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Dipole Antenna


WRUS537
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I purchased a dipole, which is 68.8 ft long, I had planned to mount it about 1 or 2ft above the roof ( I have an HOA) using poles and an insulator at each end. However my roof is only 52 ft long.

My question is what do I do with the extra 8 or so feet on each side? Can I just run it down the edge of the roof? 

For the coax, do I have to run it straight down the middle of the roof or can I run it along the roof top with the wire?

I have an HF to listen to and want to have an antenna ready to transmit when I get my license or Lord forbid and emergency.

Thanks for everyone's help

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21 minutes ago, WRUS537 said:

I purchased a dipole, which is 68.8 ft long, I had planned to mount it about 1 or 2ft above the roof ( I have an HOA) using poles and an insulator at each end. However my roof is only 52 ft long.

My question is what do I do with the extra 8 or so feet on each side? Can I just run it down the edge of the roof? 

For the coax, do I have to run it straight down the middle of the roof or can I run it along the roof top with the wire?

I have an HF to listen to and want to have an antenna ready to transmit when I get my license or Lord forbid and emergency.

Thanks for everyone's help

You can put all the excess to one end and bend it horizontally into an “L”.

You can divide the excess evenly and form the wire into a “[“.

This might help: http://webclass.org/k5ijb/antennas/Fold-Bend-and-Mutilate.htm

If your HOA allows you can lift the center (called an “inverted V”) or ends of the dipole.

You could run the dipole diagonally from one corner of your roof to the other.  

If you have a flagpole (most HOAs won’t say no to flagpoles I have heard) you could run the excess to it.

The coax should run perpendicular to the dipole as it approaches the center of dipole for best results, at least where it connects to the balun. It can lie on the roof as it approaches. Be sure to waterproof the connection if you’re using a UHF connector.

 

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On 11/13/2022 at 9:22 AM, Sshannon said:

You can put all the excess to one end and bend it horizontally into an “L”.

You can divide the excess evenly and form the wire into a “[“.

This might help: http://webclass.org/k5ijb/antennas/Fold-Bend-and-Mutilate.htm

If your HOA allows you can lift the center (called an “inverted V”) or ends of the dipole.

You could run the dipole diagonally from one corner of your roof to the other.  

If you have a flagpole (most HOAs won’t say no to flagpoles I have heard) you could run the excess to it.

The coax should run perpendicular to the dipole as it approaches the center of dipole for best results, at least where it connects to the balun. It can lie on the roof as it approaches. Be sure to waterproof the connection if you’re using a UHF connector.

 

Thank you so much for the details and making it understandable, I had this posted for awhile on Arrl and no response. 

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1 hour ago, WRUS537 said:

Thank you so much for the details and making it understandable, I had this posted for awhile on Arrl and no response. 

You’re welcome. Also, one thing to keep in mind is that the ends of the dipole are where the voltage is highest. You should make sure they are out of reach of anyone. 
 

A4F30135-F8E5-4D40-8571-28CFE74CBFE2.gif

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Since this is the Amateur Radio forum... I'd remind the OP that they likely need to do an RF exposure evaluation for that antenna. While the simple calculator found online (http://arrl.org/rf-exposure-calculator) may suffice, it may still be desirable to model the antenna as the folded ends may contribute to a less than simple RF distribution.

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2 hours ago, Sshannon said:

You’re welcome. Also, one thing to keep in mind is that the ends of the dipole are where the voltage is highest. You should make sure they are out of reach of anyone. 
 

A4F30135-F8E5-4D40-8571-28CFE74CBFE2.gif

 

1 hour ago, KAF6045 said:

Since this is the Amateur Radio forum... I'd remind the OP that they likely need to do an RF exposure evaluation for that antenna. While the simple calculator found online (http://arrl.org/rf-exposure-calculator) may suffice, it may still be desirable to model the antenna as the folded ends may contribute to a less than simple RF distribution.

Well now I am new to all this, other than the use on the fire dept. radios, I was unaware of the voltage coming from an antenna as well as any major radiation, I am wondering now if I should hire someone that knows what they are doing.

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35 minutes ago, WRUS537 said:

 

Well now I am new to all this, other than the use on the fire dept. radios, I was unaware of the voltage coming from an antenna as well as any major radiation, I am wondering now if I should hire someone that knows what they are doing.

You wouldn’t have to. Even though it’s high voltage, it’s at a very low current. Just don’t dangle it where a kid might touch it while you’re transmitting. 
RF exposure calculations might be a little tedious but I’m sure someone here would help you. Honestly I never did them for my antenna but it leads away from my house rather than directly over it. Again, it’s only an issue while you’re transmitting so while you’re in listening mode you don’t have to worry about it. 

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1 hour ago, WRUS537 said:

Well now I am new to all this, other than the use on the fire dept. radios, I was unaware of the voltage coming from an antenna as well as any major radiation, I am wondering now if I should hire someone that knows what they are doing.

RF Exposure evaluation should be introduced in any decent Technician class study guide... Though a 66ft dipole is sized for the 40m HF band -- a Technician license only grants you morse code (CW) privileges on the lower half of 40m. In truth, other than 10m (a small SSB segment), morse code on small segments of some bands (80m, 40m, 15m) is all a Technician has access to -- you'll need to reach General to have voice privileges on most bands Unless it is a trap dipole, the odds are good that 40m is the only band you'll be able to transmit on. An off-center fed dipole (OCFD) manages to get around 4 bands (mine handled 40m, 20m, 10m, and 6m -- but needs to be replaced; 6 winters appear to have stretched the wire such that it is widely out-of-band for SWR. For the replacement I intend to support the balun box with paracord so I can reduce tension on the wire ends).

