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Signal Amplifiers (Amps, Preamps, Distro Amps)

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#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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#152 ·
ASA said:
I noticed that they had a variable pre amp.
A variable preamp? I have only seen variable distribution amps. Would I be correct in assuming the adjustment is done on the amplifier and not the power injector? Did you notice if they specified how much noise it generates?
 
#153 ·
I was at Home Depot (or was it Rona?) the other day, and I noticed that they had a variable pre amp. Up to that point I had only seen "set" values for pre amps. Yaamon have you seen this?
Those at Rona are not pre-amp they are amp. 5 to 25 DB.

On another notes: I tried to attenuate one channel to reduce cross modulation using a Quarter-wave tuned stub and it's working. To build the stub I use 300 ohm twin lead wire has describe here. http://spectrum.ic.gc.ca/~emi/htmlen/solutions/annexe/annexe4.html I was not successfull using rg-59 but using 300 ohm twin lead gave good result.
 
#154 ·
The Home Depot item is a Leviton variable output distribution amp with a maximum boost of 25dB.

It is not an antenna preamp. It is suitable for situations in which one un-preamped antenna is expected to drive a whole-home multi-tuner environment from where the antenna downlead enters the building.

The best strategy is to split the amp's output into individual RG6 strands for each tuner in the house, then go to the farthest tuner from the amp and check its signal strength. Turn up the amp to get the ideal levels, then go to each of the closer tuners and attenuate them as needed.
 
#155 ·
??? I would like to know if i"m wrong here. A distribution amp, variable or not only sends the signal, good or bad that the anttena is getting. A Makes the signal stronger first. If you needed to go longer then a distrubtion amp is requiered after. Distrubution amp Cant make up for weak/multipath/blocked signal, pre amp can?
 
#156 ·
Theoretically the only real difference between a distribution amp and a preamp is that a preamp has 2 pieces (power injector and amplifier) so that the amplifier can be as close as possible to the antenna while allowing you to keep the power injector inside where it is safe from the elements.

In reality, preamps tend to have a higher gain and lower noise, but this is more of a marketing issue than a technical issue and there are exceptions to this rule (Channel Master and Winegard make good quality distribution amps and Radio Shack makes poor quality preamps).

Assuming equal quality amplifiers, a preamp should be used when the original signals are weak since the closer you can get the amplifier to the antenna, the better the signal to noise ratio will be. A distribution amplifier can be used when the original signals are strong, but you are wanting to split them to multiple sets, and thus weaken the signal to each set.
 
#158 ·
Some other points of comparison: antenna preamps are built specifically for outdoor punishment right up there with the antenna, while distribution amps usually forbid outdoor mounting without some sort of watertight casing.
roger1818 said:
a preamp has 2 pieces (power injector and amplifier) so that the amplifier can be as close as possible to the antenna while allowing you to keep the power injector inside where it is safe from the elements.
That's an important point. A preamp uses the coax downlead going into the house both for conducting the antenna signal and also for carrying the power that the preamp circuitry requires (which is usually between 12-18VDC at low current). On the other hand, a distribution amplifier doesn't inject any power because it runs on 120VAC from a wall plug, but that means you'd need a receptacle somewhere up there and/or a long extension cord. That's a lot of power up there for just one small electrical job! :eek:

Antennas need to be free of local electrical fields for best performance. The low power signature of a preamp does not interfere with the antenna's operations, while a distribution amp mounted right up there with the antenna might.
 
#159 ·
Antennas need to be free of local electrical fields for best performance. The low power signature of a preamp does not interfere with the antenna's operations, while a distribution amp mounted right up there with the antenna might.

In that case, wouldn't a variable amp (if it was an amp that I saw and not a pre amp) work just as well as a pre amp if it wasn't placed close to the antenna but still close enough (as in under 10 feet from the antenna)?

Example. When I was up in my friend's attic last year helping him insulate it better, I saw that the home builder had left a blocked off wall plate on one of the joists. When I unscrewed the box cover I noticed that it had a 14/3 (I think that's what was in there) electrical cable caped off. This was not for the room below the attic. There was a dedicated line going up to that box with nothing else conected to it. My friend assumed that they left it there so he could add in attic light later on. Now if a pre amp and amp are simular (except for the weather proof thing and some other little things inside like roger1818 mentions in his post), and there is a power plug available, would the amp do the same job as a pre amp? Considering the Pre amp should be placed as close as possible to the antenna for the best results, I would assume that an amp placed as close as possible to the antenna (but instead placed just inside the roof.... under 10 feet from the antenna) would work too. No? :confused:
 
#160 ·
For weak signals, the closer the amp is to the antenna, the better, but 10' should be OK. Just make sure that the amp isn't to noisy. If a noise rating isn't given, that is probably because it is too high for them to want to advertise.

