To Amp or Not To Amp

[TydalForce]

OK I need some collective wisdom from all you Smart Folks....

I have a DB2 antenna set up, connected right to my Series 3. (DB2 is hanging in the window, about 10 feet of coax). Its working pretty well.

According to the Signal Strength meter, most of my major network stations come in 70s and 80s (The worst being FOX at 72).

However: The 2 local PBS stations don't really register more than some blips, and another station comes in "meh" around 50ish.

So, my important stations come in well. My not-so-important ones don't really come in at all. I know from previous experience with a Terk HDTVlp I can get the rest of them in reasonably well (it's got a built-in preamp).

I also have an old (and presumably crappy) Radio Shack amplifier that seems to pull in the PBS stations a little, and boost my overall signal strength. But I get the impression its really only making things worse in terms of signal quality.

I am thinking about some kind of preamp for this antenna. I'd like to pull in the rest of the stations, and hopefully double as some "insurance" for the good ones (help keep them from hiccuping), but I don't want to waste money if its not going to work.
I'd also like some suggestions on what preamps to look at. I hear lots of good things about the Channel Master 7777, but I seem to recall reading somewhere that its not good within 20(?) miles of the transmitters. (I'm about 9 miles, zip code 19008 if anyone wants to look).

Also of note, all my digitals are UHF, but 2 or 3 of them are planning to switch back to VHF in 2009. I can live without VHF for today, if necessary.

Any thoughts anyone? Insight and opinions are greatly appreciated.

[btwyx]

I have a Channel Master 7775 pre-amp (the UHF only version of the 7777). It works for me, it turned some unusable channels into perfectly statble usable channels. From no stable signal up to 92 at best. Most of them are now in the high 80s-90s.

I wouldn't think that distance from the tower would be what you should be worried about. If you have enough signal, amplifying it can just make it too strong to be useable. Its vaguely possible that you low signal strength is caused by too much signal overloading the tuner. If that's the case, a pre-amp would be bad, and an atennuator is what's needed.

The best you can do is try it and see. If you really don't care about VHF channels, a 7775 is a better choice. I use a couple of VHF/UHF splitters to make a VHF bypass for the amp for the 1 VHF channel I receive.

[Jerry_K]

I use a Radio Shack 4 line distribution unit, which works very well.

[btwyx]

I use a Radio Shack 4 line distribution unit, which works very well.That's a different type of amp. A distribution amp is for sending the same signal to multiple places without degrading it. You need a good signal to start with. The pre-amp is for improving a low level signal. The most important thing about a pre-amp is its noise figure, that's how much extra noise it introduces into the signal. The Channel Master's are notably good in that respect.

I have a Rat Shack distribution amp, when I was experiementing with OTA first, I tried using it as a pre-amp. It made no difference to the "signal strength" as reported by the TiVo. The "Signal Strength" is actually more a measure of signal quality.

[TydalForce]

I have a Rat Shack signal amp; used to be in the cable closet where the CableTV came in to boost the signal strong enough to get through the rest of the house (its since been replaced with another model that's cable modem friendly)

If I hook up this amp, my signal strength numbers on the "good" channels get better by 3-5 points. My PBS stations start actually being watchable (though a little unstable) which is what makes me think "something better" would be the magic key.

btwyx, if I'm understanding your idea correctly... I start with a pre-amp and see how it does. It should get my weak stations in. But if its overloading the signal for my good stations, I add an attenuator to the mix to level things out.

Sound about right?

Thanks for the insight!

[JamieP]

I'd recommend reading the section on amplifiers here (http://www.hdtvprimer.com/ANTENNAS/basics.html) to explain when and how a preamp can help. It's really only useful if you have line/spliter loss (long cable run or spliters) or if the noise level of the amplifer is lower than the noise level of your receiver.

[TydalForce]

Jamie, I have read that... and am still confused ;-} haha
Reading that makes it sound like a preamp/amp won't help my cause... but my own experimentation seems to indicate otherwise (old ant. with preamp got these stations, new ant with crappyamp sorta receives these stations)

I am, of course, worried that adding some kind of amp will hurt my existing good stations in the process.

