LNA's cheap vs not Cheap

[PlayDoh]

So I'm considering getting a LNA, and the LNA4ALL is a top choice. Firstly I'm a serious newb and can barely make out all the technical talk on here. Yet I'm not an idiot, lol.
I've seen LNA's on Ebay for $8, $30 and $100 or more. Other than the expensive ones having a housing, I'm not sure what the difference is.
I have a DIY dipole 4' antenna, 25' RG5 to RTL to 15 Meter active USB to PC. I have 2 RTL's with the same setup. I'm 40 miles, 60 Km to the city I'm listening to. I live in the country so I don't think I need a bandpass, Bandstop, as FM isn't a problem.
This is a new hobby for me so the less I can spend the better. Happy wife happy life, lol

So if I get a LNA4ALL or any LNA I'd like to put it right by the antenna. I can shelter it from the elements, but I think a housing is almost a must. Where can I get a housing? I got a quote from a guy referenced by Adam's blog (LNA4ALL blog) yet he wants $100 each for one with housing. That seems a bit much for a $40 LNA4ALL and a housing, yet I"m not sure if putting the LNA in a housing requires soldering or anything. I can solder good so I'm not worried about that.

I can get Police brodcasts pretty good, about 60 up to 65 RSSI shown on unitrunker, yet sometimes I get digital garble. I hear dispatch tell people they went digital once and awhile so I'd guess it happens to everyone. Yet if Its $50 to boost my signal quite a bit I'm willing to spend it. Maybe an antenna is a better way to spend my first $50-$100 next investment?

Thanks for any help, much appreciated

 

[JamesO]

You want to read this thread - https://forums.radioreference.com/s...mp-10-off-december-other-useful-rx-items.html

I have played with some of the cheaper LNA's from ebay that are on open boards like the LNA4ALL, not disrespect to these guys, the LNA's do what they claim.

BUT, IMHO most of these LNA's are too high Noise Figure and too high in gain.

REALLY suggest the Mini-Circuits Amp I have listed in the thead link, I am running this now after MANY different LNA tests and installation.

I do not think you will be disappointed.

A good LNA at the base of coat hanger is better than most omni or even a beam antenna of 2-4 times the price of a good LNA like the one I listed above.

One thing I did do is mount a +5 Volt Voltage regulator and some filtering and stabilizing capacitors right at the Amp so I can run 12 Volts or even an adjustable supply so I can power other inline devices if necessary and also reduce the gain of the Amp if needed.

 

[PlayDoh]

Thanks JamesO
I had a look and tried to order one, yet their out of stock. Not only that but their one of those US companies that seem to think Canada is beside Burma or something. $100 for shipping is the cheapest option, which is laughable. It might be configured for bulk orders regarding shipping. It's $12 to shop to Montana, which is a 3 hour drive. USPS has $10 flat rate boxes that could fit a dozen of these, from anywhere in the US to Canada.
I'll try and write them. Another oddity is that everywhere else that sells that model wants $250 for 1 wtf? $8 to $250 price range for these reeks of the scenario where people charge as much as they can hoping to catch a sucker.
Ugh. I hate having to spend days of searching just trying to find an honest place to buy something. Maybe I'll just try and pick a cheap Chinese one.

 

[Ubbe]

A good LNA at the base of coat hanger is better than most omni or even a beam antenna

Agree. The worse the antenna the more use of a LNA. As a scanner use a multitude of frequencies the antenna will have a hard time trying to work on all frequencies and it will in most cases be beneficial to use a LNA.

Also most scanners use frontends with cheap semiconductors that have a high internal noise figure of 2-3dB and adding a LNA with 0,5-0,6 dB NF in front of it, even directly at the scanner, will improve reception. But you will probably suffer overload and need a variable attenuator to get the level just right.

Ebay got lots of LNAs and one even had an integrated FM trap filter, not a bad thing to use at the antenna base.

/Ubbe

 

[PlayDoh]

Thanks. eBay has so many and such a wide range of prices I'm confused as to what I should get. I mean my $20 RTL is as good as a $500 scanner for my needs. Is a $8 LNA good enough for me also?
I wonder if using 2 or more LNAs improves noise reduction, as it seems like it's suggested.
My RTL's are indoors and easy to access so I thought about a band pass filter that filters everything but the 850-900 MHz that I'm interested in.

