homebrew inductor - Page 1
Forum section: electronics / rf-microwave

author: m3vuv
author_rank: Super Contributor
timestamp: March 15, 2022, 10:04:36 am
content: hi,i need to try and make an inductor anywhere in the 100 to 400 micro henry range,its for L2 in this lna,any idea how to make one? TIA.

author: Berni
author_rank: Super Contributor
timestamp: March 15, 2022, 10:13:48 am
content: This is a pretty high value inductor that will most likely also need a ferite core to be of a reasonably small size.So you first need to find a suitable core for your inductor, the info from that core will tell you how many turns you need on it.Also since this is clearly being used in a RF application you also want to make sure your inductor functions as an inductor at the intended frequency (since at some point the winding capacitance might take over and make it act like a capacitor instead)In general its easier to just buy the appropriate inductor.

author: m3vuv
author_rank: Super Contributor
timestamp: March 15, 2022, 09:07:25 pm
content: i got thishttps://www.aliexpress.com/item/32958344410.html?gatewayAdapt=fra2glo&spm=a2g0o.productlist.0.0.315b5234iQwdc8&algo_pvid=c2c12f70-7c04-484f-be44-421fdf84ada0&algo_exp_id=c2c12f70-7c04-484f-be44-421fdf84ada0-0&pdp_ext_f=%7B%22sku_id%22%3A%2212000020659911807%22%7D&pdp_pi=-1%3B2.72%3B-1%3B1.09%40salePrice%3BGBP%3Bsearch-mainSearchive fitted the 2x 10nf caps but havent got the inductor yet,will it work with the stock inductor?,i have one for my ats-20 and one for my ts-700g,will the totaly stock one work on 144/145 mhz and the onw with the 10nf input+ output caps fitted be ok for hf?.TIA.

author: jonpaul
author_rank: Super Contributor
timestamp: March 16, 2022, 02:09:17 am
content: Use Micrometals toroid, powdered iron RF mix. Website has all information and calculate design tool.readily available cores at Epay or distributionJon

author: fourfathom
author_rank: Super Contributor
timestamp: March 16, 2022, 03:44:28 am
content: Here are a couple of "toroid calculator" pages that could be useful:https://www.66pacific.com/calculators/toroid-coil-winding-calculator.aspxhttps://toroids.info/You will want to look at the core manufacturer's or distributor's specs to be sure.

author: m3vuv
author_rank: Super Contributor
timestamp: March 16, 2022, 07:15:27 am
content: would it work on either hf or vhf with just the input+output caps changed to 10nf and the inductor left stock,will it have gain or just be an oscilator?

author: jonpaul
author_rank: Super Contributor
timestamp: March 16, 2022, 09:40:00 am
content: your questions are best answered if you can reveal the filter and systems schematic, frequency and excitation ranges etc.A TX harmonics filter handles RF power and an RX filter needs low coupling and noise pickupJon

author: RoGeorge
author_rank: Super Contributor
timestamp: March 16, 2022, 11:21:03 am
content: That inductor is for a bias tee, search online for "DIY Bias Tee".

author: m3vuv
author_rank: Super Contributor
timestamp: March 16, 2022, 11:59:46 am
content: Hi george,is not a bias "T" just for powering it over coax?,is it likley to work on hf then,i have 2 of them one is stock ,on the second one i have changed the input + output caps to 10nf,i was told to do this to fit to a homebrew hf rx,i havent changed the choke /l2 tho ,saying that i dont know if the schematic is too what i have tho,the datasheet is not very detailed on the chip and its applications,i am just trying to find out if it will work on hf with just the 2 caps i have changed,there are 2 pads on the pcb for ground and 5volts ,i assume thats vcc for the chip.?

author: RoGeorge
author_rank: Super Contributor
timestamp: March 16, 2022, 02:10:24 pm
content: Quote from: m3vuv on March 16, 2022, 11:59:46 amYes, you are correct, technically the L2 in the pdf is rather a choke inductor.However, a bias tee can be connected "in reverse" (with the side that usually goes to the antenna cable connected to the amplifier, like shown at min 8:50 herehttps://youtu.be/lxgpm-UXTNY?t=530), so to replace L2 and C6 from your pdf.If you already have ready made bias tees, the frequency range is wrote on the box, or else in the datasheet for the model you have. I don't understand what chip you are seeing in a bias tee. Bias tees are usually passive circuits, a pic with your setup might help.