One reason distribution amps often generate more noise is because if you have a strong signal, noise isn't a major concern and it will be attenuated along with the signal in the splitter or long cable run.

If you want an ultra low noise preamp and cost is not a factor, check out Research Communications' Type 9254 (the Type 9260 is a UHF only amp that filters out VHF). When you include the power injector, weather proof case and shipping it comes to about $600, but you can't beat its 0.4dB noise figure.
 
#161 ·
For weak signals, the closer the amp is to the antenna, the better, but 10' should be OK.
That's what I was thinking too, but I wasn't sure if it would work the same way as a preamp.

I know that alot of people here are worried about "how much is too much" when it comes to picking a preamp, and when I saw that variable one at the store it perked my curiosity. (hmm, a variable one that would allow me to start off at the lowest setting, and then give me the ability to slowly turn it up if needed)

If I used a preset preamp/amp, I would have to try several different ones until I found the perfect ballance. What do you guys think? (you guys have way more experience at this than I do) :confused:

I believe that where I will eventually mount the atennna, it should be pretty close to a roof vent (there are quite a few of them up there). That means I'll probbaly be able to have an amp within 10 feet of the antenna. I know the amp would be protected from the weather.... and since both a preamp and amp need a power sources to work, I don't see a problem with running a power cable/outlet to either of them. The only difference I do see, is with an indoor amp, all electrical current would stay inside the roof instead of being outside right next to the antenna (as with the low voltage preamp).

Anyway, I'll see if I can get more info on the one I saw. (can I post a price when I do?) I vaugly recall the price I saw it for, but I'm afriad to post it. lol

If you want an ultra low noise preamp and cost is not a factor
And if price is a factor what would you suggest? (under $50 or cheaper) lol

Just make sure that the amp isn't to noisy. If a noise rating isn't given, that is probably because it is too high for them to want to advertise.
I'll let you know that info when I find out.
 
#162 ·
There is another variable-output option: if you're driving just one TV or maybe two off a splitter you could go with a high power preamp and down at the bottom below the power injector put in a variable attenuator, as sold by Tin Lee.

With a bit of electronics calculation to get the proper rating a person could go to a parts shop and buy an L-Pad Attenuator to do the same job.
 
#164 ·
The CM3039 is from their old "Spartan" line that came out before the current "Titan" series.

The 3039 takes 300ohm twinlead from the antenna and delivers via 75ohm coax. This means not having to buy a balun if you don't have one already.

If the price is right it will be a good preamp for your VHF/FM/UHF needs.
 
#165 ·
Differences between certain CM and Winegard preamps

Whats the diff between the CM7777 and 7778? And between the winegard and the CM you suggest the AP-2870?
CM7777 has more gain (26dB UHF, 23dB VHF)
CM7778 has less (Gain 23dB UHF, 16dB VHF) (This is the one I have and it has a bit to much gain on UHF)
The AP-2870 has (UHF 19 dB, VHF 17 dB)
Has you can see the AP-2870 has the lowess gain on UHF and 17 db for VHF is very good (More than that you could also have problem cause by montreal station)

To buy try MontCalm and raybel then the Web.
 
#166 ·
digitalnewb said:
Okay got around 70' I think. Splitting it for same TV (1 digital (Samsung h260f) 1 analog (integrated NTSC tuner in TV)).
The rule of thumb is if you have more than 60' of cable or are using a splitter, you are a good candidate for a pre-amp.

Was thinking about spliting it once more for the amp (FM radio). But won't if picture qual will suffer. Does it make a diff if I split but don't use the other "comp" at same time? I split just before the components so added like 2 feet of cable total with splitter.
If you use a TV/FM band separator it won't significantly degrade your signal as it will send all the FM signals to the radio and all the TV signals to the TV. There will be a bit of connector loss, but not too much. A conventional 2-way splitter will send half the power to one output and half the power to the other and thus cause a 3dB loss in power (plus a bit more for connector loss).
 
#167 ·
CM 7777 pre-amp

Hello,

FYI: Using CM4228 with around 85' of RG6 and 1 splitter.

I just purchased a CM 7777 (its about the only model I could find in stock in the Montreal area (I think its going to be overkill)).

I'm planning on installing it tomorow or the day after: 3 questions.

