On 1/18/2015 11:27 AM, Tim Williams wrote:> "amdx" <nojunk@knology.net> wrote in message > news:m9gobk$77s$1@dont-email.me... >> My end thought/goal is to match a very high Q crystal radio tank >> circuit at resonance. The R at resonance could be over 1 Megaohm. >> So, I'm trying to find out, do I need a primary impedance of 4 times >> 1 megaohm? >> Then I would add a secondary winding with taps to reflect back the >> 2000 ohm headphone. > > !!?? > > Rewind the damned tank. It's just another transformer!No need to be angry. If you don't want to play with me, go home. The tank is designed to tune the AM band 550KHz to 1700kHz with a variable cap. The design also is built with minimum losses. The working numbers are around 240uh with a 15pf to 365pf variable capacitor. Did you have a different design in mind?> Better still, if you need impedance transformation in the end, construct > the tank as two coupled resonators, each with different taps suiting > their external connections. Coupling can be a bridging C, L or > proximity (k and stray C). >Yep, but you still need to match the headphones to one of the resonating high Q inductors, or the diode, witch also is match best matched to the inductor.> Tim >
The 4 times rule for matching transformer impedance
Started by ●January 17, 2015
Reply by ●January 18, 20152015-01-18
Reply by ●January 18, 20152015-01-18
On 1/18/2015 11:43 AM, bloggs.fredbloggs.fred@gmail.com wrote:> On Saturday, January 17, 2015 at 9:46:34 PM UTC-5, amdx wrote: > <snip dumb question> > > Why don't you try to find what the Bible says about it, retard. >Do you know anything about the 4 times rule? Mikek
Reply by ●January 18, 20152015-01-18
On Sat, 17 Jan 2015 20:46:23 -0600, amdx <nojunk@knology.net> wrote:>Hi all, > I have always heard and used the 4 times rule for the impedance of a >transformer winding. >Example; >To match 50 ohms to 400 ohms, the primary inductance should be 200 ohms >at the lowest frequency of interest. 4 x 50 = 200 ohms XL. >Tonight I'm searching for a reference for the 4 times. >I found this; > > >http://www.scribd.com/doc/116333646/The-Four-Times-the-Impedance-Rule-for-Broadband-RF-Transformer-Windings-Where-Does-it-Originate#scribd > > The math is more than I can handle, but his conclusion is; > > "In this article we have analyzed the impedance transformation >properties of broadband RF transformers taking into account the finite >inductive reactance of their primary and secondary windings. We have >shown that the �four times the impedance� design guideline for the >inductive reactance of the transformer windings yields an impedance >transformation that departs from its �ideal� behavior by no more than 3%, >and introduces a phase shift of no more than 14 degrees." > > Now some may quibble with the 3% and 14 degrees as being picked out >of the air (me) but something needs to be picked >and those numbers seems reasonable. > > Also, they reference Broadband RF transformers, > >Can I assume that scales to audio transformers? > > MikekAudio transformers generally spec a frequency range based on the 3dB-down points, assuming the primary and secondary are both connected to their specified resistive source/loads. -3 dB is 30% down. -- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●January 18, 20152015-01-18
On 18.1.15 20:03, amdx wrote:> On 1/18/2015 11:27 AM, Tim Williams wrote: >> "amdx" <nojunk@knology.net> wrote in message >> news:m9gobk$77s$1@dont-email.me... >>> My end thought/goal is to match a very high Q crystal radio tank >>> circuit at resonance. The R at resonance could be over 1 Megaohm. >>> So, I'm trying to find out, do I need a primary impedance of 4 times >>> 1 megaohm? >>> Then I would add a secondary winding with taps to reflect back the >>> 2000 ohm headphone. >> >> !!?? >> >> Rewind the damned tank. It's just another transformer! > > No need to be angry. If you don't want to play with me, go home. > > The tank is designed to tune the AM band 550KHz to 1700kHz with a > variable cap. The design also is built with minimum losses. > The working numbers are around 240uh with a 15pf to 365pf variable > capacitor. > Did you have a different design in mind?There is a simple way: Take the signal out from a tap in the tank coil, instead of from the top. If you want to keep the tank Q, you should also avoid coupling the antenna directly to the tank top end. Your tank circuit impedance level (or loaded Q) will vary in a wide range along with the tuning, anyway. -- -TV
Reply by ●January 18, 20152015-01-18
On 1/18/2015 1:54 PM, John Larkin wrote:> On Sat, 17 Jan 2015 20:46:23 -0600, amdx <nojunk@knology.net> wrote: > >> Hi all, >> I have always heard and used the 4 times rule for the impedance of a >> transformer winding. >> Example; >> To match 50 ohms to 400 ohms, the primary inductance should be 200 ohms >> at the lowest frequency of interest. 4 x 50 = 200 ohms XL. >> Tonight I'm searching for a reference for the 4 times. >> I found this; >> >> >> http://www.scribd.com/doc/116333646/The-Four-Times-the-Impedance-Rule-for-Broadband-RF-Transformer-Windings-Where-Does-it-Originate#scribd >> >> The math is more than I can handle, but his conclusion is; >> >> "In this article we have analyzed the impedance transformation >> properties of broadband RF transformers taking into account the finite >> inductive reactance of their primary and secondary windings. We have >> shown that the �four times the impedance� design guideline for the >> inductive reactance of the transformer windings yields an impedance >> transformation that departs from its �ideal� behavior by no more than 3%, >> and introduces a phase shift of no more than 14 degrees." >> >> Now some may quibble with the 3% and 14 degrees as being picked out >> of the air (me) but something needs to be picked >> and those numbers seems reasonable. >> >> Also, they reference Broadband RF transformers, >> >> Can I assume that scales to audio transformers? >> >> Mikek > > Audio transformers generally spec a frequency range based on the > 3dB-down points, assuming the primary and secondary are both connected > to their specified resistive source/loads. -3 dB is 30% down. > >Hmm... if the graph in the paper holds true, at 3db down the phase angle is 32*. Not that I would hear that. Thanks, Mikek --- This email has been checked for viruses by Avast antivirus software. http://www.avast.com
