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How to build a UHF antenna... - Page 135

post #4021 of 4790
Quote:
Any advantage of using closed bow-ties over open ones besides the obvious fact you reduce the chance of poking yourself?

Yes, it makes for a stiffer bowtie structure, less chance of damage from birds etc. Gain wise, its about the same as open whiskers, but for the same frequency it can be a little shorter.

Indoors, reducing the chance of poking yourself in the eye can be a big consideration. Styrofoam balls on the ends of whiskers is another option.

The downside is more labor and material.
post #4022 of 4790
Quote:
Originally Posted by 300ohm View Post

I used 10 gauge wire.

300ohm, thank you very much.

Quote:
Any advantage of using closed bow-ties over open ones besides the obvious fact you reduce the chance of poking yourself?

It looks "close" to a sloted bowtie (made of metallic plate with a triangular slot on each side). It is probably worth a study.

All - is there a dB vs frequency graph for closed end UHF bowtie antenna?
post #4023 of 4790
Because of the 1/2" mesh I used in the middle, the number of segments is near limit of the modeling engine and it takes forever and a day to compute. So when I ran the graph, I only used the channels I was optimizing for, ie 38 - 51. The gain on the low channels is much less.

Raw Gain:


SWR:


With an SWR of 2.0, you subtract .51 dbi from Raw Gain to get Net Gain.
With an SWR of 1.5, you subtract .18 dbi from Raw Gain to get Net Gain.
post #4024 of 4790
Quote:
Originally Posted by 300ohm View Post

Because of the 1/2" mesh I used in the middle, the number of segments is near limit of the modeling engine and it takes forever and a day to compute. So when I ran the graph, I only used the channels I was optimizing for, ie 38 - 51. The gain on the low channels is much less.

Raw Gain:


SWR:


With an SWR of 2.0, you subtract .51 dbi from Raw Gain to get Net Gain.
With an SWR of 1.5, you subtract .18 dbi from Raw Gain to get Net Gain.

That 16 dBi theoretical gain would seem to point to a highly curved reflector.
post #4025 of 4790
Well not really curved, just swept forward. Its a 40" X 40" reflector. Its flat in the middle section for 16", which is covered with the 1/2" mesh. Then the ends are bent/swept forward 3" on each side, which is covered with 2" X 4" mesh.

The bowties are then bent forward too, to match the sweep of the reflector.

Quote:


The gain on the low channels is much less.

For example, on channel 14 its Raw Gain is 11.9 dbi with a SWR of 7.29, so a Net Gain of maybe 7 - 8 dbi.
post #4026 of 4790
300Ohm, thanks again.

I can live with 7-8dBi on CH 14. I like the 16dBi gain for CH 40+.

Presently my double bowtie with no reflector, at a window facing TV transmitters can do a good job - 89-90% for local channels except 44 with marginal reception. I am thinking about making a 4-bay (w/o refl) that is flat enough to hang between the curtain and the window.

I have been looking for nice lightweight materials for use as 1.25" spacers.

My present 2-bay has only two pieces of spacers 0.5x1.75" each - no vertical boom.
post #4027 of 4790
Quote:


I am thinking about making a 4-bay (w/o refl) that is flat enough to hang between the curtain and the window.

I have been looking for nice lightweight materials for use as 1.25" spacers.

Pieces of Lexan (polycarbonite plastic) would be good. Its more UV resistant than plain acrylic.

If the whole kit and kaboodle is soldered together, it could be a hanging piece.

How wide is your window ? If you have 25"W X 30"H available, you may want to consider building a single bay reflector-less GH. The channel 40+ gain is the same as the above 4bay reflector-less, and is much easier to build, ie no soldering would be needed, just bending. Less wire is used too.
post #4028 of 4790
Quote:
Originally Posted by LithOTA View Post

From what I've read, it's an old ham design that the G=H was based on. Very simple and sturdy, the ends of the 2 wires are bent and tucked into drilled holes, so the whole unit has no tines or other pokiness. I used a few extra washers on the balun screws so that they wouldn't be too close to each other. For something so small and solid, it grabbed a lot of stations with and without a preamp. It does not outperform my McLapp M4 but still way better than I expected. A 4-square Cheriex looks like it would be comperable.

http://imageevent.com/holl_ands/chireix/chireix

The 8-square would be a beast at over 12 feet tall! But it would suck down low and up high. I think I'll try a 4 or 6 square.

i am trying to build a mclapp right now and just got curious if this was better.

what do you think about GH? is that better than mclapp?
post #4029 of 4790
Quote:
Originally Posted by nyc2010 View Post

i am trying to build a mclapp right now and just got curious if this was better.

what do you think about GH? is that better than mclapp?

