On Tuesday, July 12, 2016 at 1:47:56 AM UTC-4, Kevin Foster wrote:
> Would it be possible to build a single transistor Hartley oscillator by
> substituting a pancake (spiral) coil for each leg of the center-tapped
> inductor, and then placing one coil flat on top of the other so the
> insulation between them takes the place of the cap?
>
> If the current in each coil is made to flow opposite to the other, could
> their proximity to each other also be used to vary the overall inductance?
>
> Kevin Foster
You'll end up with fairly large amount of indeterminate capacitance and lower-Q coils and tank circuit. The lower Q means less frequency stability, drift and wander due to external influences that results from a weaker phase-frequency gradient. If you don't care about any of that, go ahead with it, you can still get a working oscillator.
Reply by Tim Wescott●July 13, 20162016-07-13
On Tue, 12 Jul 2016 15:47:07 +1000, Kevin Foster wrote:
> Would it be possible to build a single transistor Hartley oscillator by
> substituting a pancake (spiral) coil for each leg of the center-tapped
> inductor, and then placing one coil flat on top of the other so the
> insulation between them takes the place of the cap?
>
> If the current in each coil is made to flow opposite to the other, could
> their proximity to each other also be used to vary the overall
> inductance?
>
> Kevin Foster
If you let the headset bearings on your hog get really loose, is that a
Harley oscillator?
--
Tim Wescott
Control systems, embedded software and circuit design
I'm looking for work! See my website if you're interested
http://www.wescottdesign.com
Reply by Phil Hobbs●July 13, 20162016-07-13
On 07/13/2016 01:47 PM, John Devereux wrote:
> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> writes:
>
>> On 07/12/2016 09:51 AM, piglet wrote:
>>> On 12/07/2016 06:47, Kevin Foster wrote:
>>>> Would it be possible to build a single transistor Hartley oscillator by
>>>> substituting a pancake (spiral) coil for each leg of the center-tapped
>>>> inductor, and then placing one coil flat on top of the other so the
>>>> insulation between them takes the place of the cap?
>>>>
>>>> If the current in each coil is made to flow opposite to the other, could
>>>> their proximity to each other also be used to vary the overall
>>>> inductance?
>>>>
>>>> Kevin Foster
>>>
>>> I don't see why not. I have built such one transistor oscillators using
>>> two axial dogbone ferrite inductors side-by-side. Mine had an external
>>> capacitor but coil self capacitances might do. I found I could get
>>> suprisingly big separations like 1cm before oscillation ceased.
>>>
>>> piglet
>>>
>>
>> The mutual inductance of a Hartley reduces the impedance seen at the
>> base, but otherwise it's just like a Colpitts. The k factor of an
>> air-core solenoid is no better than 0.7 or so which is pretty poor for
>> an autotransformer.
>>
>> You can build an oscillator by just hanging an emitter follower on the
>> right tank circuit. The resistance in the emitter circuit makes the
>> input resistance negative.
>
>
> This one is my favorite
>
> <http://ee.devereux.me.uk/uhf-vfo.png>
>
> ....it's just a jfet soldered to a piece of wire
>
> I think it worked without the tuning cap but it was >25 years ago so
> I might be wrong there...
>
Yeah, but you cheated and built a Hartley. ;)
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
Reply by John Devereux●July 13, 20162016-07-13
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> writes:
> On 07/12/2016 09:51 AM, piglet wrote:
>> On 12/07/2016 06:47, Kevin Foster wrote:
>>> Would it be possible to build a single transistor Hartley oscillator by
>>> substituting a pancake (spiral) coil for each leg of the center-tapped
>>> inductor, and then placing one coil flat on top of the other so the
>>> insulation between them takes the place of the cap?
>>>
>>> If the current in each coil is made to flow opposite to the other, could
>>> their proximity to each other also be used to vary the overall
>>> inductance?
>>>
>>> Kevin Foster
>>
>> I don't see why not. I have built such one transistor oscillators using
>> two axial dogbone ferrite inductors side-by-side. Mine had an external
>> capacitor but coil self capacitances might do. I found I could get
>> suprisingly big separations like 1cm before oscillation ceased.
>>
>> piglet
>>
>
> The mutual inductance of a Hartley reduces the impedance seen at the
> base, but otherwise it's just like a Colpitts. The k factor of an
> air-core solenoid is no better than 0.7 or so which is pretty poor for
> an autotransformer.
>
> You can build an oscillator by just hanging an emitter follower on the
> right tank circuit. The resistance in the emitter circuit makes the
> input resistance negative.
This one is my favorite
<http://ee.devereux.me.uk/uhf-vfo.png>
...it's just a jfet soldered to a piece of wire
I think it worked without the tuning cap but it was >25 years ago so
I might be wrong there...
