stagger stacking #13
Rabbit73,
thank you, but someone else originally found me that B. Thompson article, i believe 300ohm and holl_ands...
I have read thru it and attempted a stagger stack using his calculations. I built 2 identical 5 element K6STI yagis (swept back) optimized for my #13 situation (using 4nec2).
I placed them at 12 ft off the ground, 6" in front of my tower, vertical separation is 33", horizontal stagger is 13.86". They were built to within 1-2 mm accuracy, however stacking and alignment on the mast pole is VERY difficult to do accurately (but i think i came close)
And the good news is i had almost a full day of uninterrupted digital reception of #13 (WVNY) for the first time
reception registered a mere 50% on the tv meter. Again it came in with 20 db attenuation on the kitztech amp.
Bad news is in the early evening i lost reception, then I had to leave the house so couldnt continue testing. I did seem to lose reception when #13 analogue from the opposite side would reappear (although very snowy).
Acording to theory this is supposed to nullify the backside co-channel, but when I modeled the pair staggered in 4nec2, i'm not clear on the result, especially given the forward gain appears skewed (this would mean tilting the antenna to compensate and even then undesired #13 would probably still come in, and the f/b ratio doesnt seem to improve much.
That said, Im not sure how to model the combined antennas correctly. Maybe some of the modelers can comment. Or maybe some other design is better suited. But there is now more reason for optimism. Im also unclear on the advantage of going to this trouble as compared to designing a specific single yagi with very high f/b ratio.
Thanks
Here is the nec file:
Code:
CM Hi-VHF, 5-El Yagi w Swept Driver, 4nec2 file by holl_ands, 19Jun2009.
CM Rev A to Brian Beezley (K6STI) design using AO 8.06 Antenna Optimizer.
CM All elements Aluminum with O.D.=3/8". SOURCE: Elem#2 middle segment.
CM Char Imp = 75-ohm. Boom Correction: Metal Boom, Insulated top mounts.
CM ALL MEASUREMENTS ARE IN INCHES. Segments per AutoSegmenter.
CE
GW 1 13 0 -13.25 0 0 13.25 0 0.1875
GW 2 13 11.625 -12.5 0 11.625 12.5 0 0.1875
GW 3 11 24 -12.25 0 24 12.25 0 0.1875
GW 4 11 40 -11.75 0 40 11.75 0 0.1875
GW 5 7 3 -15.25 0 7.875 -1 0 0.1875
GW 6 7 7.875 1 0 3 15.25 0 0.1875
GW 7 1 7.875 -1 0 7.875 1 0 0.1875
GW 8 13 13.86 -13.25 33 13.86 13.25 33 0.1875
GW 9 13 25.485 -12.5 33 25.485 12.5 33 0.1875
GW 10 11 37.86 -12.25 33 37.86 12.25 33 0.1875
GW 11 11 53.86 -11.75 33 53.86 11.75 33 0.1875
GW 12 7 16.86 -15.25 33 21.735 -1 33 0.1875
GW 13 7 21.735 1 33 16.86 15.25 33 0.1875
GW 14 1 21.735 -1 33 21.735 1 33 0.1875
GS 0 0 0.0254 ' All in in.
GE 0
EK
LD 5 0 0 0 3.08e7 0
EX 0 7 1 0 1 0
EX 0 14 1 0 1 0
GN -1
FR 0 1 0 0 213 0
RP 0 1 73 1511 90 0 1 5 0 0
PS :
Rabbit73: could you provide me a link on the Salvati article also. Thank you.
Stampeder, perhaps our last few posts should be subject of a new thread or addded to the old thread of last year ("Which VHF-Hi only antenna?"), thanks