Scanner Pre-Amp

[NP3Z]

I bought the moonracker scanner pre amp , connected it and everything was fine. It works perfectly in the UHF band but in VHF and 800mhz Only the meter fills with signal and I don't receive anything, I connect the antenna without the pre amp and it receives the signal (some weak) and when I turn on the pre amp only the meter fills full lengh and nothing is heard. On VHF I do receive any signal And I turn on the pre amp, the signal drops. Anything I'm doing wrong or what I should do to improve that? I have a Whistler Trx-1 and a disconne antenna. Thanks !

 

[buddrousa]

Have you ever heard the term FRONT END OVERLOAD?

 

[prcguy]

What your experiencing is quite normal for a low level wide band preamp connected to a wide band antenna. You are probably exceeding every spec the preamp has and it’s overloading and creating lots of IMD wreaking reception. Of the few ways to fix that are placing a narrow band filter in front of the preamp to only receive a narrow range, but that limits what you can receive, or upgrade the preamp to one that will survive in your environment. That can cost a lot and still might not survive.

 

[merlin]

The better alternative to a preamp is getting the antenna as high as is practical and then, with most scanners, a step attenuator will reduce strong signals impruving reception.
If you have strong local FM broadcast stations, an FM trap helps.

 

[Ubbe]

Moonraker got the M100 where you can adjust the gain from -10dB to +20dB and a less expensive M2000 with a fixed gain set to max. I assume you have the M2000 and then you in most cases need to attenuate the signal to keep a scanner from overloading. If you connect a 1-6 splitter it probably will reduce enough of the signal and you can then connect several receivers to the same antenna.

Set the scanner to only receive analog on that frequency and set squelch to 0 and without antenna connected you should hear noise. Then connect only antenna and listen to the signal when they transmit. Then connect the amplifier and compare to what you hear. To properly use an amplifier you'll need a variable attenuator you can adjust to get the best signal with the least noise and best digital reception with the lowest possible bit errors. If you can't find a variable attenuator then you can use a stepped one, where you move jumpers to change the attenuation level, I believe it is similar to what Uniden use in their SDS scanners but controlled from the CPU, or use a set of fixed attenuators, in different combinations to find a signal level where the scanner works to reveive the best noise free signal possible.

/Ubbe