| Author |
Message |
    
Crackshot
Intermediate Member
Username: Crackshot
Post Number: 249
Registered: 10-2005
| | Posted on Wednesday, February 07, 2007 - 7:16 pm: | 
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I am building a dipole.I need to make it inverted v. What band has most DX action? 20,40,60 or 80?
KE7JFA
CEF 655
HAM 225
ARRL Member
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Slugo4449
Intermediate Member
Username: Slugo4449
Post Number: 166
Registered: 7-2004
| | Posted on Wednesday, February 07, 2007 - 11:09 pm: |
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Conditions change during the year for each band.
How much room do you have to make an antenna?
I would make a dipole for 75-80 meters and then use a tuner to tune for other bands.
You can use a tuner to tune for better receive too.
May I suggest a full wave loop? 1005/frequency in mhz. Low noise and some gain over a dipole.
73,
Marty |
Crackshot
Intermediate Member
Username: Crackshot
Post Number: 250
Registered: 10-2005
| | Posted on Thursday, February 08, 2007 - 9:08 am: |
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I have room a plenty. Tell me more of this full loop you speak of. Have any drawings or links?
KE7JFA
CEF 655
HAM 225
ARRL Member
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Slugo4449
Intermediate Member
Username: Slugo4449
Post Number: 167
Registered: 7-2004
| | Posted on Friday, February 09, 2007 - 10:40 pm: |
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Just do a search for: full wave loop antenna amateur radio and you will find link after link. You should also add a -magnetic to the search and it will throw out magnetic loops.
The formula is 1005 divided by the frequency in MHZ's. So if you wanted a full wave loop on 75 phone then you would go 1005/3.800 equals about 246 and 1/2 feet for the total length. add about an extra foot for twisting back onto itself at the feed point.
Next think about your loop configuration. Do you want a 3 point loop or a square with four points, etc.
Thread onto the wire 3 or 4 insulators(you can make em with pvc or wood or buy plastic or ceramic ones at your local hardware store)
Thread them onto the wire using just one of their 2 holes. Then attach the last one of 3 or of 4 with one end of the wire and the other end of the loop wire attaches to the other side of the last insulator. Make sure you use up that extra 6 inches on each end to wrap back onto itself. Tie each insulator off to a tree or poles, etc.
A loop is truly a loop of wire.
Now if you want to use this for transmitting on multiple bands then you would put a short piece of ladder line at the end and attach a 4:1 current balun(not a voltage balun). This is then fed into a tuner with 50 ohm coax.
If you will only be transmitting on 75 phone, then you would make a 1/4 wave, 75 ohm matching stub. Forget the balun and just attach it to the feed point then run 50 ohm coax from the tuning stub to the tuner.
A 1/4 wave matching stub with 75 ohm coax is figured by: 246/Frequency in mhz's times the velocity factor of the cable. If you need more coax to get to the shack then you just attach 50 ohm coax with a barrel connector to the 75 ohm matching stub. This will bring it close to 50 ohms at the radio, which is what all modern day transmitters want.
If you just want to fool around put the loop up just attach coax to the feed point and throw an antenna tuner on it to see what it does.
There is also a way of feeding a delta loop(triangle loop) to make it horizontal or vertical.
a CB full wave loop is approx 34 feet.
Hope I didn't bore you all.
73,
Marty |
Ferd1605
Junior Member
Username: Ferd1605
Post Number: 29
Registered: 1-2005
| | Posted on Monday, February 12, 2007 - 12:07 am: |
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why not a dipole with one feed , one coax , but several wires for different bands ? if ya have the room for one , why not ? you can use just the one feedline and have dipole performance for all the bands you can cut it for ..I have made a dipole for 5 bands , all fed with one feedline. |
Slugo4449
Intermediate Member
Username: Slugo4449
Post Number: 168
Registered: 7-2004
| | Posted on Monday, February 12, 2007 - 3:37 pm: |
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Yes Ferd, it is called a "fan dipole". Good choice but some work to get all bands working well.
73,
Marty |
Kb5lpa
Intermediate Member
Username: Kb5lpa
Post Number: 221
Registered: 8-2002
| | Posted on Sunday, February 25, 2007 - 10:12 pm: |
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If you have room for an 80 meter dipole, build that but use ladderline instead of coax. Go to balanced output on tuner and it will work 80-10 meters pretty well. Get it up as high as possible.
73,
KB5LPA |
Mikefromms
Advanced Member
Username: Mikefromms
Post Number: 984
Registered: 6-2003
| | Posted on Monday, February 26, 2007 - 10:34 pm: |
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I don't think an 11 meter loop would work too good.horizonally. I like the idea about building a 75 meter dipole or inverted-v or loop to cover 75 thru 20 with a tuner. The loop is quieter. The dipole has more gain in two directions, the inverted-v is more omini-directional and catches a little of horizonal and vertical signals. The inverted-v requires only one high hanging point and that is in the center. The length of the 75 meter dipole would be around 135 feet; the length of the inverted-v for 75 meters would be about 130 feet; the length of a 75 meter horizonal loop would be about 265 ft. The loop with insulated wire like 14 gage can be thrown over tree limbs and works great low to the ground like 20 feet. The dipole works better at higher elevations like 50+ feet. The inverted-v should have a center elevated about 55 or 60 feet (less will work) and the ends up about 12 feet off the ground when pulled out into a an inverted V shape. Whichever type of antenna you choose to build, be sure the wires are out of reach because people can get burned by high powered signals coming off the ends of the wires! Wire antennas are very effective and fun.
Let us know how you wire antenna works out. BTW, right now you will hear lots of action on 75 meter in the early mornings and at night. Forty meter is more open in days and more useable during days. At night you have to dodge megawatt foriegn talk and rock stations on 40 meters! We are in the bottom of the solar cycle so bands like 20, 15, 12, and 10 are pretty much dead. This will change drastically in about a year or two.
Mikefromms |