[wackymann]

Amps are most commonly used to avoid SNR losses from long cable runs and splitters. If you have neither of those in your setup, then it will only benefit you if the S3 has a higher noise figure than your amp, AND you avoid saturating (overdriving) the S3.

[TydalForce]

So if I'm getting 70s and 80s in my signal strength meter, do you all suppose a preamp would push me to "overdriving"? Again, being about 9 miles from the transmitters, and with about 10 feet of cable between the antenna and my S3.

[wackymann]

The proof is in the pudding... buy/borrow a good LNA, try it out, and return it if it doesn't help and/or hurts. The signal strength meter on the S3 is far from the best metric. Picture quality (and the absence of dropouts) is what you really care about.

If you ever get to the point where the amp is helping the weak signals, but killing your strong ones, then you could try reducing the gain of the amp using an attenuator. e.g. if you have 20 dB headroom before saturation kicks in, but your amp has 30 dB gain, you would want to use a 10 dB attenuator in series with the amp for optimum performance (or find an amp with 20dB gain).

The bottom line is that if the front end of the S3 was properly designed, you shouldn't need an amp in your case. But if the S3 is poorly designed, then an amp may help. The easiest way to determine the answer is to simply try it.

[JamieP]

So if I'm getting 70s and 80s in my signal strength meter, do you all suppose a preamp would push me to "overdriving"? Again, being about 9 miles from the transmitters, and with about 10 feet of cable between the antenna and my S3."Signal strength" displayed on the tivo isn't truly signal strength, but more a measure of error rate (100% is no errors). A stronger signal, with more noise, probably won't register a better error rate.

If you are concerned about overdriving the preamp, the Winegard HDP-269 can take a high input signal without overload. Its gain is lower than the CM Titans, and the noise level is a bit higher, but it's a good choice when some of the input signal levels are high.

[tgibbs]

One thing you can do to get an idea if signal strength is an issue is to see if adding some attenuation makes it worse. If you have a splitter lying around, you can try putting it in the signal path and see if the signal quality goes down. If it doesn't, you are unlikely to reap a benefit from an amplifier.

[TydalForce]

OK I think I'm getting this
TiVo's Signal Strength meter isn't so much "strength" or "power" but more a measure of "usable data received" (compared to noise or nothing). Higher numbers mean that more usable data is coming through.

A pre-amp might benefit by increasing the Signal-To-Noise ratio more than anything else in this case (since there isn't 100+ feet of cable or anything). So a powerful amp isn't necessary, as long as its quality and has low noise.

If said pre-amp gets me my weaker channels, but is overpowering the stronger stations, an attenuator would help level that off. (How would I know this is the case?)

tgibbs, that's an easy enough idea to try. I have plenty of splitters laying around. So, just plug one in and ... what exactly would I be looking for? Signal strength dropping? More obvious hiccups in the video?

[tgibbs]

OK I think I'm getting this
tgibbs, that's an easy enough idea to try. I have plenty of splitters laying around. So, just plug one in and ... what exactly would I be looking for? Signal strength dropping? More obvious hiccups in the video?

Look at the signal quality indicator. Be sure to watch it for a while to get a fair index of its average value for the channels that you are concerned about. If your signal-to-noise is actually poor, then attenuating it still further with the splitter should make the signal quality even worse (and an amplifier might help). If the signal strength is fine, and problems are due to multipath, then introducing the splitter will have no effect (in which case an amplifier won't help, and you should think in terms of a more directional antenna or futzing with the antenna orientation). If the signal is overloading your tuner, then the splitter may actually make it better (in which case you can get a Radio Shack attenuator to figure out just how much attenuation gives you the best signal).

[TydalForce]

So,
- If the numbers stay about the same, Amp won't do squat
- If the numbers get worse, Amp would probably be good
- If the numbers get better, Amp would be a step in the wrong direction

I just wish my numbers across the board were consistent. I have great stations I want to keep, and I have poor stations I want to make better.

