Wideband LNA - Page 1
Forum section: electronics / rf-microwave

author: A.Z.
author_rank: Super Contributor
timestamp: September 14, 2022, 08:03:35 pm
content: Hello; I'm on a quest for a decent, cheap and easily available COMMERCIAL preamp, with an input/output impedance near 50 Ohm, a gain around 20dB, a range going from about 5KHz to, at least, 30 MHz and possibly an integrated Bias-T; at the moment, the only (almost) one seem to be the NooElec LANA HF, but I'm seeking for alternatives; so... any suggestion/pointer ?

author: szoftveres
author_rank: Regular Contributor
timestamp: September 15, 2022, 02:06:09 am
content: 30MHz max?Shouldn't be too complicated to build one from cheap transistors, simple cascoded and 50R resistively loaded 2N3904's would do this easily

author: A.Z.
author_rank: Super Contributor
timestamp: September 15, 2022, 12:08:56 pm
content: Quote from: szoftveres on September 15, 2022, 02:06:09 amwell, 30MHz would be ok, more would be even better, but... I know it isn't so difficult to build, the point is that I'm seeking for a cheap and widely available commercial unit

author: MartinL
author_rank: Regular Contributor
timestamp: September 16, 2022, 03:15:51 am
content: Are you looking for just a board, or a housed unit in an enclosure?If you want a boxed unit, there's this one which claims 5kHz-30MHz:https://www.ssb.de/en/amplifiers/preamplifier/vox1/broadband/lna-30If you're just after a board there are a few ham designs in production:Passion Radio sell one designed by F1OPA, 500kHz-30Mhz, 20dB or so:https://www.passion-radio.com/sdr-accessory/preamp-ln4hf-284.htmlSV1AFN has this one, 30kHz-30MHz:https://www.sv1afn.com/en/products/Wideband-RF-Amplifier-LNA.htmlBe aware that there isn't really that much demand for this sort of thing as a standalone product, because in the HF bands, the noise floor is usually so high that an LNA can't gain you anything in terms of SNR.A lower end of 5kHz makes your requirements more unusual too. Check carefully on that point as it wouldn't surprise me to see designs that claim to go that low but don't actually do so, e.g. due to coupling capacitors having too low a value.

author: mag_therm
author_rank: Frequent Contributor
timestamp: September 16, 2022, 04:16:48 am
content: Agree with Martin last comment.At 5 kHz, 3dB corner of a 50 Ohm coupling capacitor needs to be about 1 uF.But look at impedance vs frequency curve **eg 0603 MLCC srf is about 11 MHz.power rail decoupling might be problem too. Parallel capacitors might do it but the inductance from the largest one is still there.I have made a few copies of a home brew High Z to 50 Ohm buffer. approx 2 ~ 23 MHzFor 455 kHz I changed the capacitor values.**Murata SimSurfer for example

author: radiolistener
author_rank: Super Contributor
timestamp: September 16, 2022, 07:08:39 am
content: Here is Chinese LNA "50k-2G" in a metal shield, like this one:https://www.aliexpress.com/item/1005001419006734.htmlit has INA-02186 inside. The chip can be easily replaced with soldering hot gun.It has significant drop down of the gain below 50 kHz, but works good above 50 kHz.Power consumption is 35 mA from 12 V.But note, Chinese guys can sell it with different IC clones, so there is no guarantee that they all have the same frequency response. But you can replace it with original IC which is pin-compatible with INA-02186.

author: A.Z.
author_rank: Super Contributor
timestamp: September 16, 2022, 12:53:00 pm
content: Ok, folks, I see that I was short in details and I'll need to expand the issue a bitLet me start by thanking all of you for the replies, but now, let me explain the "issue" with more details, the point is the following, I and another folks designed and tested an RX ONLY antenna, the points for the design were:* Good coverage of HF bands* Good impedance match over the covered range to allow using whatever preamp/other* Somewhat better characteristics than existing small antennas (still a compromise, but that can't be avoided)* Ease of build, by using commercially available components and "no soldering" or stuff which "normal people" can't do* Fit in most location due to small size and not heavy dependence on groundthe result was this critter which we (I and 13dka) called the "SULA" antenna (Small Unidirectional Loop Antenna)https://swling.net/viewtopic.php?t=55such an antenna allows to cover 1 to 30 MHz (at least) with an horizontal cardioid pattern and quite good vertical angles, and while testing it we found that it exceeded expectations (remember it's a RECEIVE ONLY antenna, not designed for TX) offering a coverage extending from MW up to about 100MHz and then from about 200MHz up to 500MHz (although up there the pattern is reversed)After a bunch of NEC modeling/simulations and field tests, we came out with the final design shown at the above URL (and NO, routing the wire "inside" the loop instead of having it "dangle" isn't a good idea, since it will ruin the pattern), the idea then was to find some commercially available (and CHEAP) components which could allow anyone to test the antenna with little effort, for a start, we used theNooElec 9:1 v2 BalUnand theNooElec LANA HF barebonespreamplifier, not because we "particularly love NooElec", just since both units were cheap and easily available worldwide (even on amazon), anyhow, getting back on the reason for my requestI'm trying to find a widely/easily (and relatively cheap, see the NooElec prices) LNA unit for that antenna, theSV1AFN unithas already been tested with dismal performance, so we're back seeking for a suitable LNA unit; notice that the antenna is not and won't be (at least NOT from me) some commercial thing, that's not the purpose at allSo... any suggestion?P.S.: by the way, if you want to give the "SULA" a spin, it will be really interesting, here's an example of what it can do (using the NooElec BalUn and LNA)(if someone is curious, the TL;DR whole story of the development can be foundhere- excluding "some" private mails/messages, that is)for the interested ones, here are the SWR/Impedance/Gain curves (note that it's all about SNR and directivity, it's an RX antenna)