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Author Topic: Part 15 Stations - Antenna's  (Read 17579 times)

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NuroSlam

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Re: Part 15 Stations - Antenna's
« Reply #15 on: January 11, 2009, 11:20:56 AM »

It's 20 Watt.  I am thinking more of avoiding interference from buildings and terrain.  It is mostly flat around here.  The ground doesn't vary more than about 100 feet in elevation over the area I trying to cover.  It mostly increases gradually as I go south.
It sounds like a 5/8 is a good choice.

5/8 is a good chioce, but what about setting up three poles in a triangular configuration, then run antenna wire between all three, that way your skip distance is shorter, also a good question is how are you grounding your antennas?

are you talking about a NVIS antenna?



heres a photo of a homebrew version of the military AS-2259 NVIS Antenna

http://home.centurytel.net/w9wis/nvisb.jpg
« Last Edit: January 11, 2009, 11:34:54 AM by NuroSlam »
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sinceredagreat

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Re: Part 15 Stations - Antenna's
« Reply #16 on: January 11, 2009, 11:58:29 AM »

It's 20 Watt.  I am thinking more of avoiding interference from buildings and terrain.  It is mostly flat around here.  The ground doesn't vary more than about 100 feet in elevation over the area I trying to cover.  It mostly increases gradually as I go south.
It sounds like a 5/8 is a good choice.

5/8 is a good chioce, but what about setting up three poles in a triangular configuration, then run antenna wire between all three, that way your skip distance is shorter, also a good question is how are you grounding your antennas?

are you talking about a NVIS antenna?



heres a photo of a homebrew version of the military AS-2259 NVIS Antenna

http://home.centurytel.net/w9wis/nvisb.jpg

Exactly that, BUT, with some field changes we experimented with in Iraq.
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NuroSlam

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Re: Part 15 Stations - Antenna's
« Reply #17 on: January 11, 2009, 01:31:12 PM »

It's 20 Watt.  I am thinking more of avoiding interference from buildings and terrain.  It is mostly flat around here.  The ground doesn't vary more than about 100 feet in elevation over the area I trying to cover.  It mostly increases gradually as I go south.
It sounds like a 5/8 is a good choice.

5/8 is a good chioce, but what about setting up three poles in a triangular configuration, then run antenna wire between all three, that way your skip distance is shorter, also a good question is how are you grounding your antennas?

are you talking about a NVIS antenna?



heres a photo of a homebrew version of the military AS-2259 NVIS Antenna

http://home.centurytel.net/w9wis/nvisb.jpg

Exactly that, BUT, with some field changes we experimented with in Iraq.

I would like to know about these changes myself
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KDus

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Re: Part 15 Stations - Antenna's
« Reply #18 on: January 11, 2009, 04:52:56 PM »

Most FM antennas are vertically polarized. You can lose up to 20dB by going horizontal, thus cross polarizing the TX and RX. AM is far more forgiving of polarization. I've heard of great results on AM by tuning into the rain gutter of a dormitory.

Part 15 limits are ERP. If you want to be legal, use up to 100mW and don't exceed about 20 micro Volts/m; at 30 meters.


WRONG!!!!!!!!!
while this post relates to a specific transmitter, the data is the same regardless when using a part 15 am transmitter
Quote
A center loaded 10 foot radiator may also be used. This involves splitting the radiator into two sections and adding an inductance to bring the radiator to resonance at the desired frequency. Approximately enough inductance is needed to resonate with the self capacitance of the top whip antenna. For 1600 kHz this will be on the order of 400 to 1000 microhenries, depending on whip length and diameter, as well as exact frequency. A good RF ground system is required, and antenna bandwidth of 10 kHz is typical. Radiation resistances of 0.1 to 0.3 ohms are typical, and the radiation efficiency of a system such as this will be a few percent at best, assuming ideal grounding, and 0.5 % for the typical home experimenter setup. However, experience at 1880 kHz with 160 meter Amateur mobile operation, using 10 watts AM and a center loaded 8 foot whip mounted on an automobile, shows that 2 way contacts at 50 to 100 km (30 to 60 miles) are possible and fairly common. Extrapolating this data based on theory, with 100 mW, (20 db below 10 Watts) therefore, ranges of 5 to 10 km. (3 to 6 miles) would seem possible without violating FCC rules. However, noise and interference will be the main limitation. Its all in the location and antenna system, and how well everything is tuned and matched.

