New roof -- new attic antenna? - Page 2

dgs · 10-18-2009, 01:12 AM

I got a new "balun" from Radio Shack and replaced the one with the broken insulation. Although the wire looked intact, all the monkeying around with the antenna was starting to take its toll and the wires were starting to break. Nevertheless, I think the electrical connection was sufficient and replacing the balun had no effect on my signal. I also adjusted tilt and azimuth with my wife watching the signal meter and could not get any improvement.

Just for kicks, I got a $5 bowtie antenna while I was at Radio Shack to see how it would do. I connected it directly to the DTV converter in the kitchen. My signal on 43.1 (40) jumped to a watchable 55! However, I lost two other channels at 13.1 (13) and 46.1 (46). 46 is my second worst channel and I could probably stand to lose it, but 13 is PBS and we've gotta have that.

I also discovered something new about the channel lineup. I thought 9.1 was broadcasting on 39, since that's what tvfool showed. Since it was my strongest signal, I couldn't understand why I was losing the adjacent 43.1 (40). Well it turns out that 9.1 is actually broadcasting on 9 and 9.2 is on 39! 39 is watchable, but the signal is not as strong as 9.

All this brings me to my next round of thoughts. I was so impressed with the difference in UHF reception on the cheap bowtie, that I'm thinking my old yagi just doesn't have what it takes in the UHF range for the attic installation. The UHF stations were always a problem for me and the main reason I added the amp. Since I'd rather buy a new antenna for the attic than move my existing one outside, I'm thinking about trying that first. If it doesn't work well in the attic, it will be a lower profile installation on my chimney and will look better than anything I can come up with for the old yagi. Any suggestions for an antenna that will work well in an attic? My lowest real broadcast frequency is channel 7 and I've read claims that multiple bay UHF antennas also typically get the Hi VHF.

I could also combine a new UHF antenna with my yagi, but I'm not sure how to do that properly. I have plenty of room in my attic to add antennas, but my outside options are limited. Any final thoughts before I pull the trigger on a new antenna?

Don_M · 10-18-2009, 10:45 AM

The best way to combine two antennas would be to designate the RS antenna for VHF signals (7, 9.2 and 13), where it performs very well, and add a new UHF antenna on to it. This is done easily and efficiently with a $5 splitter-in-reverse called a UVSJ combiner and a couple of short coaxial cables for antenna leads. The UVSJ will filter out UHF signals from the RS antenna -- a good thing, since that prevents reception issues caused by signal conflicts between the two antennas. The combiner also filters out any VHF signals that come in on its UHF side. No physical modification of the RS antenna is needed (or recommended, for that matter).

A four-bay, "bowtie"-style UHF antenna would be the way to go if the antenna might someday be called on to receive VHF signals and/or moved outdoors. The classic choices here are the Channel Master 4221HD or the Antennas Direct DB4. There's also the Tune-a-Tenna, designed and sold by one of our members. All offer roughly similar UHF gain; the Tune-a-Tenna's maker claims significantly better gain on channels 7, 9 and 13 than the other four-bays, so it's definitely worth a look.

dgs · 10-18-2009, 12:23 PM

OK. I ordered the DB4 and the UVSJ. I want to try the DB4 by itself first, but ordered the combiner in case the VHF signal is weak and I want to add the two antennas together. I'll let you know how it all works in about a week.

Just out of curiosity, I've noticed that most attic antenna installations are still on masts or bolted to the roof structure. Are there any drawbacks to "hanging the antenna from the rafters" with non-metallic rope or plastic clothesline?

By the way, I figured out last night that the antenna I have now is the Channel Master CM3016. It was probably sold under Radio Shack's Archer brand back in the day.

Don_M · 10-18-2009, 12:48 PM

Yes, please let us know. The feedback helps: Antenna work is as much art as it is science, so even seemingly good advice sometimes doesn't work out in a given situation. That explains the mantra, "YMMV."

Quote:

Originally Posted by dgs

Are there any drawbacks to "hanging the antenna from the rafters" with non-metallic rope or plastic clothesline?

None at all.

Quote:

By the way, I figured out last night that the antenna I have now is the Channel Master CM3016. It was probably sold under Radio Shack's Archer brand back in the day.

If it's got four pairs of long elements in a "V" shape at the back of the boom, you may be right: It was marketed as the Archer VU-90, which was very similar to today's CM 3016 in both design and performance. RS sold millions of them over several decades. It was discontinued a year or so ago. Even now, more than two decades after cable service became so popular, VU-90s are still ubiquitous above rooftops across the country!

EscapeVelocity · 10-18-2009, 12:55 PM

Yeah, the VU-90s are great and ubiquitous!

