Powered by Invision Power Board


Forum Rules Forum Rules (Please read before posting)
  Reply to this topicStart new topicStart Poll

> Antenna Reflection, metal roof
MacFromOK
Posted: June 03, 2016 06:59 pm
Reply to this postQuote Post


Forum Addict ++
*******

Group: Spamminator Taskforce
Posts: 15,164
Member No.: 5,314
Joined: June 04, 2006




Hey guys,

Just curious how a "long wire" style antenna supported (and insulated) a bit above our metal carport roof would work for TV/FM.

The roof has a peak in the center, so a wire all around (say 12"-24" from the edge?) should catch different reflections on each half. No idea whether a 2"-3" support would be sufficient, or if it would need to be higher above the roof.

Or am I just hallucinating here... biggrin.gif


--------------------
Mac *

"Basic research is what I'm doing when I don't know what I'm doing." [Wernher Von Braun]

* is not responsible for errors, consequential damage, or... anything.
PMEmail Poster
Top
Sch3mat1c
Posted: June 03, 2016 09:39 pm
Reply to this postQuote Post


Forum Addict ++
Group Icon

Group: Moderators
Posts: 20,519
Member No.: 73
Joined: July 24, 2002




You mean as separate pieces, or one long complete loop?

To me, "long wire antenna" means something specific: a long wire (several wavelengths), pointed in the direction of interest. Usually installed over a ground plane (like earth, for obvious reasons). Transmission line connection is unbalanced, with the shield grounded to earth (or at least to a counterpoise of 1/2 to 1 wavelength in the other direction I think?).

You may be better served with a log periodic (directional, wideband), Yagi (probably a multiband cluster), or bowtie or conical dipole. More compact for the directionality, and they get predictable bandwidth.

Tim


--------------------
Answering questions is a tricky subject to practice. Not due to the difficulty of formulating or locating answers, but due to the human inability of asking the right questions; a skill that, were one to possess, would put them in the "answering" category.
PMEmail PosterUsers Website
Top
MacFromOK
Posted: June 04, 2016 02:37 am
Reply to this postQuote Post


Forum Addict ++
*******

Group: Spamminator Taskforce
Posts: 15,164
Member No.: 5,314
Joined: June 04, 2006




I was thinking more of an almost loop. Going pretty much all the way around, but not connected in a loop. Notice I said long wire "style."

Just not a really long one... biggrin.gif


--------------------
Mac *

"Basic research is what I'm doing when I don't know what I'm doing." [Wernher Von Braun]

* is not responsible for errors, consequential damage, or... anything.
PMEmail Poster
Top
Sch3mat1c
Posted: June 04, 2016 05:04 am
Reply to this postQuote Post


Forum Addict ++
Group Icon

Group: Moderators
Posts: 20,519
Member No.: 73
Joined: July 24, 2002




Ah...

So, an incident wave will approach the wire, uh, hook let's call it then smile.gif -- from some direction, and induce some voltage and current in the line segments. At very low frequencies (up to 1/4 wave versus total line length, say?), it'll look like a whip or dipole, assuming the metal roof is grounded or connected as a counterpoise. Probably okay as a dumb SW antenna, with a couple nulls in frequency response at half wave multiples.

Going into the VHF range, there'll be more about the geometry of the line segments. It should have a radiation pattern that's null along the axes (lobes on the diagonal corners), the number of lobes depending on the number of half waves that fit onto a side. That's complicated by the fact that the line is open at one end, which means you still have zeroes at whole wavelengths (I think).

It might be better anyway to ground the end -- then you get a proper loop, and probably the directivity is more reliable, if spaced to higher frequencies.

As for the roof shape-- I don't think it will make much difference until frequencies where the wire stops looking like much of an antenna, and the roof starts looking more like a mirror (UHF+?). Over most of the range you'd use such an antenna, the roof should pretty much look like a blob of metal; the waves diffract around it too much to notice the shape otherwise.

I think I'd rather see it simulated, in any case, to reach conclusions... it certainly won't be wideband (in the sense of having flat response), but will have many nulls, both in frequency and direction. If that's good enough for you, I have no idea, it'll depend on what particular channels you're interested in. unsure.gif

Tim


--------------------
Answering questions is a tricky subject to practice. Not due to the difficulty of formulating or locating answers, but due to the human inability of asking the right questions; a skill that, were one to possess, would put them in the "answering" category.
PMEmail PosterUsers Website
Top
Nothing40
Posted: June 04, 2016 06:38 am
Reply to this postQuote Post


Forum Addict ++
*******

Group: Spamminator Taskforce
Posts: 3,764
Member No.: 181
Joined: October 05, 2002




What kind of antenna,if any,do you have now?
It'll probably be better than a standard telescopic whip,or whatever. At least it's 'wire in the air'.


--------------------
"we need an e-kick-in-the-nuts button" -Colt45
PMUsers WebsiteYahoo
Top
MacFromOK
Posted: June 04, 2016 05:05 pm
Reply to this postQuote Post


Forum Addict ++
*******

Group: Spamminator Taskforce
Posts: 15,164
Member No.: 5,314
Joined: June 04, 2006




QUOTE (Nothing40 @ June 04, 2016 12:38 am)
What kind of antenna,if any,do you have now?