The RF calculator I linked to should at least give you the basic safety range (I have a Python program based upon the original BASIC program posted back when evaluation first became a requirement -- that's where the following came from)

Quote

Evaluation for: 40m dipole

Input Parameters
Power to Antenna (from Exemption Worksheet) 100.00 Watts
TX Time Ratio (TX / (TX + RX)) 0.500  
Antenna Gain in dBi (dBd + 2.15) 2.15 dBi
Operating Frequency 7.125 MHz
Ground Reflection Included True  
Distance to Area of Interest 5.00 Feet
Maximum Permissible Exposure (MPE)
Controlled Environment 17.729 mW/cm^2
Uncontrolled Environment 3.546 mW/cm^2
 

Operating Mode/Factor: FM/AM/RTTY/PSK-31 (100%)

Average Power at the Antenna 50.000 Watts
Estimated Power Density at AoI Distance 0.71950 mW/cm^2
 
  Compliance
Distance
AoI in
Compliance
Controlled Environment 1.01 feet True
Uncontrolled Environment 2.25 feet True

 

Operating Mode/Factor: Heavily Processed SSB (60%)

Average Power at the Antenna 30.000 Watts
Estimated Power Density at AoI Distance 0.43170 mW/cm^2
 
  Compliance
Distance
AoI in
Compliance
Controlled Environment 0.78 feet True
Uncontrolled Environment 1.74 feet True

 

Operating Mode/Factor: CW/Processed SSB (40%)

Average Power at the Antenna 20.000 Watts
Estimated Power Density at AoI Distance 0.28780 mW/cm^2
 
  Compliance
Distance
AoI in
Compliance
Controlled Environment 0.64 feet True
Uncontrolled Environment 1.42 feet True

 

Operating Mode/Factor: Unprocessed SSB (20%)

Average Power at the Antenna 10.000 Watts
Estimated Power Density at AoI Distance 0.14390 mW/cm^2
 
  Compliance
Distance
AoI in
Compliance
Controlled Environment 0.45 feet True
Uncontrolled Environment 1.01 feet True


I didn't bother with estimated coax losses -- you'll have to look up the losses for whatever coax you run, and apply the result to the power to antenna entry. I also tend to use a 3min Tx/3min Rx calculation, even though my real usage is likely more like 3min Tx, 15-20min Rx (unless running FT8/PSK31. I ran this for a 40m dipole at the bottom end of the voice band.

Note that the worst case distance is 2.25 feet (uncontrolled means general public who do not know that is a transmitting antenna -- the FCC presumes anyone who does know it is willing to take the risk of being closer to the antenna 🧐 . Assuming a 6ft person reaching upwards (7-7.5ft to fingertips) the antenna would need to be 10ft at the closest point.

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I think my first problem was buying equipment (got a good deal on them) before I knew what I needed or knew what I was doing. I thank everyone for the loads of information, I have learned more here then anywhere. 

 I am going to stick with the gmrs and study for the ham tests and then go from there. If the world ends before I get licences , I will still have the HF radios in the closet.

 I have been looking for a place with more land in Indiana and then will set it up there.

My next project will be solar for my security cameras and radios.

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2 hours ago, WRUS537 said:

I think my first problem was buying equipment (got a good deal on them) before I knew what I needed or knew what I was doing. I thank everyone for the loads of information, I have learned more here then anywhere. 

 I am going to stick with the gmrs and study for the ham tests and then go from there. If the world ends before I get licences , I will still have the HF radios in the closet.

 I have been looking for a place with more land in Indiana and then will set it up there.

My next project will be solar for my security cameras and radios.

Really, you shouldn’t allow anything that KAF6045 or I said to cause doubts.  Hang the antenna like you first thought.  Listen to HF on it while you learn. Before you start transmitting you might want to look over the exposure calculations, but I suspect many people never do.  We’re supposed to look at that for GMRS as well, but almost nobody does.  What radio are you going to use for HF?  What’s the output power? 

As a reference point, there are a lot of HOA hams with antennas in their attics who don’t have RF exposure issues.  A dipole on your roof is extremely unlikely to fail the calculation unless you’re running a linear amplifier.  Hams sometimes get way too caught up in minutiae, for whatever reasons.

Antennas are fascinating and as you study for your license you’ll pick up a lot.  Off-grid power systems are fascinating also.  The path towards self reliance has many interesting subjects and amateur radio fits in with them.  I found that HamStudy.org worked great for me to learn, but everyone learns a little differently.

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On 11/15/2022 at 10:40 AM, Sshannon said:

Before you start transmitting you might want to look over the exposure calculations, but I suspect many people never do.  We’re supposed to look at that for GMRS as well, but almost nobody does.

In the case of my OCFD, it was pretty much required. On 20m the uncontrolled compliance distance is 7.5 feet. That's almost the distance between my house and neighbor's -- and they have a two story which puts the upstairs bed-rooms right at the height of my antenna. Granted, there is another 4-5 feet of paracord from mast to end of antenna. On 10m the distance is 17 feet (FM); on 6m the compliance distance is a whopping 25 feet! (Hmm, I may need to update my evaluation report -- my summary lists 6m compliance at 16.5 feet).

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On 11/15/2022 at 10:40 AM, Sshannon said:

What radio are you going to use for HF?  What’s the output power? 

I picked up two Kenwood TS-430S and one ps-430 Power Suppy, one has a low volume but I got a good deal on them and I like the big units.

I will check into the attics antenna's The crawl space up there is big.

Thanks for all the links, they are very helpful.

 

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