 

[PlayDoh]

Can someone help me out as to what I should look for in a LNA? just looking at specs, doesn't explain the price. Some pre-amps are $450 but with a NF of 5.
I'm finding the LNA's that seem to be used for my needs have Gains of 12 db to 30-40 db. Common NF is 1-3, and I can find plenty that cover the range of frequencies I'm after. The issue with Chinese products is that it takes so long to get here, that trying out one at a time could take the better part of a year to find one I like, if I just go off what limited knowledge I seem to have.

Can anyone explain why some LNA's are $200, and others $8 when looking at the specs theres is little difference? Is the difference of 1 or 2 db noise that important if I'm just looking to improve signals I can get fairly well already?

Is any voltage preferred over others in terms of noise and gain? I don't care if it takes 12v or 5v honestly. I'm only interested in 850 -900 MHz, and maybe 150 MHz if its available. the 150 MHz signals are pretty week for me, but the 850-900 are quite good. Knowing my target frequency needs is it much better to get a LNA that is as narrow to my needs as possible?

So many questions, lol

 

[JamesO]

Mini-Circuits US shows the ZX60-P103LN+ LNA in stock.

Some vendors will only sell outside of the country via an "In Country" rep or dealer.

It seems Newark electronics may be the Canadian Mini-Circuits dealer, however, when I put the part number into the Newark Element L4 site, it did not show up, you may need to contact Newark and/or Mini-Circuits directly.

It is really worth the effort.

 

[PlayDoh]

Ok, ya there now in stock. Still crazy shipping rates for Canada.
Looking at the specs I can't see why this $5 is less than 10% of the Mini circuits, other than its Chinese direct and quality control is all but absent. Yet I'm considering getting 2 of these and rolling the dice. I mean for what these are made of, I don't see how they get up so high in price. It's just an amplifier chip on a small board.
http://vi.raptor.ebaydesc.com/ws/eB...=163853&pm=1&ds=0&t=1505062483511&cspheader=1

Please have a look or better yet if anyone has one and can give a review.

 

[prcguy]

The cheap Chinese LNA may be ok for your needs based on you living in the sticks away from high levels of RF and your feeding an RTL dongle. Its cheap and will give you an idea if an LNA will benefit your reception and you can always upgrade later.
prcguy

Ok, ya there now in stock. Still crazy shipping rates for Canada.
Looking at the specs I can't see why this $5 is less than 10% of the Mini circuits, other than its Chinese direct and quality control is all but absent. Yet I'm considering getting 2 of these and rolling the dice. I mean for what these are made of, I don't see how they get up so high in price. It's just an amplifier chip on a small board.
http://vi.raptor.ebaydesc.com/ws/eB...=163853&pm=1&ds=0&t=1505062483511&cspheader=1

Please have a look or better yet if anyone has one and can give a review.

 

[PlayDoh]

Thanks prcguy, and JamesO and Ubbe.
I ordered 2 of those cheap ones. May as well give it a shot.

prcguy, can I ask as to how a RTL is less suceptible to overload? I'd guess cause it's not as sensitive?
I know a RTL is no real comparison to a good brand stand alone, yet from my understanding it's just the 'tuner' part of a standalone and the PC takes the place of everything or most of what a radio does.
I suppose knowing the real difference will come in time and a better understanding on my part. I feel like I'm on my way to a degree in telecommunications, lol. It's fascinating how complex radio tech is.

 

[JamesO]

Here is the small part that most people do not understand.

The very first stage amplifier in ANY receive system is the most critical part. The lower the Noise Figure, the better. 0.5 db NF is better than 1.0 to 1.5 dB NF.

I also prefer a lower gain Amplifier over a higher gain Amplifier. So 10-15 dB gain is far better than 20-30 dB gain IMHO.

While the cheap ebay LNA's are not bad, they often have higher noise figures and higher gain than I would like. I purchased and used some of these originally as I was working through sorting out an "Active" antenna feed system, and while they did help, at the end of the day, I was far happier with the Mini-Circuits LNA performnace which you would expect based on the specs.

