5083	2010-09-12 05:42:38	g3zoh	Coupling Coefficients
Message	Date	From	Subject
Hi all, I am using Elsie 2.36 (Student Edition) to look at HF bandpass filters for a homebrew receiver project. These filters are nothing elaborate - just top-coupled double tuned circuits with link windings for low impedance input/output. The inductors are wound on T50-6 toroids and consist of between 12 and 24 turns depending on the band. The link windings are 2 or 3 turns wound tightly over the earthy end of the primary. Now the question - Is there a "rule of thumb" for the coupling coefficient (K) that should be input to Elsie when using the "manual entry" screen to set the inductance values? Many thanks in advance for any advice. Brian G3ZOH
5084	2010-09-12 05:56:29	Leon Heller	Re: Coupling Coefficients
On 12/09/2010 13:40, g3zoh wrote: > Hi all, I am using Elsie 2.36 (Student Edition) to look at HF bandpass filters for a homebrew receiver project. These filters are nothing elaborate - just top-coupled double tuned circuits with link windings for low impedance input/output. > > The inductors are wound on T50-6 toroids and consist of between 12 and 24 turns depending on the band. The link windings are 2 or 3 turns wound tightly over the earthy end of the primary. > > Now the question - Is there a "rule of thumb" for the coupling coefficient (K) that should be input to Elsie when using the "manual entry" screen to set the inductance values? It'll be high for toroids; I usually use 0.9. You can try different values, of course, and get a feel for the effect. Leon -- Leon Heller G1HSM
5085	2010-09-12 08:05:36	chuck adams	Re: Coupling Coefficients
On Sun, 2010-09-12 at 13:56 +0100, Leon Heller wrote: > > On 12/09/2010 13:40, g3zoh wrote: > > Hi all, I am using Elsie 2.36 (Student Edition) to look at HF > bandpass filters for a homebrew receiver project. These filters are > nothing elaborate - just top-coupled double tuned circuits with link > windings for low impedance input/output. > > > > The inductors are wound on T50-6 toroids and consist of between 12 > and 24 turns depending on the band. The link windings are 2 or 3 turns > wound tightly over the earthy end of the primary. > > > > Now the question - Is there a "rule of thumb" for the coupling > coefficient (K) that should be input to Elsie when using the "manual > entry" screen to set the inductance values? > > It'll be high for toroids; I usually use 0.9. You can try different > values, of course, and get a feel for the effect. > > Leon > -- > Leon Heller > G1HSM > There is a way to measure the coupling coefficient. Measure L_p, inductance of the primary, with the secondary open-circuited. Short-circuit the secondary leads and measure the inductance again. Call this L'_p. k = sqrt(1 - L'_p/L_p) If you want to see the derivation of this, look in Electronic Communication Techniques (4ed is my copy) by Paul H. Young pages 20-34 with the technique on page 31. There are probably several hundred other EE books that also show this tidbit. The mutual inductance, M, is given by M = k * sqrt(L_p * L_s). L_p being the primary of the transformer and L_s the secondary. This should work reversing the primary and secondary. There will be some frequency dependence due to the permeability of the core material for something like a toroid and must inductance meters use a relatively low frequency for measurements. I hope this helps. FYI chuck -- chuck adams, k7qo http://www.k7qo.net/ chuck.adams.k7qo@gmail.com /* no comment */
5086	2010-09-12 09:12:34	g3zoh	Re: Coupling Coefficients
Many thanks Le
5087	2010-09-12 09:50:16	Leon Heller	Re: Coupling Coefficients
On 12/09/2010 17:12, g3zoh wrote: > Many thanks Leon and Chuck for the helpful advice. I thought the bandpass filter bit of this project would be boring but am finding it fascinating, trying different configurations with Elsie - a very fine piece of software. How did varying it affect the characteristics? SPICE is useful as well, I design the filter or whatever with ELSIE then simulate the whole circuit with SPICE. 73, Leon -- Leon Heller G1HSM
5089	2010-09-12 10:44:27	victor	Re: Coupling Coefficients
