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Signal Amplifiers (Amps, Preamps, Distro Amps)

1M views 4K replies 493 participants last post by  dsspredator 
#1 · (Edited)
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 digitalhome.ca 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: http://www.digitalhome.ca/forum/showpost.php?p=877838&postcount=604. To use it, make sure to download it rather than using it online.

Another excellent tool is majortom's Cascaded Noise Figure Spreadsheet: http://spreadsheets.google.com/ccc?...rN2poRTVIalpwT3c&hl=en&authkey=CPbi9aYO#gid=1

Cheers
 

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#127 ·
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.
 
#128 ·
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?
 
#131 ·
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?

Thanks!
 
#133 ·
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
 
#134 ·
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.
 
#135 ·
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.
 
#137 ·
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.
 
#139 ·
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.
 
#140 ·
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.
 
#141 ·
GM PART GUY,

I'm at Royal York and Bloor (roughly) - not too far from you.

I have the 4221 and I had similar results to you. The first thing I tried was raising the antenna as high as possible, which helped to lock in CBS and ABC. My NBC signal was still in consistent, and I had no luck with FOX, CITY and SUN-TV.

I installed a CM7777, which I believe has a 28bd boost. (Perhaps Stampeder or Yaamon can verify this, but I was told by a couple of knowledgeable retailers that it would be difficult to fry the tuner in the current generation of HDTVs by overloading the signal.)

Anyway, the 28db boost was too much for me - I lost nearly ALL of my reception.

So, as Stampeder suggested above, I bought a couple of 10db attenuators. When I installed both attenuators, my signal levels were almost identical to my setup prior to installing the preamp. But with ONE 10db attenuator, I got enough boost to lock in the weak stations, but not enough to overload the tuner!

Others have told me that the 4221 and 4228 will lose some of their strength over time - as the antenna succumbs to the ravages of pollution, chimney gases, etc. So I figure as the antenna ages, I might be able to remove the 10db attenuator. We'll see.
 
#142 ·
GM PARTS GUY, What do you have between your antenna and your TV (splitters, cable length, etc)? Unless you have a very short cable length without any splitters, I think a mid-range amplifier (16-20 dB) should be fine. In your case I would stay away from a high gain amplifier (above 20 dB) as you might clip strong signals and no amount of attenuation will fix that (unless you put the attenuator before the amplifier, which is not recommended).

I know I have said this before, but I think it is important enough to repeat.
dB is a logarithmic scale, such that:

3dB = 1.995 x power (approx 2 x)
10dB = 10 x power
20dB = 100 x power
30dB = 1000 x power

The exact formula is dB = 10 x log Pratio
 
#143 ·
I have 71 feet of coax, lighting arestor, ground block, nothing else. No splits.
I used google earth to verify my anteena postion and the fox tower in Buffalo,
the buildings that I thought were in the way are spaced so that the signals direct path does pass between them. I did raise the antenna 6 inchs and had a bit more stability. I watched 24 on fox last night and it dropped out only twice. I have another foot and a half I can raise it. I may try this as well.

Question, My tv came with atenuators 6db and 9db JVC says to use them for pixelation problems or ghosting. Can I use these and a indoor only amp?

Also does the aluminum cap on my chimney pipe affect the antenna at all? I heard people having problems if its over the car in the garage. Im not over the car but I am over the chiney cap buy 9 inches.
 
#144 · (Edited)
Preamp

Suggestions on preamp the two brands and models I like are the Winegard AP4700 @19db gain and the Channel master 7775 @26db.

Normally if your cable length is over 60' and you are using a 4221 and have reception problems, I would recommend the lower powered Winegard first. Still at 19db gain it has more than enough gain for you to split the signal 3 ways.

The Channel master I recommend if you have longer cable run and more splits.

If you notice any pixelating on any channels that you did not have before then that mean you have overload. You then will have to add attenuators till the picture is stable.

I use combinations of 3, 8 and 9db that can be added in series. With this you have enough combination to get the best results.

Good luck.

Ps: Gm guy at 70' with a 4221 you are losing precious signal. Any special reason why you don't like considering a preamp. :)
 
#145 ·
I have read often in this thread that a pre amp is a last resort. I also am afraid to have my tuner in the tv damaged by a preamp that has constant power. I would like to try getting as good as possable signal before needing a preamp. I posted my signal results in the ota outdoor Toronto area.

My antenna is a DB4 (similar to CM4221) I was looking at preamp'ing before stampeder redirected me to this thread and have changed my mind. I will use it as a last resort.

I still want to know if my chimey cap could cause interference like a bounce or somthing? I am baffeled by my strength and stability by ABC NBC and CBS but Fox is whacky. I used google earth and used a line of sight CLEAR to Fox. NBC looks like it is farthest with a possability of a building blocking it but is ok. Also I can go another foot and a half higher but need to lenghten the cable.
 
#146 ·
The chimey cap could cause be causing you problems, but I wouldn't bet on it. Your problem with Fox is that it is transmitting directionally to the south and only a weak signal is traveling north.

I agree that antenna gain is superior to amplifier gain, but as Yaamon said, since your cable length is over 60' and you are using a good antenna, a pre-amp should be your next step. The Winegard AP-4700 is a good choice, but I would also consider the AP-2870 as it has the same UHF characteristics but also has a separate VHF input and amplifier should you decide in the future that you also need a VHF antenna.
 
#148 ·
Preamp Input Capacity

When using an preamp in an area with strong signals, an important thing to consider is the maximum input signal it can handle. If a signal is stronger than the amplifier can handle, it will be clipped and will thus distort the signal. Typically, the higher the gain the amplifier, the lower its ability to handle strong signals.

Winegard specifically states the "Max Total Input" for all of their antennas (in uV), but Channel Master states the Output Capability (in dBmV) instead with a note that, "Maximum input is output capability minus gain." The fact that they use a different unit makes it even more difficult for the average person to do the comparison. To help DHCers with this, I will describe how to calculate the Input Capacity in uV for the CM7777's UHF amplifier.

CM7777 stats
UHF Output Capability = 51 dBmV
Gain = 26 dB​

Max Total Input = Output Capability - Gain = 51 dBmV - 26 dB = 25 dBmV

Convert to uV

uV = 1000 uV/mV x 10 ^ (dBmV / 20) = 1000 uV/mV x 10 ^ (25 dBmV / 20) = 17,800 uV

So the CM7777's UHF Max Total Input = 17,800 uV, which is much lower than any of Winegard's pre-amps.

On the positive side, the CM7777 has a VHF Max Total Input of 50,000 uV.

Input Capacity is only one thing to consider when choosing a preamp, but it is often overlooked.
 
#150 ·
I was looking at preamp'ing before stampeder redirected me to this thread and have changed my mind. I will use it as a last resort.
I'm glad to read that, and I cannot tell you the number of times people have complained to me that they were getting unsatisfactory OTA or Cable signals so they went to a big box store and bought an amplifier but now a lot more channels are fuzzy, snowy, etc. etc.

I don't ever mean to say that preamping is a last resort since good planning can sometimes include them from the beginning, but I'm glad that the message is getting out that amplifying input signals from OTA and Cable is not always the best solution. This is the ideal place to ask because we suggest other remedies too. :)
 
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