[AlexG883]

I know that some people gang two (or more) CM 4228 antennas one atop the other to maximize gain and distance. One drawback is the resulting size and weight because the 4228 is basically just two 4221s joined together side-by-side with the pipe structure(s) adding weight but not height to the arrangement.


I happen to have two CM 4221 antennas and am thinking of ganging them one on top of the other. Has anyone ever tried that? Is there any advantage in gain if properly done? One attraction to this idea is the ability to loft the combination waaaaaaaaay up on a pole since the antennas are not heavy and they also become part of the pole structure themselves the way they're designed. But would the lack of horizontal spread be more of a loss than the increased vertical spread?


Any input appreciated.

 

[videobruce]

"Stacking" antennas (one over the other) narrows the beamwidth in the vertical direction. Mounting them side by side tightens up the pattern to the sides.

Depending on your situation, if you have problems with multipath, I would say a side by side mount would improve things. I can't think of a situation where vertically stacking them would improve things except in a mountainous situation, where beam tilt would come into play. There are rotors that will address beam tilt if you want to pay for it. (IOW's big bucks.)


Vertical stacking is surely easier, all you need is a longer mast. I don't know if the overall weight would be that much less compared to the 4228.


Anyone else?

 

[nybbler]

I wouldn't be surprised if 2 4221s are slightly heavier than a 4228, as the tubing is slightly longer on the 4221 than on half a 4228. But the stress on a rotor should be less.

 

[Falcon_77]

I like the idea of a vertical stack if you are trying to improve gain while not sacrificing azimuth beam-width. It seems to work for the broadcasters. i.e. The gain for a non-directional broadcast antenna exists in the vertical. I don't see why end users couldn't try to replicate some of this on a small scale.


However, if all your stations are in the same direction, then this approach probably won't yield any significant benefits. I don't see this being useful in LA, for instance.

 

[AlexG883]

thx for your replies. My two main goals are:


1) to loft above (or as close as possible) a wall of pine trees behind our house in the direction of all wanted stations. So to answer one question, yes, all stations are in one narrow directional beam.


2) stations are also fairly far away, in the 30 - 45 mile range and are VHF in addition to UHF. I'm hoping to find a configuration that -- like the CM 4228 -- might take in VHF high band with the two 4221s.


I'm also experimenting, because it's fun and a challenge, but I'm not too technically versed in this stuff. Learning as I go.


And lastly, I'm doing it on a budget. I have two CM 4221s so that's what I'm going with, for now. I might add a Winegard YA-1713 if I can't get high band VHF with the 4221s. As a last resort I will rig up a side-by-side arrangement to make a homemade 4228 if that turns out to be best for my situation.


I did a little more on my project today and ran into an immediate problem. The 4221 reflector support (non-swaged end) drives through the mast with a metal rod anchored on the other side. It leaves only about an inch of open mast to work with for stacking. Oops. So it won't be so easy to stack, mast atop mast, after all.


My next idea was, "I wonder what might be 'gained' (pun intended) by joining the swaged ends together with a 7-8" joiner mast section and using the two 4221s horizontally spread?" This wouldn't help with topping the pine trees, obviously, but it might help in gain and high band VHF reception. ?


So just to try out this idea I sawed off a seven inch piece of mast and joined them together at the swaged ends. I now have a Channel Master 4221+1224 antenna if you get my drift. I can attach this to another mast with a U-bolt. I'm going to join the two baluns together with equal-length RG6 into a Channel Plus 2532 combiner. If there's a lower loss UHF-type combiner please advise.


Before I do any more though, if any part of this Plan B is fatally flawed I'd like to know in advance. The bow ties will flare vertically instead of horizontally. A problem? The antenna spread will be ultra-horizontal. A problem? There will be slight gap in the bow tie structure (an extra inch or two) in the middle. A problem? Any other obvious pitfalls?


As I say, I'm into experimenting as well as practically solving for my particular situation. If the ultra-wide 4221+1224 has a very narrow beam, that will be ok.


