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Signal Amplifiers (Amps, Preamps, Distro Amps)

1358782 Views 4454 Replies 493 Participants Last post by  dsspredator
This Preamplifier Comparison Chart was modified by holl_ands from an original chart at Solid Signal to show Max Input for two Strong Signals. It was reformatted into PDF form by stampeder with permission of holl_ands for the OTA Forum.

If you have any questions about the data in the chart please post in this thread.

Also see tczernec's Loss Calculator Spreadsheet in this post: To use it, make sure to download it rather than using it online.

Another excellent tool is majortom's Cascaded Noise Figure Spreadsheet:



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Thanks for the feeback stampeder. I will carefully monitor my signal strengths when I experiment with my CM7777.
Kevin what I have found is that on analog signals it hard to overload the tuner.

But with digital signals a atsc tuner can be overloaded much easier.

Normally you do not need a antenna preamp if your cable run is less than 50-60'.

If you intend to split the signal in the future a few times then a preamp will work fine.

If you find that after you connect your preamp you find that one or two channels pixelates/breakups or cannot lock in then you have overload.

You have to add attenuators till that channel is stable or if you have a variable one turn it slowly till the signal and picture improves.
Am I not correct in my assumption that a powered pre-amp actually improves the received signal from the transmitter? The SeaTac stations are >70mi away and so I would expect that the noise level would be rather high. Will the pre-amp not assist in improving the receive signal level? If my Coax run was longer it would be a distribution amp that I would be concerned with would it not?
In a nutshell, the signal from the transmitter to the receiving antenna remains essentially the same at all times (unless with Tropo or other temporary weather phenomena) so what a preamp does is boost that signal in order to compensate for any losses you might be having in your downleads due to your cable connections, length, splits, etc.

By amplifying it right up at the antenna with low noise injection circuitry, the signal is as clean as possible. If you amplify down at the bottom near the TV you are unfortunately boosting any noise that probably may have entered the signal on the way down from the antenna.

A preamp can help with lower signals, boosting them to a useable level. It has to have good source material to work with, so if the signal to the antenna is flakey then you'll just get amplified flakey signal.

In your case, if it seems like there will be a fair amount of losses in the downward cabling you should consider a preamp.
I install a pre-amp AP-8780A this was to be able to distribute the signal to 3 tv + 3VCR and have better signal for the US stations (DT and analog).

Short story the preamp overload for UHF when my antenna is directed on the US (This is also the general direction of the montreal attenna). For now I can get a very good signal (Better than with a distribution amp) by turning my attenna (So the preamp does not overload and create almost no cross modulation).

I'm thinking to get the Winegard UT-2700 variable attenuater and attenuate the 2 strong channel (35 and 17) that would give around 7 db attenuation. Do you think that chance are good that 7 Db would be enough?

Anyone experience with this device? Is it very difficult to tune?

My other option (Which cost much more) would be two Notch filter from tin lee, but they are -20 db and I guess that would kill the 2 channels.

I'm 27 km from the montreal attennas next summer the SRC will most likely be at 107kw is that enough power to overload the pre-amp?(I guess not)
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Kro if the preamp is causing overload on all the tv you can add the attenuator right after the power supply before the splitter.

If its only one or two tv then I would add the attenuators right before it enters the tv.

Its hard to say if 7db is enough, each tv tuner handles gain differently. I know with my setup using a Dish811 receiver I had to reduce the signal after the splitters -7db down(1st splitter) and another -3db(2nd splitter in basement) down add -11db of attenuators at the receiver. A total of -21db.

Example the Toshiba tv in the bedroom and the Jvc in family room gets 7db down and is fine with all channels. The LG I have in the study gets -10db because of the amount of splits and still get max signal.

You can also buy separate attenuators and add them in series. They are sold in many configurations 3db, 6db, 8db etc..

I would realign back the antenna for the stronger signal and then add attenuators to reduce any overload for that channel. If that channel comes in ok then do not add any more.

Good luck.
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Ok I was able to improve thing (FM Trap was in!:mad:, The attenna was tilt back (Just a bit) now I tilt it to look down (Just a bit) ) ...

But I still have a question. How can I distinguish between a preamp overload and a Tuner overload.

I Guess:
PreAmp Overload: the SD channel are all Unwatchable (I experience that) inserting an attenuater change nothing (I only have 1 20db attenuater)

But when there's cross modulation I cannot find a way to determine from where it's comming. If i insert an attenuater the crossmodulation disapear but that mean nothing.

If the crossmodulation is created by the pre-Amp it is attenuate so I can't see it.
If the crossmodulation is created by the Tuner (Can this happen?) I can't see it because it is attenuate.
CM7777 Question

When looking at the specifications for the CM7777, I noticed that under inputs it lists 1 VHF and 2 UHF. Since there are only 2 physical inputs (not 3), does that mean that the VHF input doesn’t filter out the UHF signals? If this is the case, and I were to connect a VHF/UHF combo antenna to the VHF input, it would combine the UHF signal from it with the signals from the UHF input (assuming the switch is set to separate). This could be useful in the case of fixed antennas pointing in different directions, but could be problematic if they are pointing in the same direction.

