Antenna strength question.

[kjnorman]

Okay, I need some feedback on antenna strength please.  I got my HD Tivo install last Wednesday but only had time to plonk a RS double bowtie attenna on to of my TV (as I was off on vacation the next day).

I used Antenna web as I guide and found that I have signals to the NW, SW, and SE (roughtly).  After some positioning of the antenna I found that WISN was the weakest and so I bias the antenna in that direction (SW) letting the others come in off the side.  Scanning the strength of the signels I find that all stations that I am interested in are in the 88 to 95 range on the Tivo strength guide.

However, when I tried to watch Lost on Wednesday night we experienced a lot of sound drop out and occassional picture breakup.  So much so that we ended up watching the SD version (which looked horrible by the way - WISN you should be ashamed of such a bad SD picture).  I find the the Tivo records and plays back Sat HD channels fine so I think this is just a reception issue and not a hard drive or tivo issue.  

Watching E-Ring tonight (NBC) we had one small spot of sound breakup and everything else was fine.  So far, I have had no break up when watching live.

So the question is, at what signal strength do I need to avoid sound and picture break ups?  I would have thought 88-95 would be enough but I guess it is not.

Thanks
Kerry

[kjnorman]

Oh by the way, I intend to relocate my bowtie up into the attic when I have a free moment and manage to drop a line down to my basement.  I would think that this should improve my signal a lot.

K.

[Mark Strube]

At one moment it might report 88-95 but that might not be consistent. There's all sorts of things that can kill your signal momentarily. When I was first positioning my OTA antenna, 18-1 was the hardest to get. (And that's the reason I got my OTA receiver in the first place!) It would hang out around 85, and then just inexplicably drop to around 50 for a moment, then back to 85. I finally found if I position my antenna near the ceiling, I get a consistent 95 signal on that station, which gives me no issues. If you're already getting around 80's with a non-powered antenna, I think a powered antenna would do wonders. This is the one I got...

http://cgi.ebay.com/NEW-Indoor-Directional-HDTV-Amplified-VHF-UHF-Antenna_W0QQitemZ5812511123QQcategoryZ73383QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Great item except I'd recommend using your own coax to go from the included amp to the antenna... the one that comes with it doesn't seem to screw in quite enough to get it consistent power... although that could've just been a problem with mine.

Once I mounted it near the ceiling in my bedroom on a little homemade shelf, it gets a 95-100 signal lock on all the locals except 24-1 and 10-1-7. (Don't really care about those anyways). That was tough to do, because while I'm only about 10 miles from the transmitters, my area is loaded with trees, and my house has aluminum siding. I believe where I placed the antenna in my room, it's able to shoot thru a bit of a clearing in the trees.

Anyway, hope this helps some.

[kjnorman]

Okay, thanks for the reply Mark.  So, I should be looking for 95-100 in the signal strength.

I think moving to the attic will help a lot; it will avoid a lot of walls, though luckily I have vinyl siding.  Basically I get:

Fox (33) to the NE (330 deg) - about 4 miles. This has to come through our N wall, the neighbors house and a bunch of trees.

ABC (34) and CBS (46) to the SW (241 & 244 deg) - 1 1/2 miles.  These have to make it through our kitchen, chimney stack (which is right in the path) and living room to get to the antenna.  These have the most difficult job.

All the rest come in from the SES (173 deg) - 2 miles.  These have an easy time as the signel comes straight through out living room picture window.  Though a few trees do get in the way.

When I come to do my final antenna placement, I thinking that I should aim it between the two main groups (ABC/CBS and "the rest") pointing it SWS (about 220 deg), which would let Fox come in on the back on the antenna.

Is this sensible?  Or is the better way of pulling in signals when they come from three differing directions?

