Two preamps?

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N4RMT

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Hello.

I was wondering, and believe it or not, can't find it in a search. What would happen if you daisy chained two preamps? Would the first one ruin the second? Would the two ruin the receiver? Just curious, and all I can find on Google relates to audio preamps.
 

jim202

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Hello.

I was wondering, and believe it or not, can't find it in a search. What would happen if you daisy chained two preamps? Would the first one ruin the second? Would the two ruin the receiver? Just curious, and all I can find on Google relates to audio preamps.

Most pre-amps are prone to strong signal overloads and intermod issues. Stacking 2 in series would just compound the problems. Plus you would raise the noise floor and probably not be able to squelch the receiver in some cases.

Stacking 2 of them is just asking for poor performance results.
 

rbm

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Good preamps typically include a spec for the maximum input signal level.
Some, mark that spec right on the amplifier as in this example.



I use two preamps in some of my feedlines but you must be very careful for a number of reasons.
(Jim202 gives some good examples)

Where I use them is in a case of one at the antenna, and another at the inside end of the feedline.
It takes careful testing and adjusting to do that. And it's not easy to make it work.
More often than not, it will cause problems.

I also have a few that I use in lines that feed splitters and multiple scanners.
But never connected directly together without some source of signal loss between them.

I use an ST2 antenna to feed 32 scanners. One of which is my Broadcastify feed.
But the amplifiers are separated by splitters with some significant loss.

But, if you have a way of testing your setup, it could be a good thing in some cases.

Rich

Edit: You may have some luck finding information by searching on ... "distributed amplification"
I haven't done a search on it lately but that's what I've always known it to be referred to as.
 
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zz0468

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One configuration that would make good sense would be a low noise preamp with a high IP3, and something that has only around 10-15 db of gain. Use that to drive a second stage with a higher noise figure and a bit more power gain, with some attenuation between the two stages. What you end up with is a low noise preamp with enough gain to drive a multiport splitter.

Two stages like that could drive a couple of dozen receivers. Done right, there is no degradation.
 
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rbm

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32 scanners OMG and my wife thinks I got too many.
That's only 'half' of the story. ;)
(or less)

There are 40 of them running 24 x 7 (Unidens) with another 30 (PRO-2006, PRO-2042, etc) ready to go at a moments notice.

I run 7 Private online feeds, one Broadcastify feed, and I have another 12 (or more) logging constantly.
Eleven computers and lots of sound cards run them all.
Along with many, many terabytes of hard drives.

My wife says she 'hates' my scanners!
But ....... she's always calling my attention to things that are happening. ;)
She's quite well informed. ;)

Rich

I almost forgot, I have 12 USB dongles running SDR# etc. also.
They're my quick 'Go To' receivers when I want to do a fast check of a signal or band segment and for antenna testing.

Edit: I just had another thought.
Have your wife watch this video of LOTS of Uniden scanners getting a Close Call hit at the same time.
She'll be thankful for how many scanners you DO have. ;-)

https://www.youtube.com/watch?v=PSPOaHaf-Qk
 

jackj

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My off-the-air TV setup is an 18db pre-amp at the bottom end of the lead in feeding an 8 port distribution amp with 3 db of gain. My closest TV transmitter is about 35 miles away. I have had no problems with overload and regularly receive stations 65 to 70 miles away.. I'm telling you this to show that you can use 2 pre-amps in cascade without problems but your results might be different.
 
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