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Bow Tie TV Antenna Designs (FF4 & M4 featured)

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antenna
697K views 1K replies 170 participants last post by  Crispysea 
#1 ·
  • CM4221 is the original Channel Master 4-bay bowtie reflector (data from HDTVPrimer site)
  • CM4221HD is the new Channel Master 4-bay bowtie reflector (data provided by CM to videobruce - a DHC member. Assumed to have been in dBd)
  • PR-4400 is a 4-bay bowtie reflector made by Winegard (data from HDTVPrimer site)
  • DB-4 is a 4-bay bowtie reflector made by Antennas Direct (data from HDTVPrimer site)
  • SBGH is a Single Bay Gray Hoverman Gold Standard (GH10 data from j3d - a DHC member)
  • * antenna not designed for 52 and higher
  • M-4 is a DIY 4 Bay 40x44 14 inch Reflector spacing fwd ele & refl (data from mclapp - a DHC member)
  • ^ is the listed gain on the next highest channel since tables did not match all channels
Hi Stampeder,

I think that it would be nice to have links in the table for these
antennas or their computer models. For example I have been unable to
find the M-4.

Thanks,
--John
 
#2 · (Edited)
j3d said:
I have been unable to find the M-4.
That's a good point, j3d - mclapp and I were discussing how several of his 4-bay bowtie reflector variants fared very well in comparisons so I downloaded a spreadsheet of his and took the net gain numbers from it.

I used the terms M-4 and M-8 because he had not given them names, so I just used mclapp 4 and mclapp 8.

Today I'll put his spreadsheet up for you folks to check out. Hopefully mclapp will drop in today too.
 
#5 ·
Are you looking for the model or the data? A bunch of models can be found here http://www.frontiernet.net/~mclapp/Antennas/Computer%20Models/ most are in .ez format, the spreadsheet stampeder posted already.

The one Stampeder is calling M-4 is a 4 bay with a 14" reflector spacing, that one has the highest peak but a narrower band width, the 4 - 5" reflector spacings are more consistant across the UHF band but with 1 db or so less peak.

I've got a 8 bay vertical stack that's up to 19dbi net but have yet to test it other than computer modeling. A version of it is in the computer models folder in the link above, look for 8 bay vert stack.
 
#8 ·
It's (2) 10" whisker 4 bays stacked vertically with the feed points 40" apart with a curved 40" wide wire fence reflector spaced 4" behind the driven elements. I have only computer modeled this antenna, I haven't finished building it so it hasn't been tested out in the field. Here is a picture of the semi built antenna. The phase lines between the 2 antennas have not been attached yet.
 
#9 ·
If you have a way to read excel spread sheets I have one on my web space called "4 bay compare 11-23-08" It has the computer simulated gain info on that antenna and many others I've modeled.
http://www.frontiernet.net/~mclapp/Antennas/plots/
Sorry, I see stampeder already posted a link to that spreadsheet. If you can't do excel I could post a gain curve of that antenna.

I'll give a quick run down here. The UHF gain peaks at about 19.1dbi net around channel 41, the gain at channel 14 is 16.5dbi net and at ch 50 it's 17.5dbi net. I've found from my field testing on the antennas I've built that the gain curve is shifted downward on UHF a few channels compared to the computer models .

For VHF-HI the peak gain is 10.8dbi net on channel 8 and drops to 9.5dbi. net on channel 7 and 5.3 dbi net on channel 13.
 
#11 ·
mclapp:

Built 3 of your m4's with excellent results. I have enough materials on hand to built your stacked 8 bay and am ready to try it out. Couple questions.
1. What is the spacing for the 10"whiskers ?
2. Is your phase line spacing still 1 1/4" ?
3. You state a 40" feed point but I don't see it on your picture. (do you have a schematic I could follow?)
 
