Modify CM-3672 ?

[300ohm]

Raw Gain Chart:


SWR Chart:


As you can see, its a very very powerful vhf-low antenna. The SWR goes a bit high for FM though. And vhf-hi is skewed towards channel 7, which we'll work on changing so that it peaks at channel 10.

[kc2cbd]

Thanks 300ohm.
If you don't mind could you added in the UHF section to see what it does?

[300ohm]

If you don't mind could you added in the UHF section to see what it does?

OK, but that will take some time, so Ill have to work on it sometime next week.

The above antenna model doesnt have any UHF pieces in it. That 32" piece, which I believe is part of the UHF corner reflector, did give me concern because of its length.

What I did notice, is that if I stuck that piece in only, channel 10 raw gain goes down to 7.87 dBi, SWR goes up to 2.68, Net Gain down to 6.85 dBi. Thats a big drop on channel 10 and for all vhf-hi channels after 7. When you took off the corner reflectors, did you take that piece off too ?

Heres the piece in question, marked by the blue arrow.


Black arrow in this more to scale picture The pink dot is where the balun connection point is :


NEC file:


CM kc2cbd's CM3672 : Channel Master 3672 no UHF section
CM With 32" UHF reflector piece in between the VHF directors
CM AGt = 1.0 (0 db) at 195 mhz, Autosegmentation = 21
CE
GW 8 73 0 52.25 0.5 0 -52.25 0.5 0.1875
GW 9 69 12.05 -49.5 0.5 12.05 49.5 0.5 0.1875
GW 10 65 23.95 46 0.5 23.95 -46 0.5 0.1875
GW 11 59 36.05 -42.375 0.5 36.05 42.375 0.5 0.1875
GW 12 55 48.05 39.1875 0.5 48.05 -39.188 0.5 0.1875
GW 13 51 60.05 -36.125 0.5 60.05 36.125 0.5 0.1875
GW 14 45 72.05 32.75 0.5 72.05 -32.75 0.5 0.1875
GW 15 41 84.05 -29.688 0.5 84.05 29.687 0.5 0.1875
GW 16 1 91.05 0.3 0.5 91.05 -0.3 0.5 0.075
GW 17 5 96.05 1.8 0.8 91.05 0.3 0.5 0.075
GW 18 5 96.05 -1.8 0.8 91.05 -0.3 0.5 0.075
GW 19 17 96.05 1.8 0.8 96.05 26 0.8 0.1875
GW 20 17 96.05 -1.8 0.8 96.05 -26 0.8 0.1875
GW 23 25 4 17 1.2 4 -17 1.2 0.1875
GW 24 23 16 15.75 1.2 16 -15.75 1.2 0.1875
GW 25 21 28 15.3125 1.2 28 -15.313 1.2 0.1875
GW 26 21 40 14.75 1.2 40 -14.75 1.2 0.1875
GW 27 21 52 14.25 1.2 52 -14.25 1.2 0.1875
GW 28 19 64 13.75 1.2 64 -13.75 1.2 0.1875
GW 29 19 76 13.0625 1.2 76 -13.063 1.2 0.1875
GW 30 17 88 12.4375 1.2 88 -12.438 1.2 0.1875
GW 31 17 100 11.875 -0.75 100 -11.875 -0.75 0.1875
GW 33 15 106 6.9375 -0.7 106 28.5625 -0.7 0.1875
GW 34 15 106 -6.938 -0.7 106 -28.563 -0.7 0.1875
GW 297 77 -12.5 55 0.5 -12.5 -55 0.5 0.1875
GW 298 15 130 27.625 0.5 130 6.5625 0.5 0.1875
GW 299 15 130 -6.5625 0.5 130 -27.625 0.5 0.1875
GW 300 3 96.05 1.8 0.8 96.05 -1.8 0.8 0.115
GW 301 23 116.5 16 0.5 116.5 -16 0.5 0.111
GS 0 0 0.0254 ' All in in.
GE 0
EK
TL 8 37 9 35 300 0.3556
TL 9 35 10 33 300 0.3556
TL 10 33 11 30 300 0.3556
TL 11 30 12 28 300 0.3556
TL 14 23 15 21 300 0.3556
TL 15 21 16 1 300 0.2032
TL 12 28 13 26 300 0.3556
TL 13 26 14 23 300 0.3556
LD 5 0 0 0 2.5e7 0
EX 0 300 2 0 1 0
GN -1
FR 0 1 0 0 195 0

[kc2cbd]

Nope I left that one on cause I presumed it was a VHF element.
I did connect my balun to where you indicate because that is where the matching bars went to before I removed the UHF section.
I didn't see the need to keep the matching bars considering I wasn't going to be using the UHF dipole at all.
I wonder if that 32 inch element is a reflector because it is right behind the UHF dipole.

