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Splitters, Filters and Multicouplers - For discussion of all inline devices used to split, combine or amplify a receive signal. This forum is not for any bi-directional (transmit) device. Use the Amateur or Commercial Radio forums for those.

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Old 04-26-2017, 7:40 AM
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Question Scanner Pre-Amp

I would like to get a final word,On a Pre-Amp that i can purchase that has a good track record, I do have a Bias-T that I can use to power it, Im looking to Install one to help me pull those weak signals in.,Looking for suggestions and reviews from those who are familiar using them.
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Old 04-26-2017, 7:46 AM
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Quote:
Originally Posted by cmed325 View Post
I would like to get a final word,On a Pre-Amp that i can purchase that has a good track record, I do have a Bias-T that I can use to power it, Im looking to Install one to help me pull those weak signals in.,Looking for suggestions and reviews from those who are familiar using them.


The most important part of the radio system besides yourself is the Antenna. Spend your money on the Antenna and the coaxial cable and you will pleasantly surprised by the performance.

If you are far from your target stations, a nice yagi or other directive array will help out immensely.

Unfortunately I live in New York City which is the most radioactive region there is. Pre-amp would only work if there is proper bandpass filters installed prior to the Input

Adam Kb2Jpd


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Old 04-26-2017, 8:48 AM
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I run LMR 400 Coax into a Diamond Discone.
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Old 04-26-2017, 10:59 AM
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I run LMR 400 Coax into a Diamond Discone.
Coax is decent, the antenna has zero gain. Discone antennas are designed to receive a very wide range of frequencies. it is a compromise.

if you only scan select bands, try and find antennas that are designed for those bands.

the problem with pre-amps, especially wideband pre-amps, is that they will amplify EVERYTHING. this includes the stuff you do not want.

modern scanners have little filtering in the front ends, and adding a pre-amp can have a detrimental effect on performance in some cases.

You will make better gains by using gain antennas for the specific frequencies you wish to listen to, with out driving up your noise floor with a pre-amp
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Old 04-26-2017, 7:55 PM
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My experiance is that the worse the antenne the more use you'll have from an amplifier.
Pick an amplifier with a low noise floor, 2dB or less is excellent. Then if you have power transmitters nearby from Broadcast FM, pager 150Mhz or whatever, choose an amplifier with hight IP3 value, +10dB or more. But always put a variable attenuater between scanner and coax to adjust for best performance. Most scanners can't cope with strong signals in other frequency bands if they are too strong and you'll need to attenuate the signal until the it performs as expected without overloading.

Pick one of these and if it doen't have bias T you just add a 10uH smd coil between the coax output to scanner and the 5v power supply connector, or search on ebay for other amplifiers. Ultra Low Noise Amplifier 10 3000 MHz Gain 20dB NF 0 65 dB with ESD Bias Tee | eBay

/Ubbe
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Old 04-26-2017, 8:35 PM
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If your going to connect a wide band preamp to a wide band antenna with no narrow band filter, then a preamp with an IP3 of only 10dBm will have lots of problems. You want a preamp with an IP3 more in the +35dBm or higher range and not too much gain, 15dB is nice and no more than 20dB.

Even my narrow band preamps like 118-174Mhz or 400-512Mhz have an IP3 close to +40dBm and some of them will put out nearly a watt of power and with a very low noise figure. And I would still recommend a band specific filter with those if you don't want any IMD problems.
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Originally Posted by Ubbe View Post
My experiance is that the worse the antenne the more use you'll have from an amplifier.
Pick an amplifier with a low noise floor, 2dB or less is excellent. Then if you have power transmitters nearby from Broadcast FM, pager 150Mhz or whatever, choose an amplifier with hight IP3 value, +10dB or more. But always put a variable attenuater between scanner and coax to adjust for best performance. Most scanners can't cope with strong signals in other frequency bands if they are too strong and you'll need to attenuate the signal until the it performs as expected without overloading.

