Scanner Pre-Amp

[JamesO]

the better approach is to use a better antenna and lower loss coax

Preamps amplify interference and noise which will overload and desense scanners

This tends to be the general attitude of people with no first hand experience with decent Pre-Amps and a set up that has been messaged and the details have been worked out! Often a "better antenna and coax" is out of the question due to cost and/or installation considerations. True, if you blindly go into the Pre-Amp world with limited knowledge and understanding of not only the Pre-Amp, but the overall effects of the complete receive system from the antenna to the receiver, you can end up with poor results.

Read this - https://forums.radioreference.com/s...mp-10-off-december-other-useful-rx-items.html

 

[dlwtrunked]

This tends to be the general attitude of people with no first hand experience with decent Pre-Amps and a set up that has been messaged and the details have been worked out! Often a "better antenna and coax" is out of the question due to cost and/or installation considerations. True, if you blindly go into the Pre-Amp world with limited knowledge and understanding of not only the Pre-Amp, but the overall effects of the complete receive system from the antenna to the receiver, you can end up with poor results.

Read this - https://forums.radioreference.com/s...mp-10-off-december-other-useful-rx-items.html

Definitely true. Often a pre-amp on a scanner will require filters and will depend on the gain. The optimal configuration will depend on the location and may be change with time. If one is not willing to deal with that, then a pre-amp should not be tried. If one understands that and can afford the time and money for an optimal configuration, then it is often the way to go. Also, too many people focus on the pre-amp gain. What one wants to do is improve the noise figure over that of the scanner and have enough gain to make that worthwhile without overload the receiver or introducing intermodulation.

 

[rbm]

This tends to be the general attitude of people with no first hand experience with decent Pre-Amps and a set up that has been messaged and the details have been worked out! Often a "better antenna and coax" is out of the question due to cost and/or installation considerations. True, if you blindly go into the Pre-Amp world with limited knowledge and understanding of not only the Pre-Amp, but the overall effects of the complete receive system from the antenna to the receiver, you can end up with poor results.

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I couldn't agree more.
A good part of my working career has been with Near Earth and Deep space reception.

If we didn't have good pre-amps, you may as well just go home.

At one time, all of my feedlines were BIG hardline and the connectors back then were around $75 each!
That's $150 per feedline just for two connectors! (I only had 2 or 3 antennas back then)

There's no way I was going to run hardline up to my 6-7 antennas today.

Now, I use good quality, solid copper center conductor RG6 cable and good quality, low noise, high IP3, and MODERATE gain pre-amps.

Along with some variable attenuators to keep everything clean.

With that setup, I get reception as good as I ever did (or even better) with hardline.
If there's any RF in the air, I can receive it.

Rich

 

[JamesO]

I have been dealing with Land Mobile and global Satellite communications for many years.

Dealt with everything from the LNA's at the antenna to baseband signal distribution using both RF and RF-> Fiber to Fiber->RF networks. Have dealt with very long signal path runs, used to have 4-5 stories of cable to feed reference signals to spectrum analyzers for daily operation. Also had RF receivers tied into the same reference feeds for demodulating interfere signals. Dealt with signal direction finding and interference problems both at earth stations and at receiver sites and in the field.

Anyone that has any real working experience knows the first stage amplifier directly after the antenna is the most important part of any receive configuration. Even the cell phone sites have LNA's right at the receive antenna, how do you think the get the 800 MHz signals down the towers and into the receivers?

The benefit we all have as hobbyist today is the quality, technology and price of top quality Pre-Amps has come WAY down due the wide use in the Land Mobile and Cellular industry. You can even get some decent surplus parts for Cellular and retune and tweak them for Public Safety monitoring.

Sure, it is hard to pick a Pre-Amp and put it in a receive path and have great results. It does take a lot of trial and error as well as testing and tweaking to get things optimized.

I have VERY strong FM Broadcast, TV Transmitters and Paging Towers near me, but with the right Pre-Amp and a decent FM Broadcast filter right after the antenna, you would be surprised what I have been able to accomplish for say, $150 at the end of the day. I spent more up front with different active and passive parts, but it did not take long for me to narrow down what worked best.

