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[aprssig] APRS buoy - transmit power and antenna?

Ray Wells vk2tv at exemail.com.au
Tue Sep 11 05:53:51 UTC 2007


Because of the high probability of the matching section of the J-pole 
radiating, the radiation from the matching section and that from the 
dipole portion will be out of phase, and this could result in the J-pole 
having a higher angle of radiation than a quarter wave (ground plane). 
If the quarter wave is just a whip, with no means to simulate the 
missing half, it's anybody's guess as to its angle of radiation. Since 
the buoy is bobbing about all over the place, does it really matter?

I'd opt for maximum antenna efficiency and use a suitably matched 
halfwave whip. These are sold as a ground plane independant antenna or GPI.

Ray vk2tv

Scott Miller wrote:

> Assuming you're in the open ocean and only care about hitting a 
> satellite, is the J-pole going to give you a suitable radiation 
> pattern?  Or would a 1/4 wave be better?
>
> Scott
> N1VG
>
> R. Simmons wrote:
>
>> You folks should consider wave height also... in calm seas, not a 
>> problem,
>> but heavy swells in a storm can easily render a buoy obscure ( in a 
>> trough )
>> and therefore "intermittant".
>>
>> ----- Original Message -----
>> From: "Steve Noskowicz" <noskosteve at yahoo.com>
>> To: "TAPR APRS Mailing List" <aprssig at lists.tapr.org>
>> Sent: Monday, September 10, 2007 9:07 PM
>> Subject: Re: [aprssig] APRS buoy - transmit power and antenna?
>>
>>
>>>  Oh, We noticed.
>>>    The attached "Line-of-Sight" spreadsheet agrees
>>> pretty close to the URL you posted.  It is not clear
>>> if that one has any diffraction correction.  I made
>>> this sheet in response to questions about UHF
>>> controlled UAVs my son is designing.
>>>     Looks like about 9-10 miles for a bouy to a 30'
>>> station...ignoring any ducting of course.  Would make
>>> an interesting experiment, though.  You might hit a
>>> satellite at times, but 300mw. sounds pretty thin.
>>>
>>> 73, Steve, K9DCI--- "Jan T. Pharo" <la2bba at jpharo.net>
>>> wrote:
>>>
>>>> "Richard Amirault" <ramirault at verizon.net>, Mon, 10
>>>> Sep 2007 15:23:06
>>>> -0400:
>>>>
>>>>> No one seems to have noticed my comment on limited
>>>>
>>>> distance of line of sight
>>>>
>>>>> due to curvature of the earth.[...snip...]
>>>>
>>>> In eyeheight from a small craft (where you stand
>>>> with the feet approximately at sea level) we learnt
>>>
>>> in my boating course that I'd have the horizon about 3
>>> nautical miles away (and the web site mentioned above
>>> tell me the same). It might be a good idea to build
>>> the buoy so the antenna is as high above the water
>>>
>>>> as possible, in order to increase the distance to
>>>
>>> the horizon (and possibly reach a digipeater on a
>>> tower ashore)
>>>
>>>> -- 
>>>> 73 de Jan, LA2BBA
>>>> Hvaler, Norway
>>>>
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>>>>
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>>>
>>>
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