O/T: Folded Dipole

[Art Greenberg]

Low VHF (analog channels 2 through 6) likewise.

[Art Greenberg]

My bad. I just researched this ... channels 2 through 6 are still allocated to DTV use, but it looks like there will be very, very few stations using those channels for broadcast.

[Morris Dovey]

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. :)

[Leon]

I think it goes with out saying that if as the signal degrades enough you eventually get no picture. That said however most satellite receivers have a built in signal strength meter and you can check individually sources for signal strength. Not until my strength gets down to "about" 60% do I actually loose a picture. Anything in the 60 to 80 % range can cause mild to moderate picture quality loss. Typically 90% and better produces a great picture. It is not uncommon for picture quality to degrade on a daily basis and oddly some channels are worse than other.

And this is exaggerated more with satellite HD programming, signal strength has to be higher for a better picture. I have 2 TV's using the same dish but 2 completely different kind of receivers/DVR's One is HD, one is strictly regular definition. The HD receiver picture quality is much more fussy about the strength being higher to get a good picture. With the regular definition receiver signal strength can drop considerably lower than the HD unit before noticeable picture quality drops. I have a regular TV hooked up to a "off air" rabbit ear antenna and digital tuner for local channels and most of the time the picture quality if perfect. I am about 8 miles from the transmitter towers.

[Art Greenberg]

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.

[Morris Dovey]

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.

[cselby]

I worked in the Arctic and noticed that some Inuit use the heat dissapating grid off the back of old fridges as an antennae to pick up CBC. Considering that was an analog signal from 100's of miles away, it was an impressive use of recycling.

P

[charlessenf]

"the existing folded dipole antenna."

CURIOUS - Did you visit Antenna Web before deciding upon an antenna? If so, I would be interested in what they reported as far as your antenna requirements and reception probabilities. I am NOT near a big city and can only get one Public TV station with our roof-mounted antenna.

I built a dipole for the FM radio I have, but it didn't improve things all that much for "distant" stations.

Thanks

[beecrofter]

A formula that did not flow out my other ear

folded dipole length in inches is equal to 5565 divided by the frequency in megahertz

[dpb]

That's one more than we're now getting since the switchover. W/ the outdoor mast-mounted antenna, their signal is undetectable entirely during a scan although the analog was reasonably watchable most of the time. As I've noted previously, I'm not going to spend time trying to fine-tune antenna position, etc., until the other stations also switch over so only do it once to at least see what the prospects are.

The one commercial station that did switch is ok and although it is the closest of the three (~60 mi) the box sensitivity is about 43% most times. Only dropout every so often. What's really annoying about that is that the box warmup message comes on again and hangs around for a while--if it would simply just go out and come back that wouldn't be nearly such a pita.

I'm sure w/ simply a dipole Lew's close enough to his transmitters there was no need to look it up.

For us, the FCC maps and the antennaweb.org site both indicate "far fringe" but claim _should_ be viewable. The current antenna is rated for far fringe (I don't recall gain figures, etc) and relatively new having been replaced a couple years ago after big ice storm took previous one down and broke it up pretty badly.

I've noticed on those coverage maps other regional areas have very marked directional beam patterns that are leaving large sections of the formerly covered broadcast areas out entirely. It's clear the folks who thought all this up never thought a lick about fringe reception areas.

What kind of distance and terrain do you have to deal with? At least here it's flat which gives better shot. I'm guessing I may have to raise tower to get it farther from the house than it is at the moment when the others switch. I've no additional amp at the moment, either, btw.

--

[Scott Lurndal]

External rabbit ear antennae have had UHF capabilities for forty years.

scott

[Scott Lurndal]

The digital receiver _first_ must convert the modulation of an analog carrier to the '0' or '1' instead of converting the modulation into an analog NTSC signal. This is the step where the S/N ratio matters.

scott

[Leon]

That gets me to thinking. I have DirecTV on 2 televisions. From the same HD dish goes a lead to the HD DVR to a HD LCD, also to a analog DVR to an analog TV. Reception on the analog DVR and TV are basically perfect unless the weather is poor, piss poor. Almost daily my HD DVR and HD LCD TV and my neighbor, BIL, and father's SAME setup have periods of bad reception on any of the major local networks. I wonder if DirecTV is currently converting an analog signal from these stations to digital and if that could be the problem. On a 3rd going from a rabbit ear antenna to a CHEAP digital converter to an analog TV produces great results day in and day out. Non local HD channels do fine. DirecTV cannot figure out the problem nor can the installers on any of the 7 or 8 times that they have come out to replace the dish or HD DVR.

[Doug Winterburn]

I'm guessing it's more of a bandwidth issue. 1080i requires (guessing) at least 4 times the bandwidth as 480i which makes it more susceptible to pixelization/drop out.

[Nova]

They've been broadcasting digital signals in the Houston area for over four years???

[Nova]

I'm not familiar with the set up for digital TV but I was a TELCO data transmission specialist for quite a few years.

With DOV/DUV (data over voice/data under voice) the S/N ratio seldom cause problems with the data, unless the noise was severe, while it would greatly impact the modulated analog signals. Phase jitter on the other hand would wipe out the data with little impact on the analog.

The same help true for the Async data using 2024, 2028 and 2029 modems.

[Leon]

Satellite has been digital way longer than that. But I have been watching local digital directly from local broadcast with rabbit ear for almost 4 years. It was just a couple of stations to begin with, the local advertising, local news, and day time was in standard. Most prime time was about the only time you could watch in HD.

[Leon]

720 for me. My LCD is relatively old, almost 4 years old. 720i was expensive enough, 1080 was way more expensive and my set is only 46". At the time I was told that above 46" was pretty much when you needed to go with 1080.

The weird thing, if I switch from Satellite to rabbit ear the reception from the locals if fine. If I switch to satellite the HD reception is fine on all 70 or so channels EXCEPT the local channels.

[CW]

So do your bedsprings but it doesn't make them efficient.

[J. Clarke]

Yes they have, and most of the rest of the country as well.

And my personal experience with digital is that there's perfect picture, frozen picture, or black screen. I've never seen anything that looks like "doing mushrooms" however I am willing to grant that there may be some sets out there that show pixelation when they lose bits.