I built this Antenna today CM4228 clone almost.

gary350

DTVUSA Member
#1
Tell me what you think. If you have suggestions for changes let me know.

I built this antenna from information on this link. Temporary page

The finished antenna weighs 4.5 lbs.

Each bowtie elements are 9.75"long, 5" from tip to tip. Space between each bowtie is 1.5" mounted on a plastic insulator. Aluminum wire is 1/8" diameter. Elements are longer than the CM4228 but I have more aluminum wire so I can make some 8" like the CM4228 or 6.2" like the DB-8. The reflector screen is 8" wider than the CM4228 and 4" from the elements.

Space between each bay or each set of elements is 9.5".

Harmess has been changed according to suggestions on the link. An 18" long 75 ohm coax cable goes from each side to a combiner on the back side of the reflector screen. I took the back off of the combiner it has a balun inside. For the moment I am not putting a 300 to 75 ohm balun on each side I am only using the balun inside the combiner.

I took the back cover off on the combiner it looks about the same as a T splitter inside. There is a tiny farrite donut inside with wires from each terminal wrapped around the donut like a balun.

I thought I would test the antenna then make changes and test it again. I can put on 2 baluns to see if it works better or worse. I seem to recall there is a dB loss going through a balun so I figured by not using a balun I avoid the loss. Seems like the balun thing inside the combiner might work in the place of 2 baluns. Have to test it and see.

The link says the screen should be insulated from the frame. I plan to make the change tomorrow with a 1/8" plastic spacer and 6 more screws.

I have a 10 foot pole for a tower I plan to bolt to the side of my brick chimney this will put the antenna 27 ft from the ground. I also have a 60 ft tower in 6 sections since the neighborhood does not allow antennas I need to keep a low profile and not use this.

I need to go back and read that information again I seem to recall both wires on the phase line should be the exact same length. If the top wire is bent up and over to maintain a space of 1" then it will be longer than the bottom wire. If I make the bottom wire longer then I some how need to find a way to make it so the wire fits in that small space without just hanging down on the metal frame. Maybe I can bend it zig zag like a saw tooth to shorten the wire.

The ARRL Antenna Handbook shows several different length dipole connected together in parallel as one common antenna. It say 1 antenna can be made to pick up several different frequencies. Since the antenna that I build has 8 bowtie dipoles I should be able to do the same thing. What if the antenna has whiskers for 300, 400, 500, 600 MHz all in parallal like the ARRL book says?

http://i43.photobucket.com/albums/e358/gary350/Ant-01.jpg

http://i43.photobucket.com/albums/e358/gary350/Ant-02.jpg

http://i43.photobucket.com/albums/e358/gary350/Ant-03.jpg

http://i43.photobucket.com/albums/e358/gary350/Ant-04.jpg
 
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SWHouston

Moderator
Staff member
#3
Gary.

As HTN has said, you links to the picks on Photobucket are not working.
Could it be that you have made your account there "private" ?
You might check that, and change it to "Public" if you want the "IMG" or other links to work here.

Have a good Day ! :)
S.W.
 

gary350

DTVUSA Member
#4
Photobucket has been a problem for several days. I won't let me access any page except the very first page and it won't let me delete unwanted photos. OK it is fixed now.
 

FOX TV

Contributor
#5
Nice antenna work

Photobucket has been a problem for several days. I won't let me access any page except the very first page and it won't let me delete unwanted photos. OK it is fixed now.
Photobucket let me see all of the photos, and that is some very nice antenna fabrication work you have done there. Very clean and neat in appearance, but I would like for you to report on how your feed point design works as opposed to a 300 ohm balun feed.
 

M4ny

DTVUSA Member
#6
Very nice workmanship on that antenna it will be interesting to see how your test works out. I can see by your build that you are handy with equipment and can build some really nice stuff that will blow away most any commercial antenna.

I've built and studied this style antenna and I see some potential pit falls that may hurt you besides the horrable mismatch you may have by feeding this antenna with 75 ohm coax and no balun.
Your phase lines vary in size and the insulation on the wire can potentially change the velocity factor, the phase line is nothing more than a transmission line that connects the elements together to keep them all in phase. When you change the conductor size of a line like that you change the impedance of the line, when you change the velocity factor you change the speed that the signal travels through the line. I'm not sure how much your phase lines will throw off the balance since the impedance on these antennas are all over the place across the TV band anyways but it will have an effect, maybe positive.

The other thing I see is the way you connected the coax connector to the antenna, the loop running to the center conductor has a longer path to the antenna than the connector body does, this will throw the 2 halves out of phase some, 1 inch of phase line difference is a lot on UHF.