1- They say to mount closest to TV (really)? I was thinking on mounting it where the RG6 enters the house (8 feet from ant (In attic)). Getting the power there is very easy for me... So up in attic or near tv?

2- In the image they have a standout on the downlead. The RG6 cable is like 3'' from ant. mast. I was planning on just taping the cable to the mast. Is the standout really important?

3- How close to the balun does the pre amp go (I know they say closest). But is that like 2'' from the balun (middle of ant (Using 4228)). Or like 2-3 inches below "back mesh" of the ant. (so like 2-3 feet from balun). Cause I think if I put it in the middle it might create interference.

Lastly, I'm around 9 miles from Montreal stations (on the south shore). Going to try and get Mt. Mansfield as well. I purchases 10,6,3 db attenuators... Any things else that would be good to know (apart from putting the 10DB on and checking strongest stations then moving up...)?

Thanks again,

Cheers,

Newb
 
#168 ·
They say to mount closest to TV (really)? I was thinking on mounting it where the RG6 enters the house (8 feet from ant (In attic)). Getting the power there is very easy for me... So up in attic or near tv?
I always put the power injector box near the TV. You are free to try your solution and see how it goes, but I would stick with the original suggestion based on experience.
In the image they have a standout on the downlead. The RG6 cable is like 3'' from ant. mast. I was planning on just taping the cable to the mast. Is the standout really important?
I've never had a problem with just taping the coax to the pipe. I always use standoff insulators with unshielded 300 ohm twinlead, but with coax I've never had a problem with direct contact.
How close to the balun does the pre amp go
I mount the preamp about 5 or 6 inches below the reflector of the CM4228 and make sure that the coax has a nice, round drip loop as it goes from the balun to the preamp. A drip loop on the preamp output is important too before it heads downward.

Good luck with your testing! :)
 
#169 ·
digitalnewb if you find that with all the attenuators that you are still getting over load I would use a indoor booster 10db or a two way indoor distribution amp mounted inside your attic instead of the preamp.

I did a install once 4221 and a cm7775 and even after I added 25db of attenuation the samsung plasma tv would not get any stations other than cbc. Remove it and all station came in.

I did a install last year where the cable from the antenna to a customer fuse box was only 40' and from there another 75' across his basement up to his familyroom.

I used a cheap indoor 2 way distribution 3.5db per port amp and it worked well in his setup.

So if you find the channel master is too strong try and low power indoor booster amp.

Good luck.
 
#170 ·
CM 7777 (its about the only model I could find in stock in the Montreal area (I think its going to be overkill)).
It will most likely create a lot of cross modulation and this will impact your reception. To check for crossmodulation simply iterate true all channel using the analog tuner.
You should see snow and ear a nice pshhh.
For Low Power channel such has 27, 44 and 52 you should have a nice image or a snowy one but no other artifact.

If you see Tele Quebec on other channel than 17 and 24, tele quebec is causing you problem, try to identify all those that create problem. Most likely you will find that Tele Quebec and maybe TQS are causing problem. Check also if you see CFCF 12 and or other VHF channel where you should not.

If you only have problem with tqs and tele quebec buy a 75 ohm UFH/VHF diplexer (RONA has some) connect it to your CM-4248 put a 6 db attenuater on the UHF output
then to the CM-7777 UHF and the VHF output from the diplexer to the CM-7777 VHF. This way you may have a chance to pick up ABC. (Don't forget to double check the FM trap)

Personnaly I use a UT-2700 which I tune to attenuate 35 (TQS) and 17 (Tele quebec) and it's working perfectly.
 
#175 ·
Question about FM trap

I'm located 40 miles south of Quebec city and I have trouble since a few years with my OTA installation and a FM radio station located 3 miles from home.

One FM station uses frequency 100.50 and scrap reception of most of my VHF channels specially 11.

I have a FM trap on my Radio Shack amplifier 15-1109 amplifier but it's not enough. I've added a Tru-Spec FM trap inside home between the amplifier and its power supply. I've fixed most of the problem but i'm still have some FM interferences.

Do I have positioned my FM trap at the most effective location?

Should I get better results if I position the trap outside home between the 75/300 Ohm Balun and the outside amplifier?

My current setup is:
4242 channel master antenna
75/300 Ohm Balun
6 ft of RG6 cable
Outside Radio Shack 15-1109 amplifier ( I should get a CM 7777 next week)
125 ft of RG6 cable
Ground installation
3 ft of RG6 cable
True-Spec FM trap
3 ft of cable
Radio Shack power supply for amplifier 15-1109
3 ft of cable
Distribution on 4 different TV's

Thank you

Stan
 
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