http://www.northcountryradio.com/Articles/part15.htm
WRONG!!!!!!!!!!!!!
YOU GET 20 micro Volts at 30 meters. PERIOD.  Reception will depend on the sensitivity of the receiver!
FURTHERMORE, the author is off by a factor of 10. In his theory, he should expect .5 to 1 km with .1 W. Propagation with AM isn't that predictable, so it doesn't matter.
If you're not trying to be legal, use as much power as you want into the best antenna you can get: to accomplish your goal.
« Last Edit: January 11, 2009, 06:23:32 PM by KDus »
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NuroSlam

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Re: Part 15 Stations - Antenna's
« Reply #19 on: January 11, 2009, 10:24:11 PM »

WRONG!!!!!!!!!

WRONG!!!!!!!!!!!!!

MY bad, i didn't even think to check the facts from the manufacturer
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KDus

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Re: Part 15 Stations - Antenna's
« Reply #20 on: January 25, 2009, 08:49:22 PM »

I need to correct myself. It looks like I've been using a "Slim-Jim" antenna. It radiates like a 5/8. It is a 1/2 wave, end fed, using a tuning stub. I found a drawing similar to the one I used to build it.
http://www.i1wqrlinkradio.com/antype/ch24/chiave285.htm
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KDus

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Re: Part 15 Stations - Antenna's
« Reply #21 on: February 22, 2009, 01:51:03 PM »

http://www.qsl.net/ve2dbe/
There it is. FREE software to draw RF radiation patterns. It is way overkill but it works. The map it drew for me is very similar to the one I made by driving around with a map and making notes.
It took me a couple hours to figure it out.
The tricks are:
Use the installer program.
Let the software gather data from the internet.
Setup at least 2 "units"
Save as a new picture when you add maps or contours
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KDus

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Re: Part 15 Stations - Antenna's
« Reply #22 on: June 10, 2009, 08:28:28 PM »

http://bfn.org/~bn589/antenna.html

http://www.csgnetwork.com/antennae3ycalc.html

Since my antenna is hanging in the garage, I was able to simply hang wires near it to direct the signal. It made an obvious difference in my pattern and makes better use of the little bit of power that I dare to run.

Looking out over the valley from my back yard, I see lots of ham and TV antennas.
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KDus

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Re: Part 15 Stations - Antenna's
« Reply #23 on: June 29, 2010, 08:02:48 PM »

For years, I've been using a folded 5/8 for broadcast. I found the dimentions on a ham/ pirate site that was also showing dimentions for a 2 meter J-pole. When I dig up the plans, I'll post them on libertyactivism. The folded 5/8 has no ground radials and has more gain than any 1/4 wave. It costs about $10 to make and is really just a 7 foot legnth of PVC with a wire in it.

I'm working on a new version that will be easier to adjust and more robust. I've had problems with the solder joints.
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KDus

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Re: Part 15 Stations - Antenna's
« Reply #24 on: August 01, 2010, 04:18:59 PM »

For years, I've been using a folded 5/8 for broadcast. I found the dimentions on a ham/ pirate site that was also showing dimentions for a 2 meter J-pole. When I dig up the plans, I'll post them on libertyactivism. The folded 5/8 has no ground radials and has more gain than any 1/4 wave. It costs about $10 to make and is really just a 7 foot legnth of PVC with a wire in it.

I'm working on a new version that will be easier to adjust and more robust. I've had problems with the solder joints.
Photos of the improvement can be seen in the pirate radio section of libertyactivism.info  I put the tuning section in a plastic, weatherproof, electrical box and miounted the connector so that it doesn't feel the weight of the antenna during assembly.
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