna will bend back in the wind as you go down the road so that 2" shouldn't be a problem. If you mount it closer to the driver side of the vehicle you'll avoid trimming overhanging trees with the antenna, since the trees are usually over the passenger side.
92F350 CrewCab 4x4 351/C6
LoadNGo service body
69Bronco ATC250R CR500
20' BigTex flatbed carhauler
B&W TurnoverBall g-neck Curt Magnum rr DrawTite ft
HD springs Rancho9000s Bilsteins poly sway bushings
285/75-16E BFG AT on 16x8 Stocktons
4.56's & Lock-Rite rear
|
DAS26miles
San Fernando Valley, California
Senior Member
Joined: 10/11/2003
View Profile
Offline
|
SoCalDesertRider -I went online to the CA DMV and found the max height allowed statewide is 13feet 6 inches. You're right! So I just readjusted the mount down a little and I am at 13 feet 5 inches. But I still think I should get a 2 footer, as it changed the match up a bit. I don't want to do any drilling on the side of the MH and since I have a good ground where I am, I'm staying with the ladder.
Also, I went to the other CB shop off the I-10 in Ontario. They were cheaper by $30.
|
time_to_go_now
La Mirada, CA
Senior Member
Joined: 03/10/2004
View Profile
|
Sounds like you found a good solution!
Good job!
Jim and Deanna
Tiffin Allegro 35QBA
2007 Carson Trailer 22' Titan TH
Trailer Toad
Me, Wife, Boy/10, Boy/7, Girl/5
Faith/Springer
1985 Toyota 4Runner
five quads, three kids, two motorcycles, one wife, one dog, one cat!
|
donee
Simi Valley, Ca. 93063
Senior Member
Joined: 03/05/2006
View Profile
Offline
|
Correct me if Im wrong, but did understand correctly that if you have to add coax, add it in 9' lengths?
|
DAS26miles
San Fernando Valley, California
Senior Member
Joined: 10/11/2003
View Profile
Offline
|
Donee-I have heard everything from 3, 6, 9, 12 and 18 feet. All from reliable sources. Firestik told me 12 and 18 feet. There is no way 18 feet of coax will reach a radio in a MH unless its mounted on the side. Like I mentioned before in my related topics, I had to add 12 feet to the reach from my ladder to my radio and my Minnie Wiinebago is only 22 feet long.
|
|
|
