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Question about toroid vs. air core coil.
Greetings,
As a newbie to RF building, I have noticed that some instructions tell you how to wind the coil, and they give you the value of the coild as well... In my scenario, the inductor in question is a .72uhy which the directions state to use 17 turns of #30 around a toroid. I don't have the requested toroid, so I was just going to wind a .72uhy inductor around a 1/2W 5M ohm resistor. This will just the same right? Whether its a .72 on a toroid, or a .72 on a resistor... they are both the same, correct? Thanks for your help. James Shrum - KC9FFX |
"J Shrum" wrote in message ... Greetings, As a newbie to RF building, I have noticed that some instructions tell you how to wind the coil, and they give you the value of the coild as well... In my scenario, the inductor in question is a .72uhy which the directions state to use 17 turns of #30 around a toroid. I don't have the requested toroid, so I was just going to wind a .72uhy inductor around a 1/2W 5M ohm resistor. This will just the same right? Whether its a .72 on a toroid, or a .72 on a resistor... they are both the same, correct? Thanks for your help. James Shrum - KC9FFX There will be differences in the coil Q and sheilding (toroids are self-shielding and often have better Q than air-wound). I don't have the vaguest notion of what your circuit is, but you can probably get away with it, at least until you've ordered the right coil form. |
"J Shrum" wrote in message ... Greetings, As a newbie to RF building, I have noticed that some instructions tell you how to wind the coil, and they give you the value of the coild as well... In my scenario, the inductor in question is a .72uhy which the directions state to use 17 turns of #30 around a toroid. I don't have the requested toroid, so I was just going to wind a .72uhy inductor around a 1/2W 5M ohm resistor. This will just the same right? Whether its a .72 on a toroid, or a .72 on a resistor... they are both the same, correct? Thanks for your help. James Shrum - KC9FFX There will be differences in the coil Q and sheilding (toroids are self-shielding and often have better Q than air-wound). I don't have the vaguest notion of what your circuit is, but you can probably get away with it, at least until you've ordered the right coil form. |
"J Shrum" ) writes:
Greetings, As a newbie to RF building, I have noticed that some instructions tell you how to wind the coil, and they give you the value of the coild as well... In my scenario, the inductor in question is a .72uhy which the directions state to use 17 turns of #30 around a toroid. I don't have the requested toroid, so I was just going to wind a .72uhy inductor around a 1/2W 5M ohm resistor. This will just the same right? Whether its a .72 on a toroid, or a .72 on a resistor... they are both the same, correct? Well maybe not. They'd be the same inductance, but other factors come into play. What's the application? In various wideband applications, a core material is specified to give it broadband response. There might be a specific reason for using a toroid, because of it's self-shielding qualities. If you're building in a small space, it may be counting on that self-shielding. Michael VE2BVW |
"J Shrum" ) writes:
Greetings, As a newbie to RF building, I have noticed that some instructions tell you how to wind the coil, and they give you the value of the coild as well... In my scenario, the inductor in question is a .72uhy which the directions state to use 17 turns of #30 around a toroid. I don't have the requested toroid, so I was just going to wind a .72uhy inductor around a 1/2W 5M ohm resistor. This will just the same right? Whether its a .72 on a toroid, or a .72 on a resistor... they are both the same, correct? Well maybe not. They'd be the same inductance, but other factors come into play. What's the application? In various wideband applications, a core material is specified to give it broadband response. There might be a specific reason for using a toroid, because of it's self-shielding qualities. If you're building in a small space, it may be counting on that self-shielding. Michael VE2BVW |
Depending on the app you might luck out but I doubt it. Order the toroid
but while you're waiting you might try increasing the number of turns. Experiment and improvise, that makes the hooby more intersting. Also try to read up on air inductiors and those on toriods, I assume it;s ferrite. 73 Hank WD5JFR "J Shrum" wrote in message ... Greetings, As a newbie to RF building, I have noticed that some instructions tell you how to wind the coil, and they give you the value of the coild as well... In my scenario, the inductor in question is a .72uhy which the directions state to use 17 turns of #30 around a toroid. I don't have the requested toroid, so I was just going to wind a .72uhy inductor around a 1/2W 5M ohm resistor. This will just the same right? Whether its a .72 on a toroid, or a .72 on a resistor... they are both the same, correct? Thanks for your help. James Shrum - KC9FFX |
