Signal Amplifiers (Amps, Preamps, Distro Amps) - See Chart in Post #1

[wizzinator]

OK, thanks. Which pre-amp would you recommend? CM7775 or Winegard 4700 (neither have separate VHF inputs, but is there any reason I would)?

[EdT]

Do they sell FM traps other than the one built into pre-amps ?

While we are on the subject, what is the operating life of pre-amps and drop amps ? I am trying to design my system that in the event of amp failure I don't have to go onto my roof in the dead of winter and still be able to watch OTA with simple line switching or amp replacement indoors.

[stampeder]

Yes, they are also called filters.

http://www.digitalhome.ca/forum/show...4&postcount=14

[roger1818]

Originally Posted by EdT

Do they sell FM traps other than the one built into pre-amps ?

Yes, although they can be hard to find. Radio Shack used to sell one, but it has been discontinued, but I gather you can pick them up on e-bay. Tinlee also makes one, but it is quite expensive. Another option is to use an FM splitter/combiner (such as the Winegard CA8800), but it may not be tuned very well for receiving channel 6. If channel 6 is important, you want to be able to tune the lower end of the trap to optimize reception of it with respect to the strength of the lower FM stations. Not all traps let you do this.

[roger1818]

After doing a bit more searching, I discovered that Winegard makes a nice collection of FM Traps.

[holl_ands]

Tin Lee also makes FM Trap Filters:
http://www.tinlee.com/FM_Products.php?active=2

[goforit]

It is my understanding that the purpose of a pre-amp is to make the signal that is received via the antenna stronger- increase gain.

So if we have a pre-amp of say of 28 gain, and then signal loss of 3.5 at the balun, 3.5 at the coupler, 7 from 100 feet of coax, and say 3.5 from a splitter; the signal strength will still be increased to about 8.5 db (28 -(3.5 + 3.5 + 7 + 3.5) = 8.5), correct?

Therefore, higher powered amps should be used on very long cable runs, that have splitters, couplers, etc..

Lower powered amps on short cable runs and one device of signal loss (e.g., splitter).

Using high powered amps on short runs might overload the tuner.

[goforit]

What's the difference between a drop amp and a distribution amp?

[Jase88]

A drop amp is designed for the cable industry. The term "drop" refers to the cable line running from a distribution tap to your home. Gain can vary by model (and requirements), but typically fall around 15dB.

It amplifies signal over a broader range of spectrum than a VHF/UHF amp, typically 5-42MHz (return path amplification in reverse) and 54-1000MHz forward spectrum.

Like a pre-amp for OTA, drop amps can be installed at the beginning of the line (typically at the "pedestal" [cable box]). A power inserter within your home delivers current down the cable line to power the amp.

[ota_canuck]

To simplify the purpose of a pre-amp:
Your antenna is an electro-magnetic receiver [basically it is a tuning fork in reverse] that converts the flow of ions within an electro-magnetic field into a static charge of electrons. The designed purpose of a pre-amp is to use a low electrical current ciculation within your downlead to ensure that the static charge [or signal] generated by the antenna reaches the end of the downlead by driving that signal down the center copper core of the downlead cable. It does not make or add more signal than the antenna has already received from the electro-magnetic field in the air. A pre-amp can in some cases overcome the potential of losses that may be caused by cable joiners/splitters/etc.

To further simplify what a pre-amp accomplishes. Adding a pre-amp is only as effective as if you had physically moved your TV right up the mast to the antenna.


Scenario #1:
If you are using only one antenna, no splits or joiners, and one straight 30ft downlead, then you may not see a significant gain by using any kind of pre-amp.

Scenario #2:
If you use multiple antennas,a coupling devices and a pre-amp into one downlead, then you are adding losses with each balun on each antenna, the jumpers going to the joiner, an additional loss caused by a slpitter/combiner and then a loss from the jumper from the splitter/combiner going into the pre-amp.

Truth #1:
All of these losses are theoretical losses based on the characteristics of each individual added device and it isn't as simple as mathematically adding all those numbers into one lump sum.

