Short Mobile Antenna

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  • #172
    KI6UGB
    Moderator

    (From Google Groups, started by Jim KJ6MRV)

    Folks,

    I need some advice. I’m looking for a mobile antenna for my Yaesu FT-2900.
    I have been using 38″ mag mounts and the antenna keeps hitting low trees. A
    19″ model would be better, but what will that do to my range? Any
    suggestions?

    Thanks,
    Jim Robison
    KJ6MRV

    Click here to Reply

    KZ6T Charlie
    9/22/13

    Hi Jim,

    I do have some experience with trees and antennas so here is my 2 cents.

    Before you make a change, what is your mag mount mounted to? Do you have enough ground plane area to support a 1/4 wave? In my current Jeep situation, my antenna mount is essentially on the end of a mast that has virtually no ground plane area. A 1/2 wave antenna works great there, but a 1/4 wave is almost useless. So before you make the change, make sure you have enough ground plane. 1/4 wave in every direction will give decent results.

    Are you still apt to hit branches with the 1/4 wave? If so, those short antennas don’t bend nearly as much as the longer ones. If using a rigid NMO mount you might end up bending some sheet metal as well.

    So back to your basic questions. I had very good luck with a Comet (now NGC) B-10 when it was mounted to the top of my van. Its quite short, only 12-inches but works as both a 2m and 70cm antenna. Thats the good part, the down side is there is virtually no gain to speak of, and it does need a ground plane. If I put it on my Jeep mount, its a little better than a dummy load. I think Doug KF6LMB is using the same on top of his pickup. When I had it mounted on the van, I could hit any repeater in this area. Santa Rosa to Vacaville and Novato with 50 watts. Not nearly as far as a 1/2 wave with gain. A 1/2 wave on the same mount will get me into the Palo Alto repeater from Santa Rosa using 50 watts.

    I do have a spare 1/4 wave mag mount that I won in the SCRA raffle that you are welcome to borrow as a comparison test between your 1/2 wave and a 1/4 wave before you go drilling any holes.

    Charlie… KZ6T

    jim_robison
    9/22/13

    Re: {SCRA} Re: Short mobile antenna

    Charlie,

    Thanks for the thinking points. I will be mounting it on my Volvo wagon, so I guess the ground plane is as big as most SUVs, though not as big as an American van. Thank you for the loan offer. I have a mag mount, I just don’t know what to stick in it.

    Jim
    – show quoted text –

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    Doug on Earthlink
    9/22/13

    Re: {SCRA} Re: Short mobile antenna

    Jim, not sure what Charlie said I had on my pickup, but it was one of those MFJ (mighty fine junk), antennas 1/4 wave. Cost used to be 29 bucks. I seem to have good luck luck with it. It stands about 18 inches tall. The only bad luck I had with it, was that I forgot to take it out when I went in the carwash. OOPS. An example of its use was above Nice on the hill. I contacted Charlie on the old English Hill antenna in Sebastopol with 60 watts. Same story contacting Mt Diablo, from up at Loon Lake 30 miles east of Georgetown, or 50 miles east of Auburn. This may be the loaner that Charlie has to loan to you. Good luck KF6LMB
    —– Original Message —–
    From: Jim Robison
    To: scra-us…@googlegroups.com
    – show quoted text –

    Bob
    9/23/13

    Re: {SCRA} Re: Short mobile antenna

    Hi Jim,
    Just a note of caution, I think that not all mag mounts will be tuned for all antennas, I believe they have a matching coil built into them to both couple to the ground plane and match the antenna. I think that for a proper match and best results be sure and use one that was designed for the antenna being used. (i.e. one designed for a 5/8 wave antenna will be different then one designed for a 1/4 wave etc.)

    Good Luck
    73,
    Bob KG6ZDN
    – show quoted text –

    n6…@arrl.net
    9/23/13

    Re: {SCRA} Re: Short mobile antenna

    Hi Bob,

    This might be the case if you are using a mag mount with a non-standard interface. This probably means the mag mount was intended to be no more than a part of a complete antenna system, not a separate product.

    But all mag mounts that I’ve seen that are sold as mag mounts and use standard interfaces such as SO-239 or NMO can acccommodate virtually any antenna with the proper connector.

    I have used NMO mounts on my vehicles (both permannent and mag mounts) and have freely interchanged between 5/8 wave and 1/4 wave antennas with no ill effects. I have 1/4 wave antennas on the permanent mounts since that allows me to put the vehicles in the garage. But if I know I’m going to be in an area where a little extra oomph will be welcome, I swap out the 1/4 wave antenna for the 5/8 wave (once I’m out of the garage, that is!).

    The 5/8 wave antennas I’ve used have their loading coil in their bases, between the NMO mount and the whip.

    73,
    Brian, N6IIY
    – show quoted text –
    – show quoted text –

    Joe K6AWA
    9/23/13

    Hi Jim,

    I’m a little late with a suggestion for a short mobile mag mount antenna, but here it goes:

    I have MP Antenna’s “Super M Classic” tri-band mobile mag mount. This is a very well built all stainless 2m/220/440
    ham band antenna that has an overall height of 19″ It handles 200 watts, and works especially good in town and in the hills
    due to it’s quasi-circular polarization. You can see it in Universal radio’s catalog, or online from other sellers

    Best,
    Joe K6AWA

    jim_robison
    9/25/13

    Thank you for all the great suggestions.