Depending on the app you might luck out but I doubt it. Order the toroid
but while you're waiting you might try increasing the number of turns. Experiment and improvise, that makes the hooby more intersting. Also try to read up on air inductiors and those on toriods, I assume it;s ferrite. 73 Hank WD5JFR "J Shrum" wrote in message ... Greetings, As a newbie to RF building, I have noticed that some instructions tell you how to wind the coil, and they give you the value of the coild as well... In my scenario, the inductor in question is a .72uhy which the directions state to use 17 turns of #30 around a toroid. I don't have the requested toroid, so I was just going to wind a .72uhy inductor around a 1/2W 5M ohm resistor. This will just the same right? Whether its a .72 on a toroid, or a .72 on a resistor... they are both the same, correct? Thanks for your help. James Shrum - KC9FFX |
I am trying to make the Micronaut. I have put it together manhattan style
(which I find soooo much easier). I have tried using the air core and a toroid I had... The trouble is at this point, is the thing won't oscillate. The only substitues I made was, instead of a 2n2222, i used a 2n3904... I also had to use 220pF caps instead of 270pF's for C1,C2 and C3. I have checked w/ a freq counter, and I see no oscillation coming of of any test points. Has anyone made this? http://imagenisp.ca/jsm/Tuna.html Thanks in advance. "J Shrum" wrote in message ... Greetings, As a newbie to RF building, I have noticed that some instructions tell you how to wind the coil, and they give you the value of the coild as well... In my scenario, the inductor in question is a .72uhy which the directions state to use 17 turns of #30 around a toroid. I don't have the requested toroid, so I was just going to wind a .72uhy inductor around a 1/2W 5M ohm resistor. This will just the same right? Whether its a .72 on a toroid, or a .72 on a resistor... they are both the same, correct? Thanks for your help. James Shrum - KC9FFX |
I am trying to make the Micronaut. I have put it together manhattan style
(which I find soooo much easier). I have tried using the air core and a toroid I had... The trouble is at this point, is the thing won't oscillate. The only substitues I made was, instead of a 2n2222, i used a 2n3904... I also had to use 220pF caps instead of 270pF's for C1,C2 and C3. I have checked w/ a freq counter, and I see no oscillation coming of of any test points. Has anyone made this? http://imagenisp.ca/jsm/Tuna.html Thanks in advance. "J Shrum" wrote in message ... Greetings, As a newbie to RF building, I have noticed that some instructions tell you how to wind the coil, and they give you the value of the coild as well... In my scenario, the inductor in question is a .72uhy which the directions state to use 17 turns of #30 around a toroid. I don't have the requested toroid, so I was just going to wind a .72uhy inductor around a 1/2W 5M ohm resistor. This will just the same right? Whether its a .72 on a toroid, or a .72 on a resistor... they are both the same, correct? Thanks for your help. James Shrum - KC9FFX |
"J Shrum" wrote in message ... I am trying to make the Micronaut. I have put it together manhattan style (which I find soooo much easier). I have tried using the air core and a toroid I had... The trouble is at this point, is the thing won't oscillate. The only substitues I made was, instead of a 2n2222, i used a 2n3904... I also had to use 220pF caps instead of 270pF's for C1,C2 and C3. I have checked w/ a freq counter, and I see no oscillation coming of of any test points. Has anyone made this? http://imagenisp.ca/jsm/Tuna.html Thanks in advance. "J Shrum" wrote in message ... Greetings, As a newbie to RF building, I have noticed that some instructions tell you how to wind the coil, and they give you the value of the coild as well... In my scenario, the inductor in question is a .72uhy which the directions state to use 17 turns of #30 around a toroid. I don't have the requested toroid, so I was just going to wind a .72uhy inductor around a 1/2W 5M ohm resistor. This will just the same right? Whether its a .72 on a toroid, or a .72 on a resistor... they are both the same, correct? Thanks for your help. James Shrum - KC9FFX Oh boy. When circuits get that small they cease being "simple" and start getting "subtle". Every componant value makes a difference. That