Or point the null to eliminate one source of multi-path.
I probably should try OTA where I am now but there was no hope where I was before.
Yes, the driven element of a yagi is a dipole.
It is a dipole. ;-)
In our case there are many stations such as Fox-40 where there is no null. You always have tons of signal but sometimes the TV can't decipher any of it, other times it sorta works. 80-90% of the time, at the most. That was our "digital dividend" :-(
DTV, what a joke. I think it means "disrupted television" or something.
Other than evening news (which you can get on the web), some old movies (if you are lucky and the signal path holds for 2h) and Dancing with the Stars it's hardly worth it. In contrast to the election our favorite candidate won yesterday on Dancing with the Stars.
Sometimes they are fed a bit off center to find a match compromise. My portable EMC antenna is like that.
-- Regards, Joerg http://www.analogconsultants.com/
If you found the BTY-10-U cut for your channel for $100, I'd get it. Worse comes to worse, you put it back on ebay. That price is about half of what Solid Signal charges.
I only build antennas for what I can't buy. It is way more work than you think.
If you don't want to buy the BT antenna, I would suggest building a biquad. They don't take long to build. You would probably have to scale a biquad designed for wifi.
Your reflector would be Al screen rather than PCB at these dimensions.
The thing with yagis or log periodics is that you need to align a lot of things for the magic to happen. The biquad doesn't have many critical dimensions.
Well! It _is_ successful. It's breaking you of relying on OTA TV, is it not ?>:-}
You mean you're still watching "Dancing with the Has-been Stars ?:-)
[snip]I get 1000's of Channels with beautiful picture quality and useless content :-( ...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Yup. But it backfired on the stations. This is a fairly affluent middle-class neighborhood and many people can't see much OTA TV anymore. Got miffed, pulled the plug. Now they get the news via Internet and the movies via Netflix. Guess what that does to the ad revenue of the stations.
Until yesterday, that was the grand finale. My wife and I did a lot of ballroom dancing so we always thoroughly enjoy that. And ok, the hi-res is nice for such events. If the signal holds, that is.
Now you know why we have neither cable nor satellite TV.
-- Regards, Joerg http://www.analogconsultants.com/
Well, that brings up the issue of what kind of dipole. From what I've read, using a folded dipole as the driven element has two advantages - it provides a broader bandwidth (which isn't really important in my case because I only need one channel), and it provides a better match to a standard
300/75 balun. Apparently a simple dipole presents matching problems, although to tell you the truth I don't understand why.I found a video on Youtube which looks like a good example for me to duplicate - adjusted a bit for the difference in frequency. It's a 6-element Yagi which uses a folded dipole:
Of course this is an Aussie design, so I'll probably have to turn it upside down.
Would it be possible to connect two antennas 180* out of phase then find a couple of happy directions to cancel a portion of multi-path of the Fox-40 signal. Just a thought. Mikek
Line of sight is very important. If the hill is big enough, it can completely block the signal. As I mentioned, a big high gain antenna does nothing if there's no signal to receive. I can run the numbers for you if you send me the station call sign, your EXACT lat-long, and the proposed height above the ground. Something like this: The catch is that I'm rather busy during the holiday madness month and may not have much time to do it right. If you want to try it yourself, you can do a fair job with Google Earth.
Reading between the lines, are you proposing to build an indoor TV antenna? If so, that will limit the size of the antenna boom. It would still be worthwhile, but not as much as simply putting the antenna on the roof. Think of devious ways you can install a rooftop antenna. I recently built a yagi out of sheet mylar and aluminum duct tape. It worked.
Also, if you do it indoors, you will not have much feed line. The purpose of the antenna mounted amplifier is mostly to compensate for the losses of the coax cable between the antenna and receiver. However, if the coax cable is short (less than 10m) don't bother with the amplifier.
Indoor antennas through glass has another problem. The IR reflective coating found on all new construction windows is quite effective at blocking RF signals. That's another reason for a roof mounted antenna.
I'm trying to forget. There was more garbage sold as converters than I ever saw in my worst nightmare. Fortunately, most of those were either trashed, recycled, or sold on eBay.
The channel number has been virtualized allegedly in order to prevent user confusion. Of course, it did quite the opposite. At this time, the channel number has NOTHING to do with the actual transmit frequency. Various frequency lists will have both the indicated channel and the real transmit channel.
The Zenith DTT901 is actually one of the better converters. The limiting factor on almost all of them is receive sensitivity but the Zenith box was better than most.
Any proper antenna is better than rabbit ears and a loop.
That's why I suggested building a crude wooden prototype before diving into a proper constructed version. If the rabbit ears are as bad as I suspect, anything will gain will make a substantial improvement.
