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Discussion Starter #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
 

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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.
 

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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
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.
 

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8 bay vertical stack 19dbi Mclapp

Does anyone know I would find the specs on this antenna?element length and feed line spacing and stuff like that? Thanks
 

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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.
 

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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.
 

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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?)
 

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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
 

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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.
 

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Well I started building one of these but I already had my whiskers made up so it won't be exact. 9.5"whiskers with 9.25 spacing.I give update when done.
 

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bow-tie help

Anyone:

Any comments for changes to my DYI bow tie antenna for improved channel reception in the west island (Pointe-Claire), or should I scrap and build anew!

Thanks



 

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What dimensions did you use?

It looks like the V shaped whiskers are spaced too close together vertically and too far apart horizontally.

It's also best to use some sort of plastic spacer so the antenna elements are not directly mounted to the wood.
 

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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
 
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