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Author Topic: Broadband 2m antenna?  (Read 1745 times)
KD7JNW
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Posts: 20




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« on: September 09, 2002, 08:10:25 PM »

I have, in addition to the normal complement of gear, a 2m commercial radio programmed for the local SAR and public service frequencies that our ARES/RACES group is authorized to use (when directed to, of course.)

To make this radio more usable (read: justify the investment) I also programmed in the ham band freqs that we use. However, the problem is that the 5/8 wave 2m antenna I have isn't broadband enough to use both the public service freqs (in the 151-155mhz range) and the 2m ham freqs and get acceptable SWR on both.

Is there an antenna solution out there? (I can live with 2 antennas and a switch if I have to, but would like to use a single antenna if at all possible.)

Homebrew is OK (and actually preferable...)
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KC8AXJ
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Posts: 303




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« Reply #1 on: September 10, 2002, 08:40:45 AM »

After I thought of this I realized your post was in the "Mobile" forum.

 Radio Shack has a "Discone"  ( # 20-043 )

http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&category%5Fname=CTLG%5F001%5F002%5F007%5F000&product%5Fid=20%2D043

Hope the link works for you, if not, basicly:

It has a WIDE receive 25-1300 mHz

and you can transmit on some VHF UHF Amateur bands.

As far as a Mobile, I can't help you there,other than you making a 2m 1/4 wave just for your amateur use.


73
Steve
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K0BG
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« Reply #2 on: September 10, 2002, 10:49:10 AM »

Antenna Specialists make a "Railroad" antenna. It basically is a large (±2") diameter tube about 10 or so inches long. At unity gain, it covers 144 thru 160 or so. It's butt ugly, but it works.

Alan, KØBG
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KE4SKY
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« Reply #3 on: September 10, 2002, 10:52:57 AM »

Two antennas I have used successfully in applications similar to yours are the Diamond D-130N discone and the Sirio GP160 wide band commercial antenna.  Both handle from FM air band through marine VHF and commercial high band.

My D-130N discone has survived numerous snow and ice storms and one Category 2 hurricane. It works well on 2m, 220 and 440 ham bands, but poor on 6 meters.

The Sirio GP160 is rugged, being designed for shore or afloat commercial marine applications.  It is a 10cm diameter cylinder 1/2 metre high, with 10mm diameter solid aluminum radials with a completely enclosed waterproof feedpoint.  It is excellent on 2 meters and VHF high band, and but is unusable below 138 MHz or above 174 MHz.
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WB2WIK
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« Reply #4 on: September 10, 2002, 01:30:30 PM »

I'd use a standard 2m 5/8-wave Larsen whip and cut it (tune it accurately) to 149.5 MHz, the midpoint between 144 and 155 MHz.  

My own Larsen 5/8-wave NMO-mount 2m whip has <2:1 VSWR from 142 to 150 MHz as it is, and it's tuned to 146.00 MHz.  That's an 8 MHz bandwidth for 2:1 points.  You should be able to achieve <2.5 over an 11 MHz spread, and that's perfectly satisfactory for the antenna to perform well.  My 70W mobile rig, a Yaesu FT-3000M, cuts back to about 50W output power under 2:1 VSWR conditions.  That's plenty of power to be heard, almost always.

WB2WIK/6
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KD7JNW
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« Reply #5 on: September 11, 2002, 08:06:29 PM »

Thanks to all who responded.

A bit of info: I've tried tuning your basic 5/8-wave for the midpoint of the bands. However, I'm a bit worried about the ability of the old GE Phoenix SX radio to handle that much of a mismatch. Therefore, I want something a bit "flatter".

The Sirio and the "Railroad" antenna are interesting - basically, they appear to be nothing more than "fat" 1/4-wave verticals. It would appear from the responses that the fat vertical has the same wide freq range that the fat dipole does - and that's a concept I'm familiar with!

(Besides, I think I'd have no problem homebrewing one...)

Thanks to all!
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KE4SKY
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« Reply #6 on: September 27, 2002, 09:01:32 AM »

Another "fat" broadband antenna which works VERY well is a simple copper J-pole made, but made of 1" pipe. This is much more rugged and has greater bandwidth than the common 1/2" pipe that most people use.
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AB0RE
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Posts: 293




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« Reply #7 on: October 05, 2002, 07:08:53 PM »

Assuming you are requesting info on a mobile antenna, here are some you may wish to look into:

-Antenex "Genesis" CW1443.  This 5/8 mobile antenna claims to have an operating range of 144-156MHz.  It has circuitry built into the antenna coil to make it more broadbanded.

-Antenex CW1320.  End fed 1/4 wave - 15.25" long.  Claims to have an operating range of 132-174MHz.

-Maxrad MWB-1320.  "Broadband" quarter wave antenna (w/ spring between coil and whip).  Claims to have a bandwidth of 24MHz.  I believe this antenna can be found for about $19 at R&L.

Wider antennas are usually more broadbanded than narrower ones.  Perhaps another idea would be to take a piece of 3/8" aluminum rod, trim it to the appropriate length, then use a tap&die set to put 3/8x24 threads on it and mount on a 3/8x24 (CB antenna-type) mount.  I picked up a 1/4 wave groundplane base antenna from Arrow Antenna - the radiating element was as described above and it is very broadbanded.

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