A 1/4" copper loop around 16" in diameter, hanging on an inside wall of the house. Top of the loop is about a foot below the 8'-ish ceiling. biggrin.gif

We get good reception for 2 channels (well, 6 total with their subchannels), but we're on fairly high ground. One transmitter (channel 12) is around 6-7 miles from here, the other (channel 10) is probably 20-25 miles away.


--------------------
Mac *

"Basic research is what I'm doing when I don't know what I'm doing." [Wernher Von Braun]

* is not responsible for errors, consequential damage, or... anything.
PMEmail Poster
Top
Nothing40
Posted: June 05, 2016 12:32 am
Reply to this postQuote Post


Forum Addict ++
*******

Group: Spamminator Taskforce
Posts: 3,764
Member No.: 181
Joined: October 05, 2002




If the transmitters are all located in vaguely the same direction,a Yagi or something pointed in that direction might be your best bet.

*shrug* Give the 'sorta loop' a shot,and see how it works?


--------------------
"we need an e-kick-in-the-nuts button" -Colt45
PMUsers WebsiteYahoo
Top
MacFromOK
Posted: June 05, 2016 04:42 am
Reply to this postQuote Post


Forum Addict ++
*******

Group: Spamminator Taskforce
Posts: 15,164
Member No.: 5,314
Joined: June 04, 2006




Those two stations are roughly the same direction (NE from here, and the copper loop is hanging on a North oops, South wall), but I was wondering if I could pick up some farther away (Dallas is 50-ish miles South, OKC is 50-ish miles North).

Just a mental exercise ATM, wondering if it might be worth tryin' sometime.


--------------------
Mac *

"Basic research is what I'm doing when I don't know what I'm doing." [Wernher Von Braun]

* is not responsible for errors, consequential damage, or... anything.
PMEmail Poster
Top
Sch3mat1c
Posted: June 05, 2016 07:58 am
Reply to this postQuote Post


Forum Addict ++
Group Icon

Group: Moderators
Posts: 20,519
Member No.: 73
Joined: July 24, 2002




Remember that loop reception is from the edge / null on-axis. NE from a N axis probably isn't enough to notice a bit difference though.

If you want to pick up many directions, a collinear might be the way to go. These are limited in bandwidth, though.

Tim


--------------------
Answering questions is a tricky subject to practice. Not due to the difficulty of formulating or locating answers, but due to the human inability of asking the right questions; a skill that, were one to possess, would put them in the "answering" category.
PMEmail PosterUsers Website
Top
MacFromOK
Posted: June 05, 2016 07:51 pm
Reply to this postQuote Post


Forum Addict ++
*******

Group: Spamminator Taskforce
Posts: 15,164
Member No.: 5,314
Joined: June 04, 2006




Thanks guys. beer.gif

Everything else in possible range is pretty much North or South from here. No hope of getting anything East/West AFAIK.

And... the problem with putting anything tall here is lightning strikes. I lost a good CB antenna (and the best stereo system we ever owned) to a direct hit. The antenna was disconnected (the CB was stored elsewhere), but the strike jumped to the stereo and a nearby lamp, and started a small fire in the process. The melted coax is still in the wall.

The antenna's base was only a few feet above the roof peak of the house. ermm.gif

[EDIT] On a side note... the channel 10 transmitter is down ATM (not unusual in stormy weather, though it's clear now). dry.gif


--------------------
Mac *

"Basic research is what I'm doing when I don't know what I'm doing." [Wernher Von Braun]

* is not responsible for errors, consequential damage, or... anything.
PMEmail Poster
Top
cgriggs
Posted: July 03, 2017 12:59 am
Reply to this postQuote Post


Member
****

Group: Trusted Members
Posts: 196
Member No.: 40,300
Joined: December 02, 2016




Back in the 50's I read about a small town in the New England part of the states that sat in a very deep valley.
It was one of those areas that you had to move the rabbit ears just so to get even a fuzzy pic unless you were in the chips and could afford a good outside antenna, which was rare for the area.
The borough council had many outbursts during their monthly meetings in ref to installing a booster on the highest hill above their town, but the expense was the blocking factor each time. The borough just couldn't afford it as taxes would have to be raised too high.
One day it was noticed that the signals were coming in a little better and the local electronic gurus claimed sun spot activity was the reason, "but don't get your hopes up as it would soon change."
Lo and behold, it only got better and better. Joyful praises rang from the local churches! God does answer prayers!!
One day, when reception seemed to be the greatest, the town's hardware store was visited by an out-of-town worker who needed several boxes of 5 inch lag screws When asked why he needed so many, he answered that the company installing the steel quanset huts on top of the hill didn't send enough and they didn't want to drive 80 miles home to get more.
... I imagine God was smiling! ...
PMEmail Poster
Top
MacFromOK
Posted: July 03, 2017 01:30 am
Reply to this postQuote Post


Forum Addict ++
*******

Group: Spamminator Taskforce
Posts: 15,164
Member No.: 5,314
Joined: June 04, 2006




Hehe... a reflector is a reflector is a reflector... biggrin.gif


--------------------
Mac *

"Basic research is what I'm doing when I don't know what I'm doing." [Wernher Von Braun]

* is not responsible for errors, consequential damage, or... anything.
PMEmail Poster
Top
1 User(s) are reading this topic (1 Guests and 0 Anonymous Users)
0 Members:

Topic Options Reply to this topicStart new topicStart Poll

 


:: support us ::




ElectronicsSkin by DutchDork & The-Force