Sorry haters and for the folks that have not spent enough time in the field, you are really missing out!!

 

[iMONITOR]

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

I've always read you should mount the amplifier at the antenna end, not the scanner end. Otherwise aren't you amplifying noise picked up by the coax along the way?

 

[iMONITOR]

But, this is the setup I use for six of my antennas that have a preamp mounted right at the base of them.

Here's an older photo of a few of them.

How did you determine the distance required between all these antennas mounted so close together, so they don't interact with each other?

 

[rbm]

How did you determine the distance required between all these antennas mounted so close together, so they don't interact with each other?

I mount the antennas where I can.
I haven't seen any interaction problem other than one time, an ST2 got bent during a windstorm
It was touching another antenna and caused all kinds of problems.

A much bigger effect is caused by which side of the mast the antenna is mounted on.
You can see that in the screen capture of Satcom reception above.
Two identical antennas with identical preamps mounted on the same mast, facing different directions.

Depending on which antenna I use, some signals don't even exist in that direction.

I used a telephoto lens to take that photo, so it can be deceiving.
The vertical antenna in the back is actually around 5' away from the others.

There's also a Log Periodic antenna mounted below the vertical.

Rich

 

[JamesO]

I am guessing that rbm and myself are only a few of the people here that really understand LNA's and how they can improve the RX of an antenna and feed system.

Sounds like we both came from the Satcom world and we have had first hand experience understanding that the first stage LNA right at the antenna connector will actually yield outstanding results.

I would put my money and time into a quality LNA LONG before I would even worry about spending money on expensive and hard to run coax. For a receive station this make far more sense.

I know I will have all sort of comments about running LMR400 or some other coax, but in my configuration and most configurations, a quality LNA as the base of the antenna will out perform any low loss coax that costs close to or more than 3-4 times the cost of the LNA at the antenna.

I have tried to share the set up I have spent a lot of time perfecting and I do not think anyone has followed my lead as I have had no follow up with comments about improvements and positive results.

 

[rbm]

Sounds like we both came from the Satcom world and we have had first hand experience understanding that the first stage LNA right at the antenna connector will actually yield outstanding results.

Good observation there!

Edit: My first SatCom RF project was TACSAT-I back in the late 60's
After launch, we had a demo for a bunch of military Brass.
Once they saw the possibilities, they almost wet their pants!
(See the edit below.)

Several of my projects are resting on Mars and the Moon. (from a lot of years ago)
The RF payloads were my 'babies'.

Other projects were closer to home.
Some civilian, some not.

Mini Circuits used to have a great calculator page for calculating overall system Noise Figure.
But it's gone now.

Here's the closest thing I could find there with a quick search.
It's intended for microwaves but will give some idea about the effects of a low noise figure in the first stage.
https://www.minicircuits.com/applications/microwave_calculator.html

Here's an old post of mine that attempts to explain it.
http://forums.radioreference.com/sp...mplifier-coupler-noise-figure.html#post946187

Rich

Edit:
A rather large pdf file relative to TACSAT 1 is at the NASA site here;
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19710008296.pdf

Around page 74 in the pdf.

The TAC SATCOM will be the largest and most powerful communications satellite ever built and will weigh approximately 1600 pounds and be 16' high and 9' in diameter.

The satellite system is designed to communicate with aircraft, ships, and mobile field units.

Development responsibility of the Director of Defense Research and Engineering (DDR&E); the U. S. Air Force, Electronic
Systems Division (ESD) is conducting the feasibility test program for the satellite and will oversee development of the mobile ground, air, and shipboard UHF terminals.

TACSAT 1, experimental TRI-SERVICE launch -"9 Feb 1969, successful

The U. S. Army's Electronics Command at Fort Mammouth, New
Jersey, will procure the SHF microwave terminals through a
$2 million plus contract with RCA-Camden for ground and airborne
terminals in the following configurations:

1. 3 airborne using 41 parabolic antennas.
2. 6 on 1 1/2 ton trucks using 5' antennas.
3. 4 on jeeps using 3' antennas.
4. 3 team packs using 3' erectable antennas.
5. 2 receive only, 1 man pack using 1' antenna.