I have read in a number of places that calculating K by measuring the primary inductance while shorting the secondary is theoretically right but in practice is not very accurate (the loss at the shorted inductor causes a significant error). A preferred higher accuracy calculation of K is recommended by doing this: Measure the inductance of the primary and secondary in series, and then interchange the connections of one winding for a second reading. Apply the equation below: M=1/4 * (Lseries+ - Lseries-) For coupling, measure the primary and secondary separately then apply the equation below: k = M / (sqrt(Lp * Ls)) Victor - 4Z4ME > > There is a way to measure the coupling coefficient. Measure L_p, > inductance of the primary, with the secondary open-circuited. > Short-circuit the secondary leads and measure the inductance > again. Call this L'_p. > > k = sqrt(1 - L'_p/L_p) > > If you want to see the derivation of this, look in Electronic > Communication Techniques (4ed is my copy) by Paul H. Young pages > 20-34 with the technique on page 31. > > There are probably several hundred other EE books that also > show this tidbit. > > The mutual inductance, M, is given by M = k * sqrt(L_p * L_s). > L_p being the primary of the transformer and L_s the secondary. > > This should work reversing the primary and secondary. There will > be some frequency dependence due to the > permeability of the core material for something like a toroid > and must inductance meters use a relatively low frequency for > measurements. > > I hope this helps. > > FYI > > chuck > > > > -- > chuck adams, k7qo > http://www.k7qo.net/ > chuck.adams.k7qo@... > > /* no comment */ >
5093	2010-09-12 14:06:43	g3zoh	Re: Coupling Coefficients

5094	2010-09-12 14:32:06	Leon Heller	Re: Coupling Coefficients

5096	2010-09-13 07:41:07	Glen Leinweber	Re: Coupling Coefficients
Was curious about this too, in doing some tapped Hartley coils on toroids, so measured mutual coupling on a T50-6 iron-powder core. Mutual Coupling came out at 0.3, which seems kinda low. I believe permeability of this core is less than ten - for higher permeability cores (like ferrites) the coupling is much closer to one. When turns-ratio is large, with a link of only 2 or 3 turns, you can only get matching approximate. I believe Wes did a pdf note on link coupling in the the "files" section on the EMRFD website.
5097	2010-09-13 10:46:19	w7zoi	Re: Coupling Coefficients
Hi Glen, and group, Yea, I discussed this problem in a note on my web page, w7zoi.net. It was posted on 19April09 in the "designs and experiments" section with the title "Transformer Coupled LC Bandpass Filters." The measurements presented were done with a vector network analyzer. However, a VNA is not necessary. A return loss bridge with a homebrew signal source and either an AD8307 based power meter or a 50 Ohm terminated oscilloscope will provide enough information to do a good job with the matching. Be careful to avoid generator harmonic problems. I've also measured some coupling coefficients on T50-6 power iron cores and sometimes they are as low as 0.3. I was surprised at the time. I found that k depended upon the position of the link with respect to the main coil. Coupling coefficient is a parameter that should be measured, for a "rule of thumb" is often in severe error. In the "app note" of April 09 mentioned above, a parallel resistance parameter was specified. This is one of those things that is buried within a filter design and the fellow or gal using an existing computer program never sees the parameter. A point of the posted note was that this parameter is experimentally useful. I now display this parameter in the programs that I have written for my own use. For example, Rp is in the lower left corner of DTC08, which is part of the most recent versi
6117	2011-04-13 17:59:29	KK7B	Coupling Coefficients
For broadband transformers, coupling coefficients above .95 are expected and useful. But old air core networks often used coupling as one of the network variables, and it was supposed to be less than 0.5. Some of the more efficient vacuum tube amplifiers used variable link coupling with large air core inductors. They often achieved efficiencies higher than many of today's broadband amplifiers. It's a different way to design a network--fundamentally narrow-band--but that's how folks used to put clean signals on the air with relatively simple transmitters. This is a great topic...I'm enjoying the discussions. Rick