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Discussion Starter · #1 ·
Are the 2 outputs split from the amp internally?

Or are the outputs both getting a 24db boost?


Here is a pic of one, not mine.





I recently found out why it was not working well, the coax internal connecter must have been dirty-corroded.

I sprayed some rust busting light oil into the coax connectors and it works again.


I found this for specs
Quote:
Specifications:


Bandwidth 50-900 MHz

VHF Amp. Gain - 24 dB

UHF Amp. Gain - 20 dB

VHF Gain Each Output - 20 dB

UHF Gain Each Output - 16 dB

Noise Fig. - 4 dB

Retail Price: $29.95

The uhf gain being only 20db is not so good. And it drops that to 16db.
 

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Discussion Starter · #2 ·
If I put a 24db RCA vh121 amp within 10 feet of the roof antenna, then the gemini 30 feet from that, would it improve the signal strength?

Right now the gemini is about 40 feet from the roof antenna.
 

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The chances of overload which often causes loss of some channels, increases dramatically with two amps. I have tried several amps with the form factor your Gemini and they made analog signals look worse and digital signals weaker or no longer receivable.

John
 

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Quote:
Originally Posted by sdowney717  /t/1522505/24-db-gemini-dm2000-distribution-amp-with-one-input-and-2-outputs#post_24481303


If I put a 24db RCA vh121 amp within 10 feet of the roof antenna, then the gemini 30 feet from that, would it improve the signal strength?

Right now the gemini is about 40 feet from the roof antenna.

Good, God, NO!


Excessive amplification has no benefit and usually causes new problems.


The simple rule of thumb is that amplification need not exceed the sum of downstream insertion losses plus a 5-10 dB margin. That's it, any more will be of no benefit but will usually break something else.
 

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Discussion Starter · #5 ·
yes, tried two in series and lost some channels.


the gemini by itself works better than a RCA vh121 24 db with a single output going into a 5 port coax splitter,


I am using both coax outs on the gemini.


I need at least 2 coax outs,

Would putting a 36 db amplifier going into the 5 port splitter (1 in, 4 outs) work better than the gemini amp?
 

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No No Too much gain!

Why don't you post your location, TVFool results along with a description of your antenna and its installation and we can provide better info for you.

John
 

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Discussion Starter · #7 ·
zipcode is 23608


But output through a splitter drops signal strength so the gain increase is dissipated. A 5 port 1 in 4 out is going to cut it quite a bit.


I like the idea of having more coax ports to use for the future. With the gemini. I am using up all the ports.


TV has been good with the gemini, no signal drops


When I had the RCA vh121 and the 5 port splitter, channel 3 and channel 10 were a problem, signal loss upstairs..


I never get channel 27. Channel 4 will come in with the RCA vhf121 IF I turn on FM trap.
 

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You have to do the math! Don't just guess!


In rounded-up numbers, a two-port splitter will have a 4 dB insertion loss (IL), a four port will have 8 dB IL, an eight port will have12 dB IL ,and a symmetrical three port about 7 dB IL. RG6 coax has about 6 dB IL per 100', or about 16-17'/dB at the highest UHF frequencies of interest for TV usage.


A multi-output distribution amplifier is usually a simple combination of an amplifier plus a splitter in a common package. If it's a cheap amplifier with a "variable gain" control, that control is usually a simple attenuator on the input to the amp which serves the not-very-useful purpose of reducing the signal before amplifying it.


All an amp does is increase the power level of the input signal plus noise and adds its own internal noise to the mix. It does not fix signal quality issues, in fact it degrades the quality of the signal. With digital signals, it is far more important to be concerned with the quality of the signal than it's gross power level. If the incoming signal is like a pile of junk and you amplify it, all you end up with is a bigger pile of unusable junk.
 

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His zip code has over two dozen signals that are line of sight with the major networks having a noise margin of between 55 and 60 dB. That would indicate that with a small outside hi VHF/UHF antenna, no amplifier is needed even with a splitter and 100 feet of cable.

John
 

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If an amp is indeed needed, I would suggest a better quality version with a lower noise figure. Such as Channel Master 3412 or Motorola BDA-S2. Some of the noisy cheap amps do more harm than good.
 

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Discussion Starter · #11 ·
Without an amp. some channels just do not work at all, or they go in and out.

Lots of trees in the neighborhood and the antenna is an old smaller Radio Shack model.


It works ok most of the time, but would like it to work all of the time. I have a 36db distribution amp on the boat, I can swap out.

I am looking to improve the upstairs TV tuner running on the PC, an ATI HDTV wonder card.


The coax line is only a third the length compared to the coax cable going to the VBOx 3560 usb tuner on the downstairs HTPC.

Yet, ATI Wonder tuner seems to be less discriminating. Maybe more sensitive to multipath interference.


When the trees leaf out, I wonder what will happen. Last year I pruned some branches and moved the antenna over 3 feet on the other side of the chimney.


I have a really huge Maple amd water oak pushing out big branches sideways reaching over to my house or blocking a clear line of sight.


One maple branch is like a tree all by itself.. Runs off almost horizontal about 50 feet. Like an arc from base to tip, the last third of it mostly flat.


I would trim it easily except it is hanging over the neighbors yard and shed.


Maybe tie a big rope to the end and pull it as much as I can into my yard, then cut it and it would swing into my bushes, clearing the fence and his shed.
 
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