Oddly at present, you have 6.13 dBi gain on channel 9 in the BACKWARDs direction.
:confused: How did you determine that? The front, bow-tie side, is facing DC. :confused:

From Nists NEC model of the CM-4221a. Ran it for channel 9 and looked at the radiation pattern. :p


http://img833.imageshack.us/img833/3346/cm4221a198ahorizpattern.jpg

The horizontal pattern is the top down view. 90 degress is forward, 270 degrees is backwards. A .78 dBi AGT adjustment was subtracted.

To clarify:
The horizontal pattern is the top down view.
90 degress is forward, (side w/bow-ties - correct?)
270 degrees is backwards. (side w/reflector- correct?)

About the 3 different gain (dBi) figures:

Youll go from .89 dBi 20.3 SWR presently on channel 9 to 8.18 dBi 17.8 SWR in the FORWARD direction. This statement is pre & post the reflector mod?

Oddly at present, you have 6.13 dBi gain on channel 9 in the BACKWARDs direction. So if nothing else, if you turn the antenna around, you should see a massive improvement in channel 9. (unless what youre getting is just reflected signal anyway) Pre reflector mod, there is more gain for ch-9 off the backside.


Thank you for running Ken Nist's NEC model for our CM-3021 and VHF Ch-9. It's our best hope of receiving CBS as you can see from our NM and the Effective ERP. If you have time, it would be interesting to see the graph for DC ch-4.1 (UHF 48). Per our CM-7000 D-2-A converter, it consistently has the lowest signal strength of all stations from DC and thus is the 1st to be affected by the DTV "cliff effect" during a storm.

Here is a link to some home building project loop antennae in the UHF bandsCham,
Thank you for looking up this info. ARRL - the Hams strike again! My Dad is a ham & he proudly points out all the current technologies that were pioneered by the Ham community years ago.

90 degrees is forward, (side w/bow-ties - correct?)
270 degrees is backwards. (side w/reflector- correct?)
Correct on both counts.

This statement is pre & post the reflector mod?
Yes, with typical gauge 2 X 4 mesh. Finer mesh wont improve vhf-hi channel 9 by more than about 1/10th of a dBi at most. But mesh finer than 2 X 4 mesh will improve UHF channel 48 much more. The existing 1 X 2 mesh size is optimum for channel 48, but not readily available in most locations.
The trade off is wind load. No sense in increasing gain if the antenna gets blown down during a storm, heh. Ill wait until you get the material size before running a simulation on it.

Here's a link to "The Long-Boom Quagi" (Two Loops + Directors Rods) that actually works,
plus a few more links of interest. Almost as much Gain as ALL Loop Yagi, but easier to build:
http://www.w6ier.org/images/guagi.pdf
http://www.qsl.net/ik1hge/homebrew/homebrew.html
http://www.iw5edi.com/ham-radio/?the-w5un-2-meter-quagi-97,85

And here are some ALL Loop Yagis:
http://www.om3rkp.cq.sk/articles.php?lng=en&pg=4&prt=1
http://home.planet.nl/~luijk802/yagi-uk.htm
http://www.directivesystems.com/loopyagi.htm
http://www.directivesystems.com/PDF/2424LYRMK.PDF
http://5919315501503148001-a-1802744773732722657-s-sites.googlegroups.com/site/weefiproject/antennas-howto-1/WI-FI_antenna_-_loop_yagi_antenna.pdf?attachauth=ANoY7cpXjHcdM9WNLPSUMpzxet JPun7J1LwSNhwNXRIZHskVx_aKDFdBRvUybE67F59wJFDe_CXXXYpd0IJ-szvGMPyLlIR2EioaLkpWvz74pX16oGUznx4fskUdYwtEUz509H3cgl2OX47H oE0NwBXwoKItwRXPPK3xAI_Xa7WIZKFPe5qAEWnl3nVMI4zpGsGkmHVp6ZLu DoqfyQt67crjTCuYoMl5M8ZQoY_t48obviQqWDQ__7ykAcDDsXsAPkDLsBkE vvqX&attredirects=1
http://www.w6pql.com/misc/range-story.htm
http://commfaculty.fullerton.edu/woverbeck/quagi.htm
Including a Loop Yagi Calculator program:
http://sites.google.com/site/weefiproject/

G0KSC has a number of Square Loop Yagi (aka OWA Quad) designs here:
http://www.g0ksc.co.uk/

G0KSC is also home of the "Loop Fed Array (LFA) Yagi" (Folded Dipole flopped over):
http://www.g0ksc.co.uk/intro-lfa.html

FYI: I modeled Two Circular Loop Elements (Reflector + Active) for Hi-VHF , which form the
CORE of either a Loop Yagi or a Quagi - just add Director Elements of either type & re-optimize:
http://imageevent.com/holl_ands/loops/looprefl
Can be rescaled about 1/3 the size & reoptimized for UHF....

