: OTA Mounts, Towers, Rigging Hardware
2009-12-18, 08:44 PM
Snapfizzle its all described in this thread:
CM4228HD Hardware Hacks For Better Performance (http://www.digitalhome.ca/forum/showthread.php?t=103749)
2009-12-24, 12:08 PM
Freezing rain is forecast for most of southern Ontario tomorrow (Christmas day). Here's hoping that everyone's gear makes it through the weather safe and sound!
2009-12-25, 01:19 AM
My OTA setup was working fairly well for a few months. I had two antennas on a 10-foot mast, connected to my chimney with one of those metal-strap chimney mount kits. The weight of the mast was on the roof with the chimney mounts just maintaining vertical and aim. I had a 4-bay amplified antenna aimed for the CN Tower, and an 8-bay for Grand Island (and an A-B switch.) I'm in the south part of Ajax, so there'a good bit of angular separation from Buffalo to Toronto.
I got most of Buffalo well (2-1, 29-1 marginal, 51-1 absent) and good local reception.
Then the windstorm came. Bye-bye mast. One mount twisted 90 degrees. Mast down on roof. 8-bay is now a 7-bay.
I'm hesitant to go back with the strapped mount method. I've seen some roof tripod kits and was wondering just how secure those are (and how do you keep the roof sealed) - how are they held down? Should I just get a tower? Is a tower a DIY job, or is it better left to a pro? Are towers expensive (or even available easily?)
My wife is considering cable now (shudder) - any advice would be appreciated...
2009-12-25, 12:50 PM
That sounds like a lot of load for a chimney to handle. You're lucky you didn't damage your house. The problem with such a mounting system is that there's no give...no flexing of the mount to absorb wind energy. Whereas a tower will flex...spreading the force throughout the structure.
When I read the instructions for the Channel Master 8-bay, they indicate that a tower installation isn't recommended. Presumably the design of such an antenna generates too much wind load. This contributed to my decision to go with a Yagi model (91-XG) on my tower.
If you were to attempt a roof mount again, I would separate the antennas. One (or both) on a (separate) tripod. And perhaps one on the chimney mount. Or even on separate masts on the chimney....
However, in your case, I would likely go with a tower (if local bylaws allow). Mostly because I'm interested in tropo and getting the best possible signal (if that's your thing too). If you're satisfied with your current reception, then the roof setup as mentioned above is likely a better choice.
2009-12-25, 01:36 PM
Tripods work great aslong as they`re installed properly. That means using large screws and getting them into the roof joists. I`m more worried about my antenna flying apart than the tripod letting loose in a wicked wind. Tripods go for around $40 . I love mine for the easy access to testing. For sealing after installing you can purchase a small can of roof tar . Coat the tripod base and screws good with this. With the wind load on your equipment i`d definitely separate the antennas .
2009-12-25, 03:03 PM
More chimney straps would help. Using braces between the roof and mast could also help with the chimney mount. It also sounds like there was too much wind resistance with two antennas. Whether any roof mount will hold depends on the quality of the roof mount and how well it is secured to the roof. I would place the antennas on separate masts and keep the masts short to reduce leverage on the mounts and straps. A tower is an ideal solution but is very expensive compared to roof or chimney mounts. Towers can also buckle if poorly secured or underrated.
2009-12-26, 06:32 PM
First, my apologies if this has been discussed earlier in this thread.
I have a Delhi DMX-MD-24 tower going up in the spring on a hinge up base. I decided it would be best if I could physically mount 3 CM 4228 antennas aimed in the direction of the major cities we receive our channels from IE: Erie, Cleveland, London. This decision was based on channel surfers in our family. I do have a good quality rotor but it will not withstand constant use for channel surfing.
I'm looking for tower hardware that will permit me to hang three CM 4228s on the side of my Delhi tower in different directions. Or would I be better off buying some 1.5 inch galvanized water pipe, renting a pipe threader and fabricating something on my own? Or maybe EMT conduit might suffice?
