DoctorZ
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Posts posted by DoctorZ
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I actually have two (if you want to really get into the reasoning of why that particular antenna is installed where it is)…the other was on my Trailblazer, on the roof. One night I was coming down a dimly lit city street and hit the antenna a little more than half way up on a low hanging tree branch traveling roughly 15 MPH, which is frankly slow to me. By then, the damage was done. The antenna had actually pulled the NMO mount out of the roof of the vehicle.
Notice now, Comet sells a spring for that antenna. I guarantee you I'm not the first one who has pointed out to them (out of first hand experience) that the antenna they market as a Search and Rescue antenna, is way too stiff to be useful in a real Search and Rescue environment. They may have also been looking like they were facing several lawsuits.
Back to the antenna being on my Trailblazer. While it was on the roof, I actually took the time to hook the antenna up to an analyzer and the results I got, are what I quoted in my previous post.
Now back to where that antenna happens to be on my Jeep. I'm not sure if you've ever spent a lot of time in heavily wooded areas, especially driving vehicles through them, but you're always gonna hit antennas on something. After witnessing what happened to the roof of my daily driver, I carefully picked a mounting location that would both be sturdy enough for that antenna (until I found a different antenna solution that would suit my bandwidth needs). So I chose to sacrifice some signal to mount the antenna on something much more sturdy than the roof. I might also add, the only current use for that VHF 1/4 wave antenna on the roof of that Jeep, is for an APRS tracker I have in that Jeep.
Here is another interesting little tit bit to look at. A quarter wave antenna (VHF or UHF) cost roughly $5-12 (or I can even get a Larsen NMO150WB for $30). My wideband UHF knobs, $30. The last CA2x4SR I bought cost roughly $75. However, if roof mounted, the CA2x4SR can cost you several hundred dollars at a body shop if one was to hit the antenna on something in the right spot. For the other options, you'd be worrying about dragging the roof before you ever even considered the antennas doing damage to the roof from snagging on something.
That is the primary difference between commercial antennas and amateur antennas. Commercial antennas are designed to take a beating through a parking garage, in the woods, over rough terrain, even survive a roll over. You break a base, you can usually buy a base without buying a new antenna. You snap a whip, you can generally get another for less than $10. You just don't get that kind of quality out of an amateur antenna, and you definitely don't get that out of the 2x4SR.
I live in the woods, but trim my trees when the antennas start clipping them. I've also done a fair amount of four-wheeling, but take the antennas off for that. If I'm upside down, I can then put them on the undercarriage and call for help. LOL. I mainly use my radios for Storm Chasing and SkyWarn Spotting, hense I need a little bit of gain.
So where do you find a commercial equivlent to the 2x4SR?
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Here is a little diagram taken from a very old book I have called, "The Big Dummy's Guide To C.B. Radio." I realize that 11-meters is not the same as UHF 400Mhz, but the same principles still apply:
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The
I have one on my Jeep and had one on my Trailblazer. They work as advertised as far as bandwidth goes but that's really the only good thing I have to say about them. I've never noticed one outperforming a 1/4 wave antenna and they aren't built to what I would call commercial standards. In fact for a while I actually switched to a Austin 500C (highly recommend that antenna but UHF is only about 10 MHz wide...after consulting with Richard he didn't think he could build one with enough UHF bandwidth to cover both 70 cm and GMRS) an noticed no change, especially on the VHF bandwidth.
I don't see much of a point in DX'ing UHF FM. 10 miles simplex is more than adequate for me, especially for any simplex family road trip GMRS activities one might be doing. The only difference I've noticed between a common 5/8 over 5/8 and my little PCTEL knob is about 1/2 mile less repeater usage over flat terrain.
I just run a regular Larsen NMOQ for VHF on my DD. For UHF I run this.
http://www.hol4g.com/ac/product.aspx?number=MAX-BMLPV430&p=164550&sc=3566
My XJ currently has a CA2X4SR...it's okay. Working on moving over to the PCTEL and a NMO150WB where the Comet is. I may move the APRS tracker over to the 150 and then just run the Sti-Co quarter wave being used for ARPS for my VX-4000.
Most current pics I have of the Jeep (has a Larsen NMO-Q with spring instead of the Sti-Co).
http://i1245.photobucket.com/albums/gg586/zap_uh_lack/536357ED-81D3-4249-BA0A-D791BABD1506_zpszce0jkwz.jpg
http://i1245.photobucket.com/albums/gg586/zap_uh_lack/3eb1317a-26f5-4207-befd-ae5ed1640f7f_zps0c093522.jpg
I guess antenna preference is a matter of personal taste. I have tried Larsen monoband antennas because others swear by them, and they have been the WORST pieces of junk I've ever tried. No matter if you like them, that's great. I'm glad you're happy with them. I do question your testing techniques though, considering after close examination of your pictures, the Comet CA2x4SR seems to be buried down about half way below your roof line, while your precious 1/4 wave is mounted at the prime location top-center of your vehicle. Do you think it's a fair test to compare those two antennas this way?
