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Old 2011-10-28, 11:33 AM   #316
balm
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rabbit73,

Are you referring to these 4-bays:

http://imageevent.com/holl_ands/multibay/hivhf4bay

These measure 50 ft^ (10 ft x 5 ft). Building this would be easy, but as you say an encasement cage would be CUMBERSOME . Modeling it would probably be a task ...I wonder what the F/B ratio would give.

1. Maybe I could try something like this on the ground, in front of the cottage front wall, using the wall as the backstop, and bring metal sheets out from the wall for the sides - (come to think of it I don't think I tried placing the yagi there, right in front of the wall, say at about 6 ft high.)

The front beam would probably also have to be narrowed also since I would still be receiving signals off the boathouse.

2. Perhaps this 4 bay could be scaled down a bit, since MAYBE i won't need as high a gain.

3. Then again, would it be possible to encase my yagi (at the tower) sufficiently to make a difference.


To be continued...


Thank you
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Old 2011-10-28, 05:47 PM   #317
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Due to it's size, I was reluctant to model Hi-VHF 4-Bay Bowtie w Reflector Screen,
esp. knowing that it might take several HOURS to run, assuming 2inx4in Grid Size.
And NO, you can't simply make it smaller to reduce the Gain a bit without ALSO
totally messing up the SWR...for example babblin5's way too small 4-Bay U-Tube Defect...

F/B Ratio with Reflector (at about 3 x 4.5in = 13.5in Seperation) would be in the
range of 15-20 dB, similar to UHF CM4221, if it were Rescaled....more for Angled Reflectors.
Hi-VHF 2-Bay & 4-Bay dimensions were tweaked for Hi-VHF Band, so a 4nec2 run would be
needed to find out for sure....and mounting it near the ground also needs to be modeled....

If you want a smaller antenna, consider the 5ftx5ft Hi-VHF 2-Bay Bowtie:
http://imageevent.com/holl_ands/multibay/hivhf2bayrefl

Or the smaller, lower Gain Hi-VHF Loop with Screen Reflector...or the simpler, but
even lower Gain Hi-VHF Loop with Loop Reflector, with high F/R on ONE Channel:
http://imageevent.com/holl_ands/loops/looprefl

An array of Reflector Rods can be used in lieu of a Screen Reflector (like CM4221HD).
But I haven't (yet) modeled this configuration with the Hi-VHF antennas to determine
the "best" Lengths and Spacings.....but I think this approach would COST MORE....

Bear in mind that the Size of the Reflector Screen can have a profound effect on
Gain. If it is too small bad things can happen to Gain and SWR....up until the point
Gain pokes out the BACK of the antenna!!!

Also bear in mind that whatever building is behind the antenna is acting as a very
large Reflector, whether you intended it to or not. Walls can be metallic, such as
the chicken wire in stucco or Aluminized Foil in insulation....or moisture in wood.

To estimate what an enclosure does, a 4nec2 run should be undertaken, using
different sized enclosure models surrounding the chosen antenna model....
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Old 2011-12-05, 01:02 PM   #318
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Default Some pics of my K6STI build

Member Balm was asking if I had any pics of my K6STI build. I did but had never gotten around to figuring out how to convert them for the web and how to post them. I have done that now and have also made my first album. Unfortunately I uploaded them in a jumbled order so I got that part wrong. However I have added comments for each pic in the album except one. I will attempt to paste a couple into this post.

------------------------------------------------------------



K6STI -5EL

This is my build of the K6STI 5 element yagi. I made the receiving elements from 1/2 inch skid strapping. They are attached to the 2-liter bottle cap at the front with small screws and nuts. On each a wire is attached inside the cap. At the opposite side which you can see where I drilled a large enough hole to accept a coax coupler. I needed to use 2 screws on the coupler. One to hold it in place and the second to hold the wire from one of the receiving elements firmly in place. The wire from the second element was just inserted into the hole of the coupler. Since the K6STI Yagi is already 75-ohms all that is needed is a direct connection. No balun required.

Note also the platform on which the receiving elements sit. In order to maintain the correct angle for the elements I had to scrape slit holes for the skid strapping to be embedded in. I then used 10mm coax cable clips that you get at the dollar store to hold the elements in place along the slits.

You can see on the top of the cap that there is a screw head. That is a long screw that holds the cap to the platform to the hockey stick. It comes out about a 1/2 inch on the bottom of the hockey stick. Another shorter screw is used to mate the front of the platform to the hockey stick and prevent the platform from shifting.

------------------------------------------------------------


Another pic of the K6STI 5-element yagi. If you look near the end of the receiving element you can see where I drilled a small hole. That was supposed to be the attachment point to the cap. Unfortunately it was way off and I had to redo it at the other ends. This time I made the screw holes right near the very ends and it seems to have worked. There is only a 1/4 inch separation between the elements at the feedpoint. I got as close as I could.

The reflector elements are made from those signs that you see on the side of the road. After a while the plastic sign itself seems to disappear and all that is left is the wire frame. So I figured I'd recycle some of it. Note that some of these are made from galvanized steel and are quite rigid. I needed to use those 2 handed bolt cutters to cut them.

If you look closely where the reflector elements enter the boom you might notice that there are little grommets fitted to each side of the reflectors. I used some car engine vacuum hose I had on hand. I did this to prevent the reflectors from shifting out of position.

Using the K6STI yagi I am now able to get CKVR rf10 from Barrie. With the KROSS antenna I would get about 15% signal on the meter with 40 needed for decode. With this yagi I was getting from 45 to 55 on the signal meter. There would be some minor pixellation like where one line on the screen would trail zip across and that would be the extent of it. Not really major pixellation where the whole picture breaks up. Maybe tweaking the aim would help. As of now I have it pointed towards WBBZ monitoring signal levels.
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Old 2011-12-05, 01:33 PM   #319
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Quote:
Originally Posted by mrpeter105 View Post
Since the K6STI Yagi is already 75-ohms all that is needed is a direct connection. No balun required.
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
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Old 2011-12-05, 03:26 PM   #320
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K6STI,

Your webpage specifies 3/8" tubing for the DIY build. I only have access to 1/4" inch tubing and plan to build this antenna at the Christmas break. Do I build to your specified dimensions or resize? If a resize is needed, what dimensions should I use? I plan on using a folded dipole (per Holl_ands modeling) so I can use a common 4:1 balun for this antenna. Thanks!
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Old 2011-12-07, 08:06 AM   #321
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Quote:
Originally Posted by k6sti View Post
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/show...&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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Old 2011-12-07, 09:37 AM   #322
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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.

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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Old 2011-12-07, 01:04 PM   #323
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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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Last edited by Jase88; 2011-12-09 at 01:41 AM. Reason: Removed unnecessary quote.
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Old 2011-12-20, 03:54 AM   #324
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Default Best Gain

Balm from post 1 said:
Quote:
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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Old 2012-02-07, 11:10 AM   #325
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Default 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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Old 2012-02-07, 02:06 PM   #326
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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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Old 2012-02-07, 02:17 PM   #327
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I just found this thread ... http://www.digitalhome.ca/forum/showthread.php?t=128429. Let see what this has.

Dave, thanks for the reply.
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Old 2012-02-07, 08:59 PM   #328
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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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Old 2012-02-07, 09:59 PM   #329
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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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Old 2012-03-01, 07:52 PM   #330
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Default 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.../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 ╝ 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 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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