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Will a metal boom work for a Yagi 13 element antenna?

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Old 02-15-2010, 10:34 AM   #1
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Default Will a metal boom work for a Yagi 13 element antenna?

I built a Yagi antenna 13 elements, 1 driver, 1 V screen reflector, with a 3/4"x 3/4" wood boom as instructed in Radio Amature Handbook designed for channel 7 Knoxville TN 120 miles away.

I used this web site to determine element length. http://www.csgnetwork.com/antennaedcalc.html

I have the antenna upstair inside the house about 6 ft off the floor in front of a window aimed at Knoxville. I am getting a good 90% signal. This station is about 120 miles. This is the station I want, non stop movies. I could probably mount this antenna in the attic but I need to watch this station for a few weeks to see how the signal does.

Now that I know it works I might like to build a better Yagi antenna. PVC pipe is too flexable. Wood may be ok outside but I worry it will get wet and water logged in our extremely wet rainy springs and falls we have every year. I bet this will be a tricky antenna to deal with on a windy day outside. Just playing round today having fun it is 26 degrees snow on the ground and I am a prisoner in the house.

Will a metal boom work on a Yagi antenna???

Last edited by Gary350; 02-15-2010 at 11:45 AM.
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Old 02-15-2010, 12:00 PM   #2
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WVLT - I think that you do not understand real channels and virtual channels.

WVLT is not on channel 7, it is on digital channel 30 UHF!

The answer is yes you can use aluminum or even stainless steel if you wish. Round or square - it does not matter as long as you have the hardware to attach the directors to the boom.

As is the case with most people wanting to do something themselves, they understand how to follow simple directions, yet they cannot express themselves when it comes time to explain what type of antenna they have or how it works.

If your antenna is made out of coat hangers or metal wire, the first strong wind and the relationship of the wires to each other might change and your reception might dissappear. Requiring many trips up to the roof to repair your handywork.

My advice is to spend some real money and buy a real antenna and put it up on the roof with a real antenna rotor. As the barometer changes your signals will drift from one place to another and might dissappear for days or even weeks at a time. When the antenna is on the floor of your bedroom, it does not take much effort to move the antenna to the relationship of the signal, you just move it. No big deal. When the antenna is mounted to the side of the house and is bolted stationary, it is a big deal - because there is no way to move it or to keep it stationary if you decide to move it by hand.
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Old 02-15-2010, 12:17 PM   #3
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Hi Gary,

Interesting! Do you have a picture of your yagi? Which channel are receiving from Knoxville? According to tvfool, there are no virtual ch 7 stations in Knoxville but there is a real channel 7, WMAK. Is this the channel you are receiving? What is the network? THIStv?

Rabbitears.info has information about the channels in the Knoxville area, see: http://www.rabbitears.info/search.ph...=&lon=&height=
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Old 02-15-2010, 12:46 PM   #4
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Originally Posted by IDRick View Post
Hi Gary,

Interesting! Do you have a picture of your yagi? Which channel are receiving from Knoxville? According to tvfool, there are no virtual ch 7 stations in Knoxville but there is a real channel 7, WMAK. Is this the channel you are receiving? What is the network? THIStv?

Rabbitears.info has information about the channels in the Knoxville area, see: http://www.rabbitears.info/search.ph...=&lon=&height=
I was receiving channel 7 last week then I lost it. Watched it for 2 days then it was gone. I don't recall seeing any advertisements or station identification it was non stop movies. I built this Yagi antenna today to see if I could get channel 7 again. I had channel 7 for a while now it is gone too. I thought it was Knoxville but now I'm not sure. I was just having fun experementing I'm snowed in needed something to do.
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Old 02-15-2010, 01:13 PM   #5
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Sounds like you're having fun! THIS network is the only OTA station that I know of that runs predominantly movies. Our NBC affiliate has it has a sub channel.

Have fun playing with your DIY antennas!

Rick
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Old 02-15-2010, 01:22 PM   #6
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To Gary350,

Lets for a moment assume both you and JBantennaman are correct, and for a brief time you were receiving WVLT from 120 away.

And now suddenly, a few days later, you no longer get it.

Which now means we all have to ask, why the change in reception?

1. Maybe we can assume that you built some miracle whiz bang antenna, but even sitting upstairs and inside, it just lost its structural integrity and the miracle thus just died.