 

[JamesO]

Unfortunately too many members of this and other forums do not understand how good a properly set up LNA actually works and they are clearly missing out on a LOT of signals.

I kind if wish I had captured many the spectrum analyzer plots that I gathered while experimenting with the best configuration of my system.

Maybe next time I get back hands on I can pull out the spectrum analyzer and connect it directly to the antenna feed with the spectrum analyzer Pre-Amp turned on and provide an
A<->B comparison.

Granted the spectrum analyzer front end may not be as sensitive as many of the scanners, but with the Pre-Amp in the spectrum analyzer turned on it should give a good comparison.

 

[prcguy]

In most cases it should be a band pass filter then an LNA, both located near the antenna. For many if not most folks, most preamps made by Minicircuits will create some IMD if connected to a broad band antenna and it will make reception worse at some frequencies. I've tried countless Minicircuits preamps on Discones where I live and there are no models I've found that will survive in suburban Los Angeles RF hell without a specific band pass filter in front of it.

For example, I can pick out some weak VHF air ATIS frequencies in my area and log signal strength and approximate signal to noise ratio on a Discone. Then I add various high end Minicircuits preamps and the ATIS stations then register stronger on the receivers S meter but the signal to noise is much worse and in many cases I can't make out the voice with the preamp in line vs easy copy without the preamp. The noise floor on my receiver (Icom R-7100 in this case) will show a higher noise floor like S3 or S5 with a preamp when it was S0 or S1 without.

If I add a VHF air band band pass filter in front of the preamp with the above setup I get better signal to noise ratio and higher signal level, win win.

I can count maybe two high end wide band preamps I've ever used (out of dozens tried) that do not create IMD or affect the noise floor when connected to a wide band Discone type antennas at my house. I covet these two preamps and have no idea where you would buy one new as they were surplus from some military project.

So when you recommend buying a preamp before upgrading coax, you better know more about the users location and RF surroundings. If I had taken your preamp advice that didn't include a band pass filter you would have wasted my money and wreaked my reception.
prcguy

I am guessing that rbm and myself are only a few of the people here that really understand LNA's and how they can improve the RX of an antenna and feed system.

Sounds like we both came from the Satcom world and we have had first hand experience understanding that the first stage LNA right at the antenna connector will actually yield outstanding results.

I would put my money and time into a quality LNA LONG before I would even worry about spending money on expensive and hard to run coax. For a receive station this make far more sense.

I know I will have all sort of comments about running LMR400 or some other coax, but in my configuration and most configurations, a quality LNA as the base of the antenna will out perform any low loss coax that costs close to or more than 3-4 times the cost of the LNA at the antenna.

I have tried to share the set up I have spent a lot of time perfecting and I do not think anyone has followed my lead as I have had no follow up with comments about improvements and positive results.

 

[JamesO]

prcguy, I am going to challenge most of what you stated above and I would bet that rbm will either agree and/or add to my comments.

First you and everyone must understand that EVERY monitoring configuration and location is different and may have its specific challenges. So regardless of what information has been provided, there can and will be issues that will often need to be addressed and overcome on a case by case basis. This will likely include AT LEAST an FM Broadcast Band notch/reject filter, not necessarily an input Band Pass filter in front of the LNA. In some cases it may may sense for an input Band Pass filter, but this will usually drive up the system cost quickly and may limit the broadband nature of the receive system..

Additionally, an LNA with less gain in more urban and city ares is almost always better than a very high gain LNA. Even most high gain LNA's have multiple gain stages which are not ideal to have in a single package. This can and will often overdrive the receiver on the end of the feedline and sometimes added attenuation may be required at the input of the receiver depending on the receiver specifications, the length and type of feedline and the Pre-Amplifier total gain. As I stated it is often better to have a lower gain Amplifier than a higher gain Amplifier.

I have to fully disagree with this statement you made " If I had taken your preamp advice that didn't include a band pass filter you would have wasted my money and wreaked my reception."

I would NOT have wasted YOUR money or wreaked your reception. Going in, people do need to understand that sometimes adding a Pre-Amp is a process and it may not be a simple single purchase and installation.

I can almost guarantee that what happened in your case was a multifold problem.

