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Author Topic: Antenna Help  (Read 1229 times)
KI4CYB
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Posts: 47




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« on: April 21, 2006, 05:39:22 AM »

Hello guys/Gals..   I was wondering if you guys can provide some input and help save me some money also..

Here is the scoop, I have 3 friends of mine that their kids have been somewhat interested in HAM radio, but they are young (ages 11 -13) After talking to my friends about my plans they are super cool with it..

They are the typical kids playing with those cheaply GRMS type radios and can only play with the radios when they are together...

My plan:  I have allot of old ham equipment (hehe what ham doesn't)  I was thinking of lending them and help them setup a simple setup using some old commercial radios type accepted for MURS operation (2w max).. I also have good coax I can use...  But my question is antenna selection?   Keep in mind, this is all out of my pocket so I need to keep costs down to keep XYL happy... Smiley

The parents will allow attaching a 15ft tv mast and vertical antenna...    

What vertical antennas can accomplish communication amongst these fellows?  Assume 10 miles as the crow flies (max distance) 9.1 miles is the max between 2 kids houses.. the others are shorter distances..

Building an antenna should be saved for when they get exited and start studying for HAM test.. Im just trying to spark their interest so they can take it to the next level...

I have everything except antennas...  I was thinking about those cheap 5/8 wave verticals that sell for 25 bucks or so, but will this be enough?  

The MURS rules state, radios must be type accepted
(narrow band) and 2 watts max...  No limit on antenna gain, and anntenna hight is not an issue (5 ft or so above roofline)


The last thing I want to do is buy some cheap antennas and realize it doesn't work or work well...

We are in Miami, Florida so its FLAT...   Within the grid of the kids QTH, the tallest objects are 2 story houses here and there..  No buildings.. Trees are 2 story high, approx...


Your Inputs welcomed...

Joe/KI4CYB
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KE4SKY
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Posts: 1045


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« Reply #1 on: April 21, 2006, 06:21:21 AM »

Ten miles on VHF simplex with 2 watts in flat terrain using commercial communications gear could be difficult with a 5/8 wave omni.  Typical range for Marine VHF handhelds in this RF output ranges, used  between pleasure boats down on the water is about 3 nautical miles (6 km), and increasing RF output to 25w and using a 5 dB antenna up on the mast 30 ft. above the waterline may get you ten miles in good conditions.  

Better would be to use a 3-4 element yagi if limited to this power level.  One roblem may be in the limited sensitivity of commercial rigs you are using, as they wouldn't hear as well as a ham rig with the squelch opened up.

If limited to low power power operation, at least be sure the antenna is resonant at your working frequency and get it up high, at least 30 feet, and use decent coax, something better than RG8X.

   
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N4CR
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Posts: 1694




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« Reply #2 on: April 21, 2006, 06:23:44 AM »

Copper J-Poles are sturdy, cheap, easy to make and have a little gain over a 1/4 ground plane.

Usually less than $15 per, depending on what you have in your junk box, like SO-239 connectors. Takes about an hour to build.
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73 de N4CR, Phil

Never believe an atom. They make up everything.
KI4CYB
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Posts: 47




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« Reply #3 on: April 21, 2006, 06:40:18 AM »

I thought about the Yagi but an omni would be a better choice so all kids can d othe round table thing...


I think I will need more than a J-pole and/or 1/4 wave...    


bummer... I was hoping I can pull this off...
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KI4CYB
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Posts: 47




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« Reply #4 on: April 21, 2006, 06:55:12 AM »

The radios are not hand held units but actually mobile radios...
 
For a fact, I will be using low loss coax, short runs...

I dont want to freak out my friends suggesting I need to install a 30 foot mast...

Maybe better antennas (more money) are in order...  But what antenna?
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WB2WIK
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« Reply #5 on: April 21, 2006, 08:26:17 AM »

I've achieve distances of way over 10 miles with MURS and a home station antenna, lots of times, using a 2W rig and my 2m home station omnidirectional vertical (unmodified, and not re-tuned for MURS).  My antenna is a vertical colinear array of stacked 5/8 WL over 5/8 WL radiators up about 40' and fed with 1/2" hardline.

The *problem* with MURS isn't so much finding the range, but finding a clear frequency.  Once you add an external antenna, especially a decent, high one with any gain and any horizon, you start hearing an awful lot of stuff.  There's only five channels, and they're saturated.

Of course, my experience goes back a few years and maybe it's not like that, today.  But when I plugged in my largish 2m antenna, all five channels were full of activity and it was difficult to distinguish a desired signal.

The big benefit of ham radio is we have unlimited "channels" available...