#13 ·
mclapp:

Built 3 of your m4's with excellent results. I have enough materials on hand to built your stacked 8 bay and am ready to try it out. Couple questions.
1. What is the spacing for the 10"whiskers ?
By spacing I think you mean bay to bay (vertical) spacing. I use 9 3/4" spacing on mine.
2. Is your phase line spacing still 1 1/4" ?
Yes
3. You state a 40" feed point but I don't see it on your picture. (do you have a schematic I could follow?)
I don't use stand offs at the feed point if I don't have to. I plan on soldering the co-phasing wires at the feed point of each 4 bay (which is the dead center of each 4 bay)
No I don't have a diagram of this yet I'm building mine off of the computer model dimensions.
The co-phase line is a little different, I'm going to use a tapered spaced phase line where the wires start at 1 1/4" at the feed point of each antenna narrow to 3/4" then open up to 2" at the center between the two 4 bays.

The tapered spaced line is an effort to get a better impedance match over a wider range of channels. I'll try to get a drawing made of the co-phase line the rest of the antenna is really just two 10" whisker 4 bays vertically spaced 40" center to center. It was modeled with swept forward elements (2") and a curved reflector 40" wide and 80" tall spaced 4" behind the elements. My as built uses two 40" wide x 38" tall reflectors and I left a 2" gap between the reflectors.
 
#12 ·
If there exist some detailed measurements for construction, I might be able to insert this antenna into a test lab equipped with a Spectrum Analyzer and Tracking Generator.. the output of which would be a plot of *actual* frequency response across the UHF band..

Need the measurements in easy-to-digest form, though.

Cheers
 
#18 · (Edited)
mclapp:

whiskers are spaced at 5 3/4" in the vertical and 3" in the horizontal, they are 7 1/2" long - I know, I'm guilty, I copied the youtube, just to try - guess I was lucky that it got me all the US HD channels (UHF of course) and 2 of the 3 local HD channels!

My understanding is that I should have calculated the whisker length as follows:

- take the highest available channel wanted (#53, CBS) frequency - 700 Mhz
- calculate (300/700) x 1/2 = .214 m = 8.4"

calculate whisker vertical separation = say 8.4" - .4" = 8"

use whisker horizontal separation = 1 3/8"

use 10 gauge wire for the whiskers and lines, is that optimal?

I know I have many details, connections, stand-offs to improve...

also I noted that the reflector (24" x 30") did not improve my reception capabilites too much in any direction...

Does this make any sense, or should I try your 9.5" x 9" plans

Now that I am gaining more knowledge about the physics, thanks to people like you, I am addicted and have found a new hobby!

I plan on making a better version, or maybe build another type (SBGH..)

thanks for the HELP
 
#21 ·
Balm,

the 9 1/2 x 9 covers the UHF band up to ch45 quite well but after that it starts to lose gain. If your stations above 45 are fairly strong it shouldn't be a problem. If you need more gain up high the just resclae the whisker length and phase line vertical spacings a little shorter like 9 x 8 1/2".

A reflector should make a noticable difference on your weaker stations it should be spaced 4" behind the elements for best UHF reception. 10 gauge wire should be fine for the whisker elements and will work for the phase lines but 14 or 16 gauge is better for the phase lines, not so much for gain but for the sake of cost and ease of construction.
 
#22 ·
mclapp:

Thanks. That is what I have done. I am now building a better model.

REGARDING MY NEW MODEL:

A) In your experience or studies how critical is vertical planity (in the z-axis)- for the following components, if you could comment each:

1- whiskers relative to phase lines (placing the whisker on top of phase line, instead of placing whisker bend adjacent (same elevation) to phase line);

2- one phase line relative to the other (if one is more elevated than the other);

3- cross-over points (uneven - one bridging over the other and/or one undercutting the other) - at one end I have one phase line bridged up and over the other (about 1/2" up and out of the plane of the phase lines), at the other end it's the opposite, I have one phase line passing beneath the other (about 1/2" under the plane of the phase lines)


B) How critical the location of the phase line cross-over relative to the top and bottom whisker connections (in the y-axis) - I saw a dimension of 2 1/4" to start of bends, 2 1/2" in the diagonals


C) What is the simplest, and/or optimal method of connecting the balun to the phase lines. Also is it always best to avoid using stand-offs and bolt connections for this.

I will probably ask you some questions later on about the reflector method, dimensions, but first I will study up!

Thanks for your patience...
 
#24 ·
mclapp:

Thanks. That is what I have done. I am now building a better model.

