Moonraker M-100 Professional Scanner Pre Amplifier

[prcguy]

I think the real secret to using an amplifier is placing it right at the antenna and choosing an amount of gain to just make up for feedline loss and maybe just a little more. Worst case if you are feeding multiple receivers just enough gain to overcome splitter losses. That way you don't have to deal with attenuators and everything just works, that is if you chose an amplifier with high enough IP1/IP3 so it never comes close to generating IMD.

The secret to using an amplifier sucessfully are to not have the scanner being feed with a too high signal level. It will first start to de-sense and if the signal are strong enough it will overload and go into intermodulation where you'll hear a lot of frequencies spread over the whole freqeuency band where they actually are not sent over the air, they are produced in the scanner.

Active multicouplers can be sensitive to overload, like Stridsberg, that doesn't like seeing stronger signals on it's input. Stridsberg even did a modification to one guys multicoupler to reduce the input signal as he had nearby transmit towers that ruined the reception in the multicoupler.

If an amplifier doesn't have a variable gain control, then you probably must use an external attenuator after the amplifier to reduce the signal to a safe level. A variable 0-20dB attenuater are perfect for this use.

An example of a good $30 low noise amplifier that can handle fairly large signal levels are this one: Ultra LNA 2GHz Gain>20dB PGA103 ESD Gain Stabilization USB cable PGA-103 NF .5dB | eBay

You have to add cables and connectors to suit your needs and add a $15 variable attenuator like this one, or use fixed attenuators if you know how much to attenuate: ATTENUATOR IEC or F type in line aerial signal reducer 3 6 9 12 15 20dB variable | eBay

A good FM trapfilter are always a good investment, something that doesn't attenuate the VHF airband if you are critical listener to that band.

/Ubbe

 

[Audiodave1]

Thank you for this discussion. I'm digging around on Ebay for some variable gain amps. I need 4-8dB on a couple of antennas. Challenge is the 50KW 99.5FM (PAR filter pre-amp should take care of that) and (2) 50w and 100w erp 800 TRS 1.5 miles away. Back side of the TX lobe helps a little. Got a favorite from Ebay etc anyone?

 

[Ubbe]

There's no good variable gain amplifiers out there. The good ones are always fixed and you have to regulate the gain by using attenuators. Either fixed ones or use splitters that attenuates a lot or a variable 0-20dB attenuator are perfect for dialing in the exact attenuation to not get into desense and overload issues, that depends of the quality of the scanners receiver. Attenuation should be done somewhere between receiver and the antenna coax.

Look for low-noise versions, lower than 2dB or good, and high signal tolerant that are shown in IP3 figures, that should be at least 30dBm and preferable 40dBm. Amplifiers that use the PGA103+ chip have those qualities

/Ubbe

 

[cpfinlay]

I had a specific need to put a scanner antenna roughly 100' from 2 scanners. Based on information on RR, I purchased a used Mini-Circuits amp and splitter from eBay. The amp would end up installed at the antenna to overcome the loss from the coax and the splitter to feed the resulting signal to the 2 scanners. Since it was a used amp, I tested it first with a truly crappy antenna in the shack (under a tech shield roof). I could barely hear the control channel over the noise floor. Turned it on and BAM! What a difference! It served me well for years.

 

[Ubbe]

I tested it first with a truly crappy antenna in the shack (under a tech shield roof). I could barely hear the control channel over the noise floor. Turned it on and BAM! What a difference! It served me well for years.

That's my experiance as well. The crappier antenna the higher the improvement when using an amplifier. For wide frequency band use with scanners where there's often antennas used that aren't perfectly matched to the frequency it will give the most improvement.

Using an amp with a tuned antenna will only improve as much as the coax attenuates and the difference between the internal noise in the amp compared to the scanners, as there's then no matching needed, as the amp automaticly will do for you when it's working as a buffer between a bad antenna with high SWR and the coax/scanner.

/Ubbe

 

[cpfinlay]

Using an amp with a tuned antenna will only improve as much as the coax attenuates and the difference between the internal noise in the amp compared to the scanners
/Ubbe

Totally agree! That was the actual intent (to overcome 100' of coax loss), but I wanted to make sure that the used amp worked at all. It was fun to turn it off/on and see how much it made a difference. I am sold on using remote pre-amps at the antenna for long coax runs when needed! Glad I read first and purchased a quality amp for my use case.

 

[Audiodave1]

The secret to using an amplifier sucessfully are to not have the scanner being feed with a too high signal level. It will first start to de-sense and if the signal are strong enough it will overload and go into intermodulation where you'll hear a lot of frequencies spread over the whole freqeuency band where they actually are not sent over the air, they are produced in the scanner.

Active multicouplers can be sensitive to overload, like Stridsberg, that doesn't like seeing stronger signals on it's input. Stridsberg even did a modification to one guys multicoupler to reduce the input signal as he had nearby transmit towers that ruined the reception in the multicoupler.

If an amplifier doesn't have a variable gain control, then you probably must use an external attenuator after the amplifier to reduce the signal to a safe level. A variable 0-20dB attenuater are perfect for this use.

An example of a good $30 low noise amplifier that can handle fairly large signal levels are this one: Ultra LNA 2GHz Gain>20dB PGA103 ESD Gain Stabilization USB cable PGA-103 NF .5dB | eBay

You have to add cables and connectors to suit your needs and add a $15 variable attenuator like this one, or use fixed attenuators if you know how much to attenuate: ATTENUATOR IEC or F type in line aerial signal reducer 3 6 9 12 15 20dB variable | eBay

A good FM trapfilter are always a good investment, something that doesn't attenuate the VHF airband if you are critical listener to that band.

/Ubbe

I purchased one of these preamps off of Ebay and attenuators, adapters etc and it performs exactly as needed in my tough RF environment. Thank you.

 

[ra7850]

Has anyone ever used or have experience with the Stridesberg PRE-20?

Pre-Amplifiers