O/T: Folded Dipole

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wrote:

Here's a link to the now famous coat hanger antenna.

http://www.youtube.com/watch?v=EWQhlmJTMzw

There are a couple variations of this but this is the basic idea. It's mostly a UHF antenna but some guys get upper VHF channels especially with an added reflector. That version builds the bowties on one edge of a 2x4 with a piece of plywood (or cardboard) covered with foil attached to the other edge. You can also combine 2 for more gain and some guys are mounting them on a rotor.
I built one and set it the back yard and it worked just fine. I used pieces of romex I found laying around the jobsite for the bowties. I haven't fished a wire from the basement to the attic yet so now it's hanging in the floor truss space for emergencies. Basically that's at ground level and it even works there.
You can buy practically the same antenna for not a whole lot of money but where's the fun in that?
Mike O.
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Mike O. wrote:

I'll probably build a seven-element quad much like the 2m (146 MHz) antenna that let me check into a Rhode Island FM repeater net from my Minnesota home using a 14W transceiver.
Swingman helped me draw the hubs with SU a while back. :-)
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Morris Dovey
DeSoto Solar
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SU is the bomb! But how did he work around the line of sight problem?
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MikeWhy wrote:

Good electronics, good antennas (IIRC they had a Phelps-Dodge omni at 60'), and a 1200 mile "wormhole" is the only explanation I can offer. There was considerable surprise at both ends - that's a /long/ way for a low-power VHF signal to travel.
SU did well until I tried to add a threaded hole for a setscrew. :-(
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Morris Dovey
DeSoto Solar
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Me too! I learned a trick or two about 10d nails from that. At this rate, I'll be ready to test again, oh say, 2012 when the auroras descend again to the plains states. Wondering if Skynet and Nostradamus will cooperate. (I worked Moscow on 3 watts in 2000 on an attic wire. That was special enough for me.)
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Morris Dovey wrote:

Signal propagation is a wonderful thing.
I remembrer one night I was watching something on Channel 4 in Jacksonville, Florida, and the picture faded out and came back with a different show from the one I had been watching. Then there was a station break and I found that I was now watching the Channel 4 that was in some place more than a thousand miles away (I forget where--that was at least 40 years ago).
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On Tue, 21 Apr 2009 22:16:45 -0500, Morris Dovey wrote:

Tropo duct, no doubt.
I think the bandwidth of that quad is going to be a bit narrow for even one digital channel, let alone a whole range of channels. You ought to be able to put together a simple log-periodic yagi that would likely do much better.
Hmmm... what would a log-period quad look like?
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Art Greenberg
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Art Greenberg wrote:

An interesting question. Configured for the highest gain I've managed to achieve, the element lengths made a geometric progression, and the element spacings an arithmetic progression.
Way back I built one for a friend who lived in Philly so he could watch a NYC sports channel (Channel 9?) and it worked well sitting on a pair of sawhorses in his garage. He was a /very/ happy camper. :)
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Morris Dovey
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On Wed, 22 Apr 2009 09:57:37 -0500, Morris Dovey wrote:

Antenna theory is definitely not one of my arrows, and I've never really learned/understood the things that go into computing proper (or optimal) element length and spacing for a yagi or LPY. What you describe sounds vaguely familiar. I assume your multi-element quads use a single driven element. But a log-periodic antenna uses multiple driven elements of varying length, and this is what gives it wider bandwidth. I don't see why that couldn't be done using quad elements rather than dipole elements. But as I said, I just don't know.