If you were able to have a spectrum analyzer connected and watch how a quality, low Noise Figure LNA will actually pull signals out of the noise, you would quickly be convinced that they are well worth adding into a receive system assuming you know how not to overload the scanner and if necessary add front end FM Broadcast filtering which is often required in more Urban areas, but may not be a problem in more rural areas.

 

[prcguy]

If I said an RTL is less susceptible to overload somewhere I meant they are more susceptible, sorry. They do not have front end preselection or high level rated components to operate well under high RF conditions because they were specifically designed for TV reception using small indoor antennas. I'm not sure if the RTL dongle is a superhetrodyne/SDR where it downconverts the spectrum to a low IF then digitizes, or if its a direct conversion, digitizing everything at your selected frequency.

Either way they might have a front end amplifier or a mixer but will definitely have an analog to digital converter with limited dynamic range compared to more expensive receivers. Cheaper front end amplifiers if used inside the RTL can overload easily as can low level mixers and A/D converters with limited dynamic range. The RTL dongle is all of the RF portions of a receiver and only sends I/Q data to the computer which then takes care of final band width filtering, mode, demodulation, etc.

I agree a general purpose wide band preamp should not have too much gain and 10 to 15dB gain should be adequate with about 20dB being the max to consider. Its nice to have .5dB noise figure or less but up to 1dB is generally fine for scanner use. I also think you should look at what comes off your antenna with a spectrum analyzer to help determine if you need a preamp and if so what kind of signal handling capability it will need instead of hoping what you bought will do the job.

What ruins reception for me using preamps is the large signal handling capability and I need preamps with 1dB compression points of maybe 27dBm (a half watt) or greater to avoid generating lots of IMD due to lots of strong signals in my area and the large antennas I use. Some of my preamps will put out a full watt of power if driven hard but still have low noise figures and modest gains of 15-18dB. Its difficult if not impossible to find affordable preamps in that range unless you buy them used and the Chinese Ebay preamps do not come close to those specs.
prcguy

Thanks prcguy, and JamesO and Ubbe.
I ordered 2 of those cheap ones. May as well give it a shot.

prcguy, can I ask as to how a RTL is less suceptible to overload? I'd guess cause it's not as sensitive?
I know a RTL is no real comparison to a good brand stand alone, yet from my understanding it's just the 'tuner' part of a standalone and the PC takes the place of everything or most of what a radio does.
I suppose knowing the real difference will come in time and a better understanding on my part. I feel like I'm on my way to a degree in telecommunications, lol. It's fascinating how complex radio tech is.

 

[PlayDoh]

Thanks a lot guys. I have a better understanding now for sure. From my limited knowledge the LNA I got has impressive specs. It's also the best seller which gives me some confidence it might help.

Here's the specs

Specifications:

Voltage: 5V

Current: 90mA

Gain: 18dB@0.9G

Input/Output Impedance: 50Ω

Max. Output Power: P1db 22dBm(@2GHz)

Input Signal: <+10dBm(as low as -110dBm. If input >+10dBm, output is distorted)

Bandwidth 0.05-4GHZ(differs at different frequency, refers to S21 curve)

Noise Factor: 0.6dB@0.9GHz


So 18 dB of gain and 0.6 dB NF where I need it look fairly good.
I'm afraid I don't have access to a ocilliscope, and knowing how to interpret the readings would involve learning a lot if imagine. $5 and a plug n play will be my initial test.

I would have to assume a $70-$200 LNA would greatly outperform a $5 one. Yet looking at the specs alone doesnt give that impression. I'll presume the cheap ones are either exaggerating their specs, and or they don't last long and quite likely arrive dead.

However with China's ability and willingness to counterfeit anything, it's also possible 1 or more manufacturers made orders of LNAs for a reputable company that charges $70 for them. Then after the order is fufilled they make another thousand or so and sell them on eBay. Quality control goes out the window and the finer details go by the way side, yet for general use their no different.

