4-bay Using Metal Tubes Instead Of Bowties

[BOUVAL]

Mister 300ohm,

Thinking of it, I could give it a last try, but with a 2 inch spacing from the elements.

What do you think ?
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[300ohm]

IMO, I think you'll probably be making the reflectors act even more like directors with the relatively short reflector and 2" R to DE spacing, for the opposite direction.

What I would do is to put some wider mesh on the reflector, so that its a good 5 to 10 percent wider than the driven elements. Also leave it at the 3.5" (better for the higher channels) to 5" (better for the lower channels) reflector to element spacing.

[BOUVAL]

IMO, I think you'll probably be making the reflectors act even more like directors with the relatively short reflector and 2" R to DE spacing, for the opposite direction.

The good thing is I have no transmitters behind the reflector and now my chubby is 5 inches in front of it. See the picture, it's shown with a Philips preamp, but I usually use a CM7778.
My TV Fool: http://www.tvfool.com/?option=com_wr...267eee22a6d100

I also stuck this antique of my reflector, still getting all my channels

[300ohm]

Yup, I can see why. That 2 bay bowtie is an oldie but goodie. For your LOS channels you need a somewhat wide beam width antenna.
Beam width and gain are correlated. High gain antennas have very narrow beam widths (of course the reverse is not be true, as I can design a narrow beam width low gain antenna, which would totally suk, heh) . And in your case, for the LOS stations, you don't need a lot of gain.


Also, this weekend may not be a good time for comparative testing as a tropo is forming near you.

[BOUVAL]

Here it is in all of its splendour after getting more than 7 inches of snow this morning. Installed since more than 6 months, it's still doing great.

So last summer, I did some test switching the bowties with the tubes and aiming in different directions. In conclusion, the tubes are not any better than the bowties and not any worst as well.
My next build when I have time will be a vertical stack 8 bay with the tubes again as I have plenty of them.

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For that build I will use aluminum tubes 7/8" O.D. The elements will be 9.75" long and spaced 9.625" ctr to ctr. The horizontal spacing between the tubes will be 1.625" and I'll use 8 AWG AL. grounding wire for the phase lines.

The reflector will be made 24 AL. rods (don't the O.D. yet) and 31" long. For Christmas, I'd like to have that 8 bay modelised

Happy New Year to all.
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[mclapp]

I've messed around with flat metal elements like the winegard antennas use and I would suspect that it would be similar to the tubing. The flat metal ones liked a shorter driven element as compared to the whisker type. So instead of a 9 1/2 x 9" they would be more like 8 3/4" x 9" the bigger the OD the shorter they would have to get within reason. That appears to be proven when yours got better on the lower channels using the 9 1/2" x 9" dimensions. Those tubing elements would be hard to model with wire phase lines as already noted so cut and try looks like the best method with some educated guessing. It appears you are close. Happy Holidays

[BOUVAL]

the bigger the OD the shorter they would have to get within reason

That is why I used 7" long 1" OD tubes on the first build (see post #1 in this thread).

The reason I'll go with 9.75" long elements in the next build is to get Balm's famous channel 13 as I get a sniff of it when I do a scan.

I also intend to cross the phase lines between the 2nd and 3rd bay from the top and the bottom; any comment on that Mike ?
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[mclapp]

Originally Posted by BOUVAL

The reason I'll go with 9.75" long elements in the next build is to get Balm's famous channel 13 as I get a sniff of it when I do a scan.

I also intend to cross the phase lines between the 2nd and 3rd bay from the top and the bottom; any comment on that Mike ?
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The phase line cross should be just like any other 4 bay if that's what you mean.

I'm not sure if that's real RF ch13 but if it is I've found the phase line spacing is more critical than the element length for VHF-hi.

[300ohm]

the reflector and now my chubby is 5 inches in front of it. See the picture

Regarding the first picture in post #48, don't your tubes twist in the wind with that copper wire tie ? A better solution for the square tube to round tube connect would be to pick up a couple of (3/4") pipe hangers and twist them 90 degrees to mount.

Also regarding the J mount bracket to the roof. Did you use sealant under it ? A slow leak there can rot out the wood underneath the shingles in a short time. (been there, done that, heh)

[BOUVAL]

Mclapp,

What I mean for my 8 bay stack is, instead of using a co-phase harness arrangement like you did, I'd cross the phase lines BETWEEN the 2nd and 3rd bay from the top and 2nd and 3rd bay from the bottom.

As for getting real RF 13, I'll stay with 1.625" phase line spacing mentionned above. I think it's the right spacing for the best impedance.

Looking at the left part of your drawing: http://m4antenna.eastmasonvilleweath...se%20lines.pdf Isn't FRONT VIEW instead of TOP VIEW ?
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[BOUVAL]

Mister 300ohm, my dear GURU

Nope, my tubes don't twist in the wind as I added two more of these 6" metal plates (the ones with holes in them) on the other side. And the 2 litle lengths of copper wire are used when I switch antennas; all my builds and some 4 bay clones have 2 holes in the spine for that purpose.

Nope, I did not use any sealant, the screws are so tight in the wood that the shingles act like a washer between the J-Pole bracket and the plywood.
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[300ohm]

Nope, I did not use any sealant, the screws are so tight in the wood that the shingles act like a washer between the J-Pole bracket and the plywood.

Keep in mind shingles are just small gravel over a bit of tar and tar paper. Even with high compression, its near impossible to get completely water tight seal with a flat metal surface.

[rabbit73]

BOUVAL:

What I mean for my 8 bay stack is, instead of using a co-phase harness arrangement like you did, I'd cross the phase lines BETWEEN the 2nd and 3rd bay from the top and 2nd and 3rd bay from the bottom.

The description of your 8-bay is not clear to me. Is it a vertical stack of 8 bays with just one feed point in the center? Can you please post a diagram of the antenna that shows how you intend to cross the phasing lines?

[BOUVAL]

I know that I'm french and spanish speaking, but my english was clear.

bay 1

bay 2

Crossing

bay 3

bay 4

Center feed point

bay 5

bay 6

Crossing

bay 7

bay 8

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[mclapp]

Yes, I guess front view would be a better description of that co-phase line diagram.

I should have said bay spacing not phase line seperation as the critical factor in VHF-hi tuning, 8 1/2" or so would be best for ch13.

I had a 8 bay 9 1/2 x 9 vertical stack that would pull in distant ch's 11 and 13 when a same sized 4 bay would only intermittently lock at best, the 9 x 8 1/2" 4 bay would lock them most of the time but still not as good as the 8 bay. I'm thinking of putting together a 9 x 8 1/2" 8 bay to try at a similar location to see how much better that would be on those channels.

I tried a 6 bay once that used one phase line to tie all bays together and found it performed marginally better on a few channels than a 4 bay at best.

Your english was clear enough I just wasn't getting it, the last description cleared it up for me perfectly.

BTW you would have to do a cross between every bay except the center feed point, maybe that's why it wasn't making sense to me. The wave changes polarity every 1/2 wave and the bay spacings are approx. a 1/2 wave apart so you have to swap polarity between the bays to keep them all working in phase.

If the RF wave and bay spacing are not perfectly matched things could get of of phase quite fast when trying to use one phase line to feed the whole 8 bay vertical so that doesn't seem to work very well, the outer bays will get out of phase worse and worse as you go away from the frequency the bay spacing is perfectly tuned for.