However, there's nothing sacred about building a yagi. It just happens to be fairly easy to build and delivers lots of gain. There are plenty of other designs that work. Try a Gray Hoverman antenna:
$100 without any mounting hardware or coax. Add a few dollars for those. I just was forced to buy a 10ft 1.25" mast at Radio Shock. $32 each. OUCH! Oh swell. The price went up for Christmas.
Incidentally, you can compare many commercial antennas at:
Yep. That's the suggested plan.
All elements are one piece except the driven element. However, you're not going to be building it like the typical yagi calculator shows. It's not going to be a simple dipole. Build a folded dipole instead. The feed point will (hopefully) be about 300 ohms. At the feed point attach a 300 ohm to 75 ohm balun, and then the coax cable to the TV. One of these things: There are better matching networks, but this is the easiest.
Yes it matters and no it's not a simple 1/2 wave dipole. With a folded dipole, the 300 ohm feed point is at the wire ends.
A few more details... I suggested building a single channel yagi instead of a broadband antenna because it's easier and because it delivers more gain. If you build the yagi from any of the online calculators, you'll end up with a fairly narrow band antenna. The more elements, the narrower the bandwidth. When the bandwidth starts to approach that of the TV channel (6MHZ) you're going to run into critical design parameters and cut dimensions that can't be worked out by trial and error. So, don't make it with too many elements and you should be ok. Otherwise, borrow an antenna analyzer that covers the frequency range, a reflection coefficient bridge with sweep generator, a network analyzer, or some manner of RF test equipment that can determine if you've hit the correct tuning frequency.
A rough guess as to bandwidth for the single channel yagi would be about 15% or about 90MHz (see bottom graph) so you should be ok.
Here's an antenna a friend built: It should work, but doesn't. Note the creative use of hardware store materials.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
List prices is $215. It comes in several mutations by channel range: A (14-19), B (20-26), C (27-34), D (35-44), E (45-56), F (57-69) Gain is about 12-14dBi.
Yeah, but I get paid to do it. The initial concept is tricky. The design is fairly easy depending on complexity. The initial prototypes are also fairly easy. Shoving it into production is difficult. Dealing with customer illusions, deranged marketing executives, creative applications, and impossible installations are my nightmares.
The official buzzword is a "loop yagi". However, that gives me an idea. I designed a 2.4GHz patch antenna made from foam board building construction insulation panels. It's basically polystyrene foam sandwiched between two layers of aluminum foil. It comes in various thicknesses. The same design would work for 600MHz. Gain was about 8dBi.
Sorta. The problem is that everything affects everything else. Too many parts and pieces make it difficult to build and optimize. Fewer parts are easier.
The biquad is nothing more than a loop yagi, where the elements are one wavelength long instead of 1/2 wave. The same dimensional tolerances apply to both antennas. The reason yours were not critical was that they probably didn't have much gain. At 2.4Ghz, anything less than 10dBi gain can be thrown together with little concern for tolerances. However, above about 14dBi, things get rather critical. At 24dBi and up, you're looking at about 80MHz bandwidth, which is the entire 2.4GHz band. Miss a little on the dimensions, and you could easily chop off the upper or lower ends of the band.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
I think the connections between the top and bottom dipoles need to cross over.
One without a modifier. ;-)
Bandwidth you can get by detuning the directors and reflectors, at least somewhat. If you need more, a Yagi isn't the right topology. A log-periodic is a better choice.
I don't understand the 300/75 balun thing. Isn't a 1/2 wave dipole 75 ohms directly? It's been a long time...
...and it'll yell at you, calling you autistic.
Nope. See: Note the feed point in the middle of the phasing lines instead of at the ends, which I think was the major problem. When it's built correctly it's actually a very good indoor antenna.
The bow tie elements really should be a solid sheet of copper or aluminium in order to get a broad bandwidth. It will work using "fan" type wire dipoles, but solid is better.
"The uglier the antenna, the better it works" Me about 1989
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Oh, good info. Thanks. And I agree, the elements would be better if solid.
The spacing from the rear reflector could also be a factor if not correct.
Years ago I built up a ten foot yagi from 1/2 inch copper pipe on Ch-22 and put it in the attic. It really worked well. I used a pre-amp that went from
300 ohms balanced to 75 coax to the basement distribution system. Used it for when the cable (often) went out (Comcast).Regards, tm
Just connecting the ends together will make a big improvement. Some creativity as to what is a solid bow tie dipole is also interesting: See the artistic fractal antennas. Stranger antennas have been built.
