PDI splitter amp

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wildbillx

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Ok, I have been reading up and tring to figure out what I can buy thats better. I have a PDI407-ar splitter/amp. It says 54-1000mhz forward gain 7dbi, it has 1 input and 4 outputs. I have been using it for about 2 years and it helped the distant signals. But now I want more... I have it installed about 1 ft. from the scanners which I know is not as good as one thats on the antenna. Thats where the questions start. I would like to spend under $60 for a new one, but want better. I have a diamond discone about 25ft up with 40 ft. of LMR400 to a 796D and a Pro-97. I live about 1 mile from the Delaware bay in south jersey. I listen to everything from local vhf to milair uhf and want to get the distant stuff. I do have a wilson yagi 800mhz about 20 ft. for trunked systems. Any help on what exact unit to buy would be great. Thanks again.
 

zz0468

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Ok, here's the thing to watch out for...

The drop amp you have has a rated noise figure of 2.4 db. That's actually pretty damned good for the type of service you're putting it to. The ONLY way you will make any improvement is to add an amplifier with a better (lower) noise figure than that.

That precludes a LOT of what's being sold out there for scanner users. You can put any old amplifier in front of your splitter and it'll make strong signals stronger, but at some point, it'll make weaker signals worse.

So, you want to actually improve things? Find a preamp with a noise figure of around 1 db or less, I'd suggest something from Advanced Receiver Research, and expect to pay around $120 or so.

If you spend less, expect a worse noise figure than what you already have, and expect it to not work very good.

Oh, and if you're going to put a low noise preamp at the antenna, be prepared for the thing to get overloaded if you don't have any filtering in front of it. What sort of filtering? You want to filter out EVERYTHING except exactly what you want to listen to. Try it without the filters, you may not have a problem.

And one more thing... If you put a preamp in front of the splitter, you'll probably have to put some attenuation between the preamp and the splitter to avoid overloading the already pretty decent amplifier in the splitter. Taking a 1 db NF preamp, and putting it in front of a 2.4 db NF amp is fraught with all sorts of potential problems, namely overloading the second amp. You'll end up wiping out the noise figure of the entire system and making it 10 or 15 db, which is horrendous. It's not unreasonable to find a 0.5 or 1 db preamp with 15 or 20 db of gain, install it right at the antenna, put 10db of attenuation after it, then your 40 feet of LMR, then the 2.4 db NF splitter. Then, you'll probably see an improvement.

Reality is, it's probably not worth the extra expense and trouble.
 
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wildbillx

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What if I did away with the splitter/amp and just went with a new preamp at the antenna? Does anyone know if they make anything wideband 150-850mhz preamp for under $60?
 

zz0468

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You're shopping preamps with the wrong criterion. I understand wanting to stick to a price range, but limiting yourself to $60 is a major barrier to finding something that will actually work better than what you have. There are plenty of wideband preamps for under $60. Many of them have a worse noise figure than what you already have, some substantially worse. A worse noise figure than what you have now will be detrimental, not helpful.

Shop for something with a NF of 1 db or less. Once you find a few, THEN start looking at the price. If the NF isn't listed in the specs, drive through, and keep looking.
 
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