Pick one of these and if it doen't have bias T you just add a 10uH smd coil between the coax output to scanner and the 5v power supply connector, or search on ebay for other amplifiers. Ultra Low Noise Amplifier 10 3000 MHz Gain 20dB NF 0 65 dB with ESD Bias Tee | eBay

/Ubbe
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Old 04-27-2017, 5:44 AM
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I use a Uniden BC 004 pre amp, when mobile and when at home. Show a reception gain in receive of 2-3 bars while 6 bars is full scale. When mobile, made a great difference in recewption. Never noticed over load or reception of other signals except what I was listening too. Here at home, trunking reception show 2 bar gain with a 396xt scanner. Antenna is a dual band diamond 18ft tall version. As others have commented, I am sure I would have the same results with beam and better coax maybe. Coax is belden 7713 hard line.
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Old 04-27-2017, 6:00 PM
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So with the Pre-Amp shown here,It looks really small,Where does it get mounted?,,At the radio end or antenna end?,Im not really familiar how to hook it up so be nice.
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Old 04-28-2017, 5:00 PM
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You have to get a box for it and install at the antenna. One that are used to protect a satellite-TV LNB switch are good as it protects from the weather and doesn't trap condensation. Those amplifiers on a circuit board use SMA connectors so you'll want to get proper adaptors or pig tails to adapt between antenna-amplifier-coax-power inserter-scanner.



/Ubbe
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Old 04-30-2017, 5:48 PM
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Any other Pre-Amps that anyone has used with success with a Bias T To power it?
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Old 04-30-2017, 6:39 PM
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Quote:
Originally Posted by cmed325 View Post
I would like to get a final word,On a Pre-Amp that i can purchase that has a good track record, I do have a Bias-T that I can use to power it, Im looking to Install one to help me pull those weak signals in.,Looking for suggestions and reviews from those who are familiar using them.
You didn't mention the range(s) you want to cover or the price range you have in mind.
But, this is the setup I use for six of my antennas that have a preamp mounted right at the base of them.

Also, it's a good idea to have some way to control the signal level.
A variable attenuator etc.

Here's an older photo of a few of them. You can see the housing below one of them.


The housings:



I use mostly RF Bay Inc. and Mini-Circuits preamps. You can find them on ebay and elsewhere.
RF Bay LNA-580 for everything below 600 MHz
RF Bay LNA-1000 for wider coverage.
Mini-Circuits ZQL-1900MLN for 500 MHz and up including aircraft ASD-B

I use PVC pipe and fittings to make a housing for them.

There's some additional information in this thread.
http://forums.radioreference.com/sca...tml#post860180

Rich

And a few of my 'spare' amps.


Edit:
I didn't attach this initially, but it shows a way to feed DC up the coax with a DC block BEFORE the preamp.
Depending on the Bias-Eee you use, you may not need it.
I have lots of DC Blocks and they're cheaper than my preamps, so I normally use one.




Here's a sample of SatCom signals.
Two USB dongles, on two different ST2 antennas, both with LNA-580 preamps at the base.


Last edited by rbm; 04-30-2017 at 6:55 PM..
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Old 05-01-2017, 10:34 AM
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I have used the cheapest $10 line amplifier for satellite dish to special $300 amplifiers and I cant say that one is much better than the other. They all make a hugh difference with wide band coverage scanner listening, especially outside the antennas frequency range.

And as mentioned use a variable attenuater to overcome any overload. Even if it ends up with no total gain it will at least make the antenna more broadbanded as the amplifier makes a perfect match to the coax, independent of the antennas missmatch.

I would go for an amplifier that can be easily and cheaply replaced if it gets damaged from static discharge, thunder strikes or similar. Something in the range $20-$50 are probably reasonable.

/Ubbe
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Old 05-01-2017, 11:01 AM
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Where I live nearly all wide band preamps I've tried make reception worse on many bands. Sure the S meter reads more with the preamp but the noise floor goes up more and out of proportion to the signals I want to receive. This is because most preamps I use here are being overloaded to some extent and the thousands of signals passing through it is creating thousands of IMD signals that are adding to the noise floor.