Does anyone have any experience with this?
I have a cm 7778 and the VHF input filter out UHF and the UHF input filter out the VHF. But if you have strong local station and you have some ghost on analog then I guess it's worth trying to add filters before the pre-amp.
I don't actually have one (yet), but was just trying to understand its behavour. Looking at the specifications again, I think I misunderstood what they are saying.
preamp question

Ok guys, just wondering about a preamp. i have a cm4228 on the roof, that i can't easily get access to. I am wondering if i put the preamp about 10ft down the line with it be just as effective as at the antenna? I have to rent a ladder to get up there and i will just put it in the attic for now..

any ideas/concerns?

10 feet.. I think you'll be okay. The question is how long is the cable run below it, and are there other signal-costing devices downstream as well (splitters, etc.)?
the total run is 75ft (RG6) nothing in the line but one tv. right now i have a simple distribution amplifier in the attic where i want to put the preamp, it does help catch some channels i want boosted but i would prefer a high quality preamp. at some point i will split the line and run a cable to my computer.. was thinking winegard ap4800
Double Amplifiers (can it work?)

I'm looking for guidance in regards to the following set up. I wired my house with coax cable to all rooms (9 in total) for distributed video. The amplifier is a DigiMax 6 watt (Model 1230) going first to a 4 way splitter then to a 8 way splitter to obtain the 9 feeds.

Can I hook up the SS - 2000 antenna with the supplied amplifier and continue using the DigiMax as well without over powering the system? What do I need to make this work properly? Look forward to your responses.
Hello, if you run an amplifier over a short length into another amplifier you'll probably have an overload. Amplification is only to be used when the signal coming out of the antenna is too weak to be usable.

I've relocated your other questions to the GTA Outdoor reception results thread.
i don't think 2 amps will help. a preamp will amplify the noise and interference just as much as signal. you could try and let us know if it works
Tonis, Although there are cases where using multiple amplifiers is possible and even necessary, but for the reasons Stampeder and Tom.F.1 said, you are better off not doing so if at all possible. Trying to split a signal 9 ways is not going to be easy, but I will give you some suggestions to try and help you out.

First of all I recommend using an antenna without built-in pre-amp. This will allow you to use a pre-amp with a much higher gain. You also might want to use an antenna with a higher antenna gain as this is noise free gain (though you have to be careful that you don't overload your pre-amp).

Secondly, you want to intelligently choose how you are going to split the signals. You say you are using both an 8-way splitter and a 4-way splitter. This should result in 11 outputs, 2 more than needed. Are these for future expansion? If so, is this something you will likely need?

Regardless, connecting the splitters this way results in an unnecessarily large signal loss. Assuming perfect splitters (which are impossible to make), the outputs of the 8-way splitter will 1/32 of the power into the 4-way splitter (a 15 dB loss). Dividing the power evenly among the all 9 feeds would result in 1/9 of the signal on each feed (or a 9.5 dB loss), once again assuming perfect splitters.

You can't buy 9-way splitters, but you could build one using 4 3-way splitters (be sure to use the type the splits evenly to all outputs). Since 3-way splitters tend to not be as efficient as 2-way splitters (or multiples there of), you might be better off connecting first to your 8-way splitter and then use a 2-way splitter on one of the outputs. The output of the 2-way splitter will be 1/16 of the original input (or a 12dB loss) and the other outputs will be 1/8 (or a 9dB loss). These losses are once again assuming perfect splitters. If you want to add another feed, just put a 2nd 2-way splitter on a different output of the 8-way splitter.

FYI, dB is a logarithmic scale such that each 3dB of loss is approximately 1/2 of the power and each 10dB of loss is exactly 1/10 of the power. You can calculate the power lost by adding up the actual losses in dB the splitters are rated for. A perfect 2-way splitter will have 3dB of loss, a perfect 3-way splitter (evenly split) will have 4.77dB of loss, a perfect 4-way splitter will have 6dB of loss and a perfect 8-way splitter will have 9dB of loss.

I hope this helps.
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DB4 Antenna preamping in Toronto?

Would using a high powered one ie 20db be bad or should I find one around 16db? I dont think I want to try and sell this antenna. I made my bed on this one. (wifes had up to her neck)
Have a look through this thread for great signal amplification info. There are 2 ways for you to go about preamping your DB4:
  1. use a lower power preamp (about 10dB boost)
  2. use a higher power preamp but with attenuators
In your case I don't think a high power preamp is necessary but if you do go that route, such as with a Channel Master 7777, drop by The Source and pick up a couple of attenuators (about $5 to $10 each) and make sure you have one or two inline when you first power up the preamp. After some testing you can try removing one or both of them to see how it goes.
Thank you stampeder. I have read through this forum and now belive I may either have to buy a better antenna, or live with it. I am nervous about ruining my ATSC tuner as it is built into my tv. JVC Iart Pallete 40" lcd. Hopefully dixing will solve the prolem in the summer time. I will revisit my antenna situation in the fall/winter. I dont feel like using a pre amp if its a last resort type of item as I have read often. Your help has made this something of a hobby for me and I do enjoy reading the many posts here. A big and heartfelt Thank you.
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