[300ohm]

I wonder if that 32 inch element is a reflector because it is right behind the UHF dipole.

Thats what Im thinking, its a UHF reflector part of the UHF corner reflector setup.
Hmm. Extending that 32 inch piece out to 58 inches, so its in line with the other two vhf directors, gives 9.28 dBi Raw Gain, SWR 2.35, 8.51 dBi Net Gain. So youre still better off removing it completely.

So I used the shorter ones which are 30 5/8 inch long but all the other measurements are the same for the wings.

So what was this red line distance ?

[kc2cbd]

That distance is 27 1/8 inches.
I might remove that if I decide to change the other elments.
Right now channel 5 is at 95 percent, channel 8 is 73 percent, and channel 10 is at 86 percent. These are all signal quality which to me is more important than signal strength.
All the stations I receive have a symbol quality of 100 percent.
So I'm just working on signal strength and quality.
Channel 23 seems to be my problem channel now as I can seem to get signal quality above 65 percent during the day, but at night I can get better.
I think at this point I won't see any better till I can get my 40ft tower installed and that won't happen till I can afford the concrete.

[300ohm]

and that won't happen till I can afford the concrete.

Keep in mind that you can decrease concrete use and have a stronger base by reusing old chunks of concrete, bricks, old scrap pieces of iron and especially old wire fencing/chicken wire.

[kc2cbd]

Yeah I know, but it all needs to be poured at once and you can't do that by using a mixer and bags of concrete.
The local concrete companies have a minimum of I think 3 yards which is about what I need to fill a 4 x 4 x 4 ft hole for my Rohn-25 tower.
I could save by using guy wires but I prefer not to have any and that is why when I found this freestanding tower I jumped on it.
Paid $100 and got the 2 antennas with it, so I saved about 800 on the tower and if I really wanted to I could sell the 4251 and come out ahead. )
So still looking at about 400 more to get it put up.

[300ohm]

OK, with the additional 3 wing directors 10.5 inches in front of the last vhf director and the 32 inch piece in place:

Channel 10, 8.84 dBi Raw Gain, SWR 2.67, Net Gain 7.83 dBi.
Channel 8, 9.23 dBi Raw Gain, SWR 2.00, Net Gain 8.72 dBi.


With the 32 inch piece removed, with the additional 3 wing directors :

Channel 10, 11.54 dBi Raw Gain, SWR 1.92, Net Gain 11.09 dBi.
Channel 8, 11.66 dBi Raw Gain, SWR 1.52, Net Gain 11.47 dBi.

That 32 inch piece is causing a disturbance in the Force, heh.
I dont think the 6 inch uhf directors etc are causing any problems, but Ill check that later this week.

The additional 3 wing directors also increase the vhf-low gain even more and since the vhf-hi peak is still occuring a little before channel 7, more tweaking should get another db or so of gain on channel 8 and 10, to around 12.5 dBi.

NEC file with 3 wing directors added and 32 inch piece removed:

CM kc2cbd's CM3672 : Channel Master 3672 no UHF section
CM With 32" UHF reflector piece in between the VHF directors removed
CM With additional 3 winged vhf directors
CM AGt = 1.0 (0 db) at 195 mhz, Autosegmentation = 21
CE
GW 8 73 0 52.25 0.5 0 -52.25 0.5 0.1875
GW 9 69 12.05 -49.5 0.5 12.05 49.5 0.5 0.1875
GW 10 65 23.95 46 0.5 23.95 -46 0.5 0.1875
GW 11 59 36.05 -42.375 0.5 36.05 42.375 0.5 0.1875
GW 12 55 48.05 39.1875 0.5 48.05 -39.188 0.5 0.1875
GW 13 51 60.05 -36.125 0.5 60.05 36.125 0.5 0.1875
GW 14 45 72.05 32.75 0.5 72.05 -32.75 0.5 0.1875
GW 15 41 84.05 -29.688 0.5 84.05 29.687 0.5 0.1875
GW 16 1 91.05 0.3 0.5 91.05 -0.3 0.5 0.075
GW 17 5 96.05 1.8 0.8 91.05 0.3 0.5 0.075
GW 18 5 96.05 -1.8 0.8 91.05 -0.3 0.5 0.075
GW 19 17 96.05 1.8 0.8 96.05 26 0.8 0.1875
GW 20 17 96.05 -1.8 0.8 96.05 -26 0.8 0.1875
GW 23 25 4 17 1.2 4 -17 1.2 0.1875
GW 24 23 16 15.75 1.2 16 -15.75 1.2 0.1875
GW 25 21 28 15.3125 1.2 28 -15.313 1.2 0.1875
GW 26 21 40 14.75 1.2 40 -14.75 1.2 0.1875
GW 27 21 52 14.25 1.2 52 -14.25 1.2 0.1875
GW 28 19 64 13.75 1.2 64 -13.75 1.2 0.1875
GW 29 19 76 13.0625 1.2 76 -13.063 1.2 0.1875
GW 30 17 88 12.4375 1.2 88 -12.438 1.2 0.1875
GW 31 17 100 11.875 -0.75 100 -11.875 -0.75 0.1875
GW 33 15 106 6.9375 -0.7 106 28.5625 -0.7 0.1875
GW 34 15 106 -6.938 -0.7 106 -28.563 -0.7 0.1875
GW 111 13 140.5 13.037279 10.0000497 140.5 28.75 0 0.0625
GW 112 13 140.5 28.75 0 140.5 13.037201 -10 0.0625
GW 113 1 140.5 13.037279 10.0000497 140.5 13.738573 10.8797149 0.0625
GW 114 1 140.5 13.037201 -10 140.5 13.738516 -10.879649 0.0625
GW 115 13 140.5 13.738573 10.8797149 140.5 28.250421 1.55401058 0.0625
GW 116 1 140.5 28.75 0 140.5 28.250421 1.55401058 0.0625
GW 117 13 140.5 13.738516 -10.879649 140.5 28.250411 -1.5540169 0.0625
GW 118 1 140.5 28.75 0 140.5 28.250411 -1.5540169 0.0625
GW 119 19 140.5 1.625 0 140.5 28.75 0 0.1875
GW 120 3 140.5 28.75 0 140.5 33.5625 0 0.1875
GW 121 13 140.5 -13.037279 10.0000496 140.5 -28.75 0 0.0625
GW 122 13 140.5 -28.75 0 140.5 -13.037201 -10 0.0625
GW 123 1 140.5 -13.037279 10.0000496 140.5 -13.738573 10.879715 0.0625
GW 124 1 140.5 -13.037201 -10 140.5 -13.738516 -10.879649 0.0625
GW 125 13 140.5 -13.738573 10.879715 140.5 -28.250421 1.55401063 0.0625
GW 126 1 140.5 -28.75 0 140.5 -28.250421 1.55401063 0.0625
GW 127 13 140.5 -13.738516 -10.879649 140.5 -28.250411 -1.5540169 0.0625
GW 128 1 140.5 -28.75 0 140.5 -28.250411 -1.5540169 0.0625
GW 129 19 140.5 -1.625 0 140.5 -28.75 0 0.1875
GW 130 3 140.5 -28.75 0 140.5 -33.5625 0 0.1875
GW 297 77 -12.5 55 0.5 -12.5 -55 0.5 0.1875
GW 298 15 130 27.625 0.5 130 6.5625 0.5 0.1875
GW 299 15 130 -6.5625 0.5 130 -27.625 0.5 0.1875
GW 300 3 96.05 1.8 0.8 96.05 -1.8 0.8 0.115
GW 302 13 151 13.037279 10.0000497 151 28.75 0 0.0625
GW 303 13 151 28.75 0 151 13.037201 -10 0.0625
GW 304 1 151 13.037279 10.0000497 151 13.738573 10.8797149 0.0625
GW 305 1 151 13.037201 -10 151 13.738516 -10.879649 0.0625
GW 306 13 151 13.738573 10.8797149 151 28.250421 1.55401058 0.0625
GW 307 1 151 28.75 0 151 28.250421 1.55401058 0.0625
GW 308 13 151 13.738516 -10.879649 151 28.250411 -1.5540169 0.0625
GW 309 1 151 28.75 0 151 28.250411 -1.5540169 0.0625
GW 310 19 151 1.625 0 151 28.75 0 0.1875
GW 311 3 151 28.75 0 151 33.5625 0 0.1875
GW 312 13 151 -13.037279 10.0000496 151 -28.75 0 0.0625
GW 313 13 151 -28.75 0 151 -13.037201 -10 0.0625
GW 314 1 151 -13.037279 10.0000496 151 -13.738573 10.879715 0.0625
GW 315 1 151 -13.037201 -10 151 -13.738516 -10.879649 0.0625
GW 316 13 151 -13.738573 10.879715 151 -28.250421 1.55401063 0.0625
GW 317 1 151 -28.75 0 151 -28.250421 1.55401063 0.0625
GW 318 13 151 -13.738516 -10.879649 151 -28.250411 -1.5540169 0.0625
GW 319 1 151 -28.75 0 151 -28.250411 -1.5540169 0.0625
GW 320 19 151 -1.625 0 151 -28.75 0 0.1875
GW 321 3 151 -28.75 0 151 -33.5625 0 0.1875
GW 324 13 161.5 13.037279 10.0000497 161.5 28.75 0 0.0625
GW 325 13 161.5 28.75 0 161.5 13.037201 -10 0.0625
GW 326 1 161.5 13.037279 10.0000497 161.5 13.738573 10.8797149 0.0625
GW 327 1 161.5 13.037201 -10 161.5 13.738516 -10.879649 0.0625
GW 328 13 161.5 13.738573 10.8797149 161.5 28.250421 1.55401058 0.0625
GW 329 1 161.5 28.75 0 161.5 28.250421 1.55401058 0.0625
GW 330 13 161.5 13.738516 -10.879649 161.5 28.250411 -1.5540169 0.0625
GW 331 1 161.5 28.75 0 161.5 28.250411 -1.5540169 0.0625
GW 332 19 161.5 1.625 0 161.5 28.75 0 0.1875
GW 333 3 161.5 28.75 0 161.5 33.5625 0 0.1875
GW 334 13 161.5 -13.037279 10.0000496 161.5 -28.75 0 0.0625
GW 335 13 161.5 -28.75 0 161.5 -13.037201 -10 0.0625
GW 336 1 161.5 -13.037279 10.0000496 161.5 -13.738573 10.879715 0.0625
GW 337 1 161.5 -13.037201 -10 161.5 -13.738516 -10.879649 0.0625
GW 338 13 161.5 -13.738573 10.879715 161.5 -28.250421 1.55401063 0.0625
GW 339 1 161.5 -28.75 0 161.5 -28.250421 1.55401063 0.0625
GW 340 13 161.5 -13.738516 -10.879649 161.5 -28.250411 -1.5540169 0.0625
GW 341 1 161.5 -28.75 0 161.5 -28.250411 -1.5540169 0.0625
GW 342 19 161.5 -1.625 0 161.5 -28.75 0 0.1875
GW 343 3 161.5 -28.75 0 161.5 -33.5625 0 0.1875
GS 0 0 0.0254 ' All in in.
GE 0
EK
TL 8 37 9 35 300 0.3556
TL 9 35 10 33 300 0.3556
TL 10 33 11 30 300 0.3556
TL 11 30 12 28 300 0.3556
TL 14 23 15 21 300 0.3556
TL 15 21 16 1 300 0.2032
TL 12 28 13 26 300 0.3556
TL 13 26 14 23 300 0.3556
LD 5 0 0 0 2.5e7 0
EX 0 300 2 0 1 0
GN -1
FR 0 1 0 0 195 0