I'll take your word on it with confidence, JamesO that they don't hold a candle to the Micro ones, yet as suggested perhaps my needs don't require high performance. Noise might not be much of an issue if there is no noise getting to me.
I once brought my SDR to the closest town, a 20 min drive away and I couldn't get anything. There were huge signals all over the spectrum. My guess was FM and or Wifi routers. The closest city is an hours drive away yet no real hills or obstacles in between. I can get a couple FM stations just well enough to receive stereo, but most are mono and noisy.

I guess I'll know in a month or more, lol.

Thanks again for the replies and advice. Very much appreciated.

 

[prcguy]

I would have trouble with the P1 level of 22dBm which is too low for my needs. Gain is cheap, low noise figure cost more, high IP1/IP3 cost more and low noise figure plus high IP1/IP3 is expensive.

The little amplifier chip on the Chinese amp costs under $1 and is probably common to many amplifiers. The more expensive LNAs have all discreet components soldered to a circuit board and are hand tuned for frequency, gain and noise figure. The enclosures on some higher end LNAs can cost $20 or more for the machined empty box.
prcguy

Thanks a lot guys. I have a better understanding now for sure. From my limited knowledge the LNA I got has impressive specs. It's also the best seller which gives me some confidence it might help.

Here's the specs

Specifications:

Voltage: 5V

Current: 90mA

Gain: 18dB@0.9G

Input/Output Impedance: 50&#937;

Max. Output Power: P1db 22dBm(@2GHz)

Input Signal: <+10dBm(as low as -110dBm. If input >+10dBm, output is distorted)

Bandwidth 0.05-4GHZ(differs at different frequency, refers to S21 curve)

Noise Factor: 0.6dB@0.9GHz


So 18 dB of gain and 0.6 dB NF where I need it look fairly good.
I'm afraid I don't have access to a ocilliscope, and knowing how to interpret the readings would involve learning a lot if imagine. $5 and a plug n play will be my initial test.

I would have to assume a $70-$200 LNA would greatly outperform a $5 one. Yet looking at the specs alone doesnt give that impression. I'll presume the cheap ones are either exaggerating their specs, and or they don't last long and quite likely arrive dead.

However with China's ability and willingness to counterfeit anything, it's also possible 1 or more manufacturers made orders of LNAs for a reputable company that charges $70 for them. Then after the order is fufilled they make another thousand or so and sell them on eBay. Quality control goes out the window and the finer details go by the way side, yet for general use their no different.

I'll take your word on it with confidence, JamesO that they don't hold a candle to the Micro ones, yet as suggested perhaps my needs don't require high performance. Noise might not be much of an issue if there is no noise getting to me.
I once brought my SDR to the closest town, a 20 min drive away and I couldn't get anything. There were huge signals all over the spectrum. My guess was FM and or Wifi routers. The closest city is an hours drive away yet no real hills or obstacles in between. I can get a couple FM stations just well enough to receive stereo, but most are mono and noisy.

I guess I'll know in a month or more, lol.

Thanks again for the replies and advice. Very much appreciated.

 

[Ubbe]

Why don't you buy from GPIOLabs in canada? I bought several things from them and their ultra low noise amplifier works fantastic connected to a 5/8 155MHz antenna with a 1-3 splitter and 6dB added attenuation.

/Ubbe

 

[JamesO]

A number of the lower cost items and I think my FM Broadcast filter came from those guys. Iseeabluewhale is their ebay user name. Lots of nice goodies for a reasonable price.

 

[paulmohr]

I can tell you why you see cheap amps with the same specs as expensive ones. You see the same thing with audio amplifiers for home and auto. To put it quite bluntly they lie. Or they distort the numbers or meanings. A more expensive item is probably more likely to actually achieve the numbers they claim, and do it with less distortion or noise.

I can use car audio amplifiers as an example. If you see a car amp for 50 or 100 dollars that claims it has 1,000 watts of power they are either flat out conning you, or that is the peak amount of power it can put out for all its channels driven at 14 volts with a fairly high low level input voltage. And usually right before it catches on fire from overheating. And they normally have a 18 gauge power wire and a 10 amp fuse. A true 1,000 watt amp would pop that fuse and melt the power wire in heart beat. Where as a 500 dollar amp from a well known company will probably put out the power they claim in RMS, and if not it will say Peak Power, and then give an RMS power figure.