[JamieP]

Lots of good informed antenna advice over here (http://www.highdefforum.com/forumdisplay.php?f=9) if you want more opinions on what might improve your situation. As close as you are to the antenna towers, your problem may be multipath, and a more directional antenna may be what you need.

[Cormode]

You have 10 ft of cable between the tivo and the antenna? -> an amp won't do much for you.

The Signal to noise ratio will not be significantly improved because the 10ft of cable only interjects a small amount of noise and takes away a small amount of signal.

... having said that, different devices have different S/N sensitivities. The quality and design of the first transistor a signal meets as it enters the box will determine this sensitivity. The "Noise" in Signal to Noise ratio is noise generated inside the reception device.

It is entirely possible that a very high quality amp such as a CM 7775 will have a better intrinsic S/N ratio than the S3. If this happens to be the case, an amp would help.

For example I have ATI HDTV wonder with a truly awful tuner. For that device, any kind of amp will improve reception since even the $10 radio shack 10 dB amp has a better S/N sensitivity.

btwyx mis-represented the difference between a distribution amp and the amp designed to hand 3 ft or less from the antenna. The "pre-amp" as he calls it is designed to have a wonderfully acute S/N ratio while the distribution amp is less so. The output power (per channel) is the same in both cases. The pre-amp is located next to the antenna since that is where the signal is strongest.

[TydalForce]

I'm on my 3rd antenna now, lol, and don't really want to get yet another.

Directional is almost a problem for me. The best I can get doesn't exactly point to the towers. If anything, multipath is where I'm getting my signal :b~

Thanks for the link Jamie, I'm going to check that out too!

[btwyx]

btwyx, if I'm understanding your idea correctly... I start with a pre-amp and see how it does. It should get my weak stations in. But if its overloading the signal for my good stations, I add an attenuator to the mix to level things out.That's sounds good to me. The best you can do is fiddle and see what happens.

As I said before, a 7775 makes a great deal of differnence to my signal, from unusable on a lot of channels to perfectly stable. I don't have very long cable runs, maybe 30 ft at most.

If your problem is multipath an amp is not going to help, and may hurt. A directional antenna is the best thing for multipath.

[TydalForce]

Yeah I don't have a problem with multipath I don't think (except for one very windy night last week). And I realize an amp won't help with multipath issues

I'm just trying to pull in some signals that I don't otherwise get, without killing the ones I do

[TydalForce]

OK Here's my plan, somebody tell me if I'm crazy.

My current setup does a darned good job of picking up my main stations (ABC, NBC, CBS, FOX, etc), and an almost-good-enough job of picking up the rest (PBS, a couple others). I've got a DB2, and a 12 year old Radio Shack distribution amp. (Without the amp, PBS and others don't come in at all).

So I'm thinking, a Channel Master 7777. It gives me VHF capability for the future when I eventually need it, and has the lowest noise level I can find. This should help me push the weaker stations through, and lower my signal-to-noise ratio. (If my Radio Shack amp does a respectable job, this thing should do amazing things).

If it turns out the amp is too much and is overloading my good stations, I throw in an attenuator or two (or three). I figure, if I need it, pick up this: http://www.solidsignal.com/prod_display.asp?prod=CP2503-10 10-pack of 3db attenuators, and stack them until I reach perfection.

Good plan? Bad plan? Hopeless cause?

[btwyx]

Sounds like a good plan, except for the stacking attenuators. I'd try to find a variable one, Rat Shack used to sell a good one.

[TydalForce]

Interesting. I read somewhere last night (I can't remember where; will have to check browser history when I get home) the opposite; using Fixed attenuators is better than using a Variable.

Perhaps that's a good thing to add to the discussion... if anyone has any opinions on which is better, and of course any suggestions on good ones to get...

[btwyx]

using Fixed attenuators is better than using a Variable. If you know how much attenuation you need, it probably is. For experienting, its a lot easier to use a variable.

