Possibility of using cfl ferrite toroid cores as low pass filter for hf band - Page 1
Forum section: electronics / rf-microwave

author: Dom13c
author_rank: Regular Contributor
timestamp: July 23, 2018, 07:15:50 pm
content: I am trying to put together the Michigan mighty mite transmitter for doing some Qrp with it. I've gathered everything but the ferrite cores needed to construct the low pass filter. I was wondering if I could use green ferrite cores from old cfls. Buying them online from suppliers like Amidon is quite expensive for me. If possible mention the upper and lower limit of the working frequency of those toroids salvaged from the cfls.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 23, 2018, 07:49:24 pm
content: What LPF?http://www.qsl.net/wb5ude/kc6wdk/transmitter.htmlI don't know offhand what those green cores are, if ferrite or powdered iron. Good bet they're a low frequency material, whatever it is, unsuitable for RF (unless what you were looking for is a resistor).If you mean an LPF before an antenna, that needs to be low loss, stable value inductors, which ferrite toroids are unsuitable for. Powdered iron types are good, the ones intended for RF (the ones intended for power switching are terrible). Otherwise, there's always air core coils.Tim

author: HB9EVI
author_rank: Frequent Contributor
timestamp: July 23, 2018, 07:55:43 pm
content: Unknown toroids are a plain source of trouble. Without knowing the properties, you cannot match the needed usage for it.spare you the time, working on that and directly get the right toroids, as lpf you would choose powered iron toroids from Micrometals, material -2 for up to 10MHz and material -6 for above

author: Dom13c
author_rank: Regular Contributor
timestamp: July 24, 2018, 03:09:07 am
content: Sorry.😝😝 I forgot to mention that they are for LPF before antenna as you've mentioned. Ain't it even possible to utilize those cores as RFC?

author: Dom13c
author_rank: Regular Contributor
timestamp: July 24, 2018, 03:20:41 am
content: What you've said is absolutely true. Can you mention a place in India where I can get those T13-9 or T20 type toroids for a better and cheaper price than many other online suppliers.( don't mention mouser , in our country they've sort of taken pledge to rip our pockets off. They take near about 1$ each for every single rf toroid , being a hobbyist it do is pretty much expensive to me)

author: xaxaxa
author_rank: Regular Contributor
timestamp: July 24, 2018, 03:37:58 am
content: Quote from: Dom13c on July 24, 2018, 03:20:41 amAliexpress

author: HB9EVI
author_rank: Frequent Contributor
timestamp: July 24, 2018, 08:38:58 am
content: I ordered already some powered iron toroids on aliexpress; the majority was fine, but I've got some T50-6 which absolutley don't reach the Q they should have according to the specs. It pretty much seems that even with toroids you have to watch out what you get.btw. what is material -9? I don't find in the micrometals list.don't go too small with the toroids. Not only it's a pain winding them, also the achieveable Q is lower than with the bigger ones; personally I don't go smaller than T37-xx

author: Dom13c
author_rank: Regular Contributor
timestamp: July 25, 2018, 04:23:46 am
content: Quote from: HB9EVI on July 24, 2018, 08:38:58 am

author: vk4ffab
author_rank: Frequent Contributor
timestamp: July 26, 2018, 02:30:27 am
content: The michigan mighty mite is only going to be putting out 1/2 a watt at most, just use molded inductors of a similar inductance if they gave you numbers, if not just design a low pass filter around fixed value inductors you have in your parts box.I notice in your other post you have difficulty finding toriods, you can get them from Mini Kits in Aus, you will want iron cores in type 2 and 6 and ferrite cores in type 43 for your amp transformers.https://www.minikits.com.au/