Re: 1/4 Wave vs. 5/8 Wave Mobile Antennas for 2-Meter & 70-CM Usage?

Discussion in 'General Technical Questions and Answers' started by W2GLD, Apr 29, 2008.

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  1. W2GLD

    W2GLD QRZ Lifetime Member #191 Platinum Subscriber Life Member QRZ Page

    Re:

    Thank you all for your comments as they were all appreciated. I think, given my needs to the 1/4 wave antennas are probably the best bet. I did some stationary testing today on VHF with the 162.550 WX band on the receive side and in this area there was "ZERO" s-meter difference between the 5/8 wave Antenna Specialist Mosaic and the standard Motorola 1/4 wave antenna on receive. I realize that this is unscientific but it's just something I tried. I performed a simalar test on UHF using a distant EDACS trunked radio system control channel and actually found that the 1/4 wave standard Motorola was actually an s-meter bar or two better overall than that of the Antenna Specialist Mosaic 5/8 wave antenna, which I found very interesting.

    In any case, I guess one I get to Florida I will have to rerun the tests to see if there's a difference with the terrain.

    As for the gentleman who stated that 12" seperation was too close, it's a vehicle roof of an SUV and since I have three antenna (2-Meter, 70-CM, & 700/800MHz.), 12" was about the best I could do. The VHF is mounted with the largest ground plane area, then the UHF, and then the 700/800 at the very rear near the 2 GPS and satellite radio antennas.

    Thanks again all and if there are any more comments, please feel free to post!

    73...

    Jerry - K8GLD
     
  2. AD5MB

    AD5MB Ham Member QRZ Page

    QUOTE]Currently, I reside in Michigan .... In the coming months, I am relocating to the Southeastern Florida area [/QUOTE]

    He lives in Michigan in the winter and Florida in the summer...

    Are you from Hamtramck?

    ( Inside joke -Michigan folk will get it )

    There is no terrain in FL. There is no terrain in MI. Ergo, no difference. Pancake flat is pancake flat.
     
    Last edited: Apr 29, 2008
  3. K4AX

    K4AX XML Subscriber QRZ Page

    http://www.hamstick.com/9007.htm

    Anyone played around with a 2 Meter collinear antenna? I have one but I really have not had the time to mess with it.

    I bought it for the days I drive a lot for work and mostly on the highway. It is about 7 feet long or so, and the only way I currently have to mount it is a tri mag mount.

    I normally use a 1/4 wave on top of the cab of the truck and it works great.
    [FONT=Geneva, Arial, Helvetica, sans-serif][/FONT]
     
  4. WA2ZDY

    WA2ZDY Guest

    Here's the problem. An antenna should not have any metal objects in close proximity. For practical purposes that means within a quarter wavelength. Closer than that, as in your installation, the antenna willl interact with the other objects and that will cause tuning and radiation pattern troubles. This is why antennas side mounted on towers are ok, as long as they are properly installed. And note, an antenna for another band is just another hunk of metal to another antenna.

    So with this twelve inch spacing, your UHF antenna will be fine but the high band antenna is likely to be compromised.

    As for antennas, Florida is defintely flat; the highest point here is 345 feet. Of course repeaters are up high, so as above, your needs will depend on where YOU are in relation to most of the repeaters you use. Have you considered a collinear for UHF? 5dB gain (under ideal installation conditions) and shorter than the 2m 5/8.

    Commuting across flat central NJ, this installation worked well for me. The antennas were 21 inches apart. Quarter wave antennas would have worked just as well for me as the ground plane really should have been bigger for the gain antennas, but the antennas were already on hand.

    And whatever you do, use Larsen antennas. Best antenna for the money, widely used in Land Mobile (commercial/public safety) service, and I and several others here have 20-30 year old Larsens still in service.

    [​IMG]
     
  5. K0RGR

    K0RGR Premium Subscriber QRZ Page

    I think the answer is: it depends.

    I used to drive throughout the midwest a lot, and ran a high power mobile on 2 meters. The antennas were always trunk mounted.