WB2WIK/6
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K7PEH
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Posts: 1124




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« Reply #6 on: April 21, 2006, 09:30:09 AM »

I think you should take a different approach.  Get with the parents of these kids to make a deal.  The deal being that you will tutor the kids to pass the Technician exam and if the kids pass, the parents will reward their child by the purchase of a new 2-meter HT.  Good ones can be had for $100 to $150 and I really do not think this amount of money is out of line for most people.

Just don't tell the parents though that the $100 or so investment in a HT is not all there is.  Next is the base station, the antenna, and so on.  And, horrors if the kid ever passes their 5 wpm CW to earn HF privileges and enter the world of the big-money ham radio hobby.
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KI4CYB
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Posts: 47




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« Reply #7 on: April 21, 2006, 09:53:49 AM »

WB2WIK:
   Before all this I was monitoring to see how much activity was in the air...  And in the 151Mhz channels.. None...  And the "DOT" 154's I hear business one in a while..  And I was using a colinear 17 foot vertical siting on top of my tower.. The bottom of vertical sits approx 55 feet up in the air...


K7PEH:
  Cant do that because my friends already know how much all the equipment is.. Because of all my gear, they are fully aware costs..  Smiley

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KG6MRI
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Posts: 6




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« Reply #8 on: April 21, 2006, 11:42:25 AM »

102" CB whips are cheap. I'm sure you have equipment and could trim an' tune 'em. If nothin' works, you could teach 'em traffic handling and let 'em relay to each other.

Just a thought.
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K0IZ
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Posts: 739




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« Reply #9 on: April 21, 2006, 11:46:46 AM »

Maybe I'm wrong, but I thought MRS required a $75 license?
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N3UMH
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Posts: 153




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« Reply #10 on: April 21, 2006, 11:51:53 AM »

Antennas are still an area in ham radio where most of the cost can still be effort.

They're my bastion of straightforward homebrew, since there's no way I could knock together a tenth of the radio of my FT-857 or TS-440 in a weekend, but I can build beams with $20 and a run to home depot.

I think you should build a pair of 1/4 wavelength ground planes out of wire and SO-239's; basically the cost of SO-239's.  

So as to not disappoint the kids or lose their interest, you want something that will work the first time, so run some tests with the ground planes at 15 feet; pick a few locations 10-15 miles out and put up a temporary mast while talking to someone with a like-equipped companion station.

If the signals are marginal and you feel you need more gain at this point, you can  go for it.  I'd still stick with homebrew.  I'll get back to you on this; I think I can make a 5/8 over 5/8 collinear out of Home Depot stock for $15 or so... I've got to think about it; I always forget how much hardware can add up to if you're not thinking about it.

If you run some tests, you can be more certain that the kids will be able to turn on the radios and talk to each other.  If you build antennas, it will be cheaper.

Too bad MURS isn't BELOW 2m; harder to modify the antennas when the ham tickets come in...

73,
Dan
N3OX
www.n3ox.net
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AA4PB
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Posts: 12985




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« Reply #11 on: April 21, 2006, 12:07:45 PM »

Well, the calculated line of sight distance between two antennas 15-feet above ground is 10 miles. That is on flat ground with nothing to block the signals. Given the typical residential neighborhood there are likely to be houses, trees, etc blocking the path. Now if you could put the 15-foot masts up on the roofs then you might have a chance.

To be legal, there is a $75 per year fee for the license. A license is only good for members of a family so if these kids are all from different families then it is $75 per year per kid.
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AA4PB
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« Reply #12 on: April 21, 2006, 12:18:26 PM »

Scratch the last - MURS does not require a license. I was thinking GMRS.
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N3UMH
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Posts: 153




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« Reply #13 on: April 21, 2006, 01:01:42 PM »

Right, the earth has curvature...

Just ran the numbers for myself... 10 miles... huh.

So I guess squeezing as much power down to your radio horizon as you can is really called for if the companion station's antenna is right at the horizon.  

I just ran some calculations on a recent pair of VHF/UHF SSB QSO's with K4SO out in VA.  He's got a big beam at 105' and about 300' ASL elevation.  I was running a halo at 28' and about 70' ASL.  The LOS distance for this comes out just under the distance between he and I, and there was certainly a lot of QSB, so forth.  

I guess 6m diffracts a lot more.  I hear Al, K3TKJ on 6 all the time, and he's about 80 miles out.  Running LOS calculations (and his elevation ASL is about 30 feet) figures he needs to have his 6m antennas at 2000 feet above ground!

What's the correction to LOS for diffraction at a given frequency?

Dan
N3OX
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AA4PB
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« Reply #14 on: April 21, 2006, 01:25:05 PM »

On 6M you can get scattering that will get you maximum ranges out to several hundred miles. The key there is to run enough power to get enough scattered signal back. I doubt that you will do that with 2 watts and omni antennas.
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