My colleague Steve has taken an interest in Very Low Frequency radio reception. I have been helping Steve locate information on Pot Cores suitable for the front end of his communications receiver. This web page is a repository of the links found when searching for the information on ferrites suitable for VLF tuned circuits which may be of use to other amateurs. I have also included some web links for Iron Powder Toroidal cores.
VLF Project Links
The Active Loop Converter at VLF (by Lloyd Butler, VK5BR)
http://users.tpg.com.au/users/ldbutler/ActiveloopVLF.htm
A LowFER Receiver Using a "Software" IF (by Lyle Koehler, K0LR)
http://www.qsl.net/k0lr/SW-RX/sw-rx.htm
LOWFER and WC2XSR/13 on 166.5 KC QRSS and 168 KC LSB (by Ralph Hartwell, W5JGV)
http://w5jgv.com/lowfer_166r5.htm
A 400 Watt Low Frequency SSB Linear Amplifier (by Ralph Hartwell, W5JGV)
http://w5jgv.com/400w-ssb-amp/index.htm
136kHz technical pages - homebrew stuff (by Rik Strobbe, ON7YD)
http://www.qsl.net/on7yd/136brew.htm
200W 136 kHz transmitter (by Claudio Pozzi, IK2PII)
http://www.qsl.net/ik2pii/lf/tx200w.htm
A single board 300W transmitter (by David Bowman, G0MRF)
http://www.g0mrf.freeserve.co.uk/300w.htm
A 137 & 500 kHz Class-D Kilowatt (by Jay Rusgrove, W1VD)
http://www.w1vd.com/137-500KWTX.html
375W Carrier Class-D AM Transmitter Breadboard For 160 and 75 Meters (by Jay Rusgrove, W1VD)
http://www.w1vd.com/375wattclassD.html
400W Carrier Class-E Transmitter (by Steve Cloutier, WA1QIX)
http://www.classeradio.com/classe.htm
Radio Amateur working on VLF Project
Steve Rawlings, GW4ALG
http://www.alg.demon.co.uk/radio/136/home.htm
Dave Pick, G3YXM
David Bowman, G0MRF
http://www.g0mrf.freeserve.co.uk
R. J. Edwards, G4FGQ: the TOROID program download page
http://www.btinternet.com/~g4fgq.regp
Claudio Pozzi, IK2PII
Ralph Hartwell, W5JGV
Jay Rusgrove, W1VD: Experimental LF Station WD2XNS
Steve Cloutier, WA1QIX
http://www.classeradio.com/wa1qix.htm
Ferrite Information for VLF Tuned Circuits
Standard air wound coil formers are not really suitable for VLF tuned circuits where inductances in the order of 30 mH are required for a 100 pF tuning capacitor. The number of turns may exceed several thousand and extremely fine wire is needed to fit the coil in the confines of a shielded RF coil former. The number of windings and the fine gauge of the wire will have an adverse effect on the Q of the tuned circuit.
An alternative is to use a Pot Core. Jaycar and Altronics in Australia both sell a FX-2240 equivalent 26 mm OD 16 mm High Pot Core. The Altronics Pot Core uses F5A material and the Jaycar Pot Core uses FP4 material. Presumably these are equivalent although it is difficult to find Pot Core material information as each manufacturer has their own material identification scheme and there is little cross reference information on the web that I could find.
F5A material has an effective permeability of around 2000 and the AL of the core is about 6000 nH per turns squared. For a 30 mH inductor this amounts to SQRT(30,000,000/6,000) or about 70 turns. The F5A material is designed for a Switch Mode Power Supply (SMPS) operating at 200KHz, so should have low enough loss at 100KHz to produce a tuned circuit with reasonable Q. The material is probably not very linear, but at the low signal levels found in the front end of a VLF receiver, I doubt this would present a problem.
Manufacturers Web Sites
Ferroxcube
Micrometals Iron Powder Cores
Magnetics Inc
TT Electronics MMG Magnetic Solutions
Cosmo Ferrites Limited
TDK - Product Catalog
http://www.tdk.com/product-catalog.php
Magnetic Product - Xiang Ying ferrite Cores
http://www.magneticproduct.com/Ferrite%20Core.htm
Yuxiang - Magnet-Tech
NiCera - Nippon Ceramic Co Ltd
http://www.nicera.co.jp/indexe.htm
Toroid Information
N8IE - Ferrite and Iron Powder Core Information
http://home.woh.rr.com/n8ie/coreinfo.htm
Iron Powder Toroidal Cores
http://www.bytemark.com/products/iptcres.htm
Specs for T130-2 RF Toroids
http://toroids.info/T130-2.php
Pot Core Information
MMG Ferrite Pot Core data
http://www.mmgca.com/catalogue/MMG-Ferrite-PT2.pdf
Magnetics Pot Core Information
http://www.mag-inc.com/pdf/2006_Ferrite_Catalog/2006_Pot_RS_DS_Cores.pdf
Cosmo Ferrites - Material Cross-Reference Chart
http://www.cosmoferrites.com/product/matcomp.html
Dave Cushman - G8MZY - ETD Series Ferrite Cores
http://www.dave-cushman.net/elect/etdcores.html
Far East Electronics (They have info on FP4 material if you can manage to download the data sheet)
Jaycar - Transformer Pot Core - Cat No. LF1060 (Material FP4 - Equiv FX2240) (Bobbin LF1062)
http://www.jaycar.com.au/.....snip.....
Altronics - Pot Core Transformer Pair - Cat No L5300 (Material F5A - Equiv FX2240) (Bobbin L5305)
http://www.altronics.com.au/index.asp?area=item&id=L5300