Pre-Amplifier

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Scotty
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Pre-Amplifier

Post by Scotty » Sun Aug 12, 2012 3:36 pm

I'm looking at getting a pre-amp to boast fringe signals around the 400MHz area, but don't know what I should be looking for or what price.

There is heaps of info available on the net, but was hoping somebody on here could give me info about what I should look for and what a reasonable price is. Am I wasting my time getting one to use it with modern Uniden scanner - some seem to think so? I don't want to go overboard on features (or price), just looking for something that will work.

Thanks,
Scott

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Bigfella237
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Re: Pre-Amplifier

Post by Bigfella237 » Sun Aug 12, 2012 4:05 pm

+1 for me too

I already have pre-amps in the multi-couplers but was thinking about adding a pre-pre-amp to try and get a better decode with Unitrunker on a few of the more distant GRN sites?

I would prefer something that can be run off mains power (through an adapter)... changing batteries sucks!

Thanks in advance,
Andrew

Mike Alpha
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Re: Pre-Amplifier

Post by Mike Alpha » Sun Aug 12, 2012 8:32 pm

I'm using the JIM M-75. Cant beat it I rekon. Variable gain, battery or 12V, filters.

Really pulls the signals out of the grass.

Good to get them from the USA now while the dollar is up http://www.scannermaster.com/Pre_Amplifiers_s/45.htm

Mike

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Bigfella237
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Re: Pre-Amplifier

Post by Bigfella237 » Sat Aug 18, 2012 10:40 am

I forgot to say thanks Mike,

Jim looks like he may be just the ticket... unless anyone else has a favorite pre-amp they'd like to put up against Jim?

The only thing I'm not that impressed about is the male/female BNC connectors, I would prefer N-type both ends but it's nothing a bit of creative cabling can't get around!

Andrew

ivahri
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Re: Pre-Amplifier

Post by ivahri » Sat Aug 18, 2012 10:46 am

Andrew, it would be better if you could mast mount the preamp... preamps don't perform miracles- they can only amplify what is there (including noise) so by mast mounting it you will get a better result. Cascading amps is very dangerous... every amp adds noise so cascading will also amplify the noise generated by the first preamp.

Cheers,

Richard

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Bigfella237
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Re: Pre-Amplifier

Post by Bigfella237 » Sat Aug 18, 2012 11:06 am

Thanks Richard, good to know!

Assuming Jim would be better (or at least more adjustable) than the pre-amps in the multi-couplers, I will have a look to see if the latter can be "bypassed" so that Jim (or whichever amp I end up buying) is the only one in-line, this may be as simple as removing the power feed to the M/Cs, I think they revert to being "passive" without DC?

Andrew

system_tech
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Re: Pre-Amplifier

Post by system_tech » Sun Aug 19, 2012 6:35 pm

Normally, an amp without DC will turn into an attenuator, that of course is passive with loss! Only if it has bypass arrangements will it revert to no loss / no gain so you you would need to test it. Be careful also of intermodulation products cuased by strong signals / tx nearby. The best use of a preamp would include a preselector filter. Not common in the scaning fraternity though.

Scotty
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Re: Pre-Amplifier

Post by Scotty » Mon Aug 20, 2012 10:01 pm

Seems like an amplifier might not be the way to go then. Thanks to all for your feedback and advice. I can probably get my antenna about 2-5 metres higher...that might just make the difference for me.

system_tech
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Re: Pre-Amplifier

Post by system_tech » Tue Aug 21, 2012 4:45 pm

Scotty wrote:Seems like an amplifier might not be the way to go then. Thanks to all for your feedback and advice. I can probably get my antenna about 2-5 metres higher...that might just make the difference for me.
Height is might ....

Mike Alpha
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Re: Pre-Amplifier

Post by Mike Alpha » Fri Aug 24, 2012 10:46 pm

Scotty wrote:Seems like an amplifier might not be the way to go then. Thanks to all for your feedback and advice. I can probably get my antenna about 2-5 metres higher...that might just make the difference for me.
For what it's worth, I haven't had an issue with the Jim M75. I'm using it at the end of a 10m run of RG213 connected to a Diamond X50 antenna. It pulls faint P25 transmissions out of the noise floor with no degradation in the decoded audio. It uses a low noise GaAs FET pre-amp and the 3 selectable band-pass filters reduce the chance of RF overload. I also like the variable gain which allows attenuation as well, handy for targeting local signals only.

Sure, a masthead amp is the best technical solution, but you just don't have the ease of control the M75 gives you in the shack.

Mike

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