I did some tests on a DIY 8 bay very similar to yours comparing the 2 balun and combiner approach to the open wire feed line approach used by channel master and others and found the the 2 balun approach isn't as bad as you might think. It did change the frequency responce of the antenna but the peak gain was nearly the same, each method had some channels that were better and some channels worse.

Please let us know how this works out I'm all for some experimenting :)
 

gary350

DTVUSA Member
#8
The antenna is up connected directly to the TV with NO preamp and NO FM filter trap and it is working great. I had a lot of trouble getting it mounted the brick layers didn't use much cement every time I drilled a hole for ancher bolts it was hollow about 1" into the cement. The chimnel looks like a swiss cheese I drilled holes everywhere, now I need to patch holes. I just happen to have a 43 foot double shield coax and it is about 5 ft of so too short. The cable is banjo string tight it just barely reaches. I was running out of sun light so I didn't make any changes to the antenna. Tomorrow I will replace the cross wires and add the 2 300 ohm baluns and see what happens. I did rescan on the TV and picked up 3 new channels but they are nothing I care about.

I bought several sections of chain link fence rail the ends slide together and it makes a great antenna tower. I stood the antenna up against the house using 2 pieces of the 10 ft long fence rails this put the center of the antenna 18.5 ft off the ground. Signal on all channel are good 85% on the TV field strength meter.

After moving the antenna up to 27 ft the signal was only 65%. The SUN is low on the horizon and every day when the sun is low TV signal SUCKS. I very often loose several channels for about an hour until the sun gets below the horizon then the signal returns to normal. Not sure what is the deal with that. I never watch TV when the sun is up so I really don't care. After the sun was completely down the signal is 80% to 87% on the field strength meter on all channels.

Channel 7 is coming in at 55% not sure if this is Knoxville 120 miles away or Crossville about 90 miles away. This signal is either being picked up off the back side of the antenna or it is a reflected signal. Both have the same programming non stop movies with no advertisements.

The signal is very good. In the past channel 30, 28 and 5 were always the hardest to receive. They are all 3 coming is crystal clean now. Signal is not fading at all.

I am receiving a total of 31 channels but I am only interested in these, 2.1, 2.2, 4.1, 5.1, 5.2, 5.3, 8.1, 8.2, 17.1, 28.1, 28.3, 30.1.

Someone asked, what is the spacing between the reflector screen and the elements. It is 4.062". Someone mentioned the weight of my antenna, I weighed it with bathroom scales. Setting it on the scales it only weighs about 3 lbs but if I stand on the scales then pick up the antenna it causes me to get about 4 to 4.5 lbs heaver.

The antenna is aimed at 309 degrees I set it with a compas. All the channels I want to receive are between 295 and 322 degrees. The half way point is 308.5. I will probably experement with this angle later I might turn the antenna closer to 321 where the hardest to receive channels are.

My house is on a slight hill about 10 to 15 ft higher than the houses to the NW. This puts my antenna about 37 to 42 ft high compaired to the other houses. But about 4 blocks to the NW there are houses about the same height as mine.

More pictures.

http://i43.photobucket.com/albums/e358/gary350/Ant-5.jpg

http://i43.photobucket.com/albums/e358/gary350/Ant-6.jpg

TV Fool
 
Last edited:

Erickson54

DTVUSA Jr. Member
#9
Wrong place for my question, I deleted it.


Tell me what you think. If you have suggestions for changes let me know.

I built this antenna from information on this link. Temporary page

The finished antenna weighs 4.5 lbs.

Each bowtie elements are 9.75"long, 5" from tip to tip. Space between each bowtie is 1.5" mounted on a plastic insulator. Aluminum wire is 1/8" diameter. Elements are longer than the CM4228 but I have more aluminum wire so I can make some 8" like the CM4228 or 6.2" like the DB-8. The reflector screen is 8" wider than the CM4228 and 4" from the elements.

Space between each bay or each set of elements is 9.5".

Harmess has been changed according to suggestions on the link. An 18" long 75 ohm coax cable goes from each side to a combiner on the back side of the reflector screen. I took the back off of the combiner it has a balun inside. For the moment I am not putting a 300 to 75 ohm balun on each side I am only using the balun inside the combiner.

I took the back cover off on the combiner it looks about the same as a T splitter inside. There is a tiny farrite donut inside with wires from each terminal wrapped around the donut like a balun.

I thought I would test the antenna then make changes and test it again. I can put on 2 baluns to see if it works better or worse. I seem to recall there is a dB loss going through a balun so I figured by not using a balun I avoid the loss. Seems like the balun thing inside the combiner might work in the place of 2 baluns. Have to test it and see.

