In June 2005, with good weather, I decided to build an antenna for a digital television receiver. I had heard that DTV offered crystal clear, ghost-free reception. The TV transmitters here were in different directions, so I built a wide angle antenna (stacked cardioid) since I couldn’t buy one. The “art object” without planned camoflage looked like this:
To check the reception with the antenna, I used a splitter to feed both the digital receiver and an old TV that I used to measure the signal strength (AGC). I found the antenna was haunted (multipath). The picture on the old TV was good, but had a noticeable ghost. The digital receiver indicated receiving a strong signal, but the picture was the pit of blackness. The haunting had produced a different symptom on the DTV than the old TV. Ghost free reception for digital wasn’t really true. After I gained some experience with the quirks of DTV, I began collecting for a bibliography on DTV. If the Library did a program on DTV, the bibliography could help people (and librarians) find accurate information. As the years went by with no chance of a program, I finally gave up on the bibliography. Sadly, accurate information is still unavailable to the average viewer. KQED, the San Francisco PBS Station has on their web site the following:
Are You Ready for More Channels?
Clearer Picture?
Better Sound Quality?
No More Ghosting?
Here comes the Digital TV Transition.
On February 17, 2009, Television will be Changed Forever.
Are you Ready?
In spite of what they say about “no more ghosting?”, nowadays, there is some awareness of the DTV haunting problem. The 6th generation chip in the Zenith DTT901 resists haunting with a much better demodulator. With most granny boxes, haunting results in the usual black screen instead of pixel pus.
I winced when I read in the San Francisco Chronicle August 17, 2008 Page D6, the following: “Some history: Congress allocated more spectrum to broadcasters in 1996 so they could create digital broadcast channels.” Actually, TV viewers are losing over 200 Megahertz of prime radio spectrum. Before the big spectrum grab, there were TV channels 2 through 83. What now? Channels 2,3,4,5, and 6 are “unsuitable”. Channels 37, and 70 through 83 are gone. AT&T gets channels 54 and 59. Qual Comm gets channels 55 and 56. Verizon gets channels 60, 61, 65, and 66. Public Safety gets channels 63, 64, 68, and 69. Various Cell phone companies get channels 52, 53, 57, and 58. For Sale are channels 62 and 67. Regional Emergency Services share channels 14 through 20 with DTV stations. People must realize the $40 for each coupon came from somewhere.
A post script to the Library turning down my request to put a message about the $40 coupons on the Widescreen: they are now requesting Staff ideas for messages. For background, see:
http://thedonofpages.wordpress.com/2008/08/11/why-libraries-failed-with-granny-box-coupons/
***Edit September 14, 2008: The San Francisco Chronicle, Friday, Page C1, ”FCC steps up … digital TV” repeats the error of “Congress allocated more spectrum”. I had sent an Email to them nearly 2 weeks ago telling them of their mistake. Even if they didn’t believe me, there are several TV Broadcast stations in San Francisco with studios and Chief Engineers. Then again, the PBS Broadcast station here is still running the announcement with the “This Old House” stars saying every household is entitled to a pair of $40 coupons. The FCC is mandating the Broadcasters air an increasing number of spots about the DTV Transition, but apparently there is no requirement that the spots be factually correct. Well no, I haven’t sent PBS an Email, and I suppose I should. Maybe they can get David Brancaccio to do the spot correctly instead of Norm Abram.***
***September 18, 2008
Another error source. ME!! Coupons are still available to everyone. See my next post titled: “DTV Coupon Misinformation from ME!!” ***
I’ve been reading along for a while now. I just wanted to drop you a comment to say keep up the good work.
[...] Ankit Saxena wrote an interesting post today onHere’s a quick excerpt [...]
I found your site on technorati and read a few of your other posts. Keep up the good work. I just added your RSS feed to my Google News Reader. Looking forward to reading more from you down the road!
I live approximately 50 miles from our signal source. With the analog signal we got along fine with rabbit ears. I have purchased 2 supposedly upgraded antennas for use with my converter boxes and analog TVs. One works, one doesen’t (not well anyway). I’m a DIY’er and would enjoy building my own antenna. There are plans to build a digital antenna on the Make:television website. Yours has a more professional appearance. I don’t have a problem with rooftop/side mounting. Have you refined it to your satisfaction? Does it serve both UHF and VHF signals? Would you provide plans?
Thanks – Dean
Dean-
Professional Appearance? Hardly. Protected from weather inside an attic, I can attempt weird and fragile things like a 600 ohm UHF transmission section, or a UHF-TV stacked rhombic antenna. But for outdoors, one technique is to enclose the antenna in PVC. Generally the white PVC is piping, schedule 40 if it needs to be strong, or class 200 to be more spacious inside. White fittings are PVC schedule 40, as thinner isn’t available at the usual hardware store. The grey PVC is 1 inch nominal diameter schedule 40 electrical conduit and fittings. The gray PVC electrical tee fittings have a cover that allows soldering the transmission line junctions. Because the coax below the bazooka balun would hang for several feet, a clamp support was included inside. PVC is way too flexible to use for a stiff mast, so I transition to smaller diameter galvanized pipe. The joint between them is oiled nominal inch and a half pipe threads to allow aiming the antenna as well as joining. A condulet in the galvanized pipe allows joining the RG6 coax from the house to the coax from the antenna by a double male F connector. If I had needed a taller mast, perhaps nominal inch and a quarter thinwall electrical conduit and guywires. The UHF folded dipoles were made of #12 wire soldered to cheap brown 300 ohm twinlead. The cheap lead is flexible enough for stuffing inside the PVC parts. This antenna was a failure because the super wide angle reception allowed massive multipath. Today, the Zenith 901 might handle it, but the tuner used years ago sure didn’t.
I don’t consider saving a little money worth my time to build an antenna. But if what I want isn’t on the market, I’ll do some research at a library. At 50 miles, a 4 bay antenna on the roof would be minimum for UHF. The ARRL Handbook has a section on antennas, and the ARRL Antenna book is more detailed. I usually prefer a separate VHF and UHF antenna, and use a VHF/UHF combiner. I wonder if the following would work: build four horizontal colinears spaced vertically apart by 0.62 wavelength. Each colinear would be 3 dipoles with 2 half wave phase lines, with the colinear fed at the center of the middle dipole with good 300 ohm twinlead. The four twinleads would have to combine and be of equal lengths. If all that was put into PVC, pairs of twinlead would combine inside a pair of conduit tees, to create a pair of 150 ohm transmission lines that would meet to give 75 ohms. Another possible antenna would be a vertical parabola reflector with a horizontal 3 dipole colinear at its focus. There’s a lengthy thread here:
http://www.avsforum.com/avs-vb/showthread.php?t=798265