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Not true. See

http://ham-radio.com/k6sti/vhftv.htm

In addition to neglecting the ferrite bead at the feedpoint (not listed as optional), your element diameters are wrong. The pattern of this design, which has no backlobes worse than 21 dB down when correctly implemented, is sensitive to element lengths, element diameters, element spacing, and pickup of signals by the outside of the coax shield.

This is a fine example of how not to build a high-performance Yagi.

Brian
HI:

Once again thank you for your antenna plans and your advice. I guess your a perfectionist and that's a good thing in a theoretician. When I discovered this site and read about the SBGH Gen1 antenna I wanted to build one but I started to obsess over the minutae of if I could build it to the right tolerances with the right materials and all that kind of stuff. What I found was that that kind of thinking prevented me from trying anything because I was worrying more about getting it totally right than getting anything at all. I also figured that if I had to spend pretty well as much to make an antenna compared to buying one then it would make more sense to just buy it ready made and be done with it. So I came to the conclusion that if I was going to build an antenna that it only made sense if I could build it for next to nothing. However going this route entailed that I would have to scrounge for materials and that that would probably mean that I couldn't make it perfectly because you're limited to what materials you can scrounge up. So I told myself that if I could make it good enough with free materials rather than perfectly with paid for materials then that would be a fair tradeoff. So once I got over that hurdle I was finally able to move forward with actually doing something. That's how I approached building your antenna. Guess what, it works GOOD ENOUGH. It brought a marginal signal in my attic from about 15 % on the signal meter upto the 45 to 55 % region, with 40% needed for decode. I was finally able to watch a channel that I wasn't able to watch before. So it may not be a perfect build but she still drives! Just for the record the signal is 2-edge on rf10 at 37 miles with a NM of 13. The antenna is in my attic.

Now as to the ferrite choke, I totally forgot about that. In fact I have one around here somewhere that I bought a few years ago. If I read you right then adding the choke should help better in rejecting signals from the back, right? Would it also help with increasing the gain on more marginal signals from the front? I might try with the one I have and see but i'm not going go hunting for a new one. If it doesn't work correctly with what I have then no problem since the antenna performs adequately as is.

So, once again thanks.

P.S. I added the following comment at the end of the comment in my picture album for that picture you were referencing,
-------------------------------

P.S. Member K6STI informs me that a ferrite choke is is required on the feedline and that my build is "a fine example of how not to build a high-performance Yagi". You can see his full comment here

http://www.digitalhome.ca/forum/showpost.php?p=1359259&postcount=319

You can see my response a couple of comments down. Essentially my position is that it works good enough so i'm happy. You can see his plans for his Yagi at the following website.

http://ham-radio.com/k6sti/vhftv.htm
 

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Your losses from having different element diameters than specified, and wood holding the driven element, are miniscule in comparison to the large losses suffered in an attic compared to outside, heh.

k6sti is also a ham operator. As such, hes also concerned with transmitting which requires a much higher degree of perfection and precision lest the FCC comes to pay a visit. :p

Striving for perfection is good, but with reception only antennas theres a bit more leeway. Most commercial TV antennas are very far from perfect too.

I looks like you could slip some plexi or Styrofoam in between the wood and the driven element pretty easily just by pulling up the nails on the coax holders a bit.
 

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Hi:

Thanks for the comments. Yes striving for perfection is a good thing. For that I thank K6STI for trying to get me to do better. I would like to do it better but I think when your doing your first few builds that it's ok to just build it and get something up there thats half decent. Then as time goes on and you maybe build more you can get better. That's what I did with SBGH Gen1. Did the first and then a second which was built somewhat better. You can see it in my DHC photo album.

The driven elements on the platform are embedded in a slit of a few mm that I etched in the platform so that they would maintain the correct angle. So far the kludge seems to be holding.

I have the K6STI yagi pointed at WBBZ rf7 currently. It is a -5.8 NM 2-edge signal at 96 miles. I get a consistent 10% on the signal meter. However WBBZ is apparently very difficult to get. I'm thinking of trying another rf7 attic yagi. A monster yagi. We will see.
 