Thanks in advance. Alex


p.s. I plan to bind the reflector screens together with copper wire. p.s. 2, forget about the pine trees in answering whether the horizontal config of two 4221s is feasible or not. The practical consideration is secondary to the theoretical in this case.

 

[mclapp]

The 4221 vertical stack may not work so good on VHF-HI. The Horizontal stack (4228 style) with the reflectors bound together will work better on VHF-HI.

Either option will probably only net you about 1 -2 db more than a single 4221on some UHF channels.


Stacking identical antennas will gain about 2.5 db but due to mismatches in the matching lines and combiners or whatever you use the net will be somewhat less.


You may want to consider combining the 2 reflectors side by side or adding a larger single reflector (32" plus wide) to a single 4221, it will give you better VHF-HI reception and around 1 db UHF without having to deal with the tricky phasing of the 2 antennas.


If you were to combine the 2 reflectors it may be better to overlap them a couple of inches.

 

[AlexG883]



Quote:
Originally Posted by mclapp /forum/post/14324431


You may want to consider combining the 2 reflectors side by side or adding a larger single reflector (32" plus wide) to a single 4221...

Ok thanks. If I do decide to just expand the reflector on one existing 4221 does anyone have a recommendation for something that does the job and hopefully blends with the existing wire? Galvanized chicken wire fence?


p.s. I don't know if other people have commented on this before or not but I think I found a good, cheap "off-label" mast in the form of galvanized top railing for cyclone fencing. It comes in 10' lengths and male/female ends. 1-1/2" diam. It's light and seems strong. Looks like you could even put two or possibly three (with guy wire) together for a nice, tall antenna mast. Has anyone tried this? I guess I'll do a search for "top rail" on this site after posting this message to see if someone else has mentioned this usage. Each 10' length of rail costs a hair above $10 at Menard's.

 

[mclapp]

Chicken wire is not the best, if you do use it make sure the twists are running horizontally. Hardware cloth and welded wire fencing with the square or rectangle holes work best, 1 x 3" or 2 x 4" fence is pretty common. The key is to have a continuous closely spaced (1" - 2") horizontal wires that add up to 32" or more, if using multiple pieces make sure they are bound together tightly with wire for a good electrical connection.


Another thing that can be done with the larger reflector for slightly more gain is to curve the outer edges of the reflector forward about 2 - 4" depending on the width of the reflector (2" for a 32" wide screen). Start the curve at the outer edge of the V shaped elements. This will narrow the beam width slightly on most UHF channels. This will also add a little strength to the reflector screen.

 

[AlexG883]

thanks mclapp. I'd never heard of hardware cloth before reading your post. Did a quick web search and now I know.

I'll pick up some of that. I do have some glavanized welded wire fencing in the garage that I'd forgotten about too. I'll compare the two to see which matches up better with the horizontal screen on the 4221. Didn't know about the curving tip either so I'll try that. Strange that my 4221s both came with the reflector curving away from the signal direction. Shouldn't it be the other way around? Anyway, thanks for the tips. It's appreciated.

 

[mclapp]



Quote:
Originally Posted by AlexG883 /forum/post/14333539


thanks mclapp. I'd never heard of hardware cloth before reading your post. Did a quick web search and now I know.

I'll pick up some of that. I do have some glavanized welded wire fencing in the garage that I'd forgotten about too. I'll compare the two to see which matches up better with the horizontal screen on the 4221. Didn't know about the curving tip either so I'll try that. Strange that my 4221s both came with the reflector curving away from the signal direction. Shouldn't it be the other way around? Anyway, thanks for the tips. It's appreciated.

The galvanized wire fence is the best as long as it is 2" x 4" inch spacing or less. It will be much stronger and have less wind resistance.


I made one once with a 1" x 1" center section then added 2" x 4" wire fence wings on each side to make it 36" wide overall and it worked just fine.


If you do go for hardware cloth try to get the 1" x 1" anything smaller will do nothing for gain and just add wind resistance.


I've seen some 4221's with the bend in the outer edge going forwards too. I think they did it more for strength than anything, that little bend is not enough to really make a difference in reception.