[ARRL-OK] [ARES-OK] Near Vertical Incidence Skywave (NVIS) [1 Attachment]

[Kim Elmore]

5 miles is essentially line of sight/ground wave. NVIS operations are 
for distances that extend beyond line of sight/ground wave and would 
otherwise be within a skip zone. With true NVIS there is no skip zone, 
but propagation rarely extends beyond a couple of hundred miles. Also, 
the frequency must be below the critical frequncey (that frequency above 
which vertical radio waves simply exit the ionosphere). While during 
high sunspot numbers the critical frequency can be as high as 7 MHz in 
the day time, its typically lower, running anywhere from 2 to 5 MHz 
during the day and typically no more than 2-3 MHz at night.

73 & MX & HNY,

Kim N5OP

On 12/26/2013 11:28 AM, Jim KE5URF wrote:
> That's interesting and easy to follow. Thanks Mark.
>
>
> I have a friend lives less than 5 miles from me in Tulsa. We talked on 40m around 9:30 pm a week or so ago. My antenna is a G5RV about 25' up and he has a wire dipole in his attic. we both reported strong clear signals.
>
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> I just upgraded to general in Nov and have limited experience on HF so far. So I found it interesting that we were able to have such a solid contact so close together and hadn't thought about being able to contact simplex on HF bands.
>
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> Was that common or unusual?
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> Jim, KE5URF
>
>
> Jim Beach
> Saint Francis Tulsa Tough
> Operations Director
> Gran Fondo Maker
> 918.639.0362
>
> Sent from Mailbox for iPhone
>
> On Thu, Dec 26, 2013 at 8:46 AM, Mark Conklin <n7xyo at yahoo.com> wrote:
>
>> Attached you will find a interesting White Paper from DX Engineering
>> about building a NVIS type antenna.  Thanks Lloyd KC5FM & Ron KB5UVC for passing this along.
>>   
>> Near Vertical Incidence Skywave (NVIS) is a propagation mode which uses high angle radiation to send signals almost straight up to be reflected back to Earth for very effective short to medium distance communications. This mode of operation makes itideal for in-state communications during disasters or other emergency situations. The military has used NVIS techniques for decades to provide short haul communication with other units on the ground.
>>   
>> 73,
>>   
>> Mark Conklin, N7XYO
>> Oklahoma Section Emergency Coordinator
>> Amateur Radio Emergency Service
>> 918.232.8346
>> n7xyo at arrl.net
>> Follow me on Twitter @N7XYO
>> www.ARESOK.org
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