Attic Help, near NYC metro

[sporkman]

Hi all,

I've been free of cable and satellite for a few years now, and am really only missing PBS. I pretty much get all my content via a "Media Center" setup - lots of netflix, lots of streamed stuff, plus my library of ripped DVDs.

So as luck would have it, our NYC PBS station is the one that I'm having the most trouble with. My plot is here:

http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id%3dcd7213d3416710

The odd thing is that stations further down on the list come in without issues.

I just hung a VHF-hi/UHF combo in the attic tonight in an effort to catch the Doors movie on 13 late tomorrow night. The RatShack antenna is this:

http://www.radioshack.com/product/index.jsp?productId=3740646

I have about 20' of cable (RG-6? heavy stuff) running to the DTV converter box. No splitters, just one box on one TV. The antenna is about 23' or so above ground. I am surrounded by large trees in all directions.

Landlord prohibits any outdoor antennas.

WNET is what I really want - our "local" PBS stations (NJN) don't carry much of the national programming. Currently WNET comes in, but it blocks up and the audio stutters at times. The signal meter has some very wide swings from "bad" to "ok" (If they had a numeric scale, I'd guess at 30%-60%). The UHF stations seem to be at 60% or better. The other VHF stations seem to be around 40% and more stable.

Any ideas how to improve things?

Back in 7/09, the station posted this update about asking for more power, but nothing since:

http://www.thirteen.org/insidethirteen/2009/06/15/digital-tv-answers-still-not-getting-thirteen/

I've been considering buying the cheap RatShack inline amp to see if it will push me over the edge a bit more:

http://www.radioshack.com/product/index.jsp?productId=2103913

Mixed reviews on that thing - but it sounds like if you don't try to use it in an area with strong signals that swamp your receiver it could be helpful.

I wonder if anyone knows what devices could be contributing to noise on vhf-13? I do have some CFLs, plenty of computers, etc.

Pic of the attic setup attached - after that was taken, the antenna was levelled off and a hole was drilled for the coax a few feet back from the antenna.

[No static at all]

I would start by turning off any computers that are on the same circuit as the TV, or near the attic antenna. My computer speakers completely wipe out VHF 12 on my TV, even with a rooftop antenna.

The wild swings in signal strength usually indicate multipath signal reflections which are probably causing most of your reliability issues. Different mounting locations in the attic may help somewhat, but no guarantees. Adding any kind of signal amplification will not help the situation.

You will likely need to get something outside on the roof to improve reliability on VHF13. Do you think you could get away with a small antenna (http://www.amazon.com/dp/B0024R4B5C?tag=nengb15-20) on the roof?

Hopefully others will chime in with some suggestions.:)

[teleview]

It will help to raise the front of the antenna and lower the back of the antenna in the attic. Also here is a suggestion , Metal mounting bracket that is mounted on eave roof support or on the wall. Connect sections of antenna mast to gather to make one long mast that goes from the ground all the way up past the roof line at the peak of the roof. Also here is a suggestion , A chimney mount , metal straps that are made to wrap around the chimney. Also here is a suggestion , move the antenna to some where else on the property. Put the antenna on a antenna mast pipe. Connect the antenna with a long length of RG6 coax and walk around probing for a hot spot , to get all channels. http://www.solidsignal.com . . . http://www.starkelectronic.com . . . The out side antenna does not have to be small antenna with these suggestions.

[sporkman]

I would start by turning off any computers that are on the same circuit as the TV, or near the attic antenna. My computer speakers completely wipe out VHF 12 on my TV, even with a rooftop antenna.

Two things... One, I now have a Steely Dan song stuck in my head. :)

The other, I'll give turning stuff off a shot. The thing with multipathing though is that all my vhf signals (7, 11, 13) are coming from the same antenna on the Empire State Building - shouldn't they all be doing this? I do see WNET-13 has a fairly wimpy 9kW output, so I'm going to see if the preamp does anything - if it makes things better, then I know I'm just in a bad area (very low here, near the "Great Swamp" with a range of mountains between us and NYC). If it gets worse, then I'm dealing with interference.

Any other ideas are welcome... I'll also try to figure out how to get a monitor of some sort in the attic for some real-time aiming help.

[Dave Loudin]

The effects of multipath depend on frequency. That is, given the same scenario, what affects one channel may not affect another. Also, the antenna you have is one that comes recommended by many, the AntennaCraft HBU-33. A couple of suggestions:

* try changing the aim of the antenna a little bit. If signals are bouncing around up there, there may be an aim that penalizes/boosts one signal path over the other, settling down reception.

* move the mount to a different location. In my case, a close-by CFL on the floor below zapped VHF reception, and I suspect ceiling fans with dusty motors might also be an issue. Also, if multipath is really the issue, then a move and re-aim would help in the same way as the first idea.

* avoid that RadioShack amp. A pre-amp's role is to overcome cable losses, so the benefit in our case will just be a few dB. The extra gain in the amp does nothing to improve reception quality. Cheap amps, like the RadioShack model, also have higher-than-average internal noise - upwards of 7dB that SUBTRACTS from signal-to-noise ratio. I dare say that if you put the RS amp in, you will end up worse, not better.

A short explanation: the number to pay attention to on TVFool plots is the NM, or noise margin. Decoding a digital TV signal requires a minimum signal-to-noise ratio. NM is the measure of signal with respect to this minimum, so a 0 MN could be decoded if there were no losses. All signals fade, so a more apropriate target is +10 for NM to ensure reliable reception.

Things that impact NM:

* antenna gain (unamplified) - adds to NM, so a 7 dBi antenna picking up a signal with an NM of 25 will provide a signal with an NM of 32.

* cable loss - there's no avoiding this, and it subtracts from NM. If the loss in a cable run is 5 dB, then the above signal will have an NM of 27 at the converter box.

* pre-amp noise factor - this is the amount of noise generated inside the amp. Subtracts from overall NM, so if an amp with a 7 dB noise figure (truly bad - good ones run about 3) were to be installed in this situation, the NM before the cable run will be 25. Pre-amps zero out cable losses, so the NM at the converter box would be 25 also.

* roof shielding - at least 10 dB typical, could be more, and it subtracts from NM. In this example, that means the signal to the antenna would be no better than a 15 dB NM, likely worse.

[No static at all]

Two things... One, I now have a Steely Dan song stuck in my head. :)Excellent!! You're halfway there. Let's hope you won't need an FM trap.:D