Cebik also has several articles re Square Quad Yagi's:
http://www.cebik.com/content/radio.html [FREE Registration required.]also

But mesh finer than 2 X 4 mesh will improve UHF channel 48 much more. The existing 1 X 2 mesh size is optimum for channel 48, but not readily available in most locations.
The trade off is wind load. No sense in increasing gain if the antenna gets blown down during a storm, heh. Ill wait until you get the material size before running a simulation on it.

Thanks for the additional detail. I will attempt to locate 1 X 2 mesh size.

Today, I called 2 Lowes & 2 Home Depots. The larger local Lowes does offer 3' tall mesh with a selection of different mesh sizes. However, the shortest length roll starts at 15'. Both Home Depot stores offered the recommended mesh. However, roll sizes started at 50'.

Tomorrow I'll check our nearest True Value and Southern States. At least I know I can pick it up as a 15' roll.

Hello Holl_ands,

Thanks for the wealth of information contained in your post. Looks like I have my reading assignment for many nights. :o

Good Morning 300ohm,

I checked with Southern States, True Value & Ace Hardware w/o success. Finally, I found it in less than 50-ft, but ...
Cage Wire,
Height: 36 in.
Mesh: 1 in. x 2 in.
Gauge: 14 ga.
Material: Galvanized Steel
(http://www.tractorsupply.com/cage-wire-36-x-25-ft-1-x-2-in--3627241)

I've also called all the hardware stores in the county (none left in the city) w/o success. The days of "cut from a roll" appear to be gone.

The larger local Lowes does offer 3' tall mesh with a selection of different mesh sizes. However, the shortest length roll starts at 15'.
Red = BS alert.
Apparently, I spoke with a part-timer who told me what he thought they had & couldn't be bothered to check current inventory. Per full-timer today, nothing shorter than 50' - confirmed via Lowes web site: 36", 2"x4" x 50' = $31.

Try searching at the Lowes site for "WELDED WIRE"
30"X10ft 1/2"X1" 16 GA, $16 at my Lowes. At least its half the wind load of 1/2" X 1/2" wire and you could always clip out some vertical wires. :)

They dont seem to carry 1" X 1" welded wire in 30 inch widths.

otadtvman do you have a Tractor Supply in your area?
They carry a pretty good assortment of welded wire fencing.

kc2cbd,

Thanks for the reply.

Yes, about 1/2-hr away. This sku (http://www.tractorsupply.com/cage-wire-36-x-25-ft-1-x-2-in--3627241) was the smallest quantity I found.

Hi 300ohm,

I found a supplier that offers 3 choices of a curved reflector in an add-on kit. Which of the following reflectors would provide be most appropriate for our reception area?

a.) 36 x 36 x 1 x 2" - a larger sq area of 1 x 2"
b.) The original 20 x 36 x 1 x 2" screen centered in the middle of a 36 x 40 x 2 x 4" - a smaller sq area of 1 x 2", but a larger reflector overall.
He also offers 2 pieces of 24" x 36 x 1 x 2" overlaped and welded in the middle to create 40 x 36 x 1 x 2" - However, he said it's not too attractive.

Thanks

a.) 36 x 36 x 1 x 2" - a larger sq area of 1 x 2"
b.) The original 20 x 36 x 1 x 2" screen centered in the middle of a 36 x 40 x 2 x 4" - a smaller sq area of 1 x 2", but a larger reflector overall.
Based on my calculations of the CM4221 model, option B has .15 dBi better Net Gain on channel 9 than option A. But option A has .69 dBi better Net Gain on channel 48 than option B.

I would go for option A. The gain on channel 9 is already going to be a big increase over the present situation and .15 dBi is squat.

Hi 300ohm,

I greatly appreciate your calculations and agree with your logic. I will order the 36 x 36 x 1 x 2" curved reflector with the tilt function.

Mounting options:

Center pipe vs rear-mounting the larger reflector directly to the rotator mast

The rear mount takes the heavier reflector load off of the original reflector mounts that were only designed to support a 36 x 20 reflector - Makes structural sense.

Does having the rotator mast parallel to the backside of the reflector (vs. having the 4-bay inserted into the top of the mast) in any way negatively impact the performance?

Thanks!

Does having the rotator mast parallel to the backside of the reflector (vs. having the 4-bay inserted into the top of the mast) in any way negatively impact the performance?
No. With 2X4 mesh in front of the mast the performance impact is almost immeasurable. With 1X2 mesh, its half of that, heh.

Thanks, that's good to know.

We would like to make the larger reflector as inconspicuous as possible. Is painting it OK? If yes, what color do you recommend to achieve this goal?

One light thin coat of FLAT spray paint is fine for the reflector. I wouldnt paint the bowties or the phasing lines though.

The color for hiding depends on the background. If you have trees in the background, then a flat kelly green or Krylon camouflage green should do the trick.

I've finally found a local fence company (as you suggested) that will sell us the needed 1 x 2" welded wire without having to buy entire roll. Their 1 x 2" is 60" tall and they will cut it to 36 x 40".

They have both galvanized and green vinyl-coated? Which is better for this application?

Thanks