What kind of LNA should I get? - Page 1
Forum section: electronics / rf-microwave

author: Lord of nothing
author_rank: Super Contributor
timestamp: March 03, 2021, 03:18:19 pm
content: HiI use an Outdoor Antenna for reception only. Currently only one SDR is connect. I also got an Splitter to 8 Ports who will fit my needs barely. What for an LNA should I get?I use more from that company. The have a USB Connector who is nice to connect.https://www.ebay.de/itm/Ultra-Low-Noise-Amplifier-Gain-40dB-0-01-2GHz-LNA-NF-0-5dB-operates-to-4GHz/282908630204Is there an better option?Thanks

author: A.Z.
author_rank: Super Contributor
timestamp: March 03, 2021, 03:21:30 pm
content: Which frequency range are you mostly interested to ?Also, are you sure you need a preamp ? See in many cases optimizing the antenna system could just suffice, the task of a receiving antenna is "setting the SNR" and a wideband preamp would pull it much more noise and worsen the SNR

author: Lord of nothing
author_rank: Super Contributor
timestamp: March 03, 2021, 03:46:40 pm
content: Its an (lower) VHF Antenna who cover everything above the Radio Band and is good (enough) to goes up to the DAB+ (~220Mhz) Band. I cant access the Antenna because it would mean we must crawl on the Roof who is 5 Floors hight and falling down would mean... So I dont have any active thinks on the Antenna. The cable have just 5 - 10m I cant remember.Since I split the signal into 8 (!) Ports that mean the Signal at each port will must weaker when I understand it right?And the SDR are quite death in comparison to a +1000€ Radio.

author: radiolistener
author_rank: Super Contributor
timestamp: March 03, 2021, 07:12:16 pm
content: Quote from: Lord of nothing on March 03, 2021, 03:18:19 pmit depends on what is your receiver sensitivity. But anyway, if you want to get significant effect, it's better to use outdoor LNA (placed on antenna) powered with bias tee through coax cable.Also you will need band pass filter to avoid LNA saturation from nearby FM or TV stations

author: A.Z.
author_rank: Super Contributor
timestamp: March 04, 2021, 11:18:54 am
content: Quote from: Lord of nothing on March 03, 2021, 03:46:40 pmAssuming your reference to "Radio Band" refers to FM band (88-108), then I'd avoid using that wideband LNA, looking at the specs it has a range from 10MHz to 2GHz, now this means that it will receive and amplify signals on the WHOLE range (it's untuned, wideband), so any strong signal outside your desired range (but inside the LNA range) may (and will) overload the preamp causing a number of issues; I believe you'd better check for a narrower band preamp covering the desired range or, either, to a tuned preampor, either, place a passband filter in front of the LNA, the latter may be built or bought

author: radiolistener
author_rank: Super Contributor
timestamp: March 06, 2021, 09:20:33 am
content: Quote from: A.Z. on March 04, 2021, 11:18:54 amUsually this is not an issue, because receiver has a bandpass filter on the input. But the problem is LNA dynamic range. If there is a strong FM signal on the LNA input it will lead to LNA saturation and distortions.

author: A.Z.
author_rank: Super Contributor
timestamp: March 06, 2021, 09:47:14 am
content: which is exactly what I wroteand not just FM signals, the range starts at 10MHz so...

author: cdev
author_rank: Super Contributor
timestamp: March 06, 2021, 08:38:25 pm
content: The Mini Circuits PSA4-5043 is a good general purpose MMIC for use in VHF and UHF up to around 4 GHz. It has built in ESD protection and requires a minimum of external components. Its easy to use (although its very tiny) and it usually "just works". It likes 3-5.5 volts DC for power and a typical current draw is around 53 ma at 3.3 v. If its drawing much more or less than around that something is wrong.The best tip I was given for design is make sure its grounded really well, put your vias right under its ground pads.They cost around $2.50- $3.00 in quantity. You can make a functional LNA out of just the device and a DC block capacitor and a piece of PCB with a single trace thats the right impedance. (assuming you have a bias tee to power it through) An LNA can dramatically improve weak signal reception. You can make a pretty good LNA out of this MMIC. (photo attached, the device is in the upper left, its the crinkly black dot you see there. I learned a lot from this picture..At a moonbounce related LNA contest that is held yearly, Leif Asbrink entered in an 2meter LNA that he had used this chip (its the one in the photo) in and he was able to record an 0.6 db NF which is quite respectable considering the cost. At that time I did an exhaustive search of all the available gain devices I could find and it was the best choice. The built in ESD protection is a big thing as it saves your device in a great many common situations that might otherwise fry it. I bought 20 of them and I still have a few left. I lost one into the mess, one to too much heat, and my first few designs had issues but all the others all worked. None were defective. I gave a few away to friends. I still have a couple of them. They get a lot of use and they dramatically improve received signals. They don't overload easily and the amplified signal is clean. Highly recommended.