Assuming the SWR is still within acceptable range being the radiating element is so close to all that metal, I'd say about 50% of your signal is getting absorbed by your vehicle's metal roof, not to mention the strange take-off angles your transmissions must make from the Comet.
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I am curious about the performance of that antenna would you please enlighten us with your experience using this antenna...William
First off, let me state that no wide banded antenna will perform as well as one cut for a specific frequency range. However, I find the performance of my CA2x4SR to be excellent! It even tunes up great on my favorite VHF band, 220Hhz, and it's not even rated for that band!
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I am using a 1/2 wave EM Wave # EMFLX-M10003-GPI antenna on one of our Chaplain Responder vehicles and we can't tell the difference between that one from EM Wave and a 5/8 PCTel Mosaic 5 db gain style. No ground plane required and this one is mounted at the side of the rear spoiler on a Ford Edge.
EM Wave Link >>> http://www.emwaveinc.com/PDF/02212013_New_Data_Install_Sheets/SS_VHF-UHF/Data_Sheets/EM-M10003-GPI_2dB.pdf
Well since we're showing off our antennas of choice, here's mine:
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Not entirely accurate. You don't have attach an antenna on a fiberglass body to the metal chassis, especially with above 136 MHz communications. There are options such as no ground plane antennas (half-wave, matched antenna) which offer Unity gain without a ground plane as well as ground plane kits for running ground plane dependent antenna.
Antenna placement on the roof of a vehicle isn't as important as most people think, as long as there is a quarter wave of ground plane (sheet metal) in all directions and you can get it as high as practically possible, you're golden.
From the OP's post I gathered that he/she wanted the maximum gain out of a mobile antenna. No antenna that isn't grounded to the vehicle's metal is going to meet that spec.
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Hello All,
General Antenna Question.
Vertical mounted antennas, such as on a vehicle.
I know there's a up side to a bigger antenna,
Is there a down side (other than the awkward physical size) of using a full wave length antenna versus using a quarter wave length antenna.
Thanks in advance for your help and patience.
A general question deserves a good general answer.....
In a nut shell, the antenna is only 1/2 of the system; the other half is the ground plane. In the case of your vehicle, it acts as the ground plane. Placement of your antenna on your vehicle will also affect your transmit and receive. If you mount the antenna on the rear of the vehicle, you will have a directional (or beam) system. Your transmit and receive will work better in the direction of the most metal, or in your vehicle's case, towards the front if mounted on the rear.
For the best all around performance, mount the antenna in the middle of the vehicle and make sure it has a good contact with the metal of your vehicle. Fiberglass bodies, vinyl tops, etc., will greatly reduce your antenna's performance not to mention possibly damage your transmitter. If you have a fiberglass body, you will need to drill through it to the frame or roll cage and attach it to there.
As for wavelengths, they say the best is a 5/8 wave, or a .64 wave if you can find or make one. 5/8 = .625. A full wave antenna tends to radiate most of it's signal up in the sky. At 5/8 you have the "flatest" take off angle of your signal, which in theory helps it cover the distance the best.
As for power, for every doubling of power you will gain 3dbs. Each number on your radio's S-Meter (if it has one) is 6dbs. So if you are giving someone 3 S-units on his radio's meter at 25W of transmit power, you will need to increase your transmit power to 100W to give him 4 S-units on his meter, given you don't change anything else.
With all that said, my best advice is for you to buy an antenna that is designed for the frequency band(s) you wish to talk on (450-470) for GMRS, and mount it as close to the center of your vehicle as you can, making sure it has good contact with the sheet metal of your vehicle's body. A good ground and matched SWR on your antenna system will do more for you than anything else.
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It's been a very long time since that tower was put up. The base is composed of a welded steel cage with rebar reinforcements cemented into a 4' x 4' x8' deep hole. The total cost of the tower was around $4,500 in 1992. That's about $40,000 now days!
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Here is a video I shot of CP Rail's Christmas Train pulling into the Union Depot in downtown St. Paul, MN, last Friday night:
https://www.youtube.com/watch?v=GSBSINSFs14&hd=1
Enjoy!
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Russell,
Welcome to the forum also.I would love to have a tower like that and I have a friend who fabricates and loves radio,if you would please send me a message with the info you have on this...Thanks William
Well I guess better late than never to reply to a post.
What would you like to know? What info can I give you on the tower? -
Check out my YouTube video of my custom built 80-foot Tip-Tower:
General Antenna Question
in General Discussion
Posted
You guys and your Larsen antennas......I guess whatever other type of antenna I buy, it wouldn't be a Larsen. Speaking of antennas, my new GMRS Repeater antenna came yesterday! I won't be able to put it into operation until Spring though. Too much snow on the ground right now.