Nope. The spacing only affects the feed point impedance and the pattern. The wrong spacing might cause a loss of gain or directivity, but it won't cause the antenna to totally fail to function. Feeding the antenna at the wrong point will do that nicely.
Nice, until you have to rotate it. I've done a few attic antennas for CC&R infested homes. However, that's becoming a challenge as more homes are insulating the roof with aluminum coated foam board. The white rocks which are now required on most industrial flat roofs (for energy efficiency) also seem to block RF. I'm also finding roll roofing and shingles which are held together with wire mesh.
I've done a few "emergency" antennas for various applications. Copper pipe booms are expen$ive. I prefer wooden booms (boiled in wax or KD pine covered with Varathane. However, my favorite emergency antenna is a rope yagi. No boom at all. Just rope, wire or tubing elements, and hopefully plenty of room to deploy. I built one monster 30 meter long 144Mhz rope yagi with about 20dBi gain. I think there were 48 elements. That's a power gain of 100 turning a common 44 watt 2 meter ham radio into 4,400 watts EIRP, enough to cook your dinner. Ummm... don't stand in front of it or aim it at your neighbors.
A variation on the same idea is the roll out mylar yagi. I had a roll of mylar left over from my tape and donut black tape PCB layout days. I cut strips of aluminum duct tape forming a yagi pattern on the mylar. Dealing with the asymmetrical cross section of the elements was a bit of a modeling challenge, but worked after some guesswork. I haven't tried to apply too much power as I'm somewhat afraid it might melt. Four poles in the corners, some guy rope, and it's on the air. It could probably be turned into a TV yagi antenna, if a suitable place could be found to mount it.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
If you put up a huge mast you may get a usable signal, but it's probably beyond hope. do any of your neighbours get a good signal from that station.
We get marginal analogue UHF here and no usable digital UHF. and all the digital is UHF here.
I put up a satellite dish and tht works well except in high winds, I need to put some stay bars on it or move it to a less aesthetic, more sheltered location.
A 7 element yagi isn't going to give buckets of signal strength, but there's no saying what it might do to the signal quality.
Some designs use a loop for the driven element
yes, the geometry of the antenna is critical
-- ?? 100% natural
It looks like a bowtie phased array done wrong.
The feedpoint should be in the centre, or the vertical wires should cross. I guestimate it to be about 150 ohms, so it may need a custom balun.
That reflector may be too close too, or is that to change the impedance?
-- ?? 100% natural --- news://freenews.netfront.net/ - complaints: news@netfront.net ---
Here's the link to the TVfool.com analysis of my location:
The channel I'm trying to get is real 36 (virtual 35) KRSC, which is 29.5 miles away on a magnetic heading of 35 degrees. And going out in the back yard with my Boy Scout compass, I find that the hill situation isn't what I thought. The hill is actually more to the North. So based on the TVfool analysis and what the station engineer told me, a rooftop antenna should definitely work. But, you know, it's only one channel, and I don't think I want to got to that expense for one channel. So I'm going to try the Yagi and see what happens.
Oddly, there is one local channel that I can't get, and that's KTUL, real channel 10 (virtual 8). And that's despite the fact that real 11, within 10 degrees of 10, comes in fine. Very strange.
Of course I could play such tricks. But we have TV signals coming from four locations and the respective channels are all over the map. So this would get old really fast.
-- Regards, Joerg http://www.analogconsultants.com/
NEC2 models:
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
KRSC Noise margin is 6.6dB with 2 knife edge diffraction problems somewhere along the path. You should be able to make it work with a rooftop antenna.
You don't need much accuracy for aiming the antenna. A compass is good enough. However, if you ever want more accuracy, build a plotting board. Take a common road map and thumb tack it to the board. Find yourself on the map and insert a push pin or nail. Find a distant mountain top on the map that you can also see. Insert a 2nd push pin or nail at it's location. Sighting along the two push pins, rotate the plotting board and aim it at the distant mountain top. Your map should now be properly aligned. You can find the direction of a distant transmitter by just locating it on the map, and inserting sticks into the ground around the map with the same orientation. No compass or magnetic declination calculation required.
If you don't want to climb up on the roof to test your yagi, try a fiberglass telescoping window washing pole. I have one of those that is 25 ft long that I use for wireless site survey tests. Things work better when the antenna is clear of obstructions.
Looks right. Are you sure your converter is properly setup to deal with virtual channels? It could be listening to a different real channel. Check the virtual channel 8 status display on your Zenith or just rescan and start over.
Incidentally, if you want a clue as to what type and size of TV antenna is required to get decent TV reception in your area, just look around at the rooftops of your neighbors. What works for them, should work for you.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
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