Once this has been solved, I still need to find some low loss combiners to bring the 3 down leads into my CM7778 preamp.
I also need to consider 3 other stations NE of my location (CKCO 13 Kitchener, CITY TV 31 Woodstock, Global 6 Paris) and reception methods. For now I can use the yagi antennas on the rotor to receive these stations. But it would be nice to have something fixed in this direction for reception.
Any thoughts? And Happy Holidays to everyone here.
2009-12-26, 07:39 PM
Gentleman: I don't see a DMX medium duty tower @ 24' on the Delhi website, so I'm assuming that you're putting up a used tower. Either way, Delhi rates their medium duty towers for 6 square feet (0.56 m2) projected wind area. I believe that 3 CM4228's would exceed that. Though you could increase wind load capacity with guy wires and/or increasing the volume of base concrete.
Wind area is an important variable for you in particular to watch, as your location is near a great lake...and thus wind is a concern. Soil is another factor: Many areas near the lakes have sandy soil. Something you may need to consider....
Plus, you'll need a VHF antenna. And unless you go with one of the newer low-profile ones, such as the Antennas Direct C5, your wind load will be that much greater.
Further, Delhi does not recommend using cross bars to mount antennas on their towers. And mounting on the side of their towers is difficult, as they use a tapered design.
Finally, 24' isn't a lot of space to play with when it comes to installing the number of antennae your approach would require. Some antenna, assuming that you could keep the wind load in check with guy wires, would need to be mounted lower...at at that low height, your gain would suffer.
My recommendation is sticking with a rotor, and going with a high-gain UHF and VHF antenna, or a good combo VHF/UHF. You simply have too many directions to cover....
2009-12-26, 09:26 PM
Good point about the wind load capacity on the tower, thanks. I never thought about that.
I have the option to change this tower out to a heavy duty version @ 9 square feet wind loading capacity as my hinge up base will fit number 3 through 6 DMX sections. I currently have a heavy duty version @ 48 feet supporting my ham antenna in place. This will be a secondary tower for television reception I'm working on.
The soil conditions on my property is all heavy clay. Not too worried about the base. I over sized the concrete base on my heavy duty tower and it's solid. The only mistake I made on the heavy duty base was installing the ground rod (driven down below the bottom of the base) inside the mass of concrete and running the ground wire up through the concrete to the tower legs. I've since disconnected that and installed new ground rods outside the concrete base and grounded each leg of the tower.
2009-12-27, 12:56 PM
Gentleman: I've never bought into the "don't ground through the concrete base" argument. Unless you electrically insulate the base from the tower, energy will flow there during a lightning strike. Best to ground it anyways. Yes, you can augment grounding with external points...but don't leave the base ungrounded internally.
Besides the logistical issues of placing multiple antennae on a small tower, you'll also need to consider loss. You'll lose 3dB everytime you split your antenna feed to take on another antenna. With three or more antennae, you'll basically have no usable signal for stations beyond 30 miles.
2009-12-27, 06:41 PM
I believe that members of this forum have used a 3 antenna system successfully- see OTA_canuck in the Niagara thread. (I myself have a 3 antenna set-up, although a pair is stacked/joined outside and then one line into the house which is joined with another antenna inside the house.) There might be a separate thread in the main forum section or in the OTA research section.
For starters- I think you could have 3 antennas set-up, but the loss from a 3-way splitter could be significant as Jase88 points out, but this might be compensated by amping all 3 antennas via pre-amps right under each antenna- then 3 separate coax into the house going into 3 power injectors and then into a 3-way splitter (reversed). I think OTA_canuck has this set-up or something similar.
2009-12-28, 01:04 AM
Once this has been solved, I still need to find some low loss combiners to bring the 3 down leads into my CM7778 preamp.
