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Splitters, Filters and Multicouplers - For discussion of all inline devices used to split, combine or amplify a receive signal. This forum is not for any bi-directional (transmit) device. Use the Amateur or Commercial Radio forums for those.

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Old 03-14-2018, 12:45 AM
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Default pre amp

any suggestions for a cheap preamp that will cover the 164.00 to 174.00 Frequency range. The forest service radio comes in really week, so I like to try to boost the range a little to see if I can pick them up better. Thanks for your help.
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Old 03-14-2018, 5:15 AM
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Don't know what antenna and coax you have now but you could always try with an amplifier but those should always be used with a variable attenuator to be able to adjust for the optimum signal. The one below can also be placed at the antenna and powered with a bias-T connection.

https://www.ebay.com/itm/Ultra-LNA-0...3/282883789248
If you only would like to receive the 160-170MHz range you could probably use this bandpass filter:
https://www.ebay.com/itm/AIS-162-MHz...z/282452182050
Or at least you would probably need a FM broadcast filter:
https://www.ebay.com/itm/FM-Notch-Fi...F/282626988667
These are top of the line devices but it is difficult to recommend any cheaper ones that will work for you without knowing what antenna, coax and scanner you have and how the RF enviroment looks like.

You will also need SMA cables and/or adapters.

/Ubbe
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Old 03-14-2018, 1:13 PM
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Preamps are the last thing you should consider to improve performance. Especially in urban areas, they can introduce noise and overloading issues. Get a better antenna, put it up nice and high (above obstacles) and get good quality coax (and be sure to waterproof the ends).

Ignore these idiotic ads that claim 'x mile range'. These statements are nothing more than Reaganomics style smoke and mirrors. It's meaningless. They're carryovers from TV antenna manufacturers that try to lure customers this way. Mike
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Old 03-14-2018, 2:47 PM
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Advanced Receiver Research would be my recommendation for a decently priced, but well designed and built pre-amp. They'll build them to order, but they also have almost every frequency range covered in a few different models. The GaAsFET P160VDG is built to cover 160-170, but it's not like the drop-off is a cliff at 174 MHz. Cost @ $139 on their website. Low noise preamplifiers and microwave Gunnplexers

As mentioned above, a pre-amp won't help you at all if you've got other system problems, and it can even make things seem worse. You should have some type of front end filtering ahead of the pre-amp so you're amplifying desired signal, not just noise.
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Old 03-14-2018, 5:07 PM
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https://www.ebay.com/itm/117-170MHz-...MAAOSw~vpaI-bO
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Old 03-14-2018, 5:52 PM
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Quote:
Originally Posted by ka3jjz View Post
Preamps are the last thing you should consider to improve performance. Especially in urban areas, they can introduce noise and overloading issues. Get a better antenna, put it up nice and high (above obstacles) and get good quality coax (and be sure to waterproof the ends).

Ignore these idiotic ads that claim 'x mile range'. These statements are nothing more than Reaganomics style smoke and mirrors. It's meaningless. They're carryovers from TV antenna manufacturers that try to lure customers this way. Mike
Best advice right here!
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Old 03-15-2018, 8:43 AM
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What people forget, usually the ones that says preamps don't work, are that you must always attenuate the signal to the optimum level the scanner requires.
It is very rare that you can use a 20dB amplification directly into a scanner without disaster happening.

I have always experienced improvement in reception with scanner at my RF hell work place with perfect 1,5/8" coax and antennas and at home with missmatch tv-antennas and coax and at friends places out in the bush with minimal signals and miles from any transmit tower.

Each place are unique with it's own configurations and you cannot expect to use another guys setup at your place and expect wonders to happen. The minimum setup are amplifier and adjustable attenuator. If you receive signals in VHF you probably also need a FM broadcast filter.

/Ubbe
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Old 03-15-2018, 9:35 AM
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Ubbe, myself and a very small number of others here know that Pre-amps can and will work.