author: fourfathom
author_rank: Super Contributor
timestamp: March 16, 2022, 03:45:42 pm
content: if this bias-tee inductor is to be used around 144 MHz then you really only need something around 1uH (which has a reactive impedance of around 900 Ohms). I suspect that a 100 uH (or bigger) inductor will be parallel resonant well below this frequency and will look more like a capacitor at 144 MHz.That module you got from aliexpress appears to use the Qorvo SPF5189Z amplifier, and presumably uses the test circuit shown in that part's spec sheet (https://www.qorvo.com/products/p/SPF5189Z). If they use the 150 nH inductor shown on the "900 MHz" version of the test circuit. that really isn't big enough for 144 MHz. If the board you have actually works down to 50 MHz they they have (I would hope) used a bigger inductor. So are you trying to replace the inductor on that board, or are you building a TEE that pulls DC off your coax to power the existing amplifier module?

author: jonpaul
author_rank: Super Contributor
timestamp: March 16, 2022, 04:27:26 pm
content: Not critical in value. Just a simple feed choke not a bias T.SRF = Self Res Freq must be far from the freq band in use.Inductor needs high Zo in freq band of interest, and have open mag ckt or a gap to avoid saturation with the DC bias current.Powdered toroid is ideal.Check Micrometals or Amidon.jJon

author: fourfathom
author_rank: Super Contributor
timestamp: March 16, 2022, 04:38:39 pm
content: Quote from: jonpaul on March 16, 2022, 04:27:26 pmYou do need to avoid core saturation, but you can often use an ungapped toroid -- this just depends on the core, turns, and current. And of course it's possible to saturate a bar-core inductor. That Qorvo amplifier draws under 100 mA, so it's not too much of a challenge to find a non-saturating inductor.

author: m3vuv
author_rank: Super Contributor
timestamp: March 16, 2022, 09:38:17 pm
content: You guys have lost me there! lol,btw that schematic i posted was from the facebook group SI47XX for radio experimenters,From what i understand the stock one will work in my old ts-700g,where is the best place to fit it in that radio,any ideas,is it in the output coax from the tx/rx relay to the nb board? or in the input to the 1st mixer?,also will the one with the 10nf caps work in my hf rx,to keep it simple,the shielding can is maybe 6mm deep at the most so no way to fit a torroid inductor,!,maybe an axial type,if A i can find one in the 100 too 250 nh range and B is it realy needed?,Tia.

author: fourfathom
author_rank: Super Contributor
timestamp: March 16, 2022, 11:15:38 pm
content: That module you have doesn't need a bias-tee if you have a local source of +5V / 100mA. Just hook up the power and input/output signals. The bias-tee is for when you want to put the amplifier at the end of a long section of coax cable, and don't want to run separate power leads.Putting a low-noise preamp at the antenna-end of your coax feedline can improve your sensitivity and lower your noise-floor. But of course if you want to transmit as well as receive, you need to use relays and control circuitry to avoid frying your preamp.Most HF receivers don't need an added low-noise preamp, their noise-figure and sensitivity are already as good as they need to be. The atmospheric noise is going to dominate. If you have some sort of very low-gain antenna, or long, lossy, feedline than a preamp may be appropriate.

author: m3vuv
author_rank: Super Contributor
timestamp: March 16, 2022, 11:21:18 pm
content: I fully understand that but it isnt what i am asking!

author: fourfathom
author_rank: Super Contributor
timestamp: March 16, 2022, 11:36:31 pm
content: Quote from: m3vuv on March 16, 2022, 11:21:18 pmOK, I will withhold any further comments until you explain in some detail what it is you want to do.

author: m3vuv
author_rank: Super Contributor
timestamp: March 16, 2022, 11:42:06 pm
content: well i have my rather deaf ts-700g kenwood that i want to fit one too,and also need to find out where is best in the radio to insert it,secondly i want to know if the one i have changed the input and output caps to 10nf will work in my homebrew hf receiver?,its the one that i have left with the original inductor L1 untouched but swapped the input+ output caps from stock to 10 nf,hope thats cleared things up,cheers Paul.

author: geggi1
author_rank: Frequent Contributor
timestamp: March 17, 2022, 03:22:24 pm
content: Do you want to use it as a pramp?If so its best to put it close to the antenna because otherwise you will also amplify the noise.When putting the preamp at the antenna you will have to use some kind of switchover relay and also probably some sequencing.If you don't use switchover you will fry the preamp and possible also damage your radio.This information can be found in the ARRL handbook.Powering of the preamp can be done in wo ways either through a power injector or a by direct wiring.

author: m3vuv
author_rank: Super Contributor
timestamp: March 17, 2022, 04:01:45 pm
content: i need to fit it in the radio.

author: m3vuv
author_rank: Super Contributor
timestamp: March 18, 2022, 07:06:43 am
content: was going to put it in the coax from the helical filter to the nb board,is that the best way?

author: m3vuv
author_rank: Super Contributor
timestamp: March 18, 2022, 01:58:00 pm
content: Orshould i say rather, in the coax to the rx side of the band pass filter as i guess this will limit out of band noise?can anyone help on this.