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Author Topic: 2 meter distance in miles  (Read 889 times)
KI4DRA
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Posts: 19




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« on: January 22, 2004, 07:13:59 PM »

Hi everybody,

I'm new to HAM, and recently bought a new HT with 5/8 wavelength mag mount for 2 meters to increase reception and transmission. I love the way it works with repeaters. I have no problems reaching repeaters up to 30 miles away with my rubber antenna, and I'm sure I could work some even farther away with my magnet mount.

But what if I want to use Simplex instead of the repeater system? I want to buy a couple bricks and mount them inside my cars so that my wife and I can have simplex conversations within the greater Nashville area. So, we are talking about distances of less than 30 miles, and probably within 20 most of the time.

What kind of power do I need to give me good quality communications on simplex for up to 30 miles? Can it be done reasonably?


Thanks in advance,

David Campeau
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K5LXP
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« Reply #1 on: January 22, 2004, 07:36:03 PM »

The reason why repeaters work so well is they are located in a place high and in the clear, such as a tall building, tower or mountaintop.  But no amount of power or antenna gain will make up for lack of good antenna location.  VHF is line of sight, meaning once the two communicating stations get far enough away from each other, obstructions and the curvature of the earth will block the signal.  The only fix for this is for one or both of the stations to elevate their antennas.  Since in the example you cite the antennas will be fixed on the vehicles, the line of sight distance between them will be fairly short, probably 8-10 miles will be about it.  However, depending on where you live, you may find "hot spots" where communications is possible.  Putting the car on a 100ft hill is as good as having a 100ft tower as far as what you're doing is concerned.  Bottom line is that there's no way to really know for sure how well it will work until you try it, depends a lot on your terrain.

Mark K5LXP
Albuquerque, NM
k5lxp@arrl.net

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K0BG
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« Reply #2 on: January 22, 2004, 07:36:59 PM »

In the business reality world, there are three very important rules to follow. They are: Location, location, location.

This is true of amateur radio too. Depending on the local terrain, all the power in the world might not get you the 30 miles you're looking for. And then again just 100 milliwatts may be enough.

More important than power is the antenna. If you want maximum performance, DO NOT use a mag mount. The center of the roof is best, the center of the trunk is second best. Gain isn't as important as most folks think as most of the gain figures are bogus anyway. You do, after all, need to know what the gain is measured against. In other words, a 1/4 wave has a lot of gain compaired to a dummy load.

Other factors are the rigs sensitivity, local electrical noise, HAAT (height above average terrain), and maybe a few more.

Your last resort is to pay your dues and support one of the local repeater groups.

Alan, KØBG
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WB2WIK
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« Reply #3 on: January 22, 2004, 08:09:34 PM »

I'll add a couple of comments:

-An HT, unless it's a very "special" HT (maybe a commercial unit, Motorola, etc), usually won't work as well as a "real" mobile rig, no matter how many amplifiers you add to it.  Reason: It isn't power output, but ability to receive weak signals in the presence of stronger adjacent interference, that makes or breaks VHF 2-way mobile working range.  And HT's, for the most part, have highly sensitive receivers that aren't nearly as good as single-band mobile rigs because they lack front end selectivity.  This is a case of having "too much" sensitivity for their own good, and no way to turn it down.

-A 5/8-wave mag mount in the center of the roof is actually a darned good 2m antenna; my Larsen mag mount base with the NMO150 5/8-wave whip/coil, stuck to the center of my station wagon roof, works exactly as well as the same whip/coil screwed onto my permanent through-hole mount, which is also near the center of my roof.  I can't tell the difference, at all.  However, the Larsen is a particularly good antenna, and the drawbacks to a "mag mount" are many, including that they're much more likely to be stolen or damaged, and they're much more likely to damage your car!

-Using a single-band 2m FM transceiver with a 5/8-wave whip on my roof, running 70W output power and an excellent receiver (Yaesu FT3000M, single band rig that has an awesome receiver -- very immune to overload and intermod), I get 30 mile car-to-car working range all the time, driving around the L.A. metro area, which is hillier than Nashville.  I'd expect to do at least as well in Nashville, if I were there, providing the "other" car has the same setup as I do.