As Ubbe mentioned, often the problem is with the set up and implementation of any amplifier.

Sure there are instances where Pre-amps may not work out so well because there are too many higher level signals, but there are just as many cases where a Pre-amp can and will work fine.

I find the majority of people that complain about Pre-amps have either never attempted to use them or have never implemented them correctly. Unfortunately you can rarely slap a Pre-amp in a system and have it work optimally or ideally without a lot of adjustments and experimentation

I have a very good LNA configuration that I have been running for a few years now and it works very well in a pretty harsh RF environment. I did have a hard time finding a decent, high rejections, FM Broadcast notch filter. I needed a lot of FM rejection because I am about 4 miles as the crow files to a number of very strong FM Broadcast transmitters. I also have a lot of OTA commercial TV broadcast towers close by as well.

I have a UHF TV transmit tower that is 650 tall with an output of 160 kW that is only about 10 miles as the crow flies to my location as well. This is not a problem with my set up.

Again, many will discount a Pre-amp/LNA. I recommend a LNA configuration at the base of the antenna if possible for best overall performance, but your local signals and coax loss between the LNA and the receiver needs to be addressed to proper performance.
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Old 03-15-2018, 9:48 AM
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Quote:
Originally Posted by JamesO View Post
Ubbe, myself and a very small number of others here know that Pre-amps can and will work.

As Ubbe mentioned, often the problem is with the set up and implementation of any amplifier.
I think many of us understand pre-amps and what they can, and can not do. You and Ubbe are not unique that regard.

The biggest problem is people thinking a pre-amp will make up for bad lossy coax, too many fittings, poor antennas and installations. Another problem is many will have the pre-amp at the radio, when it should be between the antenna and the coax. Amplify the signal, not the noise.

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Old 03-15-2018, 9:54 AM
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Default pre ampsok then i will take any suggestions

during fir season I do stream Tonto NF fire crews an towers. I can pick them up but the volume is very very low. not sure how to increase the volume so you can hear the feed during fires. Any suggestions how to solve this. I am using a pro-197 scanner. I did change the coax to a lmr 300 low lost cable.
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Old 03-15-2018, 10:04 AM
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Quote:
Originally Posted by thomasbillman1 View Post
during fir season I do stream Tonto NF fire crews an towers. I can pick them up but the volume is very very low. not sure how to increase the volume so you can hear the feed during fires. Any suggestions how to solve this. I am using a pro-197 scanner. I did change the coax to a lmr 300 low lost cable.
How does the signal level look? Is it a weak RF signal issue, and something else? Have you tried an external speaker?
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Old 03-15-2018, 10:12 AM
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Default scanner is showing good signal

scanner shows a strong signal, just low volume. I am streaming the feed so external speaker won't help
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Old 03-15-2018, 10:20 AM
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That sounds more like a low FM modulation problem and maybe the IF filter in the radio is too wide or this is some some of a bad patch that has low deviation.

If the signal is strong, you do not need an RF pre-amp, you may need an audio pre-amp but this would not be ideal if you are scanning and monitoring other high audio channels.

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Old 03-15-2018, 9:55 PM
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IF you decide to try a preamp try and find the lowest gain you can.
........
Scanners have lousy front ends and poor selectivity and preamps will only make that spec worse.
........
Find one with adjustable gain or one with as low a gain figure as possible.
........
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Old 03-16-2018, 7:21 AM
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Quote:
Originally Posted by thomasbillman1 View Post
scanner shows a strong signal, just low volume. I am streaming the feed so external speaker won't help
Then it is probably an audio issue with the stream setup. How does your setup look like? Can you increase the volume in your computers mixer settings, moving the connector from line in to mic in and adjust your mixer settings to handle that signal level?

Are you using the speaker out or headphone out jack? Is it a straight cable going from scanner to the PC?
I assume it doesn't help if you turn up the volume on the scanner? Does it sound normal when you listen on the speaker? You have the audio type set to NFM or FM and not AM or WFM?

/Ubbe
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