Tell me about TV antenna amplifiers

OK, we live in a small town in a rural area. I’d like to see what I can bring Over The Air, or broadcast TV. We have a fairly large antenna in the attic of the house (about 15-20 feet above ground level), and it will bring in 8 of the 12 channels the map at http://www.antennaweb.org says I should be able to receive. Funny thing, the 4 I can’t get are from a tower 26 miles away, while I can bring in 5 channels from a tower that is 32 miles away (I can bring those in with a table top antenna).

Anyway, I am guessing I need an amplifier. But, when I look, I find antenna pre-amplifiers as well as amplifiers. They boast between 10 and 20 dB boost, and various bypass numbers. How can I tell what to get?

Amazon reviews are not helpful, since (like nearly everything else) about 80% of the say a particular model is the best thing ever and 20% say they are the biggest load of crap ever sold.

What do I need to bring in the other channels? (FYI, it is the CBS affiliate, which is the network my wife likes best)

thanks,

Antennas are somewhat directional. Are you sure that you have the antenna pointed correctly? I have one station that I can reach if I rotate the antenna about 90 degrees. However my antenna is in the attic like yours and too much trouble to move for just one station.

Another option is to move your antenna outside and higher up.

I haven’t had much luck with antenna boosters. They just seem to make the static worse.

You need an active (powered) RF signal amp for the TV/FM frequency range. I haven’t bought one recently, so I couldn’t recommend a model, but I have a 40 year old one attached to my TV antenna line. The amp is in the basement where the line enters the house, then the cable goes to the TVs in various rooms.

I live in a fringe area. All of the TV stations are in the general south direction, so my antenna in a tall tree points that direction and doesn’t need a rotator. The stations in the 50 mile area come in quite well this way.

In the days before digital TV, I was able to get analog stations in the 120 mile range when the weather was just right, or the 90 mile range off to the side of the directional antenna.

How do you get static with digital signals?

antenna amplifiers won’t help you; they’re intended to be used when you have a long cable run from the antenna to the receiver, or intend to split the antenna’s signal to multiple receivers (or both.) it can only boost what the antenna gets; if the antenna is picking up a weak signal and a lot of noise, the amp will boost both the signal and the noise.

a different antenna design might help you here.

I beg to differ. Without an amp, my fringe area TV had (in analog days) only snowy images. With it, most stations were snow-free.

Digital, although I haven’t tested the system without the amp, I would expect the weaker stations would not have enough signal to be seen at all, as digital is all-or-nothing.

An amp amplifies the signal; it doesn’t know or care if it’s weak due to a long cable run or a fringe area, or both.

at 32 miles that is not far. a correctly sized, correctly sited, correctly aimed unamplified antenna should work fine.

also with amplifiers there are signal amplifiers (preamplifier) which goes at the antenna to amplify a weak signal, i don’t think you need this with the right antenna situation. there are also distribution amplifiers which split the signal to more than one set, you might need this if splitting the signal results in it not being strong enough.

when you go to antennaweb or to

www.tvfool.com

they report for outside antennas. if the antenna is inside then it acts like you are about 20 miles further away. for an inside the attic antenna what house structure the signal goes through will have an effect; are there metals or dense materials in the signal path. the antenna aiming has to be very exact you have just a few degrees of angle that you have to be in. you also need good connections and low loss in the coax cable, you would want to use RG-6 coax (not RG-59) with the ends in good condition.

i have a large honking outdoor antenna in the attic and i get signals at 70 miles. i have another medium sized antenna and get signals at 40 miles.

I agree, and the situation in my house is a good example. I have a huge deciduous tree in my back yard. During winter I get a clear TV signal, but in summer I need to use an antenna amplifier. Obviously the cable length isn’t changing - the signal between the broadcasting tower and the antenna is being partially blocked by the tree’s thick foliage. (The tree really is massive.)

I’d never even considered that such a thing was possible. It took me two full seasonal cycles (or as I call them, “years”) to make the correlation.

Hi, I’m Tripler, and I’m a cheap bastard. One of my favorite words in the English language is “free,” as in. . . “I don’t need a $90 Internet and Cable TV bill for 57 channels I’ll never watch.” I’m also an engineer. But one fact escapes me right now: what’s the commonly accepted threshold for analog/digital TV signals at the input of the TV?

Is it -30 dBm? -80 dBm? Something else?

Reason I ask, is that I just moved to a new town. The last place was great–had LOS ot the broadcast antennas, and was getting -20s and -30s. I’m currently using a site to figure out azimuths and strength of over-the-air broadcasts (US), and the site’s coming up with a starting strength of -52.3 dBm. It goes downhill from there. I’m good enough to build a preamplifier, with schematics I found online. The big question is would that just be a waste of my time if I can’t kick up the signal to something decent? Hell, should I build that and another antenna?

Tripler
I just gotta remember where I packed my soldering iron. :confused:

Dammit. . . I apologize. This was meant to be an original OP, but I guess it’s better in a fairly-recent zombie thread. I got my tabs mixed up when I was composing it.

Tripler
Whoops!

Tripler, unless you are doing this just as a hobby, why not just buy an antenna amp instead of building one? If you Froogle (yes, Froogle.com) for one, they are readily available for $16 to $150. And whether you build or buy, a good antenna with rotator is always a big help for DX.

Well, you should care (with respect to the last sentence) because if the signal is weak due to losses from a long cable run, an amp located at or near the antenna, before the cable run, will fix the problem. If the signal is weak at the antenna, then it’s because the antenna gain is too low for the conditions – which typically means that the signal to noise ratio (SNR) will be too poor to reliably decipher the signal. In that situation you can amplify the signal till the cows come home and it still won’t help.

