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using a vhf 1/4 wave antenna for dual band

Discussion in 'Mobile Radio Systems' started by WB7OXP, May 5, 2016.

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  1. WB7OXP

    WB7OXP Ham Member Volunteer Moderator Volunteer DX Helper QRZ Page

    i was asked to antenna a side by side for off road racing. there is a good chance the rig will get rolled, so 1/4 waves and other "simple" antennas are a good idea.

    i was reading some discussion about using a 1/4 wave vhf antenna would give a 3/4 wave antenna on uhf, and works "ok".


  2. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    It will. Far too many suggest that it won't work well due to the radiation angles. Well, I guess they don't know how to model one with EZNEC. The angles aren't nearly as messed up as they would lead you to believe.
  3. WB7OXP

    WB7OXP Ham Member Volunteer Moderator Volunteer DX Helper QRZ Page

    from "the man" himself!

    alan, thanx for the answer. i looked on your site hoping that it had already been asked. then i did some quick "math" and was frightened to think it "could be that easy".

    i know it wont be "wonderful", like a zillion dollar multi band, but those things are way more "fragile" then a stinger and a nmo mount. another stinger in the tool box is nothing.

    i gather you have exnec'd this, will the swr be "ok" at least not bad enough to "roll back" too hard? i am thinking of a simple 1/4 wave stinger
  4. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    Close enough.Most V/UHF transceivers are a bit more tolerant of moderate SWR than most HF ones. Except for a bit more loss in the feed line, 2:1 isn't anything to worry about.
    KD5BVX and WB7OXP like this.
  5. AG6QR

    AG6QR Subscriber QRZ Page

    The pattern has lobes, and nulls between the lobes, so it's less than optimum. It doesn't put out as much radiation toward the horizon as an antenna which is designed for UHF would put out. The SWR should be OK, though, since the 440 MHz is the third harmonic of 147 MHz.

    But often, for UHF, antennas don't need to be perfect. The path is often more important than the antenna, at least within reasonable limits. If you can see the other guy, or nearly so, it'll work, and if he's much over the horizon or blocked behind terrain, it probably won't work.
  6. W8JX

    W8JX Ham Member QRZ Page

    You are wrong on this one based on ACTUAL USAGE not EZNEC. The performance is consideriably inferior to a standard 1/4 wave 440 antenna. Some sit back and tell you it will work when they never really compared it in field. I have and a 3/4 wave on 440 is little more than dummy load and a good HT with a duck will out perform it. I was amazed how bad it did. Several S-units.
  7. KD5BVX

    KD5BVX Subscriber QRZ Page

    Agreed! And also based on experience, not anything else. ;) [Despite what another ham would have you believe.]
  8. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    John, if you are so good with EZNEC, send me the plot.
    KD5BVX likes this.
  9. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page


    I beg to disagree with you! Having had over 50-years associated with the commercial two-way radio arena in one way or another (from being a two-way technician in college to owning the Motorola reconditioned equipment center for the south-central United States for almost 10-years to being a consultant for over 25-years) I have, on numerous occasions, run into conditions where a 3/4th wavelength antenna worked considerably better than a quarter-wave antenna in certain areas and, for all practical purposes, about as well as the quarter-wave antenna in the remainder of the area covered.

    In urban areas, for a 450 MHz mobile, the 3/4ths wave antenna will outperform a quarter-wave antenna the majority of the time. The different radiation angles of the 3/4ths wave antenna usually "fill in" areas that are dead spots with the quarter-wave antennas and produce a stronger signal in other areas. This is especially true where the base station / repeater is located on a tall building in the center of the coverage area rather than being located a considerable distance from the coverage area.

    In areas farther away from the base station / repeater, is is often a "toss up" as to which antenna has the slight "edge".

    These observations are not "theory" nor are they pulled from my posterior! They are the result of many years of practical experience!

    Glen, K9STH
    NL7W, N3AB, AI3V and 3 others like this.
  10. N8EKT

    N8EKT Ham Member QRZ Page

    Actually a commercial whip length of 18inches works much better on the 440 ham band but in either case it will be a very poor performer on 440

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