[vstone]

What channel is PBS digital broadcasting on? Our local PBS digital is on channel 3, so I don't get a thing with my antenna.

[TydalForce]

Ah, experimenting. I just saw the 10-pack and figured I could easily add/remove them in chunks.

My local PBS (WHYY 12 Philadelphia) broadcasts on UHF 50 right now, but plans to move to VHF 12 in 2009

[TydalForce]

Found this variable attenuator:

http://www.pcalchemy.com/product_info.php/products_id/554

Opinions?

[Cormode]

OK Here's my plan, somebody tell me if I'm crazy.

My current setup does a darned good job of picking up my main stations (ABC, NBC, CBS, FOX, etc), and an almost-good-enough job of picking up the rest (PBS, a couple others). I've got a DB2, and a 12 year old Radio Shack distribution amp. (Without the amp, PBS and others don't come in at all).

So I'm thinking, a Channel Master 7777. It gives me VHF capability for the future when I eventually need it, and has the lowest noise level I can find. This should help me push the weaker stations through, and lower my signal-to-noise ratio. (If my Radio Shack amp does a respectable job, this thing should do amazing things).

If it turns out the amp is too much and is overloading my good stations, I throw in an attenuator or two (or three). I figure, if I need it, pick up this: http://www.solidsignal.com/prod_display.asp?prod=CP2503-10 10-pack of 3db attenuators, and stack them until I reach perfection.

Good plan? Bad plan? Hopeless cause?

In my opinion, not such a good plan. If I understand right, you live just 9 miles from the towers you are trying to recieve. An antenna this close to a tower connected directly to an amp will simply cause the output voltage to peg and result in total signal loss for a few microseconds out of every milisecond. Putting an atenuator after the fact will not restore the lost signal. Putting an attenuator before the amp may help some, but serves to add noise, making the amp much less useful.

If you are 9 miles away from the towers and you have poor signal, I suspect multipath. You cannot tell by looking at any Tivo display to see if multipath is the problem, the symptoms are exactly the same as weak signal. You mentioned earlier that during a windy night, you saw something that made you think of multipath. I suspect that trees in the area were moving changing the diffraction pattern your antenna sees, and causes signal quality to move up and down. This is actually a strong indication that you have multipath ALL the time.

The best solution for multipath is to move the antenna around. The UHF band is about 30 - 50 cm meaning that the diffraction pattern should have optimal spots about 10 - 15ft. Move the antenna slowly around in 3 dimensions until you find the best spot, then work the amp / atennuator angle.

[TydalForce]

Cormode, that's on my mind too. I know multipath can be an issue.

Unfortunately, one of my problems is where I can actually put my antenna. Right now, its hanging in the 2nd story bedroom window which is closest to facing the antennas. But in actuality, it's not *facing* the antennas. More like, if you were standing up, and stuck your arm out halfway to your right. That's where the antennas are.

Sadly, best I can do at the moment. Right now, it's actually pretty good on the good stations, and I'm half-tempted just to leave it as-is and forget the others since I can get them on analog cable (and I don't watch them much anyway)

[JamieP]

Unfortunately, one of my problems is where I can actually put my antenna. Right now, its hanging in the 2nd story bedroom window which is closest to facing the antennas. But in actuality, it's not *facing* the antennas. More like, if you were standing up, and stuck your arm out halfway to your right. That's where the antennas are. The DB2 is somewhat directional (see this (http://www.hdtvprimer.com/ANTENNAS/DB2.html)). If you can't point it towards the broadcast antennas, of course you'll get a weak signal. It can receive signals over ~ +-30 degree range in the horizontal.

[TydalForce]

All of the stations I'm trying to receive are clustered into the same broadcast area. Quite literally, from some parts of my town you can see the towers; there's a dozen of them I guess, all blinking their glowy red "Don't hit me" lights at night....