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Best Gain

Balm from post 1 said:
i would like to know what VHF-Hi only antenna, specifically #13, would give the maximum gain, commercial or DIY
I noticed the finco 400 hasn't been mentioned so I'll nominate it
even though trying to get it to be a broadband antenna (even over just high VHF)
has proven difficult, getting good performance on single channels or groups of 2-3 gets better performance.
This one gets 15 dBi @ 213 with swr 1.5 and a f/b ~19
Code:
CM finco 400s test bed tuned for channel 13 213 Mhz
CM fro-bac kit installed all sy variables start with "fb"
CM what follows is my mnemonic for what variables are what
CM fpg is feed point gap
CM fph is feed point height 
CM th is top height
CM s is separation
CM cl colinear length
CM sg is stub gap
CM sl is stub length 
CM r is reflector depth
CM ry is reflector inner end
CM rl is reflector length
CM fbl is frobac length
CM fbs1 is spacing for lowest fb reflector 
CM fbs2-7 next frobac reflector up: 8 total
CM fbo frobac start
CM fbr frobac radius 
CM xpl is extra phase line 
CM rad and refrad are radii
CE
SY fpg=1
SY fph=12.45153
SY th=13.896
SY s=6.0183
SY cl=11.377
SY sl=29.30401
SY rth=s+fph+th
SY sg=1.9485
SY r=-8.64
SY ry=0
SY rl=46.305
SY fbl=51.473
SY fbs1=S/5
SY fbs2=3/5S
SY fbs3=(rth-s)*1/5+s
SY fbs4=(rth-s)*2/5+s
SY fbs5=(rth-s)*3/5+s
SY fbs6=(rth-s)*4/5+s
SY fbs7=2s/5+rth
SY fbs8=4/5s+rth
SY fbo=0
SY fbr=3/8 
SY xpl=1.44
SY rad=0.05094856
SY refrad=0.5
GW	1	11	0	fpg	s+fph	0	fpg	rth	rad
GW	2	11	0	fpg	s+fph	0	fpg	s	rad
GW	20	9	0	fpg	rth	0	fpg+cl	rth	rad
GW	25	9	0	fpg	s	0	fpg+cl	s	rad
GW	31	11	0	fpg+cl	rth	0	fpg+cl	s+fph	rad
GW	32	11	0	fpg+cl	s	0	fpg+cl	s+fph	rad
GW	36	3	0	fpg+cl	s+fph	0	fpg+cl+sg	s+fph	

rad
GW	41	11	0	fpg+cl+sg	s+fph	0	fpg+cl+sg	

rth	rad
GW	42	11	0	fpg+cl+sg	s+fph	0	fpg+cl+sg	

s	rad
GW	61	23	0	fpg+cl+sg	rth	0	fpg+cl+sg+sl	

rth	rad
GW	62	23	0	fpg+cl+sg	s	0	fpg+cl+sg+sl	

s	rad
GW	302	23	r	ry	s	r	rl	s	refrad
GW	301	23	r	ry	rth	r	rl	rth	refrad
GW	50	1	-3.5	fpg	s+fph+xpl+3	-4.6480504	fpg	

s+fph+xpl+2.7716386	rad
GW	51	1	-4.6480504	fpg	s+fph+xpl+2.7716386	

-5.6213205	fpg	s+fph+xpl+2.1213205	rad
GW	52	1	-5.6213205	fpg	s+fph+xpl+2.1213205	

-6.2716386	fpg	s+fph+xpl+1.1480504	rad
GW	53	1	-6.2716386	fpg	s+fph+xpl+1.1480504	-6.5	

fpg	s+fph+xpl	rad
GW	54	1	-0.5	fpg	s+fph+xpl	-0.7283614	fpg	

s+fph+xpl+1.1480504	rad
GW	55	1	-0.7283614	fpg	s+fph+xpl+1.1480504	

-1.3786795	fpg	s+fph+xpl+2.1213205	rad
GW	56	1	-1.3786795	fpg	s+fph+xpl+2.1213205	

-2.3519496	fpg	s+fph+xpl+2.7716386	rad
GW	57	1	-2.3519496	fpg	s+fph+xpl+2.7716386	-3.5	

fpg	s+fph+xpl+3	rad
GW	58	21	-6.5	fpg	0	-6.5	fpg	s+fph	rad
GW	65	3	-6.5	fpg	s+fph	-6.5	fpg	s+fph+xpl	