[kc2cbd]

That's awesome...I wonder if I change that 32 inch elment to match either the 57 1/8 or the 55 1/4 what it would do.
Would changing the 55 1/4 element to 2 pieces instead of 4 pieces would it change anything. My thought on that element is that the smaller piece close to the boom is for UHF and the longer piece couples to it different in higher channels but I could be wrong.

[300ohm]

I wonder if I change that 32 inch elment to match either the 57 1/8 or the 55 1/4 what it would do.

I was ahead of you there in post # 50, making it 58 inches. It helps a little bit, but removing it completely is much better.

Would changing the 55 1/4 element to 2 pieces instead of 4 pieces would it change anything. My thought on that element is that the smaller piece close to the boom is for UHF and the longer piece couples to it different in higher channels but I could be wrong.

Ill take a look at that, when I add on the uhf directors, but offhand I would say it wouldnt. That uhf section is so short. When I redid the directors on my CM-1221, which has a dual uhf/vhf director just like yours, I just used the same vhf size for the element and the uhf section was replaced with just plain fiberglass rod. And I added on two more of them exactly alike. Ive 12.5+ dBi on channel 12, which I was after.
With or without the 32" piece, the peak vhf-gain is occuring before channel 7, as much as 14 dBi peak. The trick is to move that peak on the gain curve as the potential for gain is already there.