I don’t doubt that it worked for you in the situation you describe but it sounds like either an oddball case of a low-sensitivity TV tuner or the amp was overcoming losses somewhere in the cable run. It doesn’t usually work that way. In fact, if you have a sensitive TV tuner a poor preamp can actually make things worse than they were without the amp, by introducing spurious noise, or even overloading the tuner so you get nothing at all.

A typical valid use of a preamp would be a low-noise mast-mounted unit like a Channel Master CM-7777 used to overcome cable resistance in the long run from the top of the mast and down and around the house to wherever the TV is. Such amps live right up on the mast below the antenna and are powered through the same cable that brings the signal down into the house, through a kind of splitter called a power inserter that sends power up one side and isolates the TV signal on the other side, similar to how satellite receivers work.

In general, that kind of arrangement will give you a stronger signal without degrading the SNR, but in most cases it will do absolutely nothing to help receive stations if you have a short to moderate low-loss cable run and where the problem is that the antenna is inadequate to begin with and the SNR too poor. IOW, it will typically not give you better results than if the TV was on the roof right beside the antenna with no preamp at all.

That is the theory, that is the typical informed advice from antenna experts, and that has been my experience. YMMV, and it depends somewhat on the characteristics of the TV tuner and the cabling setup. Reviews of the benefits of antenna preamps are unsurprisingly all over the map for these reasons, and in many cases because of people not understanding what preamps are really for and having the wrong expectations.

wolfpup, my antenna and amp was installed by an experienced TV repairman and installer who lived just down the street. This is a fringe area, about 60 miles as the seagull flies from the nearest TV transmitter in Green Bay, and 120 miles or so from Milwaukee. He installed many installations like mine, and didn’t usually use a rotator, since all stations are in the southern quadrant of the compass from here. Nevertheless, I used to get (weakly, intermittently) stations across Lake Michigan from 100-150 miles away, off the side of the antenna, on good nights. RF travels pretty well over open water, but the antenna wasn’t pointed well for those.

My amp is near the end of the coax (not twin-lead) run, in the basement, just before distribution to the rooms in the house. If he had used a powered amp at the antenna, or had to power a rotator, that would complicate the wiring. But the 75-100 ft of coax from antenna (in a tall pine tree) to amp doesn’t seem to be a problem. In my neighborhood, this is not an oddball configuration, although most people use towers instead of pine trees.

That sounds to me like a distribution amp and not a preamp at all. Preamps are always located as close to the antenna as possible, whereas distribution amps are located prior to distribution splitters just as you describe. Since you describe “distribution to the rooms” (plural) this would seem to be the case. Splitters always introduce losses and some kind of amp in front of them – either a preamp at the mast and/or a distribution amp – is likely to be helpful.

No, it would not complicate the wiring to have a preamp at the mast. Note what I said in the previous post about how they’re powered – the power gets up to them through the same cable that brings the signal down. But I agree with you that for a 75-100 ft coax run from the antenna you probably don’t need a preamp. I don’t think your reception would be any better if you had one – this is exactly the point I’ve been trying to make!

Here are some example preamps and distribution amps:
http://www.channelmaster.com/Amplifiers_s/23.htm

I’m in an area with lots of over the air HD but some of the channels are fringe because of distance and/or low power. I played around with a 4-bay CM-4221 (the original one, not the new Chinese-made ones which are apparently inferior) with and without a high-gain CM-7777 preamp. The preamp boosts the signal levels reported by the TV on all received channels quite a lot and even maxes out one or two of them at 100% but here’s the point: in my environment, at least, it does basically nothing to help a marginal fringe channel come in more reliably, or help a channel that isn’t coming in at all because of weather.

I think there may have been one test I did once where a very marginal channel on one occasion came in with the preamp and did not come in without it – but OTOH I think I also saw the reverse, where another marginal channel with a poor S/N came in better without the preamp than with – though that may have been with a different TV. In the end, my conclusion was that the preamp didn’t help but it didn’t hurt, and since I already had it I decided to wire it in and leave it in as a contingency against future cable issues, but I doubt that it’s doing much good.

This is pretty much the behavior one would expect from a preamp if the cable run isn’t a problem. But as always, YMMV – antennas are a bit of a black art in terms of design and the fine points of location and the business of amplification. The basic principles I described should be the starting point, but beyond that, the most important principle is TIAS – “Try It And See”. :wink: Sometimes the tiniest changes in height and location can make huge differences. Don’t ask me to explain it! What I was trying to counter here was the common misconception that a preamp is always going to improve reception. It may, but it usually won’t if cable loss or poor tuner sensitivity isn’t the problem. If amplifiers could work that sort of magic, then you would never need a properly mounted high-gain antenna – just stick a coat hanger out the window and connect it to a miraculous preamp!

The system is a 2-box arrangement, a Winegard PS9000, labeled “power supply” and a dist amp DA405. The incoming cable goes thru the PS9000, then the DA405, then to a splitter, and the rest of the house.

I have tried bypassing both boxes and splitter, going directly from the incoming coax to a TV, and the signal was poor. How poor, I don’t remember – it was long ago when I fiddled with it.

So even if the amp in question is a distribution amp, it is amplifying the RF and is necessary here due to the fringe area. It proved to be quite adequate until cable was brought in ca. 1994.

I tried the system some time ago with an all-digital TV, and it seemed to work well, receiving (I think) about the same stations as it used to in analog. Since I don’t watch TV of any kind anymore, it probably doesn’t matter.