Benefits of using an inline amplifier/filter

[ArkTex]

Hi there.

I've seen stuff about using amplifiers for signals for scanners. Generally, the stuff I want to receive are 30miles away, analog in the 450mhz public safety band (Dallas, TX City PD and FD). I'm working on getting a better antenna, but I was wondering if using an amplifier would even be worthwhile. I use a TRX-1 and a BC125AT. Looking into getting a smaller dipole or high gain antenna with some coax, so would using an amplifier in the coax line provide me any reception benefits?

Same thing with a filter. Is there any reason to use it?

 

[WB9YBM]

I've seen stuff about using amplifiers for signals for scanners. Generally, the stuff I want to receive are 30miles away, analog in the 450mhz public safety band (Dallas, TX City PD and FD). I'm working on getting a better antenna, but I was wondering if using an amplifier would even be worthwhile. I use a TRX-1 and a BC125AT. Looking into getting a smaller dipole or high gain antenna with some coax, so would using an amplifier in the coax line provide me any reception benefits?

Same thing with a filter. Is there any reason to use it?

Considering the power levels and antenna heights used by public safety, hearing something 30 miles away with a reasonable antenna set-up at your station definitely sounds possible. While nothing beats a good antenna mounted out in the clear (above the ground clutter) an amp would help a bit with fringe area signals.

The best thing to do is mount the amp at the base of the antenna, before weak signals get attenuated even further by your feedline. Even with the best quality coax there are going to be losses along the way--especially when longer runs can't be avoided--so an amp at the antenna will overcome those losses. Just do a bit of comparing: you want something with a low noise floor (these amps will typically use FETs or J-FETs instead of transistors).

As for filters, the only benefit I see is if you've got some adjacent frequency signals causing interference that you need to nock out.

 

[ArkTex]

Considering the power levels and antenna heights used by public safety, hearing something 30 miles away with a reasonable antenna set-up at your station definitely sounds possible. While nothing beats a good antenna mounted out in the clear (above the ground clutter) an amp would help a bit with fringe area signals.

The best thing to do is mount the amp at the base of the antenna, before weak signals get attenuated even further by your feedline. Even with the best quality coax there are going to be losses along the way--especially when longer runs can't be avoided--so an amp at the antenna will overcome those losses. Just do a bit of comparing: you want something with a low noise floor (these amps will typically use FETs or J-FETs instead of transistors).

As for filters, the only benefit I see is if you've got some adjacent frequency signals causing interference that you need to nock out.

There is a lot of random static on frequencies that I assume are still transmitting, but no audio is coming through. As far as the amp is concerned, are there brands to stay away from or things that I should know so I don't overload my scanner?

 

[vagrant]

An amplifier may improve signal strength, as well as increase the noise floor (white noise). An amplifier would be the last item I would purchase, if at all. An antenna tuned for the frequency and quality coax are most important. Still, many of us compromise and use an antenna that covers many bands such as a discone, but doing that offers less gain and it opens the door to frequencies we may not want to hear, versus a tuned antenna for a specific frequency or limited range like 450 - 470 MHz.

As to filters, I have problems with nearby FM and AM broadcast towers. I also have issues with a local paging system on 152 MHz as well as a NOAA weather transmitter. The signals from these transmitters increases my noise floor hundreds of megahertz away. They also cause interference when they mix with other signals. To address this I use filters inline that specifically reduce those signals, yet allow others to pass. Now let's say I want to listen to signals around 450 MHz. These filters reduced the offending interference quite a bit, but they also attenuated the signals I want to hear slightly as well. At this point, if needed, an amplifier can assist with the losses of signal strength after passing through the filters and coaxial cable.

Can hear what you want now and how clear is it? The next question is what antenna and or coax are you using now and is it outdoors above the roofline? Knowing that can help others offer improved replies.

 

[WB9YBM]

There is a lot of random static on frequencies that I assume are still transmitting, but no audio is coming through. As far as the amp is concerned, are there brands to stay away from or things that I should know so I don't overload my scanner?

static can come from so many different sources, it can be a nuisance to track down... As far as not overloading the scanner, it reminds me of the amps Radio Shack used to sell--they had a gain control on them, at least in part to prevent over-load. It's been a while since I've investigated the latest that's available so unfortunately I can't add much on that point--either a general search on the Internet or checking with some places that sell scanners (or more general radio equipment) might be your best bet. (Or start a discussion thread specifically dealing with pre-amps.)

