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Author Topic: Mobile Ground Wave Expectations  (Read 445 times)
KO1D
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« on: February 10, 2008, 06:02:13 AM »

I have played a lot on 10 and 12 (even chicken band before I got license many moons ago) but not much else lower. Since we have an ulterior motive (isn't there always) we are curious to see what should work best over an area as small as a convoy to as large as 150 miles or so. Reason is our club does balloon hunts and we've been landing in areas with no repeaters and we get too far spread out for simplex.

I noticed in playing around with a buddy who uses the same antenna that during afternoon rush hour about 8 to 10 miles in a hilly urbanized area seems to be about it on 75m.

So as we play around what expectations should we have. I am not worried about DX on this. I DX all the time. Just mobile to mobile over short ground wave distances (under 250 miles).

Dan S
KO1D/4
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K0BG
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« Reply #1 on: February 10, 2008, 06:29:27 AM »

The biggest factor is the band conditions at the moment, and that's all but impossible to predict. Over a 150 mile path, 40 may be your best bet, and 10 minutes later, it'll be 80 meters. Further, as the sun spots increase, there will be times when 20 will be the band to use. At the peak of the cycle, even 10 meters might be the band of choice. In other words, there are no pat answer although a lot of folks think there is.

You're also going to get a few responses about bending over the whip to make a NVIS out of the antenna, but that idea is hogwash. The real formula is buy the best, make the overall length as long as you can, and install it the best way possible (it is the mass under the antenna, not along side that counts).

Alan, KØBG
www.k0bg.com
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KG4RUL
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« Reply #2 on: February 10, 2008, 01:06:35 PM »

"You're also going to get a few responses about bending over the whip to make a NVIS out of the antenna, but that idea is hogwash."

So you are saying that the large body of empirical data on NVIS is incorrect?
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WA8FOZ
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« Reply #3 on: February 10, 2008, 04:11:39 PM »

<<"You're also going to get a few responses about bending over the whip to make a NVIS out of the antenna, but that idea is hogwash."

So you are saying that the large body of empirical data on NVIS is incorrect?>>
 
NVIS is cool. But mobile HF antennas (at least below 10-12 m)are basically inefficient point radiators, and bending them will only further reduce their efficiency without changing the pattern a wit.
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K0BG
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« Reply #4 on: February 11, 2008, 06:15:16 AM »

Bill, that is EXACTLY what I'm saying. You see data like this all over the net, including one commercial site in Australia. It all stems from the same source. If you doubt the premise, then model an HF mobile antenna, and see for yourself.

The pattern is distorted, but the angle of radiation doesn't change much. In any case, the wave front is far from NVIS. In order to accomplish that (NVIS) requires a horizontal radiator and counterpoise.

Alan, KØBG
www.k0bg.com
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KL7AJ
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« Reply #5 on: February 15, 2008, 12:33:42 PM »

FOZ:

  What you say about the efficiency is true...but...a vertical whip has a perfect NULL off the top.  You aren't going to get ANY NVIS off a vertical whip, EXCEPT for the fact that your car body is probably radiating something.  Actually, if you bent your whip BACKWARDS you'd get more NVIS, AND more efficiency....at the expense of being a road hazard. Smiley

eric
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KF6RDN
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« Reply #6 on: February 20, 2008, 01:13:50 PM »

How about setting up a mobile repeater system & park it on a hill?
Not cheap but certainly consistent.  

The cheap version of that is you park someONE on a hill to relay messages.
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KO1D
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« Reply #7 on: February 20, 2008, 01:55:54 PM »

Path is too long and the topography and urban development nulls the idea out. I'd imagine a centrally located base station for relay might work.

Dan S
KO1D
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KE4SKY
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« Reply #8 on: February 25, 2008, 06:14:34 AM »

Dan,

2m SSB fed into a horizontal loop or Halo at 100-200w should get you reliable 100+ miles while mobile.  May be your best bet with HF bands being in the shape they are right now.  

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