RF Project, hard time with toroids from DigiKey and Mouser. - Page 1
Forum section: electronics / projects

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: November 11, 2015, 07:42:36 pm
content: So firstly I am trying to get all components from one vendor quickly, no ebay junk. The parts im looking for aresa602 or SBL-1 rf mixer1n5711 diodesT37-6 toroidsT50-6 toroidsT68-8 toroidsI am having the hardest time figuring out how to find the damn ferrite rings I need. I have never ordered specific toroids like this and I have been googling away trying to relate TDK material types to find one closest to #6, I have had no luck at all! As I understand the number like T50 is the outer diameter, so im gonna guess using a T48 is no big deal as long as it is #6 and measures correct inductance on a meter. I am tying to build trifilar balancing transformers for a discrete mixer and some if/lo/rf filterers. Some sites say yellow toroids are #6 mix, so if I pull yellow rings out of old ATX psu's can I count of these having the right frequency property's, or are some rings just colored with no meaning?There was an article in nuts an volts about an HF upconverter for the RTL SDR, and I want to improve on it so I want to build it to there specs see how it performs and then try some better filtering along with a discrete mixer vs a software based mixer. The nuts and volts mixer just has a very unique function using a variable cap to fine tune.As far as diodes go I also want to build a version of this,http://www.techlib.com/electronics/allband.htm, for a noise emission test tool. It is using the same 1n5711 shottky for RF detection. I have a bunch of old 1n191 geraniums that were used before the hot carrier diodes took over. What i am wondering is if maybe there is a more sensitive better diode than the 1n5711 I can use for mixing and detection? I have some old 3n310 dual gate fets I have been told are VERY sensitive rf front ends but, but just getting in to analog radio design I have never even heard of a dual gate FET and have no idea how this would fit in to the circuit linked in to above. One of the revised circuits shows a bat41 diode replacing the 1n5711.... Ive never used diodes for anything other than zener references, rectification, and circuit protection, so once again when it comes to RF the only thing I know I am looking for is a diode with a low vF, not sure what else. I know in a balanced ring the revers breakdown has to be able to stand enough reverse current of the LO...

author: DimitriP
author_rank: Super Contributor
timestamp: November 11, 2015, 08:01:59 pm
content: The right parts, one vendor , quickly. Pick any twoDid you try Amidon yet or have you ruled them out for some reason?http://www.amidoncorp.com/www.amidoncorp.com/ferrite-toroids/

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: November 11, 2015, 08:07:57 pm
content: Well I had never heard of them but I can only get the rings from them :/. I cant belive digikey or mouser wouldnt have common HF ham toriods... I believe its more of my ignorance on the subject than them not having them.I also didnt ask this originally but I have no way to measure Q that I know of, and for a different project I need to wind a very low q inductor for an AM LC tank in to an a to d. I know using an air core around a coke can is a very high Q, so what is the rule of thumb for getting a low q?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 11, 2015, 08:15:08 pm
content: Because you're not shopping for ferrites! D'OH!Get powdered iron parts from Amidonhttp://amidoncorp.com/not the cheapest but readily available.Or just buy the ready-made inductors. Assuming you can do the job based on E12 series parts, or whatever. I suppose you'll be making coupled inductors (tapped and multi-winding) so that's ruled out, though?Powdered irons are basically Micrometals (or whoever their ultimate supplier is, if any), you can check out core types based on color code. The generic yellow-white and blue-green cores are floor sweepings: you're lucky if you get Q > 10, and that's at power switching frequencies. They're little more than overly complicated resistors at RF.But then, if you're just doing baluns and stuff, maybe it doesn't matter that you have powder. If you need a transformer rather than coupled inductors, you should be shopping for ferrite instead. RF materials still aren't terrifically available (from the conventional distributors), but the high frequency EMI core materials (#43, 44, 61, 67) do a good job. What's the difference? Inductors are intended to store energy, carry reactive current, whatever. Transformers are not (small energy storage, low magnetizing current). Also, transformers are usually intended to have very good coupling, while coupled inductors might have any amount. At RF, a transformer is characterized by having a high impedance -- which may be inductive or lossy, but the point is, it's high enough that it doesn't matter (a 50 ohm balun having 300 ohm parallel equivalent loss is only 1.3dB insertion loss, not a big deal). This also leads to wide bandwidth, e.g., a wideband balun to go from 50 ohm coax to a multiband shortwave antenna that covers 1.5-30MHz.Also, if all you need is small signal baluns and stuff, shopping for cores at all might be a lot of extra effort -- you can buy baluns and splitters and whatnot, mass produced, THT or SMT, for a variety of bandwidths and impedances. An RTL SDR thing would probably benefit from these kinds of things. The most important feature of SMT transformers is, being very small, they'll work up to quite high frequencies (>100MHz), which is a lot harder to do with a finger-sized core and wire (especially if you don't know how to build transmission line transformers yet). Though they might not extend very low, either (for the same reason..).Tim

author: 3roomlab
author_rank: Frequent Contributor
timestamp: November 11, 2015, 08:36:43 pm
content: i bought my first batches of toroids from here, but i am guessing you are using empty cores?http://www.kitsandparts.com/the seller is really nice and quick. they also have tech specs on their parts. shipping is cheaper than amidon

author: dmills
author_rank: Super Contributor
timestamp: November 11, 2015, 09:31:34 pm
content: kitsandparts is who most folks use for small quantities of powdered iron and ferrite (NOT the same thing!) toroids, they may also have that obsolete mixer chip and maybe even the diode.Regards, Dan.

author: Bud
author_rank: Super Contributor
timestamp: November 11, 2015, 10:02:30 pm
content: kitsandparts is the best place on Earth to shop for toroids

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: November 12, 2015, 08:11:49 am
content: Find and download a program called "mini Ring Core calculator 1.2" - it is free, available from few HAM-related sites. It has a dialog that shows color coding of cores together with frequency range and calculation of resulting inductance. I had similar problem - I ended up buying bunch of cores off eBay. Local electronics store in Vancouver also had very good choice but grossly overpriced.Cores with same material come in different sizes, depending on desired number of turns you will need different diameter cores. If you want higher Q then you want to use thicker wire, thus you need bugger core.Having good software calculator allow to play with different options easily. RF cores usually NOT color-coded, they just look like nice smooth graphite-like rings covered by transparent coating.

author: 3roomlab
author_rank: Frequent Contributor
timestamp: November 12, 2015, 09:52:39 pm
content: Quote from: Alexei.Polkhanov on November 12, 2015, 08:11:49 ami like this program. for the fun of it, i order random unmarked toroids from china and calculate the "AL" using the unknown core tool + a lousy LCR. very very useful

author: mstck
author_rank: Contributor
timestamp: November 13, 2015, 03:27:56 am
content: Hi,I recently bought some toroids from this vendor:http://www.debcoelectronics.com/shop/Powdered-Iron.213/1I think he might have the toroids you require.