    I have decided to buy a Tram 1185. I like the short 19 inch height, the wide 3 inch base, and I especially like the $16 price. While researching this model, I discovered an interesting video on it at: http://youtu.be/hcrHvxHMYUU. When you’re done watching the antenna video, check out the cool Mendocino Rally videos at: http://youtu.be/OFeABN8fCeI and http://youtu.be/uvHZVnVBJQg.

    Thanks again,
    Jim
    KJ6MRV

    KE5RI
    9/25/13

    Re: {SCRA} Re: Short mobile antenna

    I am not sure you will be happy with it , Jim. Why? Because it has no gain on two meters and, I am only guessing here, you get what you pay for. There is little to be said for it on eham.net Personally, I would choose something else. No 19″ whip (1/4 wave) is going to give you gain. I am assuming that you are primarily interested in two meter operation.

    John
    KE5RI

    David Harrison
    9/25/13

    Re: {SCRA} Re: Short mobile antenna

    Hi Jim:

    I use a 19 inch whip on a NMO threaded mag mount on my SUV because it fits inside my garage. John is correct that the quarter wave antenna will not give you gain in excess of a quarter wavelength ground plane radiator. That may be entirely satisfactory for most purposes. When I need gain, I swap a longer half-wavelength antenna for the quarter wave ground plane, and get somewhat greater range. While you get what you pay for, what you pay for may be entirely adequate for your purposes.

    73, Dave W6IBC

    From: jrfk…@aol.com
    Sent: Wednesday, September 25, 2013 7:39 PM
    To: scra-us…@googlegroups.com
    Subject: Re: {SCRA} Re: Short mobile antenna

    – show quoted text –

    jim_robison
    9/26/13

    Re: {SCRA} Re: Short mobile antenna

    My theory is that I’ll get better results with a ¼ wave mounted on the roof than a ½ wave being dragged behind the car after it hit a low tree limb, or missing entirely after the whip got knocked out of the mount.

    Jim, KJ6MRV

    – show quoted text –

    KE5RI
    9/26/13

    Re: {SCRA} Re: Short mobile antenna

    Good point!

    John

    —–Original Message—–
    From: Jim Robison
    To: scra-user-group
    – show quoted text –

    Saraj KU6F
    9/26/13

    Re: {SCRA} Re: Short mobile antenna

    Hi All,

    Ditto to Jim Robinson’s remark. My Diamond NR770HAB mounted off the back of my Rav4 has survived all the oak trees and parking garages for 2+ years now. Better longevity than anything else I’ve used. It also has a fold over which is fine when I remember it.

    Saraj
    KU6F

    On Sep 26, 2013, at 9:47 AM, “Jim Robison” wrote:

    My theory is that I’ll get better results with a ¼ wave mounted on the roof than a ½ wave being dragged behind the car after it hit a low tree limb, or missing entirely after the whip got knocked out of the mount.

    Jim, KJ6MRV

    —– Original Message —–
    From: harr…@sonic.net
    To: scra-us…@googlegroups.com
    Sent: Wednesday, September 25, 2013 7:56 PM
    Subject: Re: {SCRA} Re: Short mobile antenna

    Hi Jim:

    I use a 19 inch whip on a NMO threaded mag mount on my SUV because it fits inside my garage. John is correct that the quarter wave antenna will not give you gain in excess of a quarter wavelength ground plane radiator. That may be entirely satisfactory for most purposes. When I need gain, I swap a longer half-wavelength antenna for the quarter wave ground plane, and get somewhat greater range. While you get what you pay for, what you pay for may be entirely adequate for your purposes.

    73, Dave W6IBC

    From: jrfk…@aol.com
    Sent: Wednesday, September 25, 2013 7:39 PM
    To: scra-us…@googlegroups.com
    Subject: Re: {SCRA} Re: Short mobile antenna

    I am not sure you will be happy with it , Jim. Why? Because it has no gain on two meters and, I am only guessing here, you get what you pay for. There is little to be said for it on eham.net Personally, I would choose something else. No 19″ whip (1/4 wave) is going to give you gain. I am assuming that you are primarily interested in two meter operation.

    John
    KE5RI

    —–Original Message—–
    From: Jim Robison
    To: scra-user-group
    Sent: Wed, Sep 25, 2013 11:30 am
    Subject: {SCRA} Re: Short mobile antenna

    Thank you for all the great suggestions.

    I have decided to buy a Tram 1185. I like the short 19 inch height, the wide 3 inch base, and I especially like the $16 price. While researching this model, I discovered an interesting video on it at: http://youtu.be/hcrHvxHMYUU. When you’re done watching the antenna video, check out the cool Mendocino Rally videos at: http://youtu.be/OFeABN8fCeI andhttp://youtu.be/uvHZVnVBJQg.

    Thanks again,
    Jim
    KJ6MRV

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