1. The Pre-Amp you purchased had too high a gain and the receiver was over driven
2. The Pre-Amp you purchased had too low of a 3rd order IMP
3. The Pre-Amp you purchased had too high of a Noise Figure.
4. You DID NOT purchase and install a FM Broadcast Notch filter.which is almost ALWAYS required in city/urban monitoring locations.

The Mini-Circuits Pre-Amp I recommended is only a 13 dB gain Amplifier, much lower than the typical 20-30 dB gain Pre-Amps that are often purchased and use. Additionally I recommend and suggested a very specific FM Broadcast notch/rejection filter. I went though 7 different FM Broadcast notch/reject filters before I found one that was adequate for my requirements. I also think I suggested a few options for Bias-T configurations to remotely power the Pre-Amp over the coax.

You stated you live in LA, I did live there for a period of time and also did a fair amount of work in the Land Mobile and Cellular industry while I was there, I am fairly familiar with that goes on in your area. But I live in the Washington, DC area about 10 miles as the crow flies from the White House. I have all the major Metro area AM, FM and TV Broadcast towers typically between 3 and 10 miles from my antennas. I have 2 - 22 kiloWatt FM Broadcast transmitters within 3.5 miles and a 75 kiloWatt FM Broadcast transmitter within 5 miles of where I live.

So based on my recommendation, in all but the most severe cases the LNA and FM Broadcast notch/rejection filter should work reasonably well to exceptional in most cases.

You may or may not have seen this post that outlined the equipment in more detail:

https://forums.radioreference.com/s...mp-10-off-december-other-useful-rx-items.html

From the sounds of it, you are trying to monitor Aircraft band with the set up you have, in this situation if you did not want to try a decent wideband LNA setup like I recommended, you should specifically consider something like this for Aircraft band reception -

Airband LNA preamplifier with airband band pass filter aviation RTL SDR aviation

So while I appreciate your comments, understand that what I have recommended should work for all but the most severe environments and if this set up has issues, if you would have followed my advice, I doubt I would have wasted YOUR money. I would hope that someone would contact me directly for advice if there were problems as I would be in a pretty good position to help solve any problems.

I have a fair amount of experience in RF receive and distribution systems and it is NOT uncommon for people to over driver a signal path when they do not have proper experience and make unwise choices in hardware. Even the best of intentions often end in poor results. I would still recommend a decent Pre-Amp/FM Broadcast Band notch/reject filter over spending the same amount of money on expensive coax that may be hard to install and properly terminate.

 

[prcguy]

My post was in response you your post #28 where you are globally recommending an LNA over upgrading coax with no mention of FM traps or filters or any system design. If I did as you recommended it would not work with any preamps you have endorsed because of the very high RF levels in my area.

I used the aircraft band as an example because its something I experienced but I monitor everything from basically DC to light with separate antennas, filters and LNAs for every band when needed. I know what works around here for wideband reception and what doesn't, which is most every preamp out there without additional filtering. Others are lucky in they can get away with just a preamp and no other hardware because they live "in the sticks" radio wise .

I won't go into what I did for a living but it involved what we are discussing and I am used to measuring the spectrum involved before hand, then designing a receive system based on measured frequency ranges and levels. I personally would never recommend a preamp to anyone without measuring or knowing what is hitting their antenna first, especially during busy radio times.
prcguy

Edit: I just looked at your link to the preamp and filter shaped like a little airplane. Cute, and thanks for the recommendation, but I use a little higher end preamps and air band filters like the ones in the attached pics. In one picture sits about $1,500 in Angle Linear's best and highest IP3 preamps. I didn't add a pic of the wideband preamps that work here in Los Angeles without filters because I don't think they are currently available.

My preamps usually go near the base of a particular antenna in an outdoor NEMA box with bias Tees and most all antennas here are fed with 1/2" hardline, no RG-6 used here except for TV and satellite. Nope, no 75 ohm TV coax on a 50 ohm communications or military antenna allowed here.

prcguy, I am going to challenge most of what you stated above and I would bet that rbm will either agree and/or add to my comments.