rad
GW	66	3	-.5	fpg	s+fph	-.5	fpg	s+fph+xpl	

rad
GW	59	1	0	fpg	s+fph	-.5	fpg	s+fph	rad
GW	100	33	r	fbo	fbs1	r	fbl	fbs1	rad
GW	101	33	r	fbo	fbs2	r	fbl	fbs2	rad
GW	102	33	r	fbo	fbs3	r	fbl	fbs3	rad
GW	103	33	r	fbo	fbs4	r	fbl	fbs4	rad
GW	104	33	r	fbo	fbs5	r	fbl	fbs5	rad
GW	105	33	r	fbo	fbs6	r	fbl	fbs6	rad
GW	106	33	r	fbo	fbs7	r	fbl	fbs7	rad
GW	107	33	r	fbo	fbs8	r	fbl	fbs8	rad
GX	400	011
GW	208	3	-6.5	fpg	0	-6.5	-fpg	0	0.18899
GS	0	0	0.0254		' All in in.
GE	0
EK
LD	5	0	0	0	5.8e7	0
EX	0	208	2	0	1	0
GN	-1
FR	0	1	0	0	213	0
Some of the reflector bars are kind of close together at least two could be removed with only small effect.
 

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VHF antennas discussion

Is there a VHF only discussion thread out there? If so, I can't seem to find it.

Why just VHF? My UHF antenna (clone DB8) is OK pulling in the local stations and some of the more distant US stations but it appears to be at the expensive of my local VHF station (namely CFTO - channel 9). On bad weather days ... it's on the edge of reception. Would be great if I could point something in the direction of Hamilton to pick up CHCH too.

I saw some discussion on building a loop VHF antenna but haven't come across any specific commerical ones. Just looking for something that I can add to in my attic antenna setup to make it a farm.
 

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There is a chart that distills the wisdom of antenna discussions in a sticky thread just a few rows up. The closest you'll get to a commercial VHF-hi loop is the Antennas Direct C5.
 

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threeflags, I know that you're using a DB8 clone, but you may wish to check out the Antennas Direct Antenna thread. AD is now selling a CV2E VHF kit which is a simple VHF dipole which can be combined with AD antennas--and it may work with yours.

I believe the kit includes a VHF/UHF combiner.

It doesn't offer significant gain on VHF, but it may be all you need for CFTO at your location.
 

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On your DB8 clone, just stick about four 32 inch reflector rods on it, or attach a piece of 32 inch wide mesh to it for channel 9.
 

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K7MEM Channel 7 Yagi

I plan to build a 10-element Yagi for channel 7 based on the K7MEM design tool this spring http://www.k7mem.150m.com/Electronic_Notebook/antennas/yagi_vhf.html

My target channel 7 station, WBBZ, at my location is 2EDGE with a +11.1 dB noise margin and is 82 miles distant. During the summer, I get reception about 1/3 of the time. In the winter, reception is extremely rare, but normally just below the lock level
According to the K7MEM model, I should get a gain of 11.8 dBd or 13.9 dBi at Channel 7. This compares to 9.7 dBi that my current antenna, a Nikmil GH10n3 is supposed to deliver.

My other VHF-Hi stations, CFTO & CHCH at Channel 9 & 11 respectively have 57 and 43 dB noise margins. Hence, I assume that changing to a channel 7 Yagi will not adversely impact the reception of these stations.

Question
The K7MEM calculator at a 178 Mhz design frequency and for ¼ inch tubing gives a driven element length of 812 mm. This assumes a simple 75 ohm dipole. According to the folded dipole design tool http://www.k7mem.150m.com/Electronic_Notebook/antennas/folded_dipole.html the folded dipole length should be 801 mm or 11 mm shorter. Can I use the shorter folded dipole element on the design that the K7MEM tool derived that assumes a simple dipole and still get the same performance?

I want to use a folded dipole so I can connect at 300 ohms and to simplfy construction.
 

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Discussion Starter #331
New Ch. #13 yagi...

After our attempt at the 8 element, 96" (75 ohm) Ch #13 yagi last summer, I discovered this:

a 7 element yagi, only 80" long, but a little less powerful than previous.

I put the model here, with .25" diameter elements, it gives impedance of 28 ohms, and 12.8 dbi gain...perhaps the modeling experts might want to look closer at this one, maybe it can be improved on #13, as a channel-cut with less mismatch loss and a "cleaner" pattern.

Again, I ssume some sort of capacitor might be necessary (as previous), but I'm not sure.