The link says the screen should be insulated from the frame. I plan to make the change tomorrow with a 1/8" plastic spacer and 6 more screws.

I have a 10 foot pole for a tower I plan to bolt to the side of my brick chimney this will put the antenna 27 ft from the ground. I also have a 60 ft tower in 6 sections since the neighborhood does not allow antennas I need to keep a low profile and not use this.

I need to go back and read that information again I seem to recall both wires on the phase line should be the exact same length. If the top wire is bent up and over to maintain a space of 1" then it will be longer than the bottom wire. If I make the bottom wire longer then I some how need to find a way to make it so the wire fits in that small space without just hanging down on the metal frame. Maybe I can bend it zig zag like a saw tooth to shorten the wire.

The ARRL Antenna Handbook shows several different length dipole connected together in parallel as one common antenna. It say 1 antenna can be made to pick up several different frequencies. Since the antenna that I build has 8 bowtie dipoles I should be able to do the same thing. What if the antenna has whiskers for 300, 400, 500, 600 MHz all in parallal like the ARRL book says?

http://i43.photobucket.com/albums/e358/gary350/Ant-01.jpg

http://i43.photobucket.com/albums/e358/gary350/Ant-02.jpg

http://i43.photobucket.com/albums/e358/gary350/Ant-03.jpg

http://i43.photobucket.com/albums/e358/gary350/Ant-04.jpg
 
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M4ny

DTVUSA Member
#10
Very nice construction work on that antenna, sounds like it's working good for you.

Your signals appear to be quite strong acording to your TV fool plot, a 4 bay may have been a better choice for your transmitter spread but the 8 bay sure looks great.

I'd be interested to know what the difference in reception would be between how you have it hooked up now and with 2 baluns and a combiner like many use.
 
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M4ny

DTVUSA Member
#11
The link says the screen should be insulated from the frame. I plan to make the change tomorrow with a 1/8" plastic spacer and 6 more screws.
That shouldn't be needed but wouldn't hurt, I've built several with the reflector attached to the frame with no problems, the whiskers and phase lines are the only things that need to be insulated from the frame
I need to go back and read that information again I seem to recall both wires on the phase line should be the exact same length. If the top wire is bent up and over to maintain a space of 1" then it will be longer than the bottom wire. If I make the bottom wire longer then I some how need to find a way to make it so the wire fits in that small space without just hanging down on the metal frame. Maybe I can bend it zig zag like a saw tooth to shorten the wire.
Both should be as close to the same length as possible for everything to stay in phase. Adding zig zags in the line may not give you the desired effect but it shouldn't take much,
so you may be OK doing that.
The ARRL Antenna Handbook shows several different length dipole connected together in parallel as one common antenna. It say 1 antenna can be made to pick up several different frequencies. Since the antenna that I build has 8 bowtie dipoles I should be able to do the same thing. What if the antenna has whiskers for 300, 400, 500, 600 MHz all in parallal like the ARRL book says?
The bigger problem is keeping all the antenna elements in phase rather than the whisker elements which are quite wide banded by design.
The phase lines are a fixed length and only have one frequency where they are truely keeping everything in phase as you get away from that things will go down hill.

Whisker length is important but having one that works over a much wider range than the phase lines can handle is a waste.

Keep up the good work your antenna looks great.
 
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gary350

DTVUSA Member
#12
Today I attached the 2 balun transformers to my antenna. I connected 1 coax cable at a time then I checked the field strength meter on the TV. One of the new baluns does not work so I returned to the store to get another balun. My frist reading was at 10 am the next reading was 11 am after returning with the another 300/75 ohm balun. Antenna is at 310 degrees. Signal on channel 7 was steady at 65% at 11 am.

Channel................Signal Left side................Signal Right Side

2.................................80-85%.............................85%

4...................................85............ .......................85

5.................................5-35...............................5-35

7.................................5-55.................................65

8..................................85............. ......................85

17................................85.............. .....................85

21................................85.............. .....................85

28................................85.............. .....................85

30................................85.............. .....................85


Next I connect the 75 ohm coax to both baluns and took another field strength reading on each channel of the TV at 11:10 am. Channel 7 is coming in good but channe 5 still sucks.

Channel...............Signal Both Sides

2.................................80-85%

4...................................85

5.................................5-35

7..................................65

8..................................85

17................................85

21................................85

28................................85

30................................85


Next I decided to swap the 2 wires on one of the baluns to change the polarity of one side to see if this makes the signal stronger or weaker. 11:20 am. I am getting a stronger signal on channel 5 and channel 7. Channel 7 is coming in good but channel 5 is not.