That is not to say the cheap ones will not work though, they will, just don't expect to get that much power out of them is all. I would assume the same would be true of a LNA. The more expensive ones will probably hit the numbers they claim or better though. And they will do it with a cleaner signal.

I personally use an RCA pre amp for a TV I got at lowes that cost 40 bucks. And when I tested it with my SDR it actually gave me 10db of gain with a fairly low noise floor. However the FM trap is useless and only filters out frequencies under about 90 MHz. It probably won't last that long either compared to a more expensive one either.

I can also tell you that the RTL SDR's are not as good at receiving as my 325p2 scanner is. And a scanner is now where near as good as an actual radio receiver. They work good for their intended purposes, but they have limitations because of what they were designed to do. I did a simple test with my SDR and scanner on FM broadcast signals and then compared it with my Denon home theater receiver. Neither one even came close to performing as well as my Denon did with the same antenna on each device. And I would expect that. If my 20 dollar SDR dongle out performed my 500 dollar HD radio receiver I would be a little upset lol.

By performance I mean how well each could pick up distant stations and how well they could separate channels.

 

[JamesO]

Sorry but paulmohr does not exactly know what he is talking about.

Many of the lower cost LNA designs are far from poor quality and garbage. This is because most of these low cost LNA's are the same discrete LNA chip that is used in some of the higher priced fully packaged LNA's. The better ebay LNA's are made buy enthusiast for their own purposes and many of the enthusiast that are selling these LNA's have quite a bit of background, experience and even access to very expensive test equipment.

What most of the lower cost LNA's lack are expensive aluminum housings, serial numbering and traceability. In only a few instances the "commercial" products only barely out perform the cheaper units.

Now all of this being said, many of the $10-$20 ebay LNA's do not perform like some of the better quality $30-$40 LNA that you would find. This is due to materials, design and circuit board layout. You need to know what you are looking for, but there are many lower cost LNA's that do meet their stated specs available on ebay. You just need to do you homework or ask around on the forum here for who the better suppliers are for quality, low cost LNA's.

 

[PlayDoh]

I feel Paulmohr did essentially say he was presuming, and the analogies were a stretch in logic in ways. And he did say he uses a $40 RCA preamp with good results, which was kinda counter to his own theory. I have RCA TV equipment that's working after 30 years of use.
Thanks for the details JamesO, and your opinion Paulmohr. Both appreciated. It is a fair argument that Chinese electronics make false claims, and I would never assume their specs are accurate. Yet with this LNA the seller had quite a bit of technical data and test results. Based on the popularity and reviews I felt it was worth the $7, even if it turned out to only amount to a lesson learned.

 

[JamesO]

PlayDoh,

Short of using the Mini-Circuits LNA I suggested, these guys linked below do in fact make high quality, high performance lower cost LNA's and other RF gear and should be considered. Anything they sell should meet or exceed their posted specs. While I have not offically measured the Amps for Noise Figure, I have measured gain and they perform as advertised. I have compared these LNA's to the Mini-Circuits LNA and they are very close, but not quite as high performance as the Mini-Circuits LNA.

Depending on the application, the Mini-Circuits LNA may or may not be worth the extra expense.

I would expect these guys products to clearly out perform the $7 Asian LNA's but you may not see if the difference depending on your application.

http://stores.ebay.com/GPIO-Labs?_trksid=p2047675.l2563

These are a few of the products I would consider from the GPIO Labs group:

Low Noise Amplifier 50 MHz - 6 GHz RF LNA; Ultra High Dynamic Range OIP3 +40dBm | eBay

Ultra Low Noise Amplifier 10 - 3000 MHz Gain&gt;20dB NF=0.65 dB with ESD + Bias Tee

Ultra Linear Low Noise Amplifier 10MHz - 2GHz LNA Gain &gt; 20dB NF 0.5 dB PGA-103+

A very good FM Broadcast Notch filter is this item: FM Notch Filter 88-108MHz; 85dB Rejection; Bandstop; 9th order SMA-M + SMA-F | eBay