FYI, the DB4 has the least ability on VHF High of the 3 Quad Bowtie antennas that Don mentioned....hen the CM 4221HD, with teh Tune-A-Tenna having the best gain on VHF High. However the VU-90 is superior to the Tune-A-Tenna on VHF High....assuming nothing is wrong with it. All 3 blow the VU-90 away on UHF, with the Tune-A-Tenna offering the best performance, then the CM 4221HD, then the DB4 pulling up the rear.

My 2 cents.

dgs · 10-18-2009, 05:14 PM

Quote:

Originally Posted by EscapeVelocity

FYI, the DB4 has the least ability on VHF High of the 3 Quad Bowtie antennas that Don mentioned....then the CM 4221HD, with the Tune-A-Tenna having the best gain on VHF High. However the VU-90 is superior to the Tune-A-Tenna on VHF High....

Any idea how the Clearstream C4 compares with that list on VHF high? It claims to have good performance there, but since I already have a good VHF antenna, I couldn't justify 3 times the price. How does it compare in UHF? Is it worth the price or is it all marketing?

Quote:

assuming nothing is wrong with it. ....

The antenna appears to be in perfect shape, other than the balun that I replaced. It has been well protected in the attic. Besides the obvious missing/broken element or connector, is there anything else that could be wrong with it electrically?

Quote:

All 3 blow the VU-90 away on UHF, with the Tune-A-Tenna offering the best performance, then the CM 4221HD, then the DB4 pulling up the rear.

Although I'll install and test the DB4 standalone first, I suspect my long-term solution is probably the combined antennas--at least until the VHF high stations move to UHF.

EscapeVelocity · 10-18-2009, 05:57 PM

The C4 is a great antenna...a bit pricey. I wouldnt call it a VHF High antenna.....neither is the Tune-A-Tenna really, but the Tune-A-Tenna is better on VHF High.

Im not really a fan of the C4, but I love the C2 and the C1 is alright too. I dont really like the 8 Bay side by side bowties either. Though Im fond of old discontinued American Made 4221A. I love the 2 Bay DB2 as an indoor or small UHF antenna solution...better than the old American Made CM 4220A 2 Bay...even though the CM 4220A has more gain. I really think the DB2s smaller form factor is its trump card...and if you are using it inside, its a better interior antenna from materials standpoint as well (smooth and non-jagged). If you are going to put something up outside or in the attic, I recommend a 4 Bay over a 2 Bay. The 2 Bay CM 4220 just falls through the cracks.

However the only Chinese made Channel Master Bowtie I recommend (besides the famous vintage discontined indoor uhf ones) is the 4221HD. The 8 Bay is severely flawed without hacks, and the 2 Bay I still stick with the DB2. The 4221HD has good manufacturer supplied numbers, and has tested well.

Let me state that the DB4 isnt a bad antenna, and will probably serve you well on UHF. It also has the smallest form factor of the three 4 Bays that Don mentioned.

Hope that helps.

FOX TV · 10-20-2009, 08:57 AM

Quote:

Originally Posted by dgs

First a little history on my setup.

I live in Edmond, OK. I've run the tvfool analysis and most of the stations we watch are in the 5-8 mi range and all within about a 20 degree band. They were very high power stations broadcasting from central Oklahoma to provide coverage throughout the surrounding rural areas. I don't know if their power was reduced when they changed frequencies for DTV. The local area is hilly, but I live about halfway down the backside of a hill with mostly flat land between the house and the TV stations. This should be ideal for TV reception, but it hasn't worked out that way.

I installed a large Radio Shack yagi in the attic 20 years ago and pointed it in the direction of the large antenna complex. (I intentionally bought more antenna than I thought I needed because I knew I was going to put it in the attic and lose some of its effectiveness.) I used a splitter to send the signal to 3 TVs and a VCR. The antenna is just below the "TV room" with all my gear. TV #2 is in the bedroom on the other side of the wall and TV #3 is in the kitchen (about a 50' cable run). Signal was acceptable, but weak on some of the UHF channels, particularly in the kitchen.

A few years ago (pre-digital), I decided to try to improve the signal in the kitchen. After a bit of trial and error with some amplifiers, I installed a Radio Shack 1-to-4 Bi-Directional distribution amplifier that claims an 8db signal boost. I set the adjustable gain to just above the minimum level. Picture quality was significantly improved on some of the weaker analog UHF channels.

After the DTV conversion I got excellent reception on most channels. Occasionally I'd get a weak signal that resulted in pixilization, but it was rare.

About a month ago we replaced the wood roof with a heavy duty asphalt composition shingle and foil sided roof decking. I can hear the groans now, but a good roof was my top priority. I expected I would have to deal with the loss of signal quality when it was all done. Fortunately, it was not as bad as I anticipated. On most channels I still get a good signal. However, the station transmitting on VHF-hi channel 7 breaks up some of the time, and the station transmitting on UHF channel 40 rarely comes in. According to tvfool, the signal strength is 68 and 73 dB for these stations at my location. I know I'm getting some attenuation with the new roof and cranking up the gain on the distribution amp to just under max helped a bit. What puzzles me most is that I still get good reception of stations transmitting on frequencies on both sides of the spectrum from the signal I've lost (UHF channel 40).