 

[ArkTex]

An amplifier may improve signal strength, as well as increase the noise floor (white noise). An amplifier would be the last item I would purchase, if at all. An antenna tuned for the frequency and quality coax are most important. Still, many of us compromise and use an antenna that covers many bands such as a discone, but doing that offers less gain and it opens the door to frequencies we may not want to hear, versus a tuned antenna for a specific frequency or limited range like 450 - 470 MHz.

As to filters, I have problems with nearby FM and AM broadcast towers. I also have issues with a local paging system on 152 MHz as well as a NOAA weather transmitter. The signals from these transmitters increases my noise floor hundreds of megahertz away. They also cause interference when they mix with other signals. To address this I use filters inline that specifically reduce those signals, yet allow others to pass. Now let's say I want to listen to signals around 450 MHz. These filters reduced the offending interference quite a bit, but they also attenuated the signals I want to hear slightly as well. At this point, if needed, an amplifier can assist with the losses of signal strength after passing through the filters and coaxial cable.

Can hear what you want now and how clear is it? The next question is what antenna and or coax are you using now and is it outdoors above the roofline? Knowing that can help others offer improved replies.

I can hear it alright, just it comes in really weak. My current antenna is mag mounted to the window with the antenna part facing the window and some coax that came with it. Unfortunately due to my situation I can't externally mount an antenna, so something like a wire antenna or a wall mounted antenna is going to have to do.

 

[vagrant]

Instead of mounting it to the window, can you place your magnet mount antenna on a flat horizontal metal surface? It does not have to be circular, nor magnetic. This would serve as a ground plane for your antenna. Additionally, positioning the antenna with more of the metal ground plane area toward your desired direction, may help a bit more. Near a window is best as long as it does not have a metal reflective film on it. Still, if you have a filing cabinet away from the window, or need to position the antenna and ground plane surface away from the window, give it a try. It surely will not hurt. Even a pizza/baking pan would help.

Also, please convey the exact antenna model you are using if known.

 

[Ubbe]

My current antenna is mag mounted to the window with the antenna part facing the window and some coax that came with it.

Choose an amplifier that says its using a PGA-103+ device. The actual device costs $5 but all the rest needed to be able to use it, circuit board, connectors and box, marks up the price. Those are very low noise and can handle high signal levels without being overloaded. It's just and input and an output and 5volt power to it so it doesn't matter which one you get, as long as it has suitable connectors. Even connecting it to your current antenna at the scanner will improve reception. But you will have to reduce its 15dB gain to something like +3dB and that's best done using a variable 0-20dB attenuator between amplifier and scanner.

If you plan on having an antenna somewhere else using a longer coax then the amplifier at the antenna will work better as a buffer between antenna and coax and having a 1-2 CATV splitter at the scanner end, even if you only have one receiver, also works as an impedance isolation buffer between scanner and coax and will improve things even further.

/Ubbe

 

[RRR]

.............My current antenna is mag mounted to the window with the antenna part facing the window.......

Could you please explain this, is it horizontally mounted or vertical? A Yagi?

Having the antenna "Facing the window" sounds unusual, maybe I just don't understand what you mean.

 

[ArkTex]

Could you please explain this, is it horizontally mounted or vertical? A Yagi?

Having the antenna "Facing the window" sounds unusual, maybe I just don't understand what you mean.

So, Generally, I have it mounted inside of the window frame with the antenna horizontally mounted outwards from the wall. Basically it's magnetically mounted to the frame of the window with it horizontally facing.

I also occasionally put it on a bookcase to change things up a little.

 

[ArkTex]

Instead of mounting it to the window, can you place your magnet mount antenna on a flat horizontal metal surface? It does not have to be circular, nor magnetic. This would serve as a ground plane for your antenna. Additionally, positioning the antenna with more of the metal ground plane area toward your desired direction, may help a bit more. Near a window is best as long as it does not have a metal reflective film on it. Still, if you have a filing cabinet away from the window, or need to position the antenna and ground plane surface away from the window, give it a try. It surely will not hurt. Even a pizza/baking pan would help.