Some antennaweb goodness:

* green - uhf KYW-DT 3.1 CBS PHILADELPHIA PA 66° 8.3 26
* red - uhf WYBE-DT 34.1 PBS PHILADELPHIA PA 68° 8.6 34
* red - uhf WPPX-DT 61.1 ION WILMINGTON DE 68° 8.6 31
* red - uhf WPSG-DT 57.1 CW PHILADELPHIA PA 68° 8.6 32
* red - uhf WPVI-DT 6.1 ABC PHILADELPHIA PA 66° 8.3 64
* red - uhf WPHL-DT 17.1 MNT PHILADELPHIA PA 68° 8.6 54
* red - uhf WGTW-DT 48.1 TBN BURLINGTON NJ 68° 8.6 27
* blue - uhf WHYY-DT 12.1 PBS WILMINGTON DE 67° 8.5 50
* blue - uhf WCAU-DT 10.1 NBC PHILADELPHIA PA 68° 8.6 67

Don't let the City Names fool you - these are all broadcasting from the same cluster of antennas.
61.1, 34.1 and 12.1 are giving me the most trouble. They come in, but are weak and prone to dropping out. 48.1 comes in awesome, but I don't watch it so I don't care.
3.1 comes in amazing. The rest come in "pretty darned good" (acceptable, but could be better). I even have a couple that don't show up on the list (WTXF 29.1 FOX, 65 Univision which I don't watch)...
The DB2 is doing pretty good; better than its predecessors, given where I have to put it. Again, not entirely facing the antennas, and to make things worse my house is downhill.

I don't know; this is confusing science. I wish I could get an antenna up on the roof. I'll have to inquire, I suppose, about getting something big and fancy in the attic.

[TydalForce]

Maybe I need to re-angle my thinking on this....

I know I get better reception across the board with the crappy radio shack distribution amp. So if I replaced that with a decent pre-amp, I'd probably be good to go. It sounds like the Channel Master 7777 is WAY overkill for me, even though it has the lowest noise rating out there.

So, a modest pre-amp with low noise would be best. Suggestions?

[TydalForce]

Under that logic....

Antennas Direct PA-16: http://www.solidsignal.com/prod_display.asp?main_cat=3&CAT=&PROD=AD-P16
Antennas Direct PA-17:
http://www.solidsignal.com/prod_display.asp?main_cat=3&CAT=&PROD=AD-PA17

I kinda like that the PA-17 will handle VHF. I don't need it today, but supposedly in 2009 a couple of my stations will switch to VHF. I'd hate to go through all this again then (though, by then, my whole antenna scenario may change). But the PA-17 connects via twin-lead cable, which kinda puts me off...

Either one, though, looks like a good match for where I'm at now. Comments?

BTW, thank you all for your opinions and insight!!

[JamieP]

... Again, not entirely facing the antennas, ...Why can't you rotate the DB2 to face the broadcast antennas?

[TydalForce]

Clearance, mostly. It's inside, in the window, covered by the blinds. (I'm partly trying to hide it too).

Plus, there's a roof from part of the house in that direction, and the hills.

A generally inconvenient location

[JamieP]

Clearance, mostly. It's inside, in the window, covered by the blinds. (I'm partly trying to hide it too).

Plus, there's a roof from part of the house in that direction, and the hills.

A generally inconvenient locationIt doesn't make much sense to me to use an amp to try to compensate for an antenna that's pointing in the wrong direction. You might be better off just bringing it inside if that allows you to point it the right way.

[Runch Machine]

It's very doubtful that an amp will give you more reliable reception. If you can see the towers the last thing you want to do is add an amp. You need an antenna that you can aim the proper direction to get reliable reception.

If you can pickup a Silver Sensor or a Terk HDTVi, go ahead and give those a try. They are both excellent at picking up the frequencies that you need and are smaller than what you have now. Don't get any other Terk antenna other than the HDTVi, as the others are poor performers.

[TydalForce]

I have a Silver Sensor. It was OK. I replaced it with a Terk HDTVlp which has a built-in preamp. It worked better. I replaced that with the DB2 which is working even better, mostly.