having been said an air-wound inductor should be OK in that circuit, because that filter isn't very high Q to start with, so a Q=50 coil won't be that different from a Q=75 coil. In order for that circuit to oscillate the load at the crystal frequency needs to look like an inductor in parallel with a not-too-small resistance. I have _not_ run the numbers on the circuit with the values given or with your values, but decreasing the capacitance at C2 and C3 _will_ increase the amount of power that the antenna is trying to take from your oscillator, which may cause it not to start. This may be your problem. I'd start by trying 270pF caps, or putting 47pF caps in parallel with the 220s. If that doesn't do the trick start looking for a garden-variety wiring error (I've spent days in fruitless theoretical analysis because of a cold solder joint -- it ain't fun). Good luck. --------------------------------------------- Tim Wescott, KG7LI Wescott Design Services http://www.wescottdesign.com |
"J Shrum" wrote in message ... I am trying to make the Micronaut. I have put it together manhattan style (which I find soooo much easier). I have tried using the air core and a toroid I had... The trouble is at this point, is the thing won't oscillate. The only substitues I made was, instead of a 2n2222, i used a 2n3904... I also had to use 220pF caps instead of 270pF's for C1,C2 and C3. I have checked w/ a freq counter, and I see no oscillation coming of of any test points. Has anyone made this? http://imagenisp.ca/jsm/Tuna.html Thanks in advance. "J Shrum" wrote in message ... Greetings, As a newbie to RF building, I have noticed that some instructions tell you how to wind the coil, and they give you the value of the coild as well... In my scenario, the inductor in question is a .72uhy which the directions state to use 17 turns of #30 around a toroid. I don't have the requested toroid, so I was just going to wind a .72uhy inductor around a 1/2W 5M ohm resistor. This will just the same right? Whether its a .72 on a toroid, or a .72 on a resistor... they are both the same, correct? Thanks for your help. James Shrum - KC9FFX Oh boy. When circuits get that small they cease being "simple" and start getting "subtle". Every componant value makes a difference. That having been said an air-wound inductor should be OK in that circuit, because that filter isn't very high Q to start with, so a Q=50 coil won't be that different from a Q=75 coil. In order for that circuit to oscillate the load at the crystal frequency needs to look like an inductor in parallel with a not-too-small resistance. I have _not_ run the numbers on the circuit with the values given or with your values, but decreasing the capacitance at C2 and C3 _will_ increase the amount of power that the antenna is trying to take from your oscillator, which may cause it not to start. This may be your problem. I'd start by trying 270pF caps, or putting 47pF caps in parallel with the 220s. If that doesn't do the trick start looking for a garden-variety wiring error (I've spent days in fruitless theoretical analysis because of a cold solder joint -- it ain't fun). Good luck. --------------------------------------------- Tim Wescott, KG7LI Wescott Design Services http://www.wescottdesign.com |
Nevermind... I figured it out.
I did the stoopidest thing I could imagine. I wound the coils for the 20meter band, and I had a 40 meter crystal in it. :) I must say, this little toy sings! I can't even believe how great it sounds for having 1 transistor and a couple caps. Thanks again folks. DE KC9FFX "J Shrum" wrote in message ... I am trying to make the Micronaut. I have put it together manhattan style (which I find soooo much easier). I have tried using the air core and a toroid I had... The trouble is at this point, is the thing won't oscillate. The only substitues I made was, instead of a 2n2222, i used a 2n3904... I also had to use 220pF caps instead of 270pF's for C1,C2 and C3. I have checked w/ a freq counter, and I see no oscillation coming of of any test points. Has anyone made this? http://imagenisp.ca/jsm/Tuna.html Thanks in advance. "J Shrum" wrote in message ... Greetings, As a newbie to RF building, I have noticed that some instructions tell you how to wind the coil, and they give you the value of the coild as well... In my scenario, the inductor in question is a .72uhy which the directions state to use 17 turns of #30 around a toroid. I don't have the requested toroid, so I was just going to wind a .72uhy inductor around a 1/2W 5M ohm resistor. This will just the same right? Whether its a .72 on a toroid, or a .72 on a resistor... they are both the same, correct? Thanks for your help. James Shrum - KC9FFX |
Nevermind... I figured it out.
