Low noise amp for scanner

IdleMonitor

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The Ottawa Valley - Eastern Ontario
First let me start off by saying. Please don't tell me about overloading the signals etc. I've been around this hobby long enough to understand these things and they can hinder signals, yes but yet work good for their purpose.

I've been thinking of getting one of these cheap, low noise wideband amplifiers to try out for the scanner. If it doesn't work out for me. No biggie, I can always use it on my SDR at some point.

My question is: a lot of them are powered by either a 9 Volt battery or USB. I understand you can then just plug them into the computer for power, which is fine. But when you don't have enough outlets for that. Can they be plugged into a wall outlet that accepts USB? Using say a 6 ft cord or whatever length they have. I do have USB extenders that have multiple outlets on them for the computer. I just don't like using them.

By the way, portable power chargers like those that you use for your cell phone make great portable power sources. Even at 6000 mAh. They power a portable scanner all day with no issues. Suppose I could use one of those while experimenting in a portable aspect.

Also, has anyone here used them with success on your scanner?

They look like they're the going thing these days for applications like scanners and SDR's.

My apologies if this is in the wrong forum. I like to discuss stuff like this with our locals here. :)
 

ab3a

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Oct 8, 2007
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Lisbon MD
As @prcguy pointed out, the power source can have a significant impact on the performance of the preamp.

Cheap preamps are usually more trouble than they're worth. Keep in mind that the typical use of such a preamp is to install one at the antenna to overcome coaxial loss. Do not overlook the hassle of installing it next to the antenna, weatherproofing it, and properly grounding the system so that it doesn't destroy your home's electrical system if struck by lightning.

What you should look for would be a preamp and a bias-T with good power supply decoupling (filtration). One way to help make this work would be to use the coax itself for diplexing --assuming the braid of the coax is good and the diameter of the coax is something reasonable. I wouldn't use anything like RG-58 for something like this. If you're in an urban area, think twice before using a pre-amp because you're going to have to pay extra special attention to the power supply to keep nearby transmitters from inducing voltages in to the supply lines. Generally, this is a good argument for using a Bias-T type system.

Keep in mind that you can have a pre-amp with very good IP2 and IP3 performance, and it could still present birdies all over the place if you fail to keep RF garbage out of the power supply.

And do note, this is why shortwave antenna companies like Wellbrook cost so much and yet have so many people who swear by them.

Typically you can expect to spend about $150, plus the cost of a decent coax. For an example of a company I have used in the past (though I have no affiliation with them) See Low noise preamplifiers and microwave Gunnplexers
 

technoweenie

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Joined
Mar 15, 2004
Messages
5
I highly recommend the LNA4ALL pre-amp.

The chip is very low noise ( 0.75dB ) and a high intermod rejection with about 22dB of gain. I live in the heart of the Niagara Region so I live with tons of surrounding RF sites. I get some issues, especially with FM broadcast overload, but I also have an FM trap in line.


Bryan
VE3OYN
 

IdleMonitor

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I only have one FM radio station in town here. I'm pretty close to the studio. They broadcast from the station to the broadcast tower a few kms away. That antenna is a beam directed at that tower and I'm not really in that path. That antenna is a 900 MHz Sinclair broadcast antenna I believe.

The broadcast tower however is on a high hill on the edge of town and my antenna is within direct line of site from that one. I don't get intermod or any issues with that stations broadcast on any frequencies right now as it is that I can see/hear of other than if I'm actually scanning through the broadcast band itself, there currently, it is a mess.

I'm not really worried about that part though. Besides, I do have the broadcast filter turned on in the settings. I do also have another FM broadcast station also a few km's outside of town in the opposite direction of the other station. No problems with that station other than within the broadcast band itself. That studio is about 5 km's outside of town and is at the base of the broadcast tower.

Using an SDR is much easier to listen to FM broadcast stations compared to the scanner.

The tower/area that the main broadcast tower is on, that I am direct line of site is, we do have a Weather radio transmitter on it as well. I don't get any issues right now as it is, other then it blanks out the other two possible Weather radio stations that I know I could possibly hear.

Other than that, no main issues there either, although I suspect that would change with the addition of an amp. Also here, I have the weather broadcast filter turned on here as well in the settings.

I highly recommend the LNA4ALL pre-amp.

The chip is very low noise ( 0.75dB ) and a high intermod rejection with about 22dB of gain. I live in the heart of the Niagara Region so I live with tons of surrounding RF sites. I get some issues, especially with FM broadcast overload, but I also have an FM trap in line.


Bryan
VE3OYN
 

Ubbe

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Sep 8, 2006
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5,514
Location
Stockholm, Sweden
I'm very fond of PGA103+ based amplifiers. It has a bit higher specs that can take bigger signals without going into intermod. A circuitboard with connectors are around $25 on Ebay and can be put inside the house in the attic or down at the scanner. The closer to the antenna the better to compensate for coax loss and antenna impedance match to coax. Outside usage needs a watertight box of some sort.

Some of the amplifiers has a USB connector and some can also be powered from the coax using a bias-T, that are just a choke coil powering the amplifier so that the RF signal isn't shortcircuit. The same choke coil are also sitting on the circuit board to isolate the DC current from the RF signal.

I haven't notices any interferencies from USB chargers and USB power supplies at VHF and UHF frequencies but at shortwave frequencies. But only some of the USB power supplies have problems. I bought maybe 10 different ones from China and perhaps 1/4 of them can be seen making a very faint and weak interference in the HF bands and one of them created a huge interference that drown almost all shortwave reception.

There's few or even no scanners that doesn't overload from using an amplifier with 20dB gain. You have to reduce the signal at the scanner either by using splitters that will have attenuation on each output port, different much dependent of how many splits there are, or/and you have to use additional attenuation by a $5 fixed value or a variable $20 attenuator which will be prefered to dial in the most optimum level.



/Ubbe
 
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