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Old 2011-06-07, 12:49 PM   #826
mclapp
 
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That may make it more broad banded but most likely it wouldn't be an improvement overall, the phase lines are the main limitation for band width. The antenna starts going out of phase and the lobes start to split apart losing gain fast.

A wider difference between the phase line and whisker length may give slightly more band width like a 10 or 11" whisker and 8 1/2 or 9" phase line.
That still will not have as much gain as a standard size overall.
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Old 2011-06-09, 08:01 PM   #827
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Mclapp i,m new to this forum and i came across this thread with great interest.This question may have been asked already but i was wondering what is the advantage between a phase line with a long twist vs a phase line with a short twist.Also if bigger is better would an antenna with 10 long whiskers with a large angled reflector out perform the smaller sized whisker designs.Any info would be a great help in a future antenna build.Thanks
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Old 2011-06-10, 09:53 AM   #828
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Welcome to the forum,
The long twist is easier to make in my opinion, in computer modeling the short twist shows a very slight gain advantage but only when the twist is done very accurately. It would be very hard to tell the performance difference between the 2 if at all so I think going with the easier, more forgiving long twist is the way to go for most.

Bigger is better only because the size matches the current grouping of channels here in the US ch 14 - 52 better. Any bigger than 10" whisker and 9 1/2" phase line will start to drop the gain curve of the antenna below that channel range and wouldn't be very good above ch 45 or so. It also works out that improved VHF-hi ch 7 - 13 works for the whisker/phase line sizes in the 9 - 10" range.

The large angled reflectors can generate more reflected signal but there is a point on diminishing returns that really starts to come into effect around 40" wide. Wider will still gain a little, maybe a db or less but the reflector curve has to be very accurate to take advantage of it.
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Old 2011-06-10, 04:22 PM   #829
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Thanks for the info Mclapp.My goal is to build a 10" whisker with a 36" wide by 40" tall angled reflector.Right now i,m using a store bought DB4.Its pointed roughly between Toronto and Buffalo.I recieve all my Toronto stations and most of my Buffalo stations.(no Fox unless i rotate the antenna more towards Buffalo but then I lose some Toronto stations).I,d say i get about 19 channels with my current setup.I,m looking forward to the challange of building the antnna this summer.Also is there any type of balun out on the market that you would recommend.Thanks again.
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Old 2011-06-10, 05:36 PM   #830
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Mclapp I was planning on using 3/16" wire alumminum for the whiskers,1/8" wire alumminun for the phase lines and an alumminum wire screen for the angled reflector.Will the screen size of 36"x 40" with 1"x1" squares be okay or should it be modified at all.My phase lines and bowties will be mounted to nylon blocks.
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Old 2011-06-13, 08:57 AM   #831
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1 x 1" squares would be fine anything under 2" works pretty good.

This antenna will have a slightly sharper beam than your db4 so it may require changing the antenna position more to get the stations from different directions.

If you want to try to get both you may be able to go with a flat reflector and sweep the whiskers rearward (towards the reflector) about 1 1/2 - 2". Increase the spacing of the reflector to phase lines from the more common 4" to about 5 1/2". You'll lose some gain but should still be in the range of a db4 and it will have a much wider beam pattern which may allow you to get both markets.

I can't say for sure that will work it really depends on the signal levels you're dealing with but it's worth a shot if that's what you're looking to achive.
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Old 2011-06-15, 05:13 PM   #832
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Thanks again for the advice Mclapp.I,m just wondering if my whiskers go back towards the reflector,should i also angle the reflector back as well or does the flat reflector work just as well.
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Old 2011-06-16, 10:47 PM   #833
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I would stick with the flat reflector
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Old 2011-06-17, 10:05 PM   #834
iram
 
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To mclapp

I have been contemplating building a new antenna. I have been posting some questions about SBGH with a mesh reflector 300ohm mentioned possibly a wisker type antenna may be a good choice.


Here is my TV fool fro reference:

http://www.tvfool.com/?option=com_wr...001ba7f0b65fb7

I am only interested in the south facing stations which I believe are all in the same basic location (NYC Empire State building) however my home location requires the antenna be indoors on a window sill probably

you'll see that picture in this post

http://www.digitalhome.ca/forum/showthread.php?t=141512

While HI VHF would be nice it is not mandatory since I do have access to a roof VHF only antenna on my building. UHF is most critical.

Could you recommend the best bow tie configuration that you think may work that would have a flat mesh reflector.
If there are any links to plans or nec it would be very helpful.

Thank you
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Old 2011-06-19, 11:20 PM   #835
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The 9 1/2 x 9 size would be a good size for you your stations are spread out between 24 - 51 so that covers both ends the best. For UHF only the reflector only needs to be spaced back 4" be about 24" wide going 30" wide will get the upper VHF-hi channels better but it sounds like you have another antenna option for VHF-HI. Here's then LINK to my plans. Good Luck
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Old 2011-06-20, 09:01 AM   #836
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Mclapp,
Thank you for the advice I will look into this design.

When you bend the whiskers does it make any difference if they are made straight or are closed off like a butter fly. I saw a reference to this somewhere but was unclear if it effects the antennas performance.
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Old 2011-06-20, 10:34 AM   #837
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Quote:
going 30" wide will get the upper VHF-hi channels better
What would be a good reflector size and spacing to optimize an M4 for channel 13? TIA
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Old 2011-06-20, 11:32 AM   #838
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Quote:
straight or are closed off like a butter fly. I saw a reference to this somewhere but was unclear if it effects the antennas performance.
For closed end bowties, you can make them 1/2" shorter than the open end whiskers type bowties for the same gain response.
The biggest advantage with the closed end bowtie is that its more structurally sound. And with a finishing nails in the board jig, very easy to make.
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Old 2011-06-20, 12:39 PM   #839
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I wouldn't go less than 29" to be safe for ch 13 it needs to be wider more like 34-36" to cover all VHF-hi.

There isn't much tuning to it, just has to be large enough to be a reflector at that channel/frequency which turns out to be about 2-3" wider than 1/2 wave dipole and 1/2 wave on ch 13 is about 26". If it's wider it won't hurt or help much. If you are only worried about ch13 then the regular 4-5" spacing is best as long as you are using the smaller sized 9 x 8 1/2" antenna. If you are using a different dimensions then go to the longer 15" reflector spacing to help the impedance match.
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Old 2011-06-21, 09:21 AM   #840
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Default Phase lines

Can Phase lines be made of insulated wire such as heavy gage electrical wire with insulations removed at appropriate points for connection?
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