Truth #2:
If your your jumper cable lengths are excessive to the immediate need and your connections are sloppy, then the total losses will likely exceed the sum of those theoretical loss figures. [bad joins will allow/cause noise that a pre-amp will further amplify]

Truth #3:
On the other hand, if all your jumper cable lengths between the antenna and the pre-amp are kept to the bare minimum cut lengths, and you have secure connections throughout, then your pre-amp will likely overcome the potential development of noise and may compensate for multiple connector loss factors and you will get the full gain of the pre-amp.


Overloading:
A pre-amp will only overload your tuner due to broadcast signals that are too close and/or too strong coming into the receiving antenna [sometimes overload will even occur with or without the use of a pre-amp]. Usually it is the added amplification of induced noise or amplification of multipath echoes that really causes that overloading effect. If you use a pre-amp in close proximity to your antenna and the tuner [a very short downlead] then the feedback [noise] generated between the two devices will be re-amplified over and over again and will likely exceed the signal strength.

____________________________________________________________ __
I'm not an expert in any way shape of form,... I'm just trying to 'keep it simple'

[keef]

Yes, a pre-amp compensates for all types of signal loss - or at least all signal losses downstream of the amp. A low-noise pre-amp also overcomes the poor(er) noise figure in your TV tuner.

Your add/subtract approach is the essence of simplicity and is a fair approximation of what you can expect.

If you have no strong signal sources near you, a high power pre-amp will overcome the combined losses you list. If you do have strong signals near you, they may cause overload in the high power pre-amp itself; you may be better off with a lower gain pre-amp. I think it's more the presence of strong signals that determines if a high power pre-amp is appropriate or not. The automatic gain control in your TV tuner can easily compensate for a 12 dB signal difference (as long as nothing is overloading) so combined losses aren't that important in that regard.

If you don't have lots of combined losses, there's no need for a high power pre-amp, and you shouldn't get more than you need. I think that's why so few reputable pre-amps go above 23 dB or so - most people don't need more.

[stampeder]

Remember to check out tczernec's spreadsheet (see Post #1) which you need to download in order to use at home. Just enter in all your accumulated losses to the best of your knowledge and it gives you the calculation of combined losses. With that info you can save a lot of trouble and money on amplification and other needed OTA gear.

Also see Post #14 in the OTA FAQ about amplification & attenuation.

[roger1818]

Originally Posted by keef

The automatic gain control in your TV tuner can easily compensate for a 12 dB signal difference (as long as nothing is overloading) so combined losses aren't that important in that regard.

It is true that the AGC in the first stage amp of your TV can adjust the signal level by 10 or 12 dB, but that isn't the only consideration. The tuner itself can handle much larger range of signal strengths. It isn't uncommon for there to be a difference of 60 or 80 dB between the strongest and weakest signals.

Another use for a pre-amp that is often overlooked is to compensate for a noisy first stage amp in your TV. Back when most people used OTA, all TVs would have low noise amplifiers to help receive weak signals, but now that most people have cable or satellite, many TVs have cheaper (noisy) amplifiers. A pre-amp with enough gain will cause the AGC to "turn off" the first stage amp and if your pre-amp isn't as noisy, you will be able to receive weak stations more easily. That is why the rule of thumb is to use a pre-amp with at least 10dB more gain than your system losses, though optimally you also need to consider the strength of your strongest stations.

[Jtag]

Originally Posted by Jtag

The difference between TQ (17) and a digital station is about 50dB. Also channels 10 and 12 are strong but are in VHF. I will post also SA screen capture.

TQ (ch17) will saturate the preamp (if too sensible) AND will get confused the AGC of the TV tuner also. So 2.1 will be attenuated by TV AGC (2.1 frequency is very closed to 17).
I used a filter (Winegard UT-2700) to attenuate ch17 and my ch2.1 increased from 20% to 60% just by attenuating ch17. My 2.1 was at 20% initially because my antenna was pointing US channels also.

[goforit]

I am combining two antennas (not stacked) for different directions, and thus will need to use a coupler to join them. I would like to use a pre-amp on the one antenna. After the antennas are connected I will need to split the signal for 2 TVs. I would like to use a distribution amp to split the signal, is this OK? I'm losing signal at the coupler and splitter and thought the pre-amp and distribution amp would compensate for signal loss. I've seen this setup in the Digital Home FAQ section.