Code:
CM 7 el yagi  213 Mhz - 28 Ohm , March 2, 2012
CE
GW	1	21	0	13.7265748	0	0	-13.726575	0	0.125
GW	2	19	8.66240157	12.9269685	0	8.66240157	-12.926969	0	0.125
GW	3	19	14.9259843	12.5538189	0	14.9259843	-12.553819	0	0.125
GW	4	19	27.5864173	12.2739567	0	27.5864173	-12.287283	0	0.125
GW	5	19	44.3781496	12.1007087	0	44.3781496	-12.100709	0	0.125
GW	6	19	64.1017717	12.1939961	0	64.1017717	-12.207323	0	0.125
GW	7	19	79.4275591	11.8608268	0	79.4275591	-11.860827	0	0.125
GS	0	0	0.0254		' All in in.
GE	0
EK
LD	5	0	0	0	24900000
EX	0	2	10	0	1	0
GN	-1
FR	0	15	0	0	198	1.5
RP	0	1	73	1510	90	0	1	5	0	0
 

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GHZ24 re Finco 400 Models:

You posted a 4nec2 file for a Finco 400-S in post #0324 above.
When I run it in 4nec2, I get AGT=1.11 (0.39 dB). After adjusting SOURCE wire
radius for AGT=1.0, I get Raw Gain 14.0-14.7 dBi and acceptable SWR on Ch12-13,
but Excessive SWR and lower Gain on Ch 7-11:
http://imageevent.com/holl_ands/colineararrays/finco400w20refl [See Finco 400-S - X0324 GHZ24]

Note analysis of two other Finco 400 models with 20 Reflector Screens, which had Raw Gain
of 15 dBi (or higher) on Ch7-8, but SWR was excessive on Ch9-13.

I also analyzed two Finco 400 models with 4 Reflector Screens, with Raw Gain in the
range of 13-14 dBi. Your Optimized Low SWR version was only one covering entire Hi-VHF Band:
http://imageevent.com/holl_ands/colineararrays/finco400w4refl
 

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Hi-VHF 4-Bay Bowtie with 15 or 25 Reflector Rods:

I uploaded 4nec2 analysis for Hi-VHF 4-Bay Bowtie with Reflector Rods:
http://imageevent.com/holl_ands/multibay/hivhf4bayrefl
For those in search of a MONSTER Antenna with Extreme Gain in Hi-VHF Band.

With 15-Reflector Rods, provided Max Gain=15.5 dBi on Ch13, 13.1 dBi Gain on Ch7
and SWR under 2.0, so no SWR degradation across entire Hi-VHF Band.

With 25-Reflector Rods, provided Max Gain=15.9 dBi on Ch13, 13.6 dBi Gain on Ch7
and SWR under 2.3, so no SWR degradation across entire Hi-VHF Band.

They are both 120-in High by 80-in Wide with 15-in Separation between Bowties and Reflector Rods.

Compare to X0324 Finco 400-S posted above: 74-in High by 103-in Wide x 8.6-in Deep or
VHF_Finco_400_OptLowSWR_X0104_GHZ24.nec: 89-in High x 103-in Wide x 12-in Deep.
[I think we have a new "winner".....unless, of course, you want to go even BIGGER.....]

A conveniently located wall (preferably CONDUCTIVE, due to Al. Foil Barrier or Chicken Wire inside of
Stucco, then THAT could be used instead of the Reflector Rods.....hmm, how much can the antenna
pattern be "skewed" back and forth if the Bowties are rotated in front of a fixed wall......

A slightly larger size (about 2-in more) could improve Ch7 with some Gain reduction on Ch13.
 

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Discussion Starter #334
I see youve been busy also....i will have to try more Ch #13 projects this summer....:eek:

wonder if a channel (#13) cut 4-bay would possible based on that...
 

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Nice gain

Hi holl_ands,

Wow that model got garbled !
Here is a corrected model for channel 7, the test bed model (10) and a corrected version of the above for 13
not that anyone wants them now (though the ch 7 model gets 14.8 net at 7 )
I think we have a new "winner"
Congratulations nice model.
Thanks for double checking me and keeping me honest I appreciate it.

The optimizer must have caused the AGT to vary cause I checked the test bed (un-optimized version) and it has AGT of .99 , -0 bd guess I should re-check any model that's been altered. The parabolas I had been playing with are very resistant to this so I got out of the habit.

Your Optimized Low SWR version was only one covering entire Hi-VHF Band:
Thanks for clarifying yes that is the only 400 model I have yet found that has even acceptable SWR over the whole VHF high band and it's gain is less than spectacular.

I predicated my statements about the 400S with warnings of the narrow bandwidth ~2-3 channels for the posted model (and all the 400S models I tested yet.)

