Amazon RF Amplifier

Ronnierozier2

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just curious about something. I purchased a cheap powered RF amplifier off of amazon to give it a try to see if it would help a weak site that I monitor. I'm monitoring the MSWIN P25 Phase 2 700mhz system here in Mississippi. I applied a 12v wall wort to the amplifier and when I hooked it up inline with my antenna and SDS100 the signal dropped by half and the data icon was no longer displayed. Can someone give me some insight into this cheap amplifier? Also could someone recommend a rather inexpensive RF amplifier to help out a weak signal from a P25 Phase 2 site im trying to monitor.

rf amplifier amazon.jpg
 

mmckenna

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Without any filtering, it's going to amplify everything it hears (it claims 0.1-2000MHz), which is a lot of stuff, including cellular, broadcast, etc.
My guess would be that you completely overloaded the radio with all that noise.
You either need some filtering, or you want to reduce the gain to something the radio can manage. 30dB is a lot of amplification if you have strong signals nearby.
 

dave3825

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I use one very similar. Supply voltage on yours and mine is 9 to 12 volts. Read the tips on that amazon page. I have had mine run off 6 volts and it gently increased amplification. 12 volts is full amplification. I rarely even use 12 volts anymore.




Tips:
1.When working frequency is less than 500 MHZ it get well gain flatness, can make it less than 1dB after careful adjustment. The lower frequency the higher gain consistency.
2.Amplifier working frequency of the lower limit is subject to input and output capacitor, the default value is 0.1 uF, working to 0.1 MHz. Increase the input and output capacitance appropriately, can extend the cut-off frequency, such as 10uF capacitance can work to 5KHz.
3.When the power supply voltage changes in 5-8 v, it can be used as a variable gain amplifier, gain increases with the increase of the power supply voltage, which suitable for radio frequency receive front-end circuit, using DA control power supply voltage, to control the gain of the amplifier, automatic gain control
4.When the power supply voltage in the 8-10 v, the low frequency end gain up to 30 db, at this time the amplifier has a low noise coefficient and good stability.
5.When the voltage is 12 v, reach maximum gain, the low frequency end gain of 32.5 dB.
 

dlwtrunked

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In my experience, I would never attempt to use over 20 dB of gain on any scanner (including my SDS2000). And in some cases even that much gain will be too much and I do have filters that I use even then. Remember that it is signal -to-noise ratio rather than gain is what you usually want to improve and usually is no noise figure is advertised, I find the amplifier was one too large to be worth buying.
 

dave3825

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While I have used them at the lowest voltage on my scanners, I generally use them with sdr dongles.
 

west-pac

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I use one very similar. Supply voltage on yours and mine is 9 to 12 volts. Read the tips on that amazon page. I have had mine run off 6 volts and it gently increased amplification. 12 volts is full amplification. I rarely even use 12 volts anymore.

What are you using for a power supply, and how do you adjust the voltage?
 

prcguy

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That is a very bad choice to put in front of a scanner/receiver without a preselector and a good 15dB of attenuation at the output. If a signal is weak into a receiver a preamplifier will usually not fix it. If the signal to noise ratio is poor like 3 or 6dB a preamplifier cannot magically increase the signal out of the noise.

What it can do under ideal conditions is possibly have a lower noise figure than the receiver itself and if its not getting blitzed and overloaded it can provide a slightly better system noise figure which might make weak signals sound a little better. Or you can place an appropriate preamp at the antenna which will set the system noise figure at the antenna and overcome feedline loss for an even better signal into the receiver.
 
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Ubbe

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The noise figure are 4dB so not much difference from the scanners own preamplifier. Try and get a true low-noise amp that has less than 1dB noise. And use some sort of attenuation to reduce the signal to make the total gain between 3dB-6dB to the scanners antenna input.

SDS scanners start to overload when antenna signals reach up to a -60dBm level and adding extra amplifications will make it worse. You really need to be living in an area with very few interfering transmitters to be helped by an amplifier connected to a SDS scanner.

/Ubbe
 

gary123

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I will add my 6 cents. To wide of a bandwidth with no filtering. Too much gain for most applications. What you want is a preamp for the 750-780 MHZ range. My usual supplier does not make one (ARR) but a bit of R&D you should be able to find one.
 

prcguy

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I will add my 6 cents. To wide of a bandwidth with no filtering. Too much gain for most applications. What you want is a preamp for the 750-780 MHZ range. My usual supplier does not make one (ARR) but a bit of R&D you should be able to find one.
ARR preamps were sort of state of the art in the 1970s but by todays standards their IP1, IP3 and noise figure are very lacking. You can do much better with a new MiniCircuits preamp at about half the cost of an ARR.
 
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