32 inches, on the other hand, is 1/2 wavelength on channel 8. Placed in the wrong position, it could have bad effects on channel 8 and higher channels. And like you, I would have thought it maybe would have been a vhf-hi director too. Im beginning to think CM compromised on a great VHF design to include the UHF. As Ken Nist notes, the CM-3671 is a top of the line VHF antenna. But it seems like your CM3672 is even better, especially at VHF-Lo because of the extra reflector at the end. I hope you realize, while 8 dBi for UHF is nothing, 8 dBi for VHF-Lo is pretty incredible, and should in a lot of cases, really get someone 100 mile reception, heh.

Also keep in mind the 10.5 inch spacing you did were based on my model of the CM-3671 and my CM-1221 and Stampeders CM-1111, which also did well with 10 - 11 inch director spacings. My gut feeling is telling me that your CM-3672 is going to be a bit different, maybe with wider spacings. Or maybe will have to shorten the winged directors even more (the red line distance above) to get it to respond to higher frequencies.

I didn't see the need to keep the matching bars considering I wasn't going to be using the UHF dipole at all.

Correct, youre doing everything right.

The local concrete companies have a minimum of I think 3 yards

Yeah, they keeping upping the price and the miniumum delivery.
And dont get me started on the price of shingles. In the spring of 2009, basic shingles were about $14 a pack, up from about $7 in the 90's. Then they went to $23 a pack (by a pack I mean 1/3 square). And now theyre at $29 a pack. Whats up with that ? In such a short time period ?

Is the world somehow running out of tar ?? Out of stones ??? I think not. Roofs are a significant new home cost.
And everyone seems to be scratching their heads about housing starts being so low, well, duh.

[kc2cbd]

Yeah I realize that is really good gain for VHF. Before I added in those winged directors Saturday I was getting so-so signal. Now I'm back to high 80 to 100 percent on all 3 meters. I just wish my Vizio and Haier televisions had signal meters. Especially my Haier because it is a 7inch battery operated portable. I use it all the time on the roof to see what my system will do cause I can check it with about a 2 foot coax.
If I can get good picture and signal up there I know what it should be in the house.

Yeah the price of everything is ridiculous.
I know when I have to put a new roof on my house the shingles are going to kill me, but I've been considering a metal roof.
I can do the work myself so no biggie on the labor.
I learned carpentry, plumbing, electrical work from my Pop and I've done all the improvements on my home.

As far as the directors I used 10 1/2 inch spacing cause that worked great to be able to use the existing holes from the UHF directors that removed. Looking at the spacing from the 57 1/8 to the 55 1/4 that is 24 inches so I was thinking that something needs to go in there or use that spacing for the directors in front of the 55 1/4 director element.

But I sure am curious as to what the VHF figures will be with the UHF section in place.
I sure do like what the winged elements did to my signal right now. I am curious if it would be better to have them at 55 1/4 inches and would non-winged elements be any different.

[300ohm]

I know when I have to put a new roof on my house the shingles are going to kill me, but I've been considering a metal roof.

Yeah, I also consider that for my garage, but got a distant relative of mine to do it for 3 grand with singles, and new plywood, one section was in miserable shape. Another option is Onieda ? at Lowes big (4 X 7 ft pieces) which make DIY easier. 20 year warranty, and then after that, you paint them to extend the life.

I just wish my Vizio and Haier televisions had signal meters.

Yeah, it seems like meaningful signal meters are low on the priority of TV manufacturers. The best signal and quality meters I and rabbit73 have found are the Apex DT502 and Sansonic FT-300A CECB conversion boxes, which measure both signal strength and signal quality. And rabbit73 has conversion charts to expensive signal meters.

[kc2cbd]

Yeah my HDhomerun has a really good meter on it.
Since it a network HDTV tuner I can view it from anywhere I have a computer.
Some day I will acquire a netbook and then I can use that when I'm working on the antenna. The only draw back will be getting up and down to plug or unplug the pre-amp.
The HDhomerun by silicondust has signal strength, signal quality and symbol quality.
It works great when tweaking with the rotor to get the best signal.

[300ohm]

my HDhomerun has a really good meter on it.

Which model ? Since it has those options, it would be cool if someone like rabbit73 could provide a conversion chart from a more expensive signal meter and provide conversion data like he did on the Sansonic FT-300a and the Apex DT-501 he did previously.