I'm trying to figure out what to do next to get reliable signals. I've experimented with various indoor antennas, and despite the fact that tvfool says I should be able to get all these channels with an indoor setup, the signal is still not reliable.

I added a fourth coax cable to a computer tuner. When I did that I cut out all the other splitters I was using for VCRs, DVRs, converter boxes, etc. I'm trying to keep the signal as pure as possible in case one of the splitters or other cables was creating problems.

I'm wondering if something like a Clearstream C2 will help. Although I doubt I'll get any help in the VHF-Hi range (and it may be worse than my current yagi), I wonder if it will do better for the UHF frequencies. Can I tie the antennas together to get a better combined signal? The other alternative is to move the current or a new antenna to the roof, but I'd rather not expose it to the severe weather we get in OK, so that's a last resort.

Does anybody have any thoughts about my configuration and what I could do to improve signal quality? I love the digital picture, until I start to lose it or when I can't tune a channel at all. I want to watch broadcast TV because I have no desire to spend money for cable or satellite TV with a bunch of channels I don't care to watch. I'm hoping some of the experts on this site can help me get it back. Thanks for your help and comments.

This sounds more like a multi path or signal overload issue to me. Normally when you have a lock on a signal and it breaks up or drops out and you see the dreaded "No Signal" logo, it is normally not really a low signal issue.

I wish the chip manufacturers would have divided the message up with two components, with one saying "No RF signal", and the other stating something like "Data Corruption or Data Loss, because these are two entirely separate issues, and the "No Signal" message automatically leads some people in the wrong direction in regards to antennas when they see the dreaded "No Signal" logo come up on the screen.

Digital transmitters, unlike the analogs run a consistent power level, where the visual power output of an analog transmitter varied with video content, digital transmitters run more like an FM transmitter with a consistent power output, so an actual no signal event is very unlikely unless the transmitter is off the air, or you live in a far fringe area away from the transmitters.

If you are that close to full power transmitters, the first thing I would try is to remove the amplifiers completely and hook the antenna to one TV set without splitters or amplifiers. The sensitive circuitry of digital tuners can actually suffer from to much signal. You may actually need signal attenuators in your coaxial line from the antenna if signals are really strong at your location.

dgs · 10-21-2009, 10:33 PM

Quote:

Originally Posted by FOX TV

This sounds more like a multi path or signal overload issue to me. Normally when you have a lock on a signal and it breaks up or drops out and you see the dreaded "No Signal" logo, it is normally not really a low signal issue.

...

...so an actual no signal event is very unlikely unless the transmitter is off the air, or you live in a far fringe area away from the transmitters.

If you are that close to full power transmitters, the first thing I would try is to remove the amplifiers completely and hook the antenna to one TV set without splitters or amplifiers...

I understand that it seems like I should have an incredibly strong signal. Unfortunately, with the exception of a few channels, that's not the case.

Fortunately, I have been able to go far beyond the binary signal/no-signal analysis. I have used the signal meter on the DTV converter to record relative signal strengths of each of my major channels, with and without the amp. (See my table above.) I also did another analysis with the simple $5 bowtie from RS connected directly to the DTV converter. I have all those numbers, but didn't post them. What I found was significant improvements in the UHF band compared with my old VU-90. However, it was not strong enough to make the signal reliable and kept breaking up. The signal level meter showed about 50, but other channels were unwatchable.

So I hooked up the $5 bowtie and the cable from my VU-90 to an A-B switch. When my wife wants to watch the weak UHF channels, she switches it to the bowtie. It's about 90% watchable. For all other channels she switches it to the cable from my VU-90. This is the interim solution until I get the new DB4 UHF antenna and combine it with my VU-90 via the UVSJ.

As far as multi path--I wish I had a better way to test for that. It certainly seems plausible since I have adjacent weak/strong signals. It could be the culprit, but I can't prove or disprove that theory with the equipment I have. If you have any suggestions about how to analyze or test for multi path, I'm all ears/eyes. Better yet, if you have a way to reduce its effects, I'd like to hear that, too. (Do I need to build a tin-foil wall in my attic?

)

Don_M · 10-22-2009, 09:26 AM

Quote:

Originally Posted by dgs

Do I need to build a tin-foil wall in my attic?

A grounded reflector like that actually is the way to go if nothing else works. People have done it with good results.

Here are some examples of the "state" of that particular "art," done by Bill Naivar at Georgia Tech:

Antenna in an aluminum-mesh box

Antenna in a garbage can (seriously!)


Home \| DTV & HD News \| Today's Posts \| JakesDTVBlog.com Interview \| Join DTV USA Forum