REGARDING MY NEW MODEL:

A) In your experience or studies how critical is vertical planity (in the z-axis)- for the following components, if you could comment each:

1- whiskers relative to phase lines (placing the whisker on top of phase line, instead of placing whisker bend adjacent (same elevation) to phase line);
Not sure what you're asking here but it's best to have the phase line to whisker connection so that the whiskers don't overlap too much, just enough to make a good connection. I've modeled the connection point where the whisker bend makes connection for more than 1/4" and it doesn't show any real difference.
2- one phase line relative to the other (if one is more elevated than the other);

3- cross-over points (uneven - one bridging over the other and/or one undercutting the other) - at one end I have one phase line bridged up and over the other (about 1/2" up and out of the plane of the phase lines), at the other end it's the opposite, I have one phase line passing beneath the other (about 1/2" under the plane of the phase lines)


B) How critical the location of the phase line cross-over relative to the top and bottom whisker connections (in the y-axis) - I saw a dimension of 2 1/4" to start of bends, 2 1/2" in the diagonals
The key thing to remember is that the phase line is just a feed line that attaches the whisker elements in phase. Try to keep the phase line wire spaced evenly apart at all points and keep both wires the same length between elements. This can't be done by just looping one wire over the other because you'll end up with one wire longer than the other and that element will be sligthly out of phase with the others. Where the wires actually cross in between the elements is not critical. I've found that a simple twist in the middle works as good as anything.




C) What is the simplest, and/or optimal method of connecting the balun to the phase lines. Also is it always best to avoid using stand-offs and bolt connections for this.

I will probably ask you some questions later on about the reflector method, dimensions, but first I will study up!

Thanks for your patience...
You can attach the balun to the phase lines the same way as you do the whisker elements with screws and standoffs. I prefer to attach my balun/feedline directly to the phase line by soldering and not use any screws or stand offs but that's not a must and they have worked fine either way.
 
#23 ·
Pointe_claire - new model

mclapp:

This is my new bow-tie (9 1/2 x 9):




1) can now pick up digital WVNY - ABC channel # 13, at 30 ft height, cannot lock properly below this height, any ideas how to ensure a lock at say 26 ft, preamp, reflector, longer whiskers etc...

2) lost local digital channel # 42, seems to respomd better with reflector...

3) Still cannot get local digital CBC channel # 19 or # 20, Mount Royal blocks most of the signal, however I did notice improvement here too, TV shows a 30-40% strength, compared to 10-20%...any ideas for this, as in bullet 1) above....

Thanks
 
#25 ·
You must have posted your latest build while I was posting the answers to your previous questions. Your build looks really nice those cross overs look fine from what I see in the picture. A reflector will gain you about 2-4 db on most channels.

To improve VHF-hi a 32" wide or larger reflector will be required. It could be simple rods spaced 3-4" apart vertically or some sort of wire fencing or hardware cloth with a vertical spacing of 3" or less.

The reflector should be spaced 4" behind the elements for channel 13 and UHF channels if you are using the 9 1/2" x 9" size elements and phase line dimensions.

You can squeeze a little more UHF gain out of it by sweeping forward the elements 2" and building a dished/curved reflector with about 2 1/2 to 3" of curve for a 36" wide reflector.

Heres an example of the curve how you do it is up to you, I'll also include a picture of an angled reflector that also works well but doesn't produce as even of a gain across the UHF channels but is still an improvement over a flat reflector. Neither the curve or angled reflector has any advantage over a flat reflector on VHF-HI



 
#26 ·
mclapp:

Thanks for the replies and close-ups.

you mention spacing rods 3-4" apart vertically, wheras with wire meshing to use 3" or less, why is the difference between the two, I assume it is due to the the larger diameter of the rods vs mesh...

thanks again
 
#28 ·
Yes due to the larger diameter of the rods or tubing you can get away with slightly larger vertical spacing. If using tubing or rods for reflector elements I found to get maximum gain for minimum elements it's best to put 2 reflector rods centered behind each whisker about 3 - 3 1/2"" apart like this.



This antenna uses single flat elements instead of whiskers but the same reflector layout could be used for either.

Forward gain isn't much different between this tubing reflector layout and 1" mesh but the rear rejection for the tubing reflector is not nearly as good on UHF.
 
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