BTW I got 15.62 dBi raw at 213 MHz and 14.92 dBi net gain at 213.
and an avg. net gain over high vhf of 14.26 dBi. that is impressive.

Truthfully I lost most of my interest in the finco 400 models around the 4th of Feb.because,
.....unless, of course, you want to go even BIGGER.....
I already did :D
I posted a vhf high lpda feed for the parabolas I've been testing/investigating and posted results of the feed driving an 8x12 foot quasi-parabola here notice the 15.43 dBi net at 13 (213) and the
14.41 dBi net avg. over VHF high.

And the new winner is ................just teasing ;)
probably your bow tie still cause the parabola is 96 sq ft. and the bowties are only 66.6 sq ft.

But the parabola could also give 23.36 dBi avg. net gain over UHF in addition to the great VHF gain so I wanted to play with them. Partly cause I have no VHF stations near enough to be certain that any of these could get reception. And I'd hate to build a monster only to find it,s still not enough and the monster is useless.

All the parts are on my site but if you want I'll post a copy of the assembled vhf variant .
 

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Question about Yagi

Three weeks ago I posted a question about a dipole versus a folded dipole for use in a channel 7 Yagi. Sadly, no one responded. I'll repeat my question since my planned build time is rapidly approaching.
=================================
I plan to build a 10-element Yagi for channel 7 based on the K7MEM design tool this spring http://www.k7mem.150m.com/Electronic.../yagi_vhf.html

My target channel 7 station, WBBZ, at my location is 2EDGE with a +11.1 dB noise margin and is 82 miles distant. During the summer, I get reception about 1/3 of the time. In the winter, reception is extremely rare, but is normally just below the lock level
According to the K7MEM model, I should get a gain of 11.8 dBd or 13.9 dBi at Channel 7. This compares to 9.7 dBi that my current antenna, a Nikmil GH10n3 is supposed to deliver; an improvement of 4.2 dBi.

My other VHF-Hi stations, CFTO & CHCH at Channel 9 & 11 respectively have 57 and 43 dB noise margins. Hence, I assume that changing to a channel 7 Yagi will not adversely impact the reception of these stations.

Question
The K7MEM calculator at a 178 Mhz design frequency and for ¼ inch tubing gives a driven element length of 812 mm. This assumes a simple 75 ohm dipole.

According to the folded dipole design tool http://www.k7mem.150m.com/Electronic...ed_dipole.html the folded dipole element length should be 801 mm or 11 mm (1.4%) shorter.

Can I use the shorter folded dipole element on the design that the K7MEM tool derived that assumes a simple dipole and still get the same performance?

I want to use a folded dipole so I can connect the antenna at 300 ohms and to simplfy construction.
 

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According to the folded dipole design tool http://www.k7mem.150m.com/Electronic...ed_dipole.html the folded dipole element length should be 801 mm or 11 mm (1.4%) shorter.

Can I use the shorter folded dipole element on the design that the K7MEM tool derived that assumes a simple dipole and still get the same performance?
Another program you may like to use for a folded dipole Yagi calculation is Yagi Calculator from VK5DJ http://www.vk5dj.com/yagi.html
(I note that he just updated it in February with more features)
With it I get a folded dipole inside bend measurement of 820mm for 6.5mm material for 178 mhz.

Yes, as majortom notes below, the folded dipole is more broadband than a simple dipole, so you have more construction leeway.
 

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Have you read this page (the K7MEM VHF/UHF Yagi Antenna Feed Design): http://www.k7mem.com/Electronic_Notebook/antennas/yagi_vhf_feed.html#Page_Top ?

There it says "Although it's not really mentioned, the long boom yagis, designed from that page [The VHF/UHF Yagi Antenna Design page], are intended to use a Folded Dipole antenna feed."

Elsewhere (but I couldn't find the text to quote directly), he points out that for a given frequency, a simple folded dipole without any other elements will be different in length than one loaded by adjacent parasitic elements (i.e. in a yagi array), so the length resulting from the yagi calculator is different from the simple folded dipole calculator.
 

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Thanks guys for your help. It was much appreciated. My uncertainty about element length has been solved. Folded dipole is definitely the way to go for several reasons (increased bandwidth and ease of construction). I am now looking at and comparing the models produced by the K7MEM tool as well as the VK5DJ Yagi Calculator. Once again, thanks for the help. I will likely build the Yagi over Easter weekend - two weeks from now.
 
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