    Hands-down, the winner was a homebrew 3/4 wave antenna made from an old Radio Shack CB mag-mount. Perhaps it worked so well because it was just a bit taller and more of it extended beyond the roof of the car. I don't know how, I just know that it worked better than the commercial 5/8 it replaced. Theoretically, the 3/4 should be a loser, but it depends on your installation, I think. Also, since it cost me $0 to make from the old CB antenna that somebody gave me, it looked good in the bank account.

    Half-wave antennas, including tall J-Poles make good mobiles, but survival is questionable.

    Hustler makes a very tall 2 meter mobile antenna that works very well - the CG-144. It's a 5/8 wave over a 1/4 wave. There is no substitute for capture area.
     
  6. KE6KA

    KE6KA Ham Member QRZ Page

    I've used both. I prefer the 5/8 wave.

    The 5/8 wave beats the 1/4 wave for simplex operation, in both flat, hilly and steep, and mountainous terrain.

    For repeater operation, you are seldom going to be so close to a repeater than the lobe of a 5/8 wave is going to go under it. Driving around California's varied topography, I really can't see where people think a 1/4 wave is better. I've been in areas where the repeater is 5000 feet above me, and 10 or so horizontal miles away from me with a mountain in the way. I can't say I've experienced any real problems that weren't expected with either antenna. In most cases the repeater sounds a bit choppy as I'm driving on the other side of the ridge, but the reflections from the terrain around me has kept me within reach of the repeater.

    My own opinion is a 1/4 wave is fine if you want a low-profile antenna around town, or are too cheap to buy a 5/8 wave, but a 5/8 wave is a noticeable improvement in the majority of situations.
     
  7. K8MHZ

    K8MHZ Ham Member QRZ Page

    My personal experience:

    Had a 5/8 wave antenna that I had to remove to get into the garage. Looked for and found the shortest 1/4 wave I could find so I could get into the garage without removing the antenna. Did side by side comparisons, both elements using the same mount (drilled into the roof of my Caravan). *NO* difference whatsoever.

    Hands down I will choose a 16 1/2" center loaded antenna over a 55" monster. The small antenna looks more like a cell phone antenna and works great. The large one looks like a CB antenna and works well, too, but needs much higher clearances. 55" may not matter much on the trunk of a Sundance, but it does matter on the roof of a Caravan.
     
  8. K8JD

    K8JD Ham Member QRZ Page

     
  9. K8JD

    K8JD Ham Member QRZ Page

    Yes, years ago when I was active on 2M, I operated a lot of simplex from my station wagon and I wanted all the range I could get. I ran a 140 W amp and a pre-amp in the radio.
    Since I still had a lot of trouble hearing some 10 watt stations I decided to go from a quarterwave to the biggest antenna that would go under bridges . I got a Hustler 5/8 wave over a quarter wave co-linear. I mounted it on the roof rack with 4 radials around the base.
    What a difference. I had a lot of stations who said I would be out of range soon but I talked to them for another 20-30 miles down the road. :eek:
     
  10. KD0ECN

    KD0ECN Ham Member QRZ Page

    If I might...

    If I might dredge up this old thread I found while searching and ask a question, I'd be grateful. I have a new 1/4 wave 2m/+70cm antenna that will be mouted in the center of my truck's roof; this truck has a roof rack mounted to it (thin walled steel tube & rod). Whether the rack itself is "well" grounded or not ins't known quite yet; I plan to run a flat ground strap to the mounting location under the headliner.

    The new antenna has a base spring, which is a necessity for the kind of backcountry driving I do (and use 2m whiile doing); my impression, looking at the antenna earlier (just bought it today) is that the radiating portion of the antenna begins just above the level of the flat steel roofrack.

    What might I expect in terms of issues (positive, negative, or just 'issues') might I expect from having the antenna base on the roof of the car be some 2" or below the level of the metal roofrack?

    TIA & 73,
    KD0ECN
     
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