First you and everyone must understand that EVERY monitoring configuration and location is different and may have its specific challenges. So regardless of what information has been provided, there can and will be issues that will often need to be addressed and overcome on a case by case basis. This will likely include AT LEAST an FM Broadcast Band notch/reject filter, not necessarily an input Band Pass filter in front of the LNA. In some cases it may may sense for an input Band Pass filter, but this will usually drive up the system cost quickly and may limit the broadband nature of the receive system..

Additionally, an LNA with less gain in more urban and city ares is almost always better than a very high gain LNA. Even most high gain LNA's have multiple gain stages which are not ideal to have in a single package. This can and will often overdrive the receiver on the end of the feedline and sometimes added attenuation may be required at the input of the receiver depending on the receiver specifications, the length and type of feedline and the Pre-Amplifier total gain. As I stated it is often better to have a lower gain Amplifier than a higher gain Amplifier.

I have to fully disagree with this statement you made " If I had taken your preamp advice that didn't include a band pass filter you would have wasted my money and wreaked my reception."

I would NOT have wasted YOUR money or wreaked your reception. Going in, people do need to understand that sometimes adding a Pre-Amp is a process and it may not be a simple single purchase and installation.

I can almost guarantee that what happened in your case was a multifold problem.

1. The Pre-Amp you purchased had too high a gain and the receiver was over driven
2. The Pre-Amp you purchased had too low of a 3rd order IMP
3. The Pre-Amp you purchased had too high of a Noise Figure.
4. You DID NOT purchase and install a FM Broadcast Notch filter.which is almost ALWAYS required in city/urban monitoring locations.

The Mini-Circuits Pre-Amp I recommended is only a 13 dB gain Amplifier, much lower than the typical 20-30 dB gain Pre-Amps that are often purchased and use. Additionally I recommend and suggested a very specific FM Broadcast notch/rejection filter. I went though 7 different FM Broadcast notch/reject filters before I found one that was adequate for my requirements. I also think I suggested a few options for Bias-T configurations to remotely power the Pre-Amp over the coax.

You stated you live in LA, I did live there for a period of time and also did a fair amount of work in the Land Mobile and Cellular industry while I was there, I am fairly familiar with that goes on in your area. But I live in the Washington, DC area about 10 miles as the crow flies from the White House. I have all the major Metro area AM, FM and TV Broadcast towers typically between 3 and 10 miles from my antennas. I have 2 - 22 kiloWatt FM Broadcast transmitters within 3.5 miles and a 75 kiloWatt FM Broadcast transmitter within 5 miles of where I live.

So based on my recommendation, in all but the most severe cases the LNA and FM Broadcast notch/rejection filter should work reasonably well to exceptional in most cases.

You may or may not have seen this post that outlined the equipment in more detail:

https://forums.radioreference.com/s...mp-10-off-december-other-useful-rx-items.html

From the sounds of it, you are trying to monitor Aircraft band with the set up you have, in this situation if you did not want to try a decent wideband LNA setup like I recommended, you should specifically consider something like this for Aircraft band reception -

Airband LNA preamplifier with airband band pass filter aviation RTL SDR aviation

So while I appreciate your comments, understand that what I have recommended should work for all but the most severe environments and if this set up has issues, if you would have followed my advice, I doubt I would have wasted YOUR money. I would hope that someone would contact me directly for advice if there were problems as I would be in a pretty good position to help solve any problems.

I have a fair amount of experience in RF receive and distribution systems and it is NOT uncommon for people to over driver a signal path when they do not have proper experience and make unwise choices in hardware. Even the best of intentions often end in poor results. I would still recommend a decent Pre-Amp/FM Broadcast Band notch/reject filter over spending the same amount of money on expensive coax that may be hard to install and properly terminate.

 

[JamesO]

I stand by my statement and practice what I preach, I will take a decent LNA over upgrading to a lower loss coax. Lower loss coax will not bring weak signals out of the noise.

I am running and have been running a wideband LNA with ONLY a FM Broadcast notch/reject filter on about 100-125 feet of RG-6 and I will put my system up against any short run, high quality coax and I would bet I would come out ahead in the signal reception game.

You should read my comments in this entire thread to include post #21 above as well.

