Amplifier for antenna

[ansky]

I have my Pro-163 scanner connected to a roof antenna via 100' of coax. There are a few distant frequencies that I like listening to that come in very weak. Would an amplifier help? How about something like this?:

RadioShack In-Line Signal Amplifier : TV & Video | RadioShack.com

 

[k1agh]

I think it will work, people on EHam have used it-see link. scannermaster has others listed that you may want to look into.
Pre-Amplifiers for Police Scanner Radios
Radio Shack In-Line Signal Amplifier Product Reviews

 

[ansky]

Thanks. In the link that I posted above, there are 2 pieces to this amp. I understand the part with the DC power connection would go at the end of the cable run right before I connect to the scanner. But is the other piece (the silver piece) supposed to go outside at the other end of the cable run and connect to the antenna? The online instructions are confusing (and not even in English).

 

[n5ims]

I have my Pro-163 scanner connected to a roof antenna via 100' of coax. There are a few distant frequencies that I like listening to that come in very weak. Would an amplifier help? How about something like this?:

RadioShack In-Line Signal Amplifier : TV & Video | RadioShack.com

It could help and it could hurt, depending on what other signals you have in your area. An amp like you're asking about amplifies everything in that range, stuff you want (like those weak signals) and stuff you don't want (like noise, strong broadcast, utility - think paging here not your local power company, or cell phone signals). Your scanner works by trying to pick the signals out of the noise. By increasing both the signals and the noise, you may actually get worse results. Also when you amplify those strong signals you don't want, you could over load your scanner so it can't receive much at all in certain ranges.

You say that you have 100' of coax, but there's no indication of what kind of coax that is. Often it's the coax that is eating up most of your signal. The best solution to getting stronger signals is often using a better grade of coax where you aren't also bumping up the noise level quite as much. For example, simply changing from Radio Shack RG-58 (14.414 dB loss over 100' @ 860 MHz) to LMR-400 (3.79 dB loss) or even some Andrew LDF4-50A (2.05 dB loss) can do much more good than adding the preamp will.

 

[jhutch62]

FYI, one thing that many people overlook when buying an antenna preamp, is the frequency range in which the amplifier operates. For instance, if you have an amp that operates between 5 MHz and 450 MHz, it's not going to do you much good in the 850 MHz range. So if you're connecting an amp to a multiband antenna, you may want to make sure that it's capable of operating though out those bands. Also, before you shell out big bucks on the more expensive amps, remember that even though they may have impressive dB gain and a good SNR (Signal to noise ratio), their not magic, they only work with the signal they have at the antenna and their "only" purpose is to over come the loss from long cable runs, which brings me to the cable itself. If you have a long run of very lossy, or damaged cable, your probably going to end up with the same or worse reception you had before the installation of the amp, so good cable is important. These amps are also notorious for causing overloading and cross modulation on less expensive, cheaper built radios. I know this sounds pretty basic but you'd be surprised how many people overlook this stuff.

 

[ansky]

Thanks for all the replies. My setup consists of two 50' lengths of RG-6 cable (75 Ohms) linked together by a barrel connector. Is this considered "good" cable? It's all brand new.

 

[KC8ESL]

RG-6... All in all, it's fine if it's all you have. Obviously rg8 will outperform the rg6 but realistically, its marginal for a rx only system. The preamp (if it amplifies past 900MHz) will help, and yes, to answer your question the amp is installed at the antenna. It is completely ineffective right at the reciever because it's amplifying everything including the noise floor. If you install it at the antenna, it bumps up all signals including the noise floor but by the time the coax attenuates all the signals, its as if the antenna was attached directly to the radio. Ideally you're just nullifying the cable length, it doesn't magically add gain.

I also recommend a dc blocker installed on the input of the radio anytime you use a remote preamp with dc on the coax. If the dc injector fails and allows dc to the radio, the blocker will be a secondary safety device.