For example, if I'm receiving VHF air band on an Icom R-7100, a receiver that is not known for overloading easily, I can hear distant weak aircraft signals to a certain extent with a noise floor of about zero. Adding most preamps kills off the weak signals and they get buried in the noise, where slightly stronger signals are now fuzzy and noisy sounding and the strong signals are much stronger on the S meter but now I have an S3 to S5 noise floor where before I had zero. If I was only looking at the strong signals I would think the preamp is working great, but its really not.

I have one particular wide band 1-1000MHz preamp made by a MU-DEL who makes receive front end equipment for Govt customers, and that is one of the few that amplify ok, without raising the noise floor very much and I can actually hear weak signals a little better.

I have a bunch of Angle Linear preamps but they range from maybe 10MHz wide to 100MHz wide and are band specific. Most of those work fantastic bringing weak signals out of the noise but most of these were designed to have narrow band pass filters in front of them to only allow a tiny slice of the band to pass through feeding repeater receivers.

Otherwise if I use most models of Mini-Circuits, cable TV amps, etc, my reception gets worse due to the general high levels of RF in the area I live. You can get away with some wide band preamps if your out in the sticks but you won't know if it will work until you try it.
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Old 05-04-2017, 3:18 PM
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Just need a name of a tried and true wide band unit that works with a Bias T
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Old 05-04-2017, 6:58 PM
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It's no guarantee that a working solution at one guys place will work at yours. That goes for scanners, antennas and amplifiers. Look for a PGA-103 amplifier, those are low noise and handle big signals really well. If they don't have bias-t functionallity you just add a coil 10uH or more.

/Ubbe
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Old 05-04-2017, 7:38 PM
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Quote:
Originally Posted by cmed325 View Post
I would like to get a final word,On a Pre-Amp that i can purchase that has a good track record, I do have a Bias-T that I can use to power it, Im looking to Install one to help me pull those weak signals in.,Looking for suggestions and reviews from those who are familiar using them.
I use various good ($$$) preamps and have always find it absolutely necessary to add filters in front of them to notch strong nearby signals. As a minimum, a block for the FM broadcast band. Cheap ones may be enough, I like Mini-circuits. A lot of people who do not think they have that as a problem do (it de-sense their receiver but does not give you audio to identify that is a problem). Then often one needs filters for nearby pagers on 152 MHz (see parelectronics.com). After that, things are more locations specific. Trying pre-map without bringing into account needed filters in most cases is inviting poorer than expected performance.
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Old 05-15-2017, 7:52 AM
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Anyone better than the other?
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Old 05-15-2017, 3:26 PM
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When dealing with amplifiers I would suggest to first try them out at the scanner, with the variable attenuater in between. You can always get a FM trap filter. They are cheap and effective and first trying them between scanner and amplifier will make their pass thru attenuation negligibel.

If there is a noticable differense towards a better reception when the fm filter are put between amp and antenna then the amplifier is suffering from desencing and the fm filter needs to be remained between antenna and amplifier, or go for a better amplifier.

If the end result isn't much better than without an amplifier then there is probably a frequency that needs a special filter.

One thing that everyone should have are a cheap tv usb dongle for $10. It's easy to set up to be able to look at the frequency spectrum and see where any offending strong transmitters are. You the very easy see if the filter is effective or you can tune any filter to the exact frequency. A simple filter that also will attenuate some on other frequencies are a stub filter and are easy to cut

To evaluate all this you'll need a steady signal, preferable a weak one with lots of noise. A weak wheather channel are good for VHF and on UHF you could use a constant transmitting control channel.

/Ubbe
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Old 06-05-2017, 7:43 PM
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the better approach is to use a better antenna and lower loss coax

Preamps amplify interference and noise which will overload and desense scanners
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Old 06-06-2017, 6:09 AM
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At my work we had a VHF and a UHF 4-stacked dipole antennas with 7/8 coaxes and reception still improved with an amplifier at the scanner end, and that was 200 meters from a big transmitter site with at least 10 channels and several constant transmitting control channels.

/Ubbe
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