Bow Tie TV Antenna Designs (mclapp's M4 featured)

[old sparks]

doubledot101;

All your weak one-edge & two-edge stations are in the 20's, 30's and 40's. The only stations I see in the 60's are duplicates of other stations you already get.

If you're hoping to get WBBZ, it looks like this is a VHF station...

[mclapp]

A bowtie antenna with 8 1/2" phase line spacing and whisker length should be ok for channels in the 60's. The beam width will get narrower the higher you get in the channels so it may require more careful aiming for those but with the wide spread of directions the stations are coming from that may result in losing some others.

What stations do you get that you don't want and what ones don't you get that do you want?

[darklife]

Here's my quick and dirty homebuilt 4 bay...





I am new here and this is my first post
This antenna is far from perfect but I just wanted to build one for fun. Used the basic 7" coat hangers V's. Spray painted it all aluminum colored.
Put the balun through the wood and superglued it in place so that the coax attaches behind the reflector. I find this works better to keep the coax away from the active elements.
All built from random stuff around the house. Total cost around 3$ for spray paint, and that's it!

I probably did a bunch of things wrong lol but hey it works wonderfully.

[keithr386]

That's great, darklife. Not a conventional M4, but if it works, great!

How far apart are your reflector rods from the active elements?

[300ohm]

Youve got the cooling racks mounted so that most of the wires are vertical. What that does is narrow the beamwidth and lower the gain. I would turn them around 90 degrees. The wider horizontal clamp then needed for the cooling racks will be OK, if thats your concern.

[darklife]

Well I would turn the racks but problem is they aren't as wide if I turn them causing the V elements to extend farther out than the reflector racks because they happen to be more rectangular shaped than square.
I did try it both ways and I didn't see any difference in signal gain or loss so I went with what happened to look a bit better.
Also the horizontal parts of the rack as seen are fatter than the vertical part, which if I remember right causes a higher "Q" factor, thus cancelling out any side effect of the longer parts of the rack being vertical to the horizontal parts.

Of course I could replace the racks all together, but I don't have any junk laying around at the moment to replace them with and the idea of building this was to see if I could built it using little to no money.

The spacing of the elements from the racks are about 2". I know it's a rather short distance but hey it works just fine. I'm sure using some calculations or software it would show that it shouldn't work as well, but I tried moving the elements and reflectors around while testing it and regardless of computer models, what I have here works best from real life testing.

Anyways thanks for the comments, and any further ideas are appreciated.

[300ohm]

because they happen to be more rectangular shaped than square.

Yeah, if IIRC those racks are 11" X 13".

The spacing of the elements from the racks are about 2". I know it's a rather short distance but hey it works just fine. I'm sure using some calculations or software it would show that it shouldn't work as well,

Well actually, thats not that far off from the correct spacing distance for where that 6.5" over 5" antenna peaks at, which is about the old channel 83.
Keep in mind, that the above antenna still has more gain than most indoor commercial units and its small. So if you get all your practical channels strong, its not worth redoing into a proper 9.5" over 9" mclapp model, which will get you maybe 6 dBi more on the new uhf channel range.

[balm]

I'm trying to compare one of mclapps (4 bay, curved 40x40 reflector, swept forward, 10" whisker) with the CM4228HD, on VHF-Hi and UHF, in terms of net gain AND F/B ratio.

From what I researched,



Channels #10, #12, #13:

Mclapps:
gain= 5,3,3
F/B= 20

CM4428HD:
gain= 3,5,5
F/B= 15

Channels from #14 to #49:

Mclapps:
gain= 14-16 , gain peaks after #29
F/B= 15

CM4228HD:
gain=13-15, gain peaks at #30
F/B= 28

are these model data more or less correct, perhaps someone can comment.

thanks

[mclapp]

I can't speak for the 4228 but for a 10 x 9 1/2" 4 bay I would say your findings are pretty close to what I would expect.

[balm]

I was interested in a high F/B ratio for co-channels issues, and I thought the curved 4 bay was much more directional, but it appears the 4228 is more directional,

I also was not aware of that much net gain on VHF-Hi on the curved 4-bay, which is great for catching some strong VHF channels


In general, I am quite satisfied with my curved 4-bay, it receives most of my UHFs, cexcept co-channel problems, and the stronger VHF-Hi's , thank you

[ScaryBob]

F/B ratio is usually dependent on reflector spacing and size. There is no reason why the M4 could not be tuned to have as good or better F/B as the CM4228. The down side is that it will likely reduce gain slightly, as can be seen in the comparison above.

[balm]

the simulations don't show any significant increase in F/B with change reflector spacing

[mclapp]

I think finer mesh on the reflector would help.

The curved reflector swept forward whiskers isn't the best for F/B ratio the swept forward whiskers have a wide pattern on the back side and the curved reflector helps fold that back forward. The 4228 or horizontal stacked 8 bay type has a sharp rear lobe like the front one that when you add a reflector you'll get some sharp nulls on the back side.

Changing the reflector width may also help you may find a width that is just right to be a tuned length for the certain channel(s). I've never went down that road much since F/B ratio isn't a big concern for my area.

[300ohm]

I've never went down that road much since F/B ratio isn't a big concern for my area.

Same here. In fact in my case I want lower F/B ratios.

And I totally agree, finer mesh and larger reflectors will increase the F/B ratio, and at some point like mclapp says, it will (and it must at some point) kill the back reflections. Same thing with a GH.

Balm, didnt you get that CM-4251 in the air, or am I missing something (or forgot) ?
Or youre skipping around to different threads as usual, heh ? 300 ohm cant keep up with everything, ya know.

One inch chicken wire mesh on that sucker is the equivalent of 2" X 4" mesh and finer mesh is even better. Thats going to be your tops in F/B experiments.

[balm]

Actually, youre memory is very well fine tuned

Youre right,(at the cottage) I did have the 4251 up (also tried the chicken mesh), i also had many others, including yagis, variations of M4's, 91XG, and various combinations and stacks thereof...enough to cause anyone to go dizzy I also built that super quad array for #22, but gave up on the mounting

Anyway, at the time I wasnt completely aware of the extent of the multi-path (ground level reflectons),and co-channel issues, and in between 3 markets

So I was trying to do too much with 1-2 antennas, in my case compromising accomplished less.. I need at least 3 different dedicated antennas into A/B/C switch. Eventually I took down and took apart the 4251, I found it taking too much space on tiny land for the limited results I was getting. Maybe one day I will reassemble it and reaim it, right now its in a small box in my basement

Presently, Im using (at the cottage) a curved 40x40 M4 on rotor at 25 ft for 2 markets, and a combination of fixed M4, and VHF yagi at 15 ft for the 3rd market

But since most of my channels are weak, I am constantly trying to fine tune and increase directionality

(In the city Im getting everything, including VHF-Hi with an M4, reflector 15" back).

now youre up to date

thanks