Stacking Amplifiers?

[kluken]

I just got a 921 and love the OTA stations I can get. There are a few that I coudl not get until I pit a 25db (WGCL, WPBA) amp on the line and TBS (I'm in ATL) cuts out frequently. SO it appears for 3 statiosn I am just on the edge of acceptable signal with one amp. I am using an RCA cheapo amp that is rated at between 22 and 25 db gain. If I leave that on the input to the 921 and add a Channel Master 7777 in the attice on the antenna will that be a good thing or a bad thing? Can I over amplify a digital signal? I dont; care about the analog signals, only the DTA signals. Or is there a better amp that might get me 30+db gain to lock in my 3 marginal stations?

Thanks!

 

[SimpleSimon]

Remember - amplifiers amplify noise, too.

You don't mention where you are, or what your recommended antenna type is or whether you've tried aiming your antenna, or anything.

Have you been to http://www.antennaweb.org yet?

Also, I hear there's some good local OTA info over at avsforums.com

 

[kluken]

Sorry, was just looking for general info with DTA amps. I am in Atlanta I have an old Radio Shack 90 mile VHF/UHF directional antenna in my attice. I am in Marietta, GA about 20 miles from the signals, but have several hills and a lot of trees to deal with. According to antennaweb.org map all the station I want to get are pretty much in the same direction from me, which is also not far from the old analog signals, so rotating the antenna probably will not do much as it is fairly well aimed now. I get most of the other DTZ statiosn very well, almost pegging the signal meter in the 921, but it looks like anthing with a signal less than 70 will not acquire or lock. WGCL comes in at 75, WPBA at 70 and TBS fluctuates aroun 66-70. WSB and WXIA are well over 110 (meter tops out at 125). I know that amps will amplify noise, which in analog is very visible in the picture, but I was not sure how that impacts DTA signals. Even with the 25db gain the analogs still look great, no excess noise. And again I never watch analog signals, always Dish or now the DTA channels, so if boosting the signal gets me a lock on those channels and the increased noise is not a factor with DTA then I am fine. Hence my question, it seems the 25db gain got me on the edge with 3 channles so if I could gain may 10-20db more I might be fine with them so if I stack the amps I might be able to get everything I want.

 

[SimpleSimon]

Glad to see you did your homework.

I'm still leary about stacking.

Did antennaweb give you any idea about the comparative signal strengths of the various stations? As you probably already know, many stations are putting up low-power digital transmitters just to keep the FCC off their backs.

Maybe avsforums has info - I think they've got something like a separate forum per city.

 

[Larry]

kluken:

What about using a pre-amp at the antenna location in your attic? Another thing to consider is whether the amp you are using will pass the frequencies you need. Cheaper broadband amps have a tendency to lose signal strength at higher frequencies (UHF) or perhaps not pass them at all.

 

[Claude Greiner]

Im a firm believer of not using any amplifiers at all, since that I believe all the cheap amplifiers out there in the market will intoduce too much noise into the system.

However when dealing with Digital, its nice to know that eventhough you might introduce a little noise into your system, you'll still get a clear picture.

Best thing to do is get a good commercial grade amplifier, expiriment a little bit and see what works. If your using dioplexers, try to eliminate them by running seperate cables to the back of your receiver, and as far as splitters try getting 1 big splitter instead of cascading several smaller ones.

 

[boba]

You don't state what the actual channels are that you are receiving if they are all UHF try a Channel Master 4228 8 bay bowtie it is about 3ft square so it can fit in attics. Claude is pretty much right the more signal you can receive with the antenna the better off you are.

 

[kluken]

Since almost all the DTA statsion I am looking ta or want to look at are almost in a straight line from me and then are within a few miles of each other I woudl assume the various signal strentghs would be that the ones in question are using lower power, actually TBS is the closest to me and its strength is about 65 and the NBC and ABC stations are in same direction but about 304 miles further and I get a strength of 110, the CBS station is about same distance in same direction and I get 75 strength. The ABC statsion is on 10 all others are UHF frequencies. What if I pick up a UHF antenna to comine with my exisiting VHF/UHF antenna? If I have them at opposite ends of attice and combine the signals is that worth a shot? I will eventually move the preamp up to the attic, was testing it near receiver just to make sure it made a difference.

 

[SimpleSimon]

Antenna combining is an arcane art. Problems with multi-pathing and interference patterns can run rampant.

Generally, it's only useful when used with band-apss filters so that some channels come in on one antenna, and others on the other. Useful for transmitters that are NOT in a straight-line to your location.

Remember, Digital TV is a "new" thing. It sure sounds to me like you're seeing different transmitter power levels. Moving the amp up to the antenna itself may help more than anything else.

 

[kluken]

Antenna combining is an arcane art. Problems with multi-pathing and interference patterns can run rampant.

Generally, it's only useful when used with band-apss filters so that some channels come in on one antenna, and others on the other. Useful for transmitters that are NOT in a straight-line to your location.

Remember, Digital TV is a "new" thing. It sure sounds to me like you're seeing different transmitter power levels. Moving the amp up to the antenna itself may help more than anything else.

Thanks. I am pretty sure is is transmit power levels, all the locations and distances lead me to that. I lan on moving the amp to the attic this week. I will proabbly bring back the Home Depot RCA cheapo and try the RS 30db unit or the CM 7777. I need to also re think my distribution, I have a few splits in the home theater area to feed the TV directly, the 921, my HT receiver tuner and a VCR so I know those splits are hurting, if I plug the antenna directly into the 921 I pick up 2-5 in signal strength on some channels.

 

[Bradtothebone]

My advice would be to go with the CM 7777 preamp and lose the RCA distribution amp completely. Split off to the 921 with its own feed first, then split again to your other tuners. I use a similar setup (with an attic antenna) at a similar distance from the towers, and it works great!

Brad

 

[kluken]

My advice would be to go with the CM 7777 preamp and lose the RCA distribution amp completely. Split off to the 921 with its own feed first, then split again to your other tuners. I use a similar setup (with an attic antenna) at a similar distance from the towers, and it works great!

Brad

Thanks! Didn't want to wait for a 7777, so I picked up a RS 30db amplifier. I tried it at the receiver first to make sure it didn;t make things worse and it was about the same, so I said ok time to get it near the antenna. I went into the attic and getting near my antenna is a nighmare so I figured being within 20 feet of it should be good enough so I spliced it in there and what an improvement. WGLC (CBS) was about 70-75 on meter with amp near reciever, now it is solid 95. WTBS was around 90-95 with amp near receiver, now about 107-110! FOX jumped from about 100 to 112 and ABC and NBC were pegged at 125 and still pegged, no problems with them due to the boosted signal so far. I know people rave about the 7777, but the RS 30db unit seems to perform fine. The CBS was not accessible at all without some type of amp, TBS kept dropping out and PBS had occasioanl drop outs, now all rock solid. I am about 20 miles from the towers, I am using a 12 year old RS VHF/UHFantenna ( I beleive it was their then 90 mile VHF unit, it is about 6-7 feet long) in the attic with about a 60-70 foot run of cable before the splits for various devices. The big problem is I am down a hill and and I am surrounded by trees and hills between me and the towers. Thanks everyone for your help!