I have a 3 antennas. Two 4228's stacked in the same direction and another about 50 degrees off, combined using a high quatlity Regal 3 way splitter. If you have them all in different diretions, I'd suggest the amping separatly. And I'd use inline power inserters, to avoid running 3 separate lines down the tower and into the house. If you go with separate downleads, they'll have to match exactly to be in phase.
For mounting, they have to have at least 24 inches between them if they point different directions to avoid crosstalk.
Professional tower hardware to stand-off a pipe is very expensive stuff. I'd use EMT and lots of u bolts. And i'd suggest separate stand-off pipes for each.. That will avoid a long heavy pipe and make it easier to aim.
2009-12-28, 01:20 AM
My OTA setup was working fairly well for a few months. I had two antennas on a 10-foot mast, connected to my chimney with one of those metal-strap chimney mount kits. - any advice would be appreciated...
I've installed quite a few chimney mounts with straps, they seem pretty solid to me. In one case I put two DB-8's on the same pipe, I hope it holds in a wind or ice storm.
The only one i've seen come apart wasn't because the strap broke, but because the 1/4" nut on the bottom strap came undone. Even with the bottom strap missing the top strap didn't break, the bracket bent but stopped the antenna and rotor from falling.
The owner elected to use 4" wall brackets instead. They're mounted into the bricks with 5/16 lags and lead sheilds.
2009-12-29, 05:20 PM
I'm looking for the wind surface area (resistance) for UHF antennas, more specifically the CM 4228. I'd like to know this to determine how many I can safely install on the side of my Delhi tower.
I've looked at CM specifications for their antennas, but there is no mention of wind surface area.
2009-12-29, 09:36 PM
On the side of the tower ? If the tower is well mounted and in sturdy shape, I think you could pretty much cover the sides of the tower with CM4228s.:p
You could get approx wind load calcs from looking at specs for 1" X 2" mesh.
2009-12-29, 09:50 PM
The tower base will be a 3 foot square by 5 feet deep poured concrete in the spring once the frost is out of the ground. The tower is a 24 foot Delhi medium duty and I want to mount 3 CM4228s pointing in different directions to create my own little in house MATV system.
Someone suggested this is not a good idea as it might exceed the wind loading calcs on the tower. Hence my question about wind load of the CM4228.
2009-12-30, 01:48 PM
will be a 3 foot square by 5 feet deep
Thats almost 2 yds of concrete and about a couple of tons. That tower wont be going anywhere heh.
3 CM4228s are a pretty light load for that tower compared to other antennas that can be mounted on it.
When pouring the concrete, throw in rebar and/or scrap iron and scrap mesh to reinforce, to help prevent cracking. Cover the poured concrete with plastic so it dries slowly. And I wouldnt climb the tower until the concrete has cured for at least a week.
2010-01-02, 01:50 PM
I purchased a HDView 360 unit to experiment with OTA.. I thought I could put it in the attic until spring and then move it out to the roof. If I install it in the attic, do in need to ground it or does that only apply only for outside installation?
Thanks for the help
2010-01-02, 08:05 PM
@landowner: Grounding isn't just about lightning protection. The outer sheath of coax acts as a Faraday Cage: Capturing external RF energy and noise--and grounding it out--to prevent interference of signal on the centre conductor. Obviously this feature of coax is ineffective if it has nowhere to direct that energy.
This was (and is) a major shortcoming of 300ohm "twin lead": It lacks the protection of an external conductor sheath, and is thus negatively impacted by nearby metallic surfaces and/or RF and electrical interference.
At minimum, you should bring your coax from an attic installation to a grounding block.
2010-01-02, 08:53 PM
I'm planning on mounting an antenna on my chimney and had a question about running the cable. I have a medium efficiency furnace which vents up through the chimney in a pipe of it's own. There is quite a lot of room inside the chimney as the pipe doesn't take up a lot of room.
My thought are to run the cable line down the inside of the chimney (on the outside of the exhaust pipe obviously) and into the basement. This is where all my current cable TV connections split from so I thought it would be a really easy way to get the cable inside the house etc.