I haven't progressed to a G-H yet, but a lot of these other posters have...
post #4030 of 4790
Quote:


what do you think about GH? is that better than mclapp?

For the same gain, they have similar patterns. There are a multitude of GH models of various gain. There are a multitude of mclapp models of various gain.

The best thing the single bay GH has going for it is the ease of build and only 2 electrical connection points to go wrong, versus 10 connection points to go wrong on a 4 bay.

There is no right answer as to which is better, other than in my case, both are better than corner reflector yagis.
And UHF lpda's are kind of pitiful, heh.
post #4031 of 4790
Regarding G-H antenna, which plan was well analysed by antenna modelling software? I would like to take a look at them.
post #4032 of 4790
i got the mclapp, seems to work fine. but has trouble with some channels while others are 100% signal.

if this is put on a roof, i think this will work fine.

next is the GH and see if that makes a difference. anyone here got any suggestions for making a jig for bending cable for GH? or better yet some pictures?
post #4033 of 4790
Quote:


anyone here got any suggestions for making a jig for bending cable for GH?

I used a wide board with a nail in it. Measure the stub long, bend, then measure the leg and bend and then measure the next leg and keep going in order one by one. Another flat board on top of the wire while bending keeps the elements flat. Then at the end, I trim up the stub length.

Also, to get sharper corners, I bend the angle a little more than needed, then bend back. This is fine for copper and soft aluminum, but some grades of aluminum are brittle and dont like bending much.
post #4034 of 4790
I built both the Mclapp and the Gray-Hoverman single and double bay antennas. I now have two single bay Gray-Hoverman's a 30 feet up. I built the GH's with NARODS and can attest to the increase VHF gain using the NARODs. I originally built the first GH with reflector rods as shown on this site. http://mysite.verizon.net/res11d41p/id2.html
I am between Buffalo and Rochester, NY so I took the reflectors off to make it bi-directional and I'm very pleased with the results. I'm locking stations that are 70 miles away in Toronto.

My Mclapp worked well but I think it needed some tweaking to pull in the lower UHF/upper VHF better.

http://i187.photobucket.com/albums/x...o/DSCN0328.jpg
post #4035 of 4790
Interesting U shaped NAROD holders. I take it youre in the same position I am with the main antenna farms about 90 degrees apart from each other. With probably a 50ft of cable run on each, quality preamps on each would make it even better.
post #4036 of 4790
Quote:
Originally Posted by SCHNEEDOO View Post

My Mclapp worked well but I think it needed some tweaking to pull in the lower UHF/upper VHF better.

Fringe Low UHF and upper VHF-hi is a bad combination for a 4 bay. To get best lower UHF you need a slightly bigger 9 1/2" - 10" bay spacing antenna and for best upper VHF-HI you need a slightly smaller one 8" - 8 1/2" bay spacing for absoulute best gain. Usually building one to best handle VHF-hi is the way to go because the UHF gain doesn't change that much between sizes except on the extreme edges.
post #4037 of 4790
the channels in nyc area are spread out, and i am getting a feeling GH may not work out well. what do you guys think?
post #4038 of 4790
I was just trying to use things I had for the NAROD holders. So I got creative with what I had on hand. I have about a 55 foot run from each antenna. I have each connected to a drop amplifier after the coax enters the house. The drop amps work well to boost the signal so I not putting a preamp up just yet.

I want to thank Mclapp for his great website. I'll still be tweaking my 4-bay in the weeks to come, but my wife was starting to get a little upset with my new obsession.

nyc2010,
Here is my TVfool radar plot, I can get most all channels on one GH. I have difficulty with some of the Canadian channels coming from the Northwest only because they're not broadcasting at full power yet.
LL
post #4039 of 4790
Quote:


the channels in nyc area are spread out, and i am getting a feeling GH may not work out well. what do you guys think?

Post your TVFool image. If youre close enough to the city, and still have a wide spread, a bi-quad or a double bi-quad may be the thing for you with its very wide uhf beamwidth.

The vhf-hi beamwidth on the SBGH with NARODs is also very wide. The uhf beamwidth, not so much.
post #4040 of 4790
here's the plot
LL
post #4041 of 4790
I think youll do fine with a reflector-less SBGH with NARODs like SCHNEEDOOs above, aimed at around 60 degrees for your vhf-hi and uhf channels. You may not pick up vhf-low channels 2,3,4 and 6, but then again you may because some of those signals are strong.