WB2WIK/6
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AA4PB
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« Reply #4 on: January 22, 2004, 08:53:22 PM »

Well, if you do the calculations you find that with an antenna height of 6-feet, the radio horizon is only 6 miles away. That means if both cars have an antenna height of 6-feet and they are located on flat ground with no obstructions between them then they have a line-of-sight distance of 12-miles. With reflections you may sometimes be able to get farther than that. On the other hand, if you have any signal blockage then the range could be much shorter. Of course if one or both of the cars is located on high ground then the distance can go up considerably. As a general rule I'd expect 10 to 15 miles most of the time with fairly easy to copy signals. That's about what I experience in practice here on the East coast.

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KE4SKY
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« Reply #5 on: January 23, 2004, 10:01:48 AM »

If you are an uncoded tech with no access to HF, WB2WIK's advice to get a fully featured mobile rig and to place a 5/8 wave antenna centered on the vehicle roof is the best bet.  A higher gain antenna such as a 2x5/8 collinear isn't "necessarily" going to get you better mobile range, except in flat open terrain.

This is because if you are driving in rolling hills, around mountains or urban concrete canyons, its lower radiation pattern is down on the horizon and doesn't get up and around obstructions as well.  The main lobe of its radiation pattern is also shifting above and below the horizon  as the antenna whips in the wind going down the highway.  A 5/8 wave provides about 3dB gain with a good ground plane and a "fatter" radiation pattern which is the best compromise for most mobile use.  

If you commute in an urban area and must park in indoor garages with low overhead clearance, a  quarterwave with a good ground plane, centered in the vehicle roof, works very well. Most people will not notice any practical difference in performance compared to a half or 5/8 wave, although the arguements pro and con proliferate.  A 2m quarterwave whip also works quite acceptably on 440 FM for local repeater work.  I carry an extra 1/4 wave whip in my vehicle as a spare emergency antenna and loaner.

But if you want the best mobile-to-mobile simplex, you really should consider 2 meters SSB.  Even with your vertical 5/8 whip you should be able to work other mobile stations within 50 miles or so, and fixed stations with good antennas to about 100 miles or more, if you have a clear line-of-sight path.  

I once had a 1987 Cadillac with a squalo on a 39" mast rigidly mounted on the rear trunk lid, which placed the plane of the horizontal loop about a 1/4 wave above the vehicle roof.  This gave very good results on SSB, making many contacts over 100 miles, barefoot with 25w. I also had a 5/8 wave Larson whip on the other side of the trunk, with an A/B switch on the floor console, and I really had a ball. It was the most fun I ever had on the radio operating mobile until I upgraded to General and discovered 40 meters... and more recently 60 meters!  
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KI4DRA
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Posts: 19




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« Reply #6 on: January 26, 2004, 12:11:20 PM »

Thanks for your assistance guys. If anyone else has anything to say on the subject of 2 meter propagation please jump on in.

From what I have read it's really hard to determine exactly what kind of distances I can expect from my mobile. But I have learned a lot with what I've read.
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N4PGW
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« Reply #7 on: February 04, 2004, 02:54:11 AM »

Having operated mobile simplex for a number of years, I can tell you that unless one partner is on a hill, you cannot expect to get 30 miles with your rigs.  If you are both on the desert running 100 watts mobile with good antennas and no obstructions, you might get lucky, but I wouldn't count on it.  

40 or 75 meters will probably be better suited for your direct communications needs.  Either that or plan to keep a repeater directory with you.  

Line of site for hand-helds is typically defined as 2 miles, but with hills and high power, it might be 5 or 6.  A mobile is going to range from 6 to 12 typically but all of that will be dependant on location and obstructions.  

Early morning on the east coast, I noticed a distinct increase of distance covered by 2 meters.  However, this quickly dissipates as the sun rises to its peak.  During this time, you might get the range you want but don't expect the same range on your way back home.

Good luck

Buck
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