I did the stoopidest thing I could imagine. I wound the coils for the 20meter band, and I had a 40 meter crystal in it. :) I must say, this little toy sings! I can't even believe how great it sounds for having 1 transistor and a couple caps. Thanks again folks. DE KC9FFX "J Shrum" wrote in message ... I am trying to make the Micronaut. I have put it together manhattan style (which I find soooo much easier). I have tried using the air core and a toroid I had... The trouble is at this point, is the thing won't oscillate. The only substitues I made was, instead of a 2n2222, i used a 2n3904... I also had to use 220pF caps instead of 270pF's for C1,C2 and C3. I have checked w/ a freq counter, and I see no oscillation coming of of any test points. Has anyone made this? http://imagenisp.ca/jsm/Tuna.html Thanks in advance. "J Shrum" wrote in message ... Greetings, As a newbie to RF building, I have noticed that some instructions tell you how to wind the coil, and they give you the value of the coild as well... In my scenario, the inductor in question is a .72uhy which the directions state to use 17 turns of #30 around a toroid. I don't have the requested toroid, so I was just going to wind a .72uhy inductor around a 1/2W 5M ohm resistor. This will just the same right? Whether its a .72 on a toroid, or a .72 on a resistor... they are both the same, correct? Thanks for your help. James Shrum - KC9FFX |
As others have noted, it probably won't be quite the same, but may
work. But from the numbers you gave, I guess the specified core must be a T-20-2, no? Whatever the core, you should be able to get an estimate of the Q that the toroid form will give you (for example, see http://www.amidoncorp.com/aai_ironpowdercores.htm), and you can make an estimate of the Q you'll get at the same freq with an air-wound coil, just to be sure you're in the ballpark. For coils about as long as their diameter, the Q is roughly 100*(diam,inches)*sqrt(f,MHz) There are air-core coil programs around that will estimate the Q more accurately, and the self-resonant frequency as well...Reg Edwards has one, for example. -- If I guessed right on the toroid core, you'd probably see a Q around 120-140 in the 5-10MHz region for your coil, and you'd have to use an air core coil roughly half an inch diameter to get that. (My coil program tells me that 11 turns of #22AWG 3/8" ID and a bit under 1/2" long will give you the inductance you want, at a Qu of about 150.) Cheers, Tom "J Shrum" wrote in message ... Greetings, As a newbie to RF building, I have noticed that some instructions tell you how to wind the coil, and they give you the value of the coild as well... In my scenario, the inductor in question is a .72uhy which the directions state to use 17 turns of #30 around a toroid. I don't have the requested toroid, so I was just going to wind a .72uhy inductor around a 1/2W 5M ohm resistor. This will just the same right? Whether its a .72 on a toroid, or a .72 on a resistor... they are both the same, correct? Thanks for your help. James Shrum - KC9FFX |
As others have noted, it probably won't be quite the same, but may
work. But from the numbers you gave, I guess the specified core must be a T-20-2, no? Whatever the core, you should be able to get an estimate of the Q that the toroid form will give you (for example, see http://www.amidoncorp.com/aai_ironpowdercores.htm), and you can make an estimate of the Q you'll get at the same freq with an air-wound coil, just to be sure you're in the ballpark. For coils about as long as their diameter, the Q is roughly 100*(diam,inches)*sqrt(f,MHz) There are air-core coil programs around that will estimate the Q more accurately, and the self-resonant frequency as well...Reg Edwards has one, for example. -- If I guessed right on the toroid core, you'd probably see a Q around 120-140 in the 5-10MHz region for your coil, and you'd have to use an air core coil roughly half an inch diameter to get that. (My coil program tells me that 11 turns of #22AWG 3/8" ID and a bit under 1/2" long will give you the inductance you want, at a Qu of about 150.) Cheers, Tom "J Shrum" wrote in message ... Greetings, As a newbie to RF building, I have noticed that some instructions tell you how to wind the coil, and they give you the value of the coild as well... In my scenario, the inductor in question is a .72uhy which the directions state to use 17 turns of #30 around a toroid. I don't have the requested toroid, so I was just going to wind a .72uhy inductor around a 1/2W 5M ohm resistor. This will just the same right? Whether its a .72 on a toroid, or a .72 on a resistor... they are both the same, correct? Thanks for your help. James Shrum - KC9FFX |
"J Shrum" wrote in message ...
Nevermind... I figured it out. I must say, this little toy sings! I can't even believe how great it sounds for having 1 transistor and a couple caps. Thanks again folks. What frequency xtal(s) do you have? 73 de Jim, N2EY |
"J Shrum" wrote in message ...
Nevermind... I figured it out. I must say, this little toy sings! I can't even believe how great it sounds for having 1 transistor and a couple caps. Thanks again folks. What frequency xtal(s) do you have? 73 de Jim, N2EY |
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