Thanks.
Kerry

[Mark Strube]

Well, for me that powered directional indoor antenna was the answer, since I'm pulling all my signals from the same general direction in Milwaukee (I get the best signal pointing almost completely straight east, just a tinge north). I'm not sure if there's a good omnidirectional antenna you could be using? With your short distance from all the stations, this shouldn't be too hard... I'm 10mi away and surrounded by trees getting this kind of signal... maybe something like this would even do the trick:

http://store.digital-orange.com/pejasht24737.html

Never used anything like this though, so don't take my word for it. But I'm thinking since you're so close, anything even the least bit amplified will give you an awesome signal. (Is that one amplified? It says gain control so I would assume so...)

[jfelbab]

With your close proximity to the towers you should be able to get a good signal with almost any indoor antenna. You don't a stronger signal just a more directional antenna. If you are having reception problems it is most likely caused by multipath.  To combat multipath your aim is to reduce the signal level of the offending stations more than the station you want to receive.

[jfelbab]

Your signal strength is fine and not the problem.  Your reception issues are more likely caused by multipath. OTA signals get bounced off walls, buildings and trees. These bounced signals tend to cancel out the original signal causing a loss of audio and picture. The reflected signal is usually much weaker than the one you are trying to receive so often a cure for multipath can be achieved by padding down the signal level somewhat.  Another good method is to use a more directional antenna.  This may require you to reposition the antenna for some stations but you will only know this through trial and error.  It also often helps to try relocating your antenna to find an spot where these reflected signals are not a strong.

[kjnorman]

Okay, moving antennas either via a motor or manually is not going to be an option.  This thing is running a Tivo for unattended recording.  

I have another option that I can try as well.  We actually have an enormous antenna already attached to our chimney that we are not using.  The reason being that it has a 300 ohm downlead that enters our basement and is cut off (goes no where).  

As I have no intention of climbing up on my roof at the moment to replace the lead with a new RG6 all the way to the antenna I may try connecting a 300/75 ohm balancing transformer in the basement (I know its not the best solution) and then run the RG6 from there to the living room to hook up to the Tivo.  

I have no idea how good this antenna is (it may be 40+ years old for all I know), so this may be a foolish attempt but as I already have the equipment it may be something to try.  

Kerry

[jfelbab]

All but one of the DTV stations (WMVS-DT 10.1) in the area are UHF.  If that outdoor antenna is a combo antenna you could try it but if the antenna is that old it is likely shot.  The 300 ohm flat lead in wire is certainly shot as it doesn't last that long.  

Again, you are getting a strong enough signal.  You are being troubled by these multipath, or reflected, signals.  The reflected signals are typically always at a lower strength than the signal you want to receive so if you can pad down the signal from the antenna enough to drop the multipath signal level and still receive the original signal that is the way to go.  You can buy pads as various places. I think RatShak may have them.  If you have a splitter try that, even though you may not use the other tap, as it will cut the signal strength in half. Every 3db of padding cuts your signal strength in half.

Alternately you may need a more directional indoor antenna.

[Mark Strube]

Directional may not be an option for him since he's looking to get stations from different directions. I'd suggest trying the outdoor antenna, and if that doesn't do the trick... find an indoor omnidirectional powered antenna. Those are your best 2 options without having to put up an outdoor antenna (unless you go for a directional like I showed you... with that close of proximity it might not even need to be pointing towards some that you want to pick up).

[kjnorman]

Okay, well last night I connected up my large antenna.  I tested it out with analog channels and 4, 6, 12, 41 are great, 36 gets a fair amount of ghosting and 10 and 58 get a small amount of ghosting.  I also picked up some Madison stations (though not clear enough to watch).

I hooked the line into my channel 3 feed to the other TVs in the house and the strong channel 4 totally overwhelms the channel 3 signal.  I guess I am going to have to get a channel 3/4 combiner to solve that.

I was expecting good results with digital following the results on the analog channels but the result was a disaster!     Channel 8 was pinging all over the place and most of the other channels would not even register.  For testing I tried my "paperclip" antenna method (stick an unfolded paper clip in the back of the tivo) and the channels came back, abeit with readings of 40-80.

In the end I went back to the RS bowtie I have, and instantly the channels came in about 88-95 across the board.  I tried different positions in the room and everyone seems worse.  I movement of 2 yards could make a 95 channel into a 50 channel, or a few degrees angle change can cut a stations strength by two thirds.