For everyone else out there, good luck with a 100% passive receive system. You do not know what you are missing!

 

[zz0468]

I've always read you should mount the amplifier at the antenna end, not the scanner end. Otherwise aren't you amplifying noise picked up by the coax along the way?

It's not noise picked up by the coax, it's noise GENERATED by the coax that's the problem. But yes, put the gain at the antenna end.

 

[Ubbe]

I've always read you should mount the amplifier at the antenna end, not the scanner end. Otherwise aren't you amplifying noise picked up by the coax along the way?

The antennas where used for transmitting as well, so couldn't use amplifiers at the antenna base.
But the statement is that there's no do and don'ts, just experiment until you find something that works for YOU. One guys setup are mostly not applicable to another guys enviroment.

/Ubbe

 

[JamesO]

the better approach is to use a better antenna and lower loss coax

Preamps amplify interference and noise which will overload and desense scanners

Not true when the proper parts are used and the proper specs are chosen,

Pre-Amps will pull weak signals out of the noise when the Noise Figure is low enough.

The best antenna and coax often cannot match the performance of a decent Low Noise LNA with the proper setup.

Suggest you read this, but you will not believe or agree with any of it!

https://forums.radioreference.com/s...mp-10-off-december-other-useful-rx-items.html

Unfortunately you have no idea what you are missing.

 

[JamesO]

The antennas where used for transmitting as well, so couldn't use amplifiers at the antenna base.
But the statement is that there's no do and don'ts, just experiment until you find something that works for YOU. One guys setup are mostly not applicable to another guys enviroment.

/Ubbe

Probably one of the more truer statements that makes quite a bit of sense.

The statement in BOLD is the real KEY to success.

 

[JamesO]

Edit: I just looked at your link to the preamp and filter shaped like a little airplane. Cute, and thanks for the recommendation, but I use a little higher end preamps and air band filters like the ones in the attached pics. In one picture sits about $1,500 in Angle Linear's best and highest IP3 preamps. I didn't add a pic of the wideband preamps that work here in Los Angeles without filters because I don't think they are currently available.

My preamps usually go near the base of a particular antenna in an outdoor NEMA box with bias Tees and most all antennas here are fed with 1/2" hardline, no RG-6 used here except for TV and satellite. Nope, no 75 ohm TV coax on a 50 ohm communications or military antenna allowed here.

So here is the basic problem, you are touting Pre-Amps that are approximately $250 each, not longer available as Angle Linear has closed as of April 2017. I did not find all the spec on the amplifiers you had listed, but depending on the high level Amp you are using, the Noise Figure is not low enough. So for the next situation that requires a LNA with decent performance, I highly suggest you consider the Mini-Circuits ZX60-P103LN+, I think you might be surprised at the performance and price of this device. Keep in mind this is a newer offering and newer technology than many LNA's that have been on the market in the past.

https://www.minicircuits.com/pdfs/ZX60-P103LN+.pdf

For receive applications for the use of 75 Ohm RG-6 is not a problem when properly configured and you are not going to see a problem in smart installations below 1 GHz.

While you may knock the Airband Pre-Amp I linked above, understand that price and performance vary greatly. Sure the Airband Pre-Amp I linked could have had a different, weather proof enclosure and other features, it would drive the cost up by a factor of 5 or more.

For $45 for you get some basic specs you could not touch at anywhere near this pricepoint:

- RF gain: +16.5 dB (117-137MHz)
- Extremely flat pass band: only 0.1 dB ripple
- Very low noise figure: 0.45 dB @ 125 MHz
- High attenuation for FM broadcast and for PMR band

Anyway, moving on.

We are typically talking about hobbyist on this forum, there is a very specific area on this site for commercial users that have far deeper pockets and very different requirements. I can go toe to toe even with the commercial applications when the budget allows it, but for low budget operations, I have found and shared a very good set of components that perform VERY well and assuming any "hobbyist" choose to look at, purchase and install some of the products I have suggested, they would find a significant improvement in their current monitoring set up.

Guess we will need to agree to disagree, but I want other members on this forum to understand there are some very good lower cost options that perform as well or better than some of the higher priced LNA's on the market.

Do not knock it until you have tried it.