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Actually it looks pretty compact. No, it hasnt been modeled. Not enough details available.
 

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Discussion Starter #24
model BLV6F

when i modeled the BLV6F, the far field gain pattern runs out the backside, instead of the front, is this just a lack of info in the model, or does it take a lot more optimizing to find the correct dimensions, or am i using NEC wrong?
 

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Discussion Starter #26
thank 300ohm, ive narrowed the evolvers values range on the variables, and it seems to be going te right way now....round 12 dbi gain
 

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Discussion Starter #27
swept back

can you explain in basic terms why/how the swept back active element in these yagis (K6STI) help improve gain and f/b, intuitively i would have thought sweeping it forward would help? :confused:, and can this swept back be applied to all different types of yagis?

http://imageevent.com/holl_ands/yagis/k6sti
 

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The gain and the f/b come from the interaction of the directors and reflectors to the driven element.
Sweeping back the DE normally broadens the beamwidth, which in this case it looks like it does.
Also sweeping back normally results in some loss of gain, but if done correctly its minimal.
Sweeping forward does the opposite, narrows the beam and increases gain, but if swept forward too much, undesirable sidelobes will appear.


and can this swept back be applied to all different types of yagis?
Yes, but the trick is to do so with a minimum loss of gain. In the above example, the directors and reflectors are carefully placed to minimize the loss.
 

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Hey, everyone. First post here, although I've read for years. I have to say, the Hoverman work is phenomenal, and many of you are outstanding craftsmen with your builds! 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, and the K7MEM scaled for 8-10 that holl_ands posted looks perfect. I'm a little skittish because I threw together a yagi a couple of years ago, and it was a dismal failure. :( I didn't put the proper effort into it, most likely.

Any ideas for the boom on one of these other than wood? I see that the sim was run for a wood boom, but PVC would be so much lighter. Not sure how I'd attach the elements to the top of the round conduit, though... And after last time, I think it's important to be absolutely precise.

Maybe even better, has anyone build a mclapp or other bay-type scaled to VHF-Hi? I know it would be big, but this is just a fun DX-type project and at my location space isn't a concern.

Thanks. :)
 

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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/multibay;jsessionid=w78o10bb81.frog_s

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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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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Discussion Starter #33
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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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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K7MEM On-Line Calculator comes up with 51-in 6-Element and 66.5-in 7-Element designs:
http://www.k7mem.150m.com/Electronic_Notebook/antennas/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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Discussion Starter #36
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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Discussion Starter #38
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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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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Discussion Starter #40
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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