Also, please convey the exact antenna model you are using if known.

https://www.amazon.com/Bingfu-Transceiver-Transmitter-Compatible-RadioShack/dp/B07L61ZQRD/ref=sr_1_3?dchild=1&keywords=bingfu+hf+vhf+uhf&qid=1618983882&sr=8-3

Here's the antenna model. At the time, I had a very, very limited budget. This usually is mounted on my car, but at the moment is serving as a placeholder antenna until I get a proper antenna.

As far as placing the mag mount on a groundplane, would something like a metal can work? I can place it on one of those and put it on the windowsill to see if that will help. I'm also looking into using PVC and doing something like this video here, although with a much better antenna than the one showed:

(

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This will hang from the window inside, or mounted by suction cups on the window right above my desk, so length of coax needed is very low.

 

[vagrant]

If your metal can around 18" in diameter sure, but I have a feeling it is not that large. Again, even if it is not right at the window, go get a large baking pan from your kitchen and put the antenna in the middle. Did it improve the signal? Hold the pan near the window with the antenna on top. Did it improve the signal? You need to experiment, but that antenna will probably give you improved results with a reasonable ground plane. Experiment!

* Oh wow, I just read an earlier post where you noted the antenna is horizontal. You should avoid that. The signals you wish to monitor are more than likely vertically polarized, so your antenna should be the same. You could loose up to 20dB of signal at that angle and that is a significant amount. Still, each location is different and you should experiment, but keeping it vertical will typically provide the best result for public service frequencies around 450 MHz.

 

[ArkTex]

If your metal can around 18" in diameter sure, but I have a feeling it is not that large. Again, even if it is not right at the window, go get a large baking pan from your kitchen and put the antenna in the middle. Did it improve the signal? Hold the pan near the window with the antenna on top. Did it improve the signal? You need to experiment, but that antenna will probably give you improved results with a reasonable ground plane. Experiment!

* Oh wow, I just read an earlier post where you noted the antenna is horizontal. You should avoid that. The signals you wish to monitor are more than likely vertically polarized, so your antenna should be the same. You could loose up to 20dB of signal at that angle and that is a significant amount. Still, each location is different and you should experiment, but keeping it vertical will typically provide the best result for public service frequencies around 450 MHz.

Sourced a metal baking sheet and put the mag mount on it, it'll go to the windowsill for testing.

 

[popnokick]

Forget what you saw in that video.... rubber duck antennas, especially when extended via coaxial cable... would be better termed "rubber attenuators". Their efficiency is very low to begin with, and made worse by extending them with coax away from your radio. They also depend upon your body as a ground plane, so moving them away from the handheld radio further reduces their signal pickup ability.
Here is a very inexpensive and simple antenna that you can hang in your window (highest window in your dwelling - 2nd story or attic is best). Scroll down to the wire version (it's below the copper pipe version) when you land on the RR Wiki page. Run the coax at right angle away from the hanging antenna and route it to your radio. This antenna doesn't require a ground plane, so you can forget all the fooling around with magnets, cookie sheets, tin cans, refrigerators, and file cabinets. This antenna will work FAR better than the hack job with a rubber duck shown on YouTube -
Homebrewed Off-Center Fed Dipole - The RadioReference Wiki

 

[RRR]

Ditto what Popnokick stated. "Rubber duck" antennas are good for right on top of your portable while carrying it, and not much else.

You -have- to have your antenna vertically (up and down) mounted for it to pick up any signal past a few miles away. Horizontal polarization is good for TV stations and Shortwave, and not much else.

Prop that thing up outside your window as high as you can get it, and you will see a world of difference. But stay away from Rubber Duckie antennas and horizontally mounting. The RS antenna you pictured should do ok as long as the connections are good, and there is some sort of ground plane (even if you magnet it to a window A/C unit)

Good luck, and I can appreciate you're willingness to ask for assistance, and actually accept the input you are being given. Usually I won't post trying to help folks, because they seem to have it all figured out, or so they think. I think you will be fine, and I'll look for other posts you make, in case you may have other issues as well.

Happy scanning! Please let us know what you did, and how it works!