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LRN.FM - The Liberty Radio Network => Free Radio Forum => Topic started by: NuroSlam on December 20, 2008, 12:56:07 PM
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Heres a little bit of info on vertical antennas for anyone wanting to put up a "Part 15" station
--insert--
"I found out "why not" the hard way. After assembling and mounting my vertical, I put it on the air and was underwhelmed by its performance. So I began educating myself about verticals and discovered the wonderful world of radials and counterpoise.
I did not have much space for a radial system in the backyard of my family's 50 × 100 foot city lot. I did what I could within those confines and managed to improve the performance of the vertical. It served as my primary HF antenna for years until I received a hand-me-down 55 foot tower, but that is another story.
I like vertical antennas, but they are not for everyone. If you are considering a vertical antenna, do some research. The ARRL Web site has articles that cover verticals on its How Antennas Work page and its Vertical Antenna page. The WC7I Web site provides simple Vertical Antenna Theory and also has the lowdown on Underground Radials. There is also an online Amateur Vertical Antenna Calculator on the CSGNetwork Web site that also includes a vast array of other free online calculators, converters and tools related -- and unrelated -- to Amateur Radio.
Until next time, keep on surfin'!"
http://www.arrl.org/news/features/2008/12/12/10502/?nc=1 (http://www.arrl.org/news/features/2008/12/12/10502/?nc=1)
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Verticals are great for shooting the signal in all directions. But, if you want to bias the signal in one particular direction, say because most of your audience is to the west of you, then you might do better with a J-pole antenna.
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Actually, j-poles are omni-directional but do not require ground radials/plane like simple verticals do. They also have a lower takeoff angle (better for flat lands) then a simple vertical. Slightly harder to build then a vertical, but very much worth the extra effort
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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.
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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.
Do you have an SWR meter and if so, what is the ratio, also, is it a folder dipole or what
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It is a folded 5/8 wave, essentially a loop. It is cut to frequency and tuned by moving the points where the center conductor and the shield are soldered to opposite sides of the loop. I use the forward and reflected power meters on my rig to tune the antenna to match the readings of when I put a 50 ohm load on the feedline. I haven't bothered to calculate the SWR. I use a Bird watt meter to calibrate my meters.
I'll figure out how to post photos and put them here.
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Do any of you have any opinions about the antennas listed here? http://bbs.freetalklive.com/index.php?topic=21265.msg494417#msg494417 (http://bbs.freetalklive.com/index.php?topic=21265.msg494417#msg494417)
Is there much of a difference among those?
A 5/8ths would be about 7 feet tall, right? This would be going about 50 feet up and somewhat into a large swamp white oak tree. I think it will blend in a bit.
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Yes, they are quite different; size, gain, and radiation pattern.
A folded 5/8 is about 7' and has no ground radials. Ground radials effect impedance and pattern. At 50 feet, you might shoot the bulk of your signal right over the city and into the hills. There are a multitude of factors and you have to balance them out.
Look at the terrain and work backwards. Its not always about distance. You may want to focus on penetration where most listeners will be.
Look up pictures of radiation patterns for the antennas and decide what you need. I've used 1/4 wave groundplane in hilly terrain, 1/4 wave dipole in a tree on a hill side, a 5 element beam with a rotator for a long narrow city, a 5/8 loop for a house on a hill in the middle of a valley, and on and on. It depends on the goal and the terrain.
Don't forget to match the impedance to your TX.
You're looking at antennas capable of 300 watts. If you run 300 W into a wet string, you'll get plenty of coverage.
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Yes, they are quite different; size, gain, and radiation pattern.
A folded 5/8 is about 7' and has no ground radials. Ground radials effect impedance and pattern. At 50 feet, you might shoot the bulk of your signal right over the city and into the hills. There are a multitude of factors and you have to balance them out.
Look at the terrain and work backwards. Its not always about distance. You may want to focus on penetration where most listeners will be.
Look up pictures of radiation patterns for the antennas and decide what you need. I've used 1/4 wave groundplane in hilly terrain, 1/4 wave dipole in a tree on a hill side, a 5 element beam with a rotator for a long narrow city, a 5/8 loop for a house on a hill in the middle of a valley, and on and on. It depends on the goal and the terrain.
Don't forget to match the impedance to your TX.
You're looking at antennas capable of 300 watts. If you run 300 W into a wet string, you'll get plenty of coverage.
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.
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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.
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I imagine that a few of you reading this and other posts are wondering what is meant by things like "5/8 wave" "folded" "dipole" and "j-pole". As I am not the most eloquent human on the face of the planet heres a link to basic fundamentals of antennas. While this will be most beneficial to those who may want to build there own, it will also help those understand things like how antennas are measured in wavelengths etc..
Yes, this site is geared for the amateur radio op aka ham but an antenna is an antenna
http://www.electronics-tutorials.com/antennas/antenna-basics.htm (http://www.electronics-tutorials.com/antennas/antenna-basics.htm)
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And for the geeks
Basics of Antenna Modeling
http://www.wx7s.com/wordpress/?p=28 (http://www.wx7s.com/wordpress/?p=28)
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while this post relates to a specific transmitter, the data is the same regardless when using a part 15 am transmitter
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 (http://www.northcountryradio.com/Articles/part15.htm)
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Here is a construction article for a LPAM transmitter
http://www.northcountryradio.com/Articles/am88vert.htm (http://www.northcountryradio.com/Articles/am88vert.htm)
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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?
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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 (http://home.centurytel.net/w9wis/nvisb.jpg)
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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 (http://home.centurytel.net/w9wis/nvisb.jpg)
Exactly that, BUT, with some field changes we experimented with in Iraq.
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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 (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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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
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 (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.
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WRONG!!!!!!!!!
WRONG!!!!!!!!!!!!!
MY bad, i didn't even think to check the facts from the manufacturer
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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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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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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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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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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.