{"id":1910,"date":"2012-02-02T10:48:00","date_gmt":"2012-02-01T23:48:00","guid":{"rendered":"https:\/\/www.homebrewradio.us\/blog\/2012\/02\/02\/hard-core-wisdom-and-ideas-on-toroids\/"},"modified":"2025-07-21T12:25:15","modified_gmt":"2025-07-21T02:25:15","slug":"hard-core-wisdom-and-ideas-on-toroids","status":"publish","type":"post","link":"https:\/\/www.homebrewradio.us\/blog\/2012\/02\/02\/hard-core-wisdom-and-ideas-on-toroids\/","title":{"rendered":"Hard Core! Wisdom and Ideas on Toroids"},"content":{"rendered":"
\"\"<\/a>Gerard ZS5AAC<\/div>\n

This morning the BITX20 mailing list has an interesting discussion of toroidal cores. I especially like Gerard’s use of the cores from old CFL bulbs. Farhan wraps it up with a great explanation of why we use ferrite cores in broadband transformers: <\/span>
——————————<\/span>
<\/span>Over the years I built quite a few BITX’s. In the beginning I used the<\/span>
toroids salvaged from CFL lamps. These worked quite well for the mixer<\/span>
coils. For the filter coils I used 6mm bakelite slug tuned coils that were<\/span>
stripped from old PYE radios. Wonder if anybody else experimented<\/span>
along the<\/span> same lines. I build my BITX’s Manhattan style and they work from the start<\/span> with few minor tunings. Happy BITX’ing, Gerard, ZS5AAC.<\/span>
—————————————<\/span>
<\/span>Bob<\/span>
The purists may attack us on this, but what you propose is very<\/span>
possible. I have<\/span> been using a wooden-core toroid for several years as part of an antenna<\/span> tuner.<\/span><\/p>\n

http:\/\/qrp.webhop.net\/Pictures\/Webcam-1293651325.jpeg<\/span><\/a><\/span>
<\/a>
http:\/\/qrp.webhop.net\/Pictures\/Webcam-1295140555.jpeg<\/span><\/a><\/span> <\/p>\n

I’m also using small plastic and wooden beads as toroid cores for<\/span>
several other<\/span> projects. Half inch long sections cut from thick-wall (schedule-40 or<\/span> schedule-80)<\/span> PVC pipe also makes good toroidal forms. Beauty of using non-metallic<\/span> cores is<\/span> that the core can be split to allow winding wire through the slot <\/span>without having<\/span> to thread it through the hole.<\/span><\/p>\n

http:\/\/qrp.webhop.net\/Pictures\/Webcam-1289957121.jpeg<\/span><\/a><\/span> <\/span>= 1.4 uh<\/span><\/p>\n

Bending an inductor back on itself in toroidal form concentrates the<\/span>
magnetic<\/span> field in the center, whether the core is metallic or non-metallic. This<\/span> gives you<\/span> similar self-shielding properties when using either type core material.<\/p>\n

<\/span> With<\/span> non-metallic cores you no longer have to worry about core saturation, so<\/span> running high current finals is not a problem.<\/span><\/p>\n

Key to doing this is being able to measure inductance of 5 turns, 10 turns,<\/span>
and 20 turns, so you can calculate and plot the effective AL of your wooden<\/span> core toroids. Once you know this value you can make up a chart to tell how<\/span> many turns are required for a specific inductance.<\/span><\/p>\n

Twisting wires together to make a transmission-line for bifilar or<\/span>
trifilar windings<\/span> is interesting because the impedance of that transmission line might affect<\/span> performance of your transformer. It may require a bit of experimentation<\/span> with an SWR bridge to tell when you have the best balance between twist<\/span> pitch,<\/span> wire diameter, and insulation thickness.<\/span>
Arv – K7HKL<\/span>
———————————————<\/span><\/p>\n

<\/span>Robert, Arv,<\/span>
There are two types of coils used in the bitx – the broadband<\/span>
transformers and the RF coils in the bandpass filter and oscillators.<\/span>
You could easily substitute the rf and vfo\/bfo coils with just about<\/span>
any kind of coil – as long as you are hitting the same inductance and<\/span>
Q. But there is a catch : a few years ago, I finally got down to<\/span>
measuring the Q of the nylon tap washers that I had originally used.<\/span>
The q was quite modest at 70. Wes made independent measurements with<\/span> similar results (his paper is on <\/span>www.w7zoi.net<\/span><\/a> <\/a>under technical stuff).<\/span> In short, for good performance use good old air coils wound on a<\/span>
cylindrical formers if you don’t use toroids.<\/span><\/p>\n

About the broadband transformers. These need a material that has very<\/span>
low loss, very high permeability. The reasoning is like this :<\/span>
1. We need an transformer’s inductance such that the reactance is<\/span>
at least 200 ohms at the lowest frequency. This puts the inductance at<\/span>
around 30uH at 4MHz.<\/span>
2. If we achieve 30uH through lots of turns (say 100), each turn will<\/span>
exhibit capacitance with it’s neighbor and the large number of turns<\/span>
will add up the capacitance so that the coil will provide enough<\/span>
self-capacitance to resonate at an unintended frequency in HF leading<\/span>
to pretty bad mixer performance.<\/span>
3. The only way out would be to achieve the required reactance with<\/span>
lower number of turns. This means using ferrites.<\/span>
– farhan VU2ESE<\/span><\/span>
<\/span>
Our book: “SolderSmoke — Global Adventures in Wireless Electronics”http:\/\/soldersmoke.com\/book.htm<\/a>Our coffee mugs, T-Shirts, bumper stickers: http:\/\/www.cafepress.com\/SolderSmoke<\/a>Our Book Store: http:\/\/astore.amazon.com\/contracross-20<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

Gerard ZS5AAC This morning the BITX20 mailing list has an interesting discussion of toroidal cores. I especially like Gerard’s use of the cores from old CFL bulbs. Farhan wraps it up with a great explanation of why we use ferrite cores in broadband transformers: ——————————Over the years I built quite a few BITX’s. In the … Continue reading “Hard Core! Wisdom and Ideas on Toroids”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[84,28,66,60,68,276],"tags":[],"class_list":["post-1910","post","type-post","status-publish","format-standard","hentry","category-amplifier-theory","category-bitx20","category-farhan","category-hayward-wes","category-india","category-south-africa"],"_links":{"self":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/1910","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/comments?post=1910"}],"version-history":[{"count":1,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/1910\/revisions"}],"predecessor-version":[{"id":1912,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/posts\/1910\/revisions\/1912"}],"wp:attachment":[{"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/media?parent=1910"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/categories?post=1910"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.homebrewradio.us\/blog\/wp-json\/wp\/v2\/tags?post=1910"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}