Building and Attic Installation for Hi-VHF 14-Element Zig-Zag LPA (Log Periodic Array).
Initially tried to fit the more compact STACKED Zig-Zag configuration....now that we see how much room we have to play with, will swap in the Risers for an 18-deg WEDGE Zig-Zag configuration. If we can't quite get the 18-deg WEDGE to fit, we'll either reduce the angle or wrap the trapezoid AROUND that pesky stud.
The two trapezoidal 3/4-in Sked 40 PVC frames are held together with press fit (no glue) 90-deg Elbows. Cross Braces and Risers are attached using 2+ in screws for easy reassembly...and less expensive than PVC. One trapezoidal frame fits on top of the other, with the Zig-Zag patterns in OPPOSITE directions. Standard 4:1 (300-to-75-ohm) Balun connects between upper and lower Zig-Zags at small end. In STACKED configuration, center-to-center height is 3.25-in. Both are 33-in wide and 100-in long. In WEDGE configuration, widest height separation (between wires) is 31.36-in narrowing down to zero at Balun.
RG-58, RG-59 or equivalent shield coax (0.25 in diameter) is strung in a Zig-Zag pattern within the trapezoids, using tie-wraps to minimize proximity to (likely) signal sucking PVC.
I stripped insulation off the RG-58, but 4nec2 model revealed it was unnecessary at VHF freqs (but required at UHF). I would avoid RG-6 type coax unless it has 95+% BRAIDED shield type construction....most are foil + partial braid shield.
Photos show stringing in process, where Balun connects to one Zig and completed Zig-Zags before stacking and connecting to other side of the Balun. Yes, it takes up most of that big Family Room.
Front & Rear Trapezoid PVC pieces and screws on one end of longest Cross Braces (only...no really) were removed to collapse and snake through attic access hole (est. 2.5-ft x 2.5-ft)....sorry, we were too busy to take a photo.
The bottom of the WEDGE can lie parallel to the floor and the small elevation angle might even help reception. Later, we put cardboard boxes under the antenna to keep it away from the signal sucking floor. Now if those metal nailing plates weren't there....FWIW, inner spirals in black A/C ducts feel like plastic vice metal.... But Deflecto website didn't list the Tele Flow PJ25 Series Flexible Duct....anyone know what's inside???? Current attic location may not be optimal, but avoids looking towards either of two A/C systems or CM-4228.
============================================================= HOW DOES IT WORK (so far, we aren't done.....):
Although L.A. Ch7 and 9 came in OK, it wouldn't hurt to have more margin....and like many people in L.A., we're still waiting for Ch11 and Ch13 to come up to full power....and pending maximization grants to be implemented sometime in the (near?) future.....
We rotated Stacked Zig-Zag to minimize signals coming from local low power Ch12 (ONLY 2.6 MILES AWAY!!!!) which can block reception from adjacent Ch11 and 13. Monitoring Ch12 via an analog TV, we needed a WEAK signal, so bypassed Preamp and went through 25 dB R-S Variable RF Attenuator plus 6 and 10 dB Fixed. For our situation, we needed about 30 dB.
STACKED Risers were replaced with WEDGE Risers, presumably for another 1-2 dB of Gain and deeper NULL, but there wasn't enough room to tweak the rotation again....and it was HOT!!!! (110-deg outside)
So we threw the YA-1713 on top of a duct, tweaked it a little and retreated....
Nonetheless, we're still waiting for Ch11 and Ch13 to fix THEIR problems....
============================================================ We also attempted to minimize local Ch27 coming into CM4228, but Ch28 (KCET PBS#3) is simply too weak (NM = 1.8), so returned to original orientation maximized for Mt. Wilson. New medium gain W-G AP8700 Preamp was better on UHF than original high gain C-M Spartan...so local stations probably were raising intermod noise floor. [New since original installation.]
Date(s): June 21,2009. Album by holl_ands. 1 - 12 of 12 Total. 3465 Visits.
enlarge 0KB, 1024x682 1 Stringing the Zig...Zag is next to it... Tiewraps are cheap and keep wires away from PVC. Risers for Stacked configuration are under my arm.
PS: I still have more hair than my brothers....
enlarge 0KB, 682x1024 2 Finishing the Zig with Balun attached Other side of Balun connects to Zag (on right).
enlarge 0KB, 1024x682 3 Finished Zag slides over, on top of Zig. Risers screw in for desired separation height. (See next photo in Attic.)
To move, unscrew one end of the longest cross brace and remove front & rear at Elbows...then collapse. Remaining width fit through small attic access hole.
enlarge 0KB, 768x1024 4 STACKED Hi-VHF Zig-Zag in the Attic A/C nearby on the left, nailing plates everywhere. Wedge Zig-Zag may wrap around that stud. I'ld like to get it HIGHER and to the RIGHT.....
enlarge 0KB, 1024x768 5 Deflecto TeleFLow PJ25 Series Flexible Duct
Anybody know if there is any metal inside??? "Feels" like plastic to me....
enlarge 0KB, 1024x768 6 Holland UVSJ VHF/UHF Combiner feeds Winegard AP8700 Preamp tiewrapped to back of CM4228 UHF 8-Bay Antenna.
enlarge 0KB, 768x1024 7 CM4228 8-Bay UHF Antenna in best of several locations. Looks through 3/4-in Plywood and FibreCrete tiles.
enlarge 0KB, 768x1024 8 CM4228 - Front View
My nailing plates are much smaller. Probably helps earthquake survivability, but must be affecting TV reception....
enlarge 0KB, 1024x768 9 Power Insertion Modules & E-N Router.
No Joy w 2nd CM4228 pointed south to San Diego. So removed second PIM & power strip.
Should all fit back where it came from...
enlarge 0KB, 768x1024 10 On the TO-DO list: a bigger wiring box.
Easy access to separate E-N, SAT & TV lines to each room.
enlarge 0KB, 1023x779 11 WEDGE Zig-Zag wrapped around some struts
