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Old 2010-08-28, 02:20 AM   #31
300ohm
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Quote:
Maybe even better, has anyone build a mclapp or other bay-type scaled to VHF-Hi?
Holl_ands has some VHF-Hi bowties here:
http://imageevent.com/holl_ands/mult...o10bb81.frog_s

Quote:
I have an Antennacraft version that I bought a couple months ago, and I'm surprised at how well it works. But I'm sure it's satisfying to DIY one instead.

Was looking around because I have two VHF channels (8 and 9) that I'd love to get
If you have the Antennacraft G1483, you could put NARODs and NAROD reflectors on it to get VHF-Hi.
Post your TVFool image or link so we can see what kind of gain channels 8 and 9 would need.
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Old 2010-08-28, 08:53 PM   #32
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Non-metallic materials, such as PVC and Wood do NOT require any Boom Corrections.

If you decide to use a metal boom, recalculate using K7MEM on-line calculator.
But you'll find that at Hi-VHF frequencies, the differences are small enough to ignore.....
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Old 2010-09-14, 01:46 PM   #33
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ok, i nee to build a fairly simple single channel #13 antenna soon to test, with a HIGH f/b ratio and of course higest gain possible say in the 4-5 ft long range...any suggestions....
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Old 2010-09-14, 03:00 PM   #34
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Just saw this for some reason, but thanks, 300 ohm and holl_ands... I was talking with holl_ands on the avs forum, and I'm going to try one of the VHF-hi bowties from his site. I may make it from wood at first just for ease of construction, then convert it to PVC if it works well enough to make it more permanent. (Or maybe even waterproof the wood -- I have a big can of polyurethane sitting around.)

I might try another yagi some time, and take my time with it for better precision. But first I want to try the bowtie design, partly for the wider bandwidth. (If I can get a reflector on the big thing, it has high FM gain as well.)

And 300 ohm, it's 2-edge stuff... Just a fun DXing thing I do on some stations 125 miles away when conditions are favorable.

I need to go read that link Stampeder provided on the building materials... Looks like some great ideas. Thanks for that!
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Old 2010-09-14, 03:08 PM   #35
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K7MEM On-Line Calculator comes up with 51-in 6-Element and 66.5-in 7-Element designs:
http://www.k7mem.150m.com/Electronic.../yagi_vhf.html
He provides guidance for either a 300-ohm Folded Dipole or 75-ohm Straight Dipole design.

51.0-in, 6-Element Yagi: 8.9 dBd = 11.1 dBi
66.5-in, 7-Element Yagi: 9.8 dBd = 12.0 dBi

These would need to be modeled to determine F/B and F/R Ratios...but is probably not quite
as high as K6STI's Optimized 5-Element (31-in) Yagi with 9.5 dBi Gain and 22+ dB F/B & F/R on Ch13:
http://imageevent.com/holl_ands/yagis/k6sti
K6STI developed his own Yagi Optimizer program, the results of which you see above.....

Note charts for K7MEM's (non-optimized) 4-Element (29-in) and 8-Element (100-in) Yagi designs.
Unfortunately, the formula driven Yagi designs are NOT OPTIMIZED for much of ANYTHING, including
an impedance targeted for Amateur Radio use rather than TV coax.

Hi-VHF 2-Bay with Screen Reflector has 12.5 dBi Gain on Ch13 and F/B & F/R in 15 dB region
(which I would expect to be similar to what modeling would reveal for the K7MEM 6 & 7-Element Yagi's):
http://imageevent.com/holl_ands/multibay/hivhf2bayrefl
Note that it is 56-in high, 72-in wide and 16-in deep.

Reflector Rods, rather than a Screen Reflector should be able to improve the F/B & F/R Ratios,
but would have to be modeled (full width vs split in middle).....hmmm, need to add to my TO-DO list...
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Old 2010-09-14, 08:55 PM   #36
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thanks Holl_Ands for the recap....yep, looks like the best compromise, size, gain f/b, is the 5 element 31"...
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Old 2010-09-15, 07:59 AM   #37
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It looks like a biquad can be optimized to have 10+dBi netgain on ch13
with f/b f/r around 20dB and dimensions within 57"x47"x13".
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Old 2010-09-15, 11:14 AM   #38
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im trying to decrease the beamwidth on the yagi styles, including the 5 element swept back yagi, any ideas.....

putting mesh doesnt seem to help
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Old 2010-09-15, 04:32 PM   #39
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this is the model I was talking about.

did not quite match the claims, since I was originaly wrongly optimizing for the channel above 13...