It would seem that my first "temporary" antenna placement found the sweetspot in the room.  Infact it seems the strongest location is aiming the bowtie directly at the chimney stack.  I am beginning to think that I am stack is boucing the stations that come from the side into line with the bowtie element, and that I am picking up the reflected signals and not the main one.  Who knows?

At the weekend I will see about relocating the bowtie to the attic for better reception still.  Though I am bummed about the main antenna (still, now I have connected it I will use this for analog on the other TVs).

Question, could my antenna be just too strong for the Tivo?  I seem to remember reading somewhere that the Tivo's tuner is somewhat sensitive to strong signals.  If this is the case can I reduce the signal with an antenuator?  Incidentally, I had already split the signal twice on the way to the Tivo (-7db).

Kerry

[mhz40]

I agree with everything jfelbab has stated.  You in RF hell living in the Shorewood/WFB area...
What looks like a modest ghost on an analog channel can totally wipe out a digital one - - or make it so unreliable that you don't want to watch it.
Multipath is nearly impossible to eliminate.  To do it right, you need to know what direction the multipath is coming from and combine two or four 'phased' antennas correctly to cancel out the undesired signal while increasing the gain of the array in the desired one.  Again, this is extremely difficult and usually is setup to receive only one RF signal, not an array of signals coming from 5 different directions.
Generally you want to increase the difference between the desired signal and the un-desired (multipath) one.  Raising the antenna or adding an amp does nothing to change the difference between them.. it only changes the level of the signals hitting your tuner.
I know this sounds crazy (and that I'm risking what little credibility I may have in this forum), but in your area I would keep the antenna low.  The higher you go, the stronger the multipath can potentially become.  If you have a basement, I suggest you try there (seriously).  Since you are so close to the transmitters, you should have enough signal just below grade to drive the Tivo receiver and still be in a position to shield the antenna from some of the multipath reflections.
You should also find out what the level reading really means... it it bit-error-rate, or the AGC level of the tuner?

Good luck...

[Nels Harvey]

Kerry wrote:

Fox (33) to the NE (330 deg) - about 4 miles. This has to come through our N wall, the neighbors house and a bunch of trees.

ABC (34) and CBS (46) to the SW (241 & 244 deg) - 1 1/2 miles. These have to make it through our kitchen, chimney stack (which is right in the path) and living room to get to the antenna. These have the most difficult job.

All the rest come in from the SES (173 deg) - 2 miles. These have an easy time as the signel comes straight through out living room picture window. Though a few trees do get in the way.

Fox is no longer sending from their studio location.  They are finally on the TV6 tower.  

The problem you have is you probably live in the cone under the beams of the signals, and actually receive weaker signals than someone a bit further away.  Unfortunately, the reflections are proportionally stronger as a result, and cause greater interference.

The suggestion of putting the antenna in the basement might work.  What you ought to try is experiment with antenna locations, and lower gain antennas.  Hopefully, you can find a location that gets a steady signal from each HD station.

A lower gain antenna will have a wider pickup of signals, and shouldn't need to be turned from your location.  The lower gain antenna may, or may not, pick up as much unwanted interference as well, but receiving UHF signals can be capricious!

 Good luck!

Nels....

[kjnorman]

Kerry wrote:
Fox is no longer sending from their studio location.  They are finally on the TV6 tower.  
Nels....

I was going by the AntennaWeb guide.  What direction is the TV6 tower?  Is it one of those on Capital?

Thanks.
Kerry

[kjnorman]

Don't worry on the Fox direction I found it.  I used the Broadcast Station Search site (listed on MilwaukeeHDTV home page) and entered the values into excel and plotted the locations.  This gave a much better visual of my situation.

As the signals are mostly 90 degrees from each other, would it be posible to combine two highly directional antennas that have null spots at 90 degrees, or just point my bowtie mid way between the two hot spots?

I'm no more than two miles from either transmitter, and I am beginning to envy some of you guys out there who are further away and have a single line of site to the transmitters.

Kerry