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Discussion Starter #1
I'm looking at side by side stacking of 2 CM4221HDs and was wondering if anyone had any tips on spacing or mechanically fastening both antennas.

I have aluminum square extrusion and a riveter, to in theory I could joing both antennas and make a DIY 4228, but I would like input on electrically connecting both antennas with one or more horizontal aluminum members. Is there any advantage in keeping both antennas electrically isolated? Maybe join them with wood? This is an attic install, to weather is not an issue. Attic height is the reason I am looking at side by side vs one over the other.

Thanks
 

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The spacing between both antennas will mostly affect where your secondary lobes end up in reference to your primary lobe; 60 degrees off, 65 degrees, 70 degrees etc...
 

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Discussion Starter #3
Thanks Lineloss.

Secondary lobes don't matter much for me, as in this direction (Sarnia), all my stations are almost laser straight, Detroit included (azimut +/- 1 deg, maybe 1.5).

I was mostly concerned about getting the best primary lobe gain.

No issues with making my horizontal cross beams (tying both CM4221hds together) out of aluminum, right?

I think barring any great success at a different spacing, i would make the spacing the same as the Cm4228HD.
 

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I made an old-style 4228 (not the new HD version) out of two old-style 4221s because my attic opening wasn't large enough for a 4228 to fit through. I used two horizontal metal strips (I think they're shelving brackets actually) that span most of the width of the back side of the two reflector screens and bolted the 4221s side-by-side with the edges of the reflector screens touching. U-bolts secure the antennas and brackets to a mast and hold the edges of the reflectors together.

I then used solid aluminum grounding wire to mimic (as best I could) the 4228's original connection structure between the two 4221s, and a small central piece of wood with bolts going through to secure the aluminum wires. I have a 300-to-75-ohm balun secured by wing nuts to the aluminum wires.

Mounted on a rotor in my attic (traditional plywood/asphalt shingle construction with no significant metal around), this antenna (no amp) will reach about 50-55 miles on UHF, with 60-65-mile stations occasionally coming in later at night. The advantage of attaching the reflectors side-by-side is that it adds some fairly decent VHF-high capability, as in both the old 4228 and new 4228HD. My psuedo-4228 used to also get analog VHF-high 11 and 13 (both 65 miles away) at about two-thirds of the signal strength of my Winegard YA-1713 (maybe a 6 out of 10), so it does also have some VHF-high capability (but not good enough at that distance after 11 and 13 went digital). But I would imagine that a pseudo-4228 or 4228HD might get VHF-high from an attic in digital within 30-35 miles or so just fine.
 
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