still 10.5+ dBi gain on ch13, 18+ dB F/B,F/R

Code:
CM 
CM biquad for VHF-hi
CM optimized by nikiml
CE
SY radius=0.003175
SY feed=0.03231829	'0.01, 0.07
SY y1=0.3184432	'0.1, 0.6
SY z1=0.5801599	'0.1, 0.65
SY z2=0.163965	'0.05, 0.6
SY drz0=0.1151976	'0.02, 0.2
SY rz1 = 0 +drz0
SY drz1=0.1865335	'0.02, 0.25
SY rz2 = rz1 +drz1
SY l1=0.6272845	'0.01, 0.65
SY l2=0.6169326	'0.01, 0.65
SY drz2=0.2077309	'0.02, 0.25
SY rz3 = rz2 +drz2
SY l3=0.5884499	'0.01, 0.65
SY drz3=0.2019844	'0.02, 0.25
SY rz4 = rz3 +drz3
SY l4=0.3359146	'0.01, 0.6
SY x=0.3356441	'0.01, 0.4
GW	1	35	0	feed	0	0	y1	z1	radius
GW	2	19	0	y1	z1	0	0	z1+z2	radius
GX	10	010
GW	3	67	-x	-l1	rz1	-x	l1	rz1	radius
GW	4	66	-x	-l2	rz2	-x	l2	rz2	radius
GW	5	63	-x	-l3	rz3	-x	l3	rz3	radius
GW	6	36	-x	-l4	rz4	-x	l4	rz4	radius
GX	20	001
GW	100	5	0	feed	0	0	-feed	0	radius*1.1
GE	0
LD	5	0	0	0	24900000
GN	-1
EK
EX	0	100	3	0	1	0	0	
FR	0	0	0	0	213	0
EN
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Old 2010-09-21, 04:48 PM   #40
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im trying to model an added corner reflector to a vhf style yagi, but not sure the minimum criteria, any ideas


so far my attempts have not increased either gain, or directionality, or f/b...

i read that 90 degrees and 60 degrees are typical apex angles, and the grid area should be at least 2 x the target wavelength
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Old 2010-09-21, 05:29 PM   #41
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Quote:
i read that 90 degrees and 60 degrees are typical apex angles, and the grid area should be at least 2 x the target wavelength
Yeah, 90 degrees is the most common. Keep playing with the driven element to corner distance.

Its gonna be one big corner reflector, heh.

Heres the NEC file for my Antenna Craft CC-12 uhf corner reflector. Its simple and small. Just rescale it for vhf-hi frequencies.

CM 300ohm-Yagi, converted with 4nec2 on 18-May-08 20:30
CE
GW 1 3 0.182 -0.0215 0 0.182 0.0215 0 5.05e-3
GW 2 38 0.08699 -0.204 0.09661 0.08699 0.204 0.09661 5.e-3
GW 3 38 0.12397 -0.204 0.19322 0.12397 0.204 0.19322 5.e-3
GW 4 38 0.26096 -0.204 0.2898 0.26096 0.204 0.2898 5.e-3
GW 5 38 0.08699 -0.204 -0.09661 0.08699 0.204 -0.09661 5.e-3
GW 6 38 0.12397 -0.204 -0.19322 0.12397 0.204 -0.19322 5.e-3
GW 7 38 0.26096 -0.204 -0.2898 0.26096 0.204 -0.2898 5.e-3
GW 8 10 0.182 -0.0215 0 0.182 -0.187325 0 5.e-3
GW 9 10 0.182 0.0215 0 0.182 0.187325 0 5.e-3
GW 10 10 0.252 -0.0762 0 0.252 0.0762 0 5.e-3
GW 11 10 0.353 -0.0762 0 0.353 0.0762 0 5.e-3
GW 12 10 0.454 -0.0762 0 0.454 0.0762 0 5.e-3
GW 13 10 0.555 -0.0762 0 0.555 0.0762 0 5.e-3
GW 14 10 0.656 -0.0762 0 0.656 0.0762 0 5.e-3
'GW 15 10 0.08699 -0.204 -.0254 0.08699 0.204 -.0254 5.e-3
GE 0
EK
LD 5 1 0 0 25000000.2 0
LD 5 2 0 0 25000000.2 0
LD 5 3 0 0 25000000.2 0
LD 5 4 0 0 25000000.2 0
LD 5 5 0 0 25000000.2 0
LD 5 6 0 0 25000000.2 0
LD 5 7 0 0 25000000.2 0
LD 5 8 0 0 25000000.2 0
LD 5 9 0 0 25000000.2 0
LD 5 10 0 0 25000000.2 0
LD 5 11 0 0 25000000.2 0
LD 5 12 0 0 25000000.2 0
LD 5 13 0 0 25000000.2 0
LD 5 14 0 0 25000000.2 0
EX 6 1 2 0 1 0
GN -1
FR 0 60 0 0 470 6
RP 0 1 10 1510 90 0 0 20 0 0
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Old 2010-09-21, 07:15 PM   #42
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thanks 300 ohm, simple looking antenna,

as expected at 213 mhz it gives a 3' x 4' reflector, i guess still manageable...
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Old 2010-09-22, 06:36 PM   #43
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Cebik has several articles re Corner Reflectors and SUPER Corner Reflectors that you should read:
http://www.cebik.com/content/radio.html
FREE Registration required.....and as usual, BIGGER is BETTER.....
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Old 2010-09-23, 02:14 AM   #44
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Holl_ands, any thoughts on efficiently joining a vhf-low antenna to a vhf-hi/uhf combo antenna ?
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Old 2010-09-23, 03:38 AM   #45
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A Hi-VHF Circular Loop + Reflector is another option. There are several variations on this such as hoop or screen reflector and square driven element instead of a hoop. With a little work it can be optimized for channel 13. For a commercial implementation see the Antennas Direct C5.
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