Tv balun cores as LPF and BPF inductor former - Page 1
Forum section: electronics / rf-microwave

author: Dom13c
author_rank: Regular Contributor
timestamp: December 04, 2018, 06:24:42 pm
content: Due to the lack of proper amidon ferrite toroid I'm sort of forced to include normal TV baluns in my build of Beach 40 and BiTx 20 transceiver. Is it safe to make the inductors for BPF at the receiver's front end with these cores. Also, is it safe to assume that it would work fine if transmit lpf inductors are built with it.? Also what would be the result if a L match antenna coupler is made with this type of core? Would they be lossy?( All of my work will be in QRP power range, so high efficiency is wanted)

author: HB9EVI
author_rank: Frequent Contributor
timestamp: December 04, 2018, 08:38:09 pm
content: normally balun/unun toroids are made from ferrite material (high mu values), while frequency tuned toroids require powdered iron material (low mu values)so no, you cannot use those ferrite like materials from transformers or baluns; you need the micro metals powdered iron toroids material -2 for <10MHz and material -6 for above to build your LPF/BPF inductors

author: Dom13c
author_rank: Regular Contributor
timestamp: December 05, 2018, 10:11:47 am
content: Does the type-43 material works for the same purpose?

author: JohnPen
author_rank: Regular Contributor
timestamp: December 05, 2018, 10:41:00 am
content: This link provides information on the various toroid core materials including type 43.http://toroids.info/FT240-43.php

author: bd139
author_rank: Super Contributor
timestamp: December 05, 2018, 11:22:42 am
content: You can use the baluns as coupling transformers and RF chokes fine but I wouldn't use them for anything frequency dependent.This is about the one application where using exactly the right material is pretty essential. My TX has material 2 in the LPF, my commercial tuner is air cored (MFJ) and the homebrew one uses a big material 6 toroid.Amidon cores are quite cheap to source world wide if you know where to look. Might be worth joining GQRP Club or something and buying through club sales and get them to send DX. They cost literally nothing then.

author: cdev
author_rank: Super Contributor
timestamp: December 05, 2018, 01:37:36 pm
content: UHF/VHF TV baluns typically use Type 61 cores, very small ones. They have a very low initial permeability, around 125. If your transceiver is a VHF/UHF one they are best.For HF you would likely do much better with type 43 which is around 850. You can double them up. See the Elecraft switchable balun.Quote from: Dom13c on December 04, 2018, 06:24:42 pmFor use as inductors balun cores work but powdered iron toroids (typically 2 or 6) are the usual choice-Note that if you use a ferrite balun core, as an inductor you may need far fewer turns than you would on a toroid. Depending on how you wind it. This makes getting an exact value easier with a toroid.You can make averybroadband VHF/UHF transformer with a very small #61 balun core.For the bottom of HF or MW/LF I have used #73 material balun cores (as broadband transformers) with success.Seehttps://www.fair-rite.com/

author: HB9EVI
author_rank: Frequent Contributor
timestamp: December 05, 2018, 08:48:07 pm
content: once again: you cannot use ferrite materials, neither -43, -61 nor -77 for frequency tuned filtersit's common practice to use powdered iron toroids material -2 or -6 for HF, -6 or -10 for 50MHz, and air coils for 2m and above.the matter about tuned circuits is the Q of the components, so L and C; powered iron toroids can reach a Q upto 400 with bigger core material -6you cannot achieve that with ferrite materials, they don't have the properties for that.

author: Dom13c
author_rank: Regular Contributor
timestamp: December 08, 2018, 01:03:12 pm
content: Quote from: bd139 on December 05, 2018, 11:22:42 amAny idea about where to look for them in India. I've looked for them at mouser and digikey . There, the prices are awafully high. And other sites like kitsandparts.com offers them at a fair price but importing them from USA to India would add taxes to the price which won't be an easy exercise for me.

author: HB9EVI
author_rank: Frequent Contributor
timestamp: December 08, 2018, 01:37:56 pm
content: Which ones do you need?did you check on ebay already?