Channel..............Signal Both Sides

2.................................80-85%

4...................................85

5.................................5-45

7..................................70

8..................................85

17................................85

21................................85

28................................85

30................................85


Next I turned the antenna to 320 degrees aiming it directly at channel 5. It is now 11:30am. Channel 2 got better. Its hard to tell about channel 5 signal is jumping all over the place like it has been all morning.

Channel..............Signal Both Sides

2..................................85%

4...................................85

5.................................5-40

7..................................70

8..................................85

17................................85

21................................85

28................................85

30................................85


Next I decided to use my Antenna craft pre amp to see if that would bring in the signal a little better on channel 5 it is now 62%. Using the CM7777 preamp signal dropped about 5%. The Antenna craft preamp brought channel 5 signal up 22% but there is no change to the other channels.

Channel..............Signal Both Sides

2..................................85%

4...................................85

5...................................62

7..................................70

8..................................85

17................................85

21................................85

28................................85

30................................85


Next I tried the FM filter device that came with the CM7777 preamp signal dropped 20% across on all channels. Next I tried the FM filter that came with the Antenna craft signal dripped 35% on all channels. The antenna works best with no FM filter so I am leaving that off.

I did rescan again and found no new channels. I am receiving 2.1, 2.2, 4.1, 4.2, 5.1, 5.2, 5.3, 7.1, 7.2, 7.3, 7.4, 8.1, 8.2, 17.1, 21, 30, 39, 50.1, 50.2, 50.3, 50.4, 58, 66. I deleted some duplites and they did not return when I did rescan. Duplicates were 36.1 to 36.4 that were duplicates of another channel I already receive. Also had other duplicates that were deleted.

The only channels I am keeping are 2.1, 2.2, 4.1, 5.1, 5.2, 5.3, 7.2, 8.1, 8.2, 17.1, 30, 58.

TV Fool

Here are the close up photos as requested of the 3/32" thick aluminum corner bracket. Also a close of how I attached the screen to the metal tubing. I drilled a 1/8" hole on each side of the X where the screen wire is spot welded. I put a #8 sheet metal screw in each hole. The screw heads hold the wire in place. Since there are 2 screws one across from the other the wire is trapped and can never slip out. I used 1" conduit stand off clamps for the antenna mount on both ends and the chimney too. I still need to put a radiator hose clamp over one of the EMT clamps to make sure the wind does not rotate the antenna or cause it to slip in the bracket.

http://i43.photobucket.com/albums/e358/gary350/Ant-7.jpg

http://i43.photobucket.com/albums/e358/gary350/Ant-8.jpg

http://i43.photobucket.com/albums/e358/gary350/Ant-9.jpg
 

Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#13
Gary,
Have you considered moving the combiner behind the screen? I wonder if its presence so close to your bowties might be less than ideal. It looks like we had similar weather today but my 'honey-do list' kept me off my roof doing yard work (don't tell her, but the branches I cut will allow me space to test EV's Kosmic Super Quad and a 16-bay Hoverman)! GOOD JOB Gary! :thumb:
Jim
 

M4ny

DTVUSA Member
#14
Nice work on all your testing looks like you were able to make some nice improvements form where you started. I'm surprised that the FM trap on the channel master affected the signals so much.
 

EscapeVelocity

Moderator, , Webmaster of EV's Antenna Blog
#15
Gary, great work, that is a fantastic looking antenna.

What is the space between the inside elements of the two side by side 4 bays?

Ill check my references on this, to see if I can offer some tips on that.
 

gary350

DTVUSA Member
#16
Gary, great work, that is a fantastic looking antenna.

What is the space between the inside elements of the two side by side 4 bays?

Ill check my references on this, to see if I can offer some tips on that.
The center to center spacing is 2 ft.

Not sure what the spacing between left and right side elements are. The elements are 1.5" apart on the plexaglass insulator. The elements are 9.75" long each. 24" - 9.75 - 9.75 - 1.5 = 3"

Spacing should be 3".

Someone mentioned putting the combiner behind the screen. It is already behind the screen. Another thing the combiner is really a T splitter hooked up backwards. I am planning to order some things on ebay I want to combine it all into one order to save on postage I will be me a couple of combiners soon.
 

Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#19
Gary wrote:

Someone mentioned putting the combiner behind the screen. It is already behind the screen.
------------------------------
I suggested that and was there a difference in its performance?
Jim
 

M4ny

DTVUSA Member
#20
The center to center spacing is 2 ft.
I built one very similar to yours and did a lot of computer modeling with different center to center distances I found that 22 to 26" is a good range for that size antenna. You're right in the middle so I don't think any changes there would do much, changing the center to center doesn't do all that much for gain. It changes the side lobes and beam width slightly for a particular range of channels.
 
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