You dont need the extra crosses, like SCHNEEDOOs picture above. I believe he was originally going to use reflectors. You dont want reflectors, so that the antenna will be bi-directional.
post #4042 of 4790
I did have reflectors on the first one I built. I removed them to see what kind of reception I would get without the reflectors and was happy with the results. So save yourself some money on cross-tees.
post #4043 of 4790
Also save money by using the grey electrical sch 40 pvc instead of the white plumbing sch 40 pvc. 40% plus cheaper and is UV resistant to boot.

And since your channel 33 - 38 signals are so strong, you could use the easier to make straight NAROD instead of the top hat style. Its just a piece of wire 30.25" long, same diameter as the elements, 1/2" center of wire to center of wire over the stubs.
post #4044 of 4790
I would recommend screwing the conduit together. I did this when I my Mclapp 4-bay and it has allowed me more versatility when changing configurations.
post #4045 of 4790
Quote:
Originally Posted by mclapp View Post

Fringe Low UHF and upper VHF-hi is a bad combination for a 4 bay. To get best lower UHF you need a slightly bigger 9 1/2" - 10" bay spacing antenna and for best upper VHF-HI you need a slightly smaller one 8" - 8 1/2" bay spacing for absoulute best gain. Usually building one to best handle VHF-hi is the way to go because the UHF gain doesn't change that much between sizes except on the extreme edges.

I saw that mclapp also built GH antenna for comparison testing. What would be the effect of reducing the vertical spacing to 8-8.5" between the narrow parts that look like >< on the GH?
post #4046 of 4790
Quote:
Originally Posted by swwg View Post

I saw that mclapp also built GH antenna for comparison testing. What would be the effect of reducing the vertical spacing to 8-8.5" between the narrow parts that look like >< on the GH?

You want to squeeze down a GH, like an accordion ? The effect would be a little bit less gain. 90 degrees is the optimum angle for the legs. But if you have to squeeze it down to make it fit in a window, that would be acceptable. Just make all the angles squeeze down by the same amount.
The old Hovermann patent showed angles as low as 60 degrees to be OK to use.
post #4047 of 4790
Like some others here, I added a reflector to my McLapp M4 and found that the performance suffered somewhat. So I have a question:
Should the two halves of a reflector (left and right) be in electrical contact with each other?
post #4048 of 4790
I'm not sure what you mean by connecting the 2 halves of the reflector? If it's a 4 bay then it should be 1 piece or 2 pieces electrically connected together at least 24" wide or 36" if you want to inhance VHF-HI.

The popular G-H designs use a split rod or screen reflector.

A vertical split could work but the halves have to be the right size similar to the G-H although it will hurt any VHF-HI reception.

A horizontal split in the reflector screen will not hurt anything as long as it's 2" or less.
post #4049 of 4790
Quote:
Originally Posted by mclapp View Post

I'm not sure what you mean by connecting the 2 halves of the reflector? If it's a 4 bay then it should be 1 piece or 2 pieces electrically connected together at least 24" wide or 36" if you want to inhance VHF-HI.

The popular G-H designs use a split rod or screen reflector.

A vertical split could work but the halves have to be the right size similar to the G-H although it will hurt any VHF-HI reception.

A horizontal split in the reflector screen will not hurt anything as long as it's 2" or less.

It's a vertical split, I used two wire shelves and screwed them into the sides of a 2x2, so there is a 1.5" gap between them. I could simply grind off some of the coating and solder a wire to connect them.
But you did say that a vertical split would hurt VHF, and you're right- but only when the antenna is facing those stations. With the reflector aimed at them (180 deg), RF 7 and RF 12 actually come in better.
I suppose I should stop fooling around with shelves and actually build a proper reflector.
post #4050 of 4790
Quote:
Originally Posted by LithOTA View Post

It's a vertical split, I used two wire shelves and screwed them into the sides of a 2x2, so there is a 1.5" gap between them. I could simply grind off some of the coating and solder a wire to connect them.
But you did say that a vertical split would hurt VHF, and you're right- but only when the antenna is facing those stations. With the reflector aimed at them (180 deg), RF 7 and RF 12 actually come in better.
I suppose I should stop fooling around with shelves and actually build a proper reflector.

Yes, they act as a director on VHF-hi instead of a reflector if they are less than 28" wide. The shelves make a nice cheap reflector they just need to be combined to make a continious unit. Grind off any non metallic coating where they will come together and sew them together with some bare wire.
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