author: kerrsmith
author_rank: Regular Contributor
timestamp: December 08, 2018, 02:49:35 pm
content: Have a look on Aliexpress for toroids, I have purchased quite a few sets off here and found them to be priced quite reasonably and of good quality. I quite often make tuned circuits for my home made radios and so always need these powdered iron toroids and have found this a good source for them.You will have to wait for them to arrive of course which usually takes between two to three weeks but if you are not in a hurry to build something then this should be fine.I have built both filters and oscillators using these cores and they have always worked as expected - whether it be a number of turns giving a certain inductance or a number of turns giving an oscillator a certain frequency - they always give me the expected results (or at least close enough for me to then make a minor tweak with a capacitor to get the tuning or frequency spot on).

author: cdev
author_rank: Super Contributor
timestamp: December 08, 2018, 03:09:29 pm
content: How are they specified and how do the available materials map to the ones we're used to?Quote from: kerrsmith on December 08, 2018, 02:49:35 pm

author: Dom13c
author_rank: Regular Contributor
timestamp: December 08, 2018, 05:49:33 pm
content: Quote from: HB9EVI on December 08, 2018, 01:37:56 pmEbay sellers offers them at reasonable price but they are far from my country and the delivary charges including GST are excessive, say 4 times the price of the toroid itself. Type-2,and-6 would be just fine to fullfill my demands. And size 50 fits quite well as long as I need to build the lpf or bpf only let alone be the ATU s for which larger sizes are neded

author: cdev
author_rank: Super Contributor
timestamp: December 08, 2018, 11:05:27 pm
content: kitsandparts.com ?

author: kerrsmith
author_rank: Regular Contributor
timestamp: December 08, 2018, 11:21:35 pm
content: Quote from: cdev on December 08, 2018, 03:09:29 pmThey are listed in the same way as you would find on other sites such as T50-6 or T50-2 etc. I have no way to actually test the exact materials they are made from but I did run a few tests on the ones I received such as winding a number of turns and then measuring the inductance - they were very close to the predicted values.I have also created some bandpass filters using them and used my spectrum analyser to test them - again they were very close to my theoretical calculations.I have made several oscillators of various designs and all of them have worked and have also been really close in frequency to my design.For me personally this is exactly what I need - as long as I can go on toroids.info, choose the calculator for the specific toroid I need for the frequency I am working with, calculate the required number of turns and have my real life wound one come close to the theoretical values this is perfect.I have mainly built radios using them such as the Bitx20 and have found them to work just as I wanted them to.I hope this helps - if you are not in a rush I would definitely say give these ones a try and see if they work for you.

author: cdev
author_rank: Super Contributor
timestamp: December 09, 2018, 12:12:56 am
content: How do the prices compare to a low cost US vendor of the Fair-Rite, Micrometals, etc. magnetics like kitsandparts.com ? Are they a lot cheaper?

author: kerrsmith
author_rank: Regular Contributor
timestamp: December 09, 2018, 01:26:50 pm
content: Quote from: cdev on December 09, 2018, 12:12:56 amWhen looking for parts such as these I always try to find the cheapest option to start with - if I am attempting something new I am always happiest if it does not matter if I destroy a cheap component or two when experimenting.I found the parts on Aliexpress to be much more reasonable as they pretty much always have free shipping no matter what the order size.The price for components varies a lot so it is best to have a quick hunt around all the options first - I always check the UK sites as well as some USA ones but have often found that even if they are cheaper for the actual item the shipping wipes out all the savings. Sometimes the items they sell (such as electronic modules) are just the Chinese ones but at a much higher price - in this case you may as well just get them directly from China as you are going to get the same thing, just with a slightly longer wait.I would say just have a browse around, if you want to get a product with a good, well defined specification then pick one from a known supplier, if, however, you just want a cheap item to get started and see if your idea works then pick a cheap item first and see how you get on. If your circuit kind of works but you think the cheap item may not be that great then try a more expensive version to improve your design - this is what I tend to do.