2. Or we could assume that some accident of nature in the form of freak weather conditions caused UHF signals to reflect off high clouds instead of simply going right through the clouds and off into space. And given the freak snowstorm that just hit the Southern tier of US states, dumping a bunch of snow in areas that seldom see any snow, there may be some support for the hypothesis that the same snow also brought with it optimal DXing conditions. Which would mean that any decent antenna
placed in the same place a few days ago would have given the same results. And similarly lost WVLK when the weather changed.

But as a further test, I recommend you post an exact address TVfool report for your address, and see if it even registers WVLT as a possible station.

And regardless if it does or not, its still congratulations to you for
making the effort, and for all we know, your homebuilt creation may do as well or better than a very expensive commercial antenna. After all, a commercial antenna maker does not know in advance what channels you are likely to get and not to get, so its advantage you, because you can tune YOUR creation for only the frequencies available in your locale. Which, IMHO, is the more important long term criteria. And if you can beef it up to withstand severe weather, you have a real accomplishment, both in terms of pride and a heavier wallet.
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Old 02-15-2010, 03:35 PM   #7
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When you spend your spare time DX'ing like I do. You get to know and recognize the weather patterns that it takes to do it.

I have a good working relationship with the chief meterologist over at WTAJ and he was the Senior meterologist at AccuWeather a number of years ago.

McTubber hit it on the head, except for the fact that I have no way of knowing the actual temperature, humidity, barometric pressure at the time of the reception. The only reason why I say that is because my DX reception right now is limited to about 75 miles.

To get 120 miles, you really had to have some screwed up weather.
The pressure gradient lines is where the signals gets dragged around in all sorts of directions other then a straight line. You might have to point the antenna West, when the actual signal is coming out of the south west and you might have signals which almost never appear, appear for no apparently good reason.

The stories of people driving down the road in their car and listening to a FM radio station 300 - 1200 miles away is not uncommon.
When that happens, it is usually in the lower ranges of frequencies and it doesn't last very long and it doesn't matter what type of antenna you used to receive it. After all, a car aerial is only 32 to 36 inches long for most factory antenna's.

If you had a digital television, all you had to do was check the PSIP and it will tell you which channel you are watching on the program guide. If the tuner did a scan to receive the station, then the information for that channel should still be in the tuners memory.

Just because it had movies, doesn't mean that it was This Network or was from that particular town.

TV Fool says that channel 7 is WMAK, Rabbit Ears said it was WVLT

WMAK was a Inde Channel. 36.010082 -83.932407
Maximum ERP: 95.000 kW

Here is the interesting part, it was just bought and sold and now the program guide says that it is RTV / RTN

http://www.myretrotv.com/prog_schedules/WMAK.pdf

I guess you have to be a detective sometimes to figure all this stuff out.

Now if it was on real channel 7, a UHF antenna isn't going to pick it up and a VHF antenna still would have to be pretty big to receive it.

Let's say it was channel 7 and lets say for the sake of simplicity that channel 7 was 180 Mhz, then the full wavelength of channel 7 would be 5.466 feet. I highly doubt if you built a antenna in your bedroom 11 feet wide. or a log periodic antenna. A UHF Yagi - sure, but not a VHF antenna.
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Old 02-15-2010, 07:07 PM   #8
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Quote:
Originally Posted by JB Antennaman View Post
TV Fool says that channel 7 is WMAK, Rabbit Ears said it was WVLT

WMAK was a Inde Channel. 36.010082 -83.932407
Maximum ERP: 95.000 kW

Here is the interesting part, it was just bought and sold and now the program guide says that it is RTV / RTN

http://www.rabbitears.info/search.ph...=&lon=&height=

I guess you have to be a detective sometimes to figure all this stuff out.

Now if it was on real channel 7, a UHF antenna isn't going to pick it up and a VHF antenna still would have to be pretty big to receive it.

Let's say it was channel 7 and lets say for the sake of simplicity that channel 7 was 180 Mhz, then the full wavelength of channel 7 would be 5.466 feet. I highly doubt if you built a antenna in your bedroom 11 feet wide. or a log periodic antenna. A UHF Yagi - sure, but not a VHF antenna.
No offense JB, but Rabbitears.info has ch 7 as WMAK. See: http://www.rabbitears.info/search.ph...=&lon=&height=

Last edited by IDRick; 02-15-2010 at 10:02 PM. Reason: fixed link
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Old 02-16-2010, 05:30 AM   #9
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Quote:
Originally Posted by Gary350 View Post
Will a metal boom work on a Yagi antenna???
To answer the original question...yes, I build all my antennas on a 3/4" square aluminum boom...problem is, will the elements be bonded to the boom or not bonded. I always use the unbonded element calculations. Unbonded, the elements are insulated from the boom, basically floating. I use 3/8" nylon standoffs in the boom, elements thru the standoffs. So as not to fill this whole discussion with details, I hope you can figure out the rest.
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Old 02-16-2010, 05:56 PM   #10
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TV Fool and Antenna web are both giving me goofy information. I thought channel 7 was Knoxville but not I'm not sure where it is???