When I lived in and around Philly, getting most of the NYC channels was pretty easy with even the simplest roof-top antenna.
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Art Greenberg
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Art Greenberg wrote:

I still have no clue what his problem might have been (I was living in NJ and wasn't much of a TV watcher). He complained one day at work and I took the antenna to his place the following Saturday morning, we did a quick test in his garage, and I headed home.
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Because with digital TV you need more signal to get any picture at all compared to analog. If the signal is just below the threshold, you get a totally useless picture or no picture at all. With analog, the same picture would just have a bit of snow.
Having said that, the "new better digital" antennas are not different than antennas before digital. You just *may* need one with more gain to get a picture.
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Shoot. I live so far out in the burbs that a folded dipole gets only a few FM radio stations. Rabbit ears get only WGN (the station, of course, and also white gaussian noise elsewise). There's a 20 year old, normal, ordinary log periodic TV antenna lying in the attic, that hasn't been used in 19.9 years. It would probably work well enough if I mounted it outside where it belongs, but it serves a useful purpose right now broadbanding the half wave 20m dipole, also inside, so it tunes enough to transmit on 40m and 15m. We've been on cable and dish since long ago, all digital for at least half that. Not everyone lives close to the city center.
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MikeWhy wrote: ...

Not everyone lives remotely close to a city fringe...
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Jim wrote:

Because the signal strength is much less than previously and the digital signal dies under multipath conditions that would not even be noticeable with an analog signal.

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On Tue, 21 Apr 2009 18:47:59 +0100, J. Clarke wrote

Ahhh.. that's the digital difference, it's very much an "it is or it isn't" situation from the signal stream right down to end user satisfaction.
Some sort of fractal logic at work here, perchance, the microcosm implicit in the macrocosm - the opposite of ironic?
In Britain it's become some sort of elitist game. I know plenty of people with NO worthwhile terrestrial signal unless they hang on to their five channels of analogue reception while others have a gerzillion channels of sparkling, crystal-clear worthless junk. It's going to be quite bloody when the all-noing government pulls the plug on all analogue broadcasts. Some rural areas are either going to have to go satellite or run 60-foot poles up on top of their picturesque cottages. My mother-in-law lives maybe 10 miles from a transmitter but is in a reception shadow (hilly terrain.) Like everyone else in her area, she has the digital box and an expensive new antenna rig but still watches analogue because the reception is great, channel switching is instantaneous and she is comfortable with her traditional stations and has no desire for forty channels of manga. I had a play with her set and it takes maybe 20 seconds to change from one channel to another to find out that it's something you don't want to watch.. Channel surfing is effectively impossible, and the "guide" takes just as long to scroll through.. each line takes about 20 seconds to refresh.
Everyone in the village is in a similar situation, so it's not just the senile old bat going luddite with the technik.
Progress
There are 10 types of people in the world: Those who understand bananary and those who prefer a straight answer.....
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You would't but the frequencies WILL change.
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I was wondering how they get those subchannels.
I live about 50 miles from the transmitter tower. The analog TVs were never able to get consistent signals from the UHF stations. Now, however, these stations come in quite well.
But, since nothing is broken here, there is nothing to fix (yet). Jim
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Jim wrote:

Some form of multiplexing.

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On Tue, 21 Apr 2009 14:27:36 -0500, Jim wrote:

Subchannels are on the same carrier - IOW the same frequency - as the main channel. The various data streams for all of the channels, both video and audio, are divided into fixed-length sections called packets. Each packet includes a few bits that say which stream the data in it belongs to. Then the packets from the various streams are mixed together ("multiplexed") to create the transmitted data stream.
When you switch among subchannels for a particular main channel, all you are doing is telling the receiver to pick the packets that belong to the selected subchannel.
The frequencies will change due to the need to simultaneously transmit the digital and analog versions of the channels for some period of time, and then reclaim some of frequencies from the low VHF and high UHF channels for other uses once the analog signals are turned off.
Depending upon where you are, you may still need a combination high VHF/low UHF antenna to receive all of the digital stations in your area. I know this is true in Philadelphia PA, for example, where WPVI and WHYY will relocate their digital transmissions to the high VHF band on June 12th.
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Art Greenberg
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On Tue, 21 Apr 2009 03:27:27 GMT, "Lew Hodgett"

If you ever need a antenna with a bit more capability, google "HDTV coat hanger antenna". You will likely be able to receive stations you didn't know were even there. The added plus is that it is also very economical to make. regards, Joe.
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