The Terk did better with the weaker stations - I presume due to the preamp. The DB2 does better on the good stations.

I have tried bringing the antenna in, but it doesn't do quite as well. Inside, facing the broadcast towers, has to go through brick and such.

I might try rigging something up that'll have it facing the towers through the window. Have to figure out how... but it might be worth the experiment.

[Cormode]

It doesn't make much sense to me to use an amp to try to compensate for an antenna that's pointing in the wrong direction. You might be better off just bringing it inside if that allows you to point it the right way.

Amen. I'm blown away that I've been following this thread without picking up on the fact that the antenna is not pointed at the tower.

Antenna's are VERY directional. The whole design is to make them are directional as possible so that parasitic reflections don't interfere with the picture. In the analog days we called multipath "ghosting" and good antennas were so directional that only the main beam was picked up all multipath signals were rejected.

In short ... being even 5 - 10 degrees off can cause huge headaches.

I would mount the antenna in the attic. Singles and 3/4" plywood will cause about 1/2 signal loss, but you can point the antenna directly at the tower cluster.

[Cormode]

* green - uhf KYW-DT 3.1 CBS PHILADELPHIA PA 66° 8.3 26
* red - uhf WYBE-DT 34.1 PBS PHILADELPHIA PA 68° 8.6 34
* red - uhf WPPX-DT 61.1 ION WILMINGTON DE 68° 8.6 31
* red - uhf WPSG-DT 57.1 CW PHILADELPHIA PA 68° 8.6 32
* red - uhf WPVI-DT 6.1 ABC PHILADELPHIA PA 66° 8.3 64
* red - uhf WPHL-DT 17.1 MNT PHILADELPHIA PA 68° 8.6 54
* red - uhf WGTW-DT 48.1 TBN BURLINGTON NJ 68° 8.6 27
* blue - uhf WHYY-DT 12.1 PBS WILMINGTON DE 67° 8.5 50
* blue - uhf WCAU-DT 10.1 NBC PHILADELPHIA PA 68° 8.6 67


I don't know; this is confusing science. I wish I could get an antenna up on the roof. I'll have to inquire, I suppose, about getting something big and fancy in the attic.

Using this data and google earth I put your house about 1/2 mile south of Darby Paoli Rd. If this is accurate, the hills are the problem, especially if you are in a valley. I see a cluster of apartments off of Earles lane, maybe that is you.

The difference in reception between the stations is due to the power output of the digital transmitters. WHYY only has a 89 KW ERP transmitter. They have put in an application for a 300 KW one, but who knows when that will go live.

[TydalForce]

Between the way this house is built, its location, and the direction everything is facing, this will be an interesting challenge. I think it would be easier to move... ;-}

I kinda get the feeling I'm going to find "good enough" (probably about the same as I have now) and just give up on the weaker stations.

Again, thanks to everyone for the insight!

[TydalForce]

Using this data and google earth I put your house about 1/2 mile south of Darby Paoli Rd. If this is accurate, the hills are the problem, especially if you are in a valley. I see a cluster of apartments off of Earles lane, maybe that is you.

The difference in reception between the stations is due to the power output of the digital transmitters. WHYY only has a 89 KW ERP transmitter. They have put in an application for a 300 KW one, but who knows when that will go live.

You're pretty close. My zip is 19008; I'm about a mile from where Sproul Road and Springfield Road meet. The window my ant. is currently hanging in faces North.

Absolutely hills are a problem. Not to mention trees and other houses, as always. I live about 2/3 down a decent sized hill, and have to climb out of it before I can see the towers.

I'm tempted to put the antenna in the other window, and see if the signal is bouncing off the other side of the "valley". Probably wouldn't be as good, but would be interesting to see how it works.

WHYY is the subject of much discussion over on avsforum. Apparently they have changed some aspects of their transmitter (frequency, pattern, other technostuff I don't understand) a couple times. I can get it pretty decent using the Radio Shack amp, but not at all without it.