I did a web search for zip codes, Knoxville, Memphis, Chattanooga, Nashville.

Checking with both Antenna Web and TV fool Knoxville usually does not have a channel 7 but sometimes it does it just depends on which zip code I use to do the search. Most of the time there is NO channel 7.

TV fool says Memphis has 2 channel 7s but Antenna web says there is no channel 7.

Both TVF and AW says Nashville has no channel 7.

I not sure how I got the idea I was receiving channel 7 from Knoxville one of the searches I did last week must have showed a channel 7.
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Old 02-18-2010, 07:54 PM   #11
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Knoxville does have a channel 7 after all.

http://tvlistings.aol.com/listings/t...37912&tab=grid

There is no channel 7 in Memphis even though TV Fool says there is.

There is no channel 7 in Chattanooga.

There is no channel 7 in Nashville.

There is no channel 7 in Cookville.

There is a channel 7 in Crossville with the same programming at channel 7 Knoxville.

There is no channel 7 in Huntsville AL

No channel 7 in Hopkinsville KY.

No channel 7 is Lexington KY

No channel 7 Bowling Green KY

It appears the channel 7 that I picked up had to be Knoxville or Crossville. Both have the movies I am looking for.
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Old 02-19-2010, 05:02 AM   #12
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Go play with the license SEARCH tool at http://www.fcc.gov/mb/video/tvq.html
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Old 07-03-2011, 06:09 AM   #13
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Sorry to bump such an old thread, but I was wondering, when building a yagi antenna, if the boom is made of aluminum, and the parasitic elements are bonded to the boom (electrically conductive with the boom)

Does the driven element have to be insulated from the boom or should it also be bonded?

Also can the elements be thin aluminum cylinders (hollow)?

also if the boom is metallic (conductive) and it is attached to a metal pole, wouldn't that basically alter the shape of the antenna/ essentially having the pole becoming part of the boom?

(this will be my first attempt at ever building a yagi and with hours of googling, there is just not much info in things such as bonded or unbonded elements and how to mount the driven element when dealing with a metallic boom
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Old 07-03-2011, 08:21 AM   #14
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Originally Posted by cutepuppy671 View Post
(this will be my first attempt at ever building a yagi and with hours of googling, there is just not much info in things such as bonded or unbonded elements and how to mount the driven element when dealing with a metallic boom
You may use metalic booms, but they cause the element length to change very slightly. Insulating the elements eliminates that change.
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Old 07-03-2011, 09:56 AM   #15
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Quote:
Originally Posted by cutepuppy671 View Post
Sorry to bump such an old thread, but I was wondering, when building a yagi antenna, if the boom is made of aluminum, and the parasitic elements are bonded to the boom (electrically conductive with the boom)

Does the driven element have to be insulated from the boom or should it also be bonded?

Also can the elements be thin aluminum cylinders (hollow)?

also if the boom is metallic (conductive) and it is attached to a metal pole, wouldn't that basically alter the shape of the antenna/ essentially having the pole becoming part of the boom?

(this will be my first attempt at ever building a yagi and with hours of googling, there is just not much info in things such as bonded or unbonded elements and how to mount the driven element when dealing with a metallic boom
Here are some helpful links on how to build a yagi antenna:

http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=4323
http://www.wb4jm.com/files/wid-band-2mtr-yagi.pdf
http://www.astronwireless.com/topic-...nna-mounts.asp
http://www.nrharc.org/Downloads/5%20el%202%20meter.pdf
http://www.pe1rqm.nl/overig/buildinguhfyagis.pdf


The K&MEM calculator is very useful for designing a yagi plus it gives some construction tips as well. See: http://www.k7mem.150m.com/Electronic.../yagi_vhf.html
For detail on constructing the feedpoint, see: http://www.k7mem.150m.com/Electronic..._vhf_feed.html

Last edited by IDRick; 07-03-2011 at 10:18 AM. Reason: fixed several links
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