Reply by ●January 18, 20152015-01-18
On 1/18/2015 2:40 PM, Tauno Voipio wrote:> On 18.1.15 20:03, amdx wrote: >> On 1/18/2015 11:27 AM, Tim Williams wrote: >>> "amdx" <nojunk@knology.net> wrote in message >>> news:m9gobk$77s$1@dont-email.me... >>>> My end thought/goal is to match a very high Q crystal radio tank >>>> circuit at resonance. The R at resonance could be over 1 Megaohm. >>>> So, I'm trying to find out, do I need a primary impedance of 4 times >>>> 1 megaohm? >>>> Then I would add a secondary winding with taps to reflect back the >>>> 2000 ohm headphone. >>> >>> !!?? >>> >>> Rewind the damned tank. It's just another transformer! >> >> No need to be angry. If you don't want to play with me, go home. >> >> The tank is designed to tune the AM band 550KHz to 1700kHz with a >> variable cap. The design also is built with minimum losses. >> The working numbers are around 240uh with a 15pf to 365pf variable >> capacitor. >> Did you have a different design in mind? > > There is a simple way: Take the signal out from a tap in the tank coil, > instead of from the top. If you want to keep the tank Q, you should also > avoid coupling the antenna directly to the tank top end. >yes, however would you not have a lower voltage on a tap meaning a lower drive to the headphones.> Your tank circuit impedance level (or loaded Q) will vary in a wide > range along with the tuning, anyway. >Absolutely, change the station and everything needs to be readjusted. Even the diode is characteristics are chosen depending on signal level. Thanks, Mikek --- This email has been checked for viruses by Avast antivirus software. http://www.avast.com
Reply by ●January 18, 20152015-01-18
On Sun, 18 Jan 2015 10:52:31 -0600, amdx wrote:> On 1/18/2015 3:42 AM, Tauno Voipio wrote: >> On 18.1.15 04:46, amdx wrote: >>> Hi all, >>> I have always heard and used the 4 times rule for the impedance of a >>> transformer winding. >>> Example; >>> To match 50 ohms to 400 ohms, the primary inductance should be 200 >>> ohms at the lowest frequency of interest. 4 x 50 = 200 ohms XL. >>> Tonight I'm searching for a reference for the 4 times. >>> I found this; >>> >>> >>> http://www.scribd.com/doc/116333646/The-Four-Times-the-Impedance-Rule-for-Broadband-RF-Transformer-Windings-Where-Does-it-Originate#scribd>>> >>> >>> >>> The math is more than I can handle, but his conclusion is; >>> >>> "In this article we have analyzed the impedance transformation >>> properties of broadband RF transformers taking into account the finite >>> inductive reactance of their primary and secondary windings. We have >>> shown that the “four times the impedance” design guideline for the >>> inductive reactance of the transformer windings yields an impedance >>> transformation that departs from its “ideal” behavior by no more than >>> 3%, >>> and introduces a phase shift of no more than 14 degrees." >>> >>> Now some may quibble with the 3% and 14 degrees as being picked out >>> of the air (me) but something needs to be picked and those numbers >>> seems reasonable. >>> >>> Also, they reference Broadband RF transformers, >>> >>> Can I assume that scales to audio transformers? >>> >>> Mikek >> >> >> The model applies to the low end of the frequency range. > > Yes, as I understand it, low end frequency response is the first to > degrade as the inductance of the winding is decreased. > > >> The high end is controlled by other phenomena. In a broadband >> transformer, the high end is effected by the length of the transmission >> line of the windings compared to the wavelength and associated phase >> shift. >> > I understand there is an effect increasing response of the high end > by the interwinding capacitance. > > >> For audio transformers, the formula is an usable approximation for the >> low end, although the leakage inductances of the windings will affect >> the results, adding attenuation and phase shift earlier when going >> toward the low end of the frequency range. >> > My end thought/goal is to match a very high Q crystal radio tank > circuit at resonance. The R at resonance could be over 1 Megaohm. > So, I'm trying to find out, do I need a primary impedance of 4 times > 1 megaohm?< snip > I would suggest that you tap the coil on the tank circuit, far enough down to match whatever audio transformer you can get (or possibly just your earphones). You have a tradeoff between a high impedance tapping point that'll have higher voltage to swamp out the diode drop but will be more difficult to match to, or a lower impedance tapping point that'll match better but will show more loss in the diode. -- www.wescottdesign.com
Reply by ●January 18, 20152015-01-18
On Sunday, January 18, 2015 at 12:50:14 PM UTC-5, DecadentLinuxUserNumeroUno wrote: <snip drivel> As per usual, you have no idea what you're talking about. Take your bubblegum education and go somewhere the idiots give your kind any credence.
Reply by ●January 18, 20152015-01-18
John Larkin wrote:
>
> Audio transformers generally spec a frequency range based on the
> 3dB-down points, assuming the primary and secondary are both connected
> to their specified resistive source/loads.
** The low frequency performance of an audio transformer is dominated by core saturation, so the lower -3dB point is level dependant. Honest makers spec this frequency when tested at half the rated power level.
The primary inductance of a tranny with laminated steel or permalloy core is high and non-linear, long as there is no air gap, so only rarely sets the -3dB point.
.... Phil
Reply by ●January 19, 20152015-01-19