--
John Devereux
Reply by Robert Baer●July 13, 20162016-07-13
Phil Hobbs wrote:
> On 07/12/2016 09:51 AM, piglet wrote:
>> On 12/07/2016 06:47, Kevin Foster wrote:
>>> Would it be possible to build a single transistor Hartley oscillator by
>>> substituting a pancake (spiral) coil for each leg of the center-tapped
>>> inductor, and then placing one coil flat on top of the other so the
>>> insulation between them takes the place of the cap?
>>>
>>> If the current in each coil is made to flow opposite to the other, could
>>> their proximity to each other also be used to vary the overall
>>> inductance?
>>>
>>> Kevin Foster
>>
>> I don't see why not. I have built such one transistor oscillators using
>> two axial dogbone ferrite inductors side-by-side. Mine had an external
>> capacitor but coil self capacitances might do. I found I could get
>> suprisingly big separations like 1cm before oscillation ceased.
>>
>> piglet
>>
>
> The mutual inductance of a Hartley reduces the impedance seen at the
> base, but otherwise it's just like a Colpitts. The k factor of an
> air-core solenoid is no better than 0.7 or so which is pretty poor for
> an autotransformer.
>
> You can build an oscillator by just hanging an emitter follower on the
> right tank circuit. The resistance in the emitter circuit makes the
> input resistance negative.
>
> Cheers
>
> Phil Hobbs
>
I IMAGINE you are REFLECTING a POSITIVE observation.
Reply by Robert Baer●July 13, 20162016-07-13
Phil Hobbs wrote:
> On 07/12/2016 09:51 AM, piglet wrote:
>> On 12/07/2016 06:47, Kevin Foster wrote:
>>> Would it be possible to build a single transistor Hartley oscillator by
>>> substituting a pancake (spiral) coil for each leg of the center-tapped
>>> inductor, and then placing one coil flat on top of the other so the
>>> insulation between them takes the place of the cap?
>>>
>>> If the current in each coil is made to flow opposite to the other, could
>>> their proximity to each other also be used to vary the overall
>>> inductance?
>>>
>>> Kevin Foster
>>
>> I don't see why not. I have built such one transistor oscillators using
>> two axial dogbone ferrite inductors side-by-side. Mine had an external
>> capacitor but coil self capacitances might do. I found I could get
>> suprisingly big separations like 1cm before oscillation ceased.
>>
>> piglet
>>
>
> The mutual inductance of a Hartley reduces the impedance seen at the
> base, but otherwise it's just like a Colpitts. The k factor of an
> air-core solenoid is no better than 0.7 or so which is pretty poor for
> an autotransformer.
>
> You can build an oscillator by just hanging an emitter follower on the
> right tank circuit. The resistance in the emitter circuit makes the
> input resistance negative.
>
> Cheers
>
> Phil Hobbs
>
Are you positive?
Reply by Robert Baer●July 13, 20162016-07-13
Tauno Voipio wrote:
> On 12.7.16 10:26, Robert Baer wrote:
>> Tauno Voipio wrote:
>>> On 12.7.16 08:47, Kevin Foster wrote:
>>>> Would it be possible to build a single transistor Hartley oscillator by
>>>> substituting a pancake (spiral) coil for each leg of the center-tapped
>>>> inductor, and then placing one coil flat on top of the other so the
>>>> insulation between them takes the place of the cap?
>>>>
>>>> If the current in each coil is made to flow opposite to the other,
>>>> could
>>>> their proximity to each other also be used to vary the overall
>>>> inductance?
>>>>
>>>> Kevin Foster
>>>
>>>
>>> Hardly.
>>>
>>> The tapped coil (tap is usually lower than center) is an
>>> auto-transformer. You need considerable mutual inductance between the
>>> parts.
>> * Why? How much?
>> lose proximity of the 2 coils can give decent mutual inductance. and
>> splitting the larger inductance of the Hartley into two coils that
>> sandwich the smaller can further increase the mutual inductance.
>>
>>>
>>> You need a lumped capacitor to make a tuned circuit of the coil and
>>> capacitor. I doubt that there is an useful resonance with your idea.
>> * Really? the above sandwich scheme can bring in a fair amount of
>> capacitance. Using thin high-K insulation (tape) will further add to
>> that, with minimal increase of leakage inductance.
>> May be rather good even in the mid-DC frequencies (~200Mhz region) and
>> up.
>>
>>>
>>
>
> If you distribute the capacitance alon the coil, you'll get a
> transmission line instead of a tuned circuit.
>
Never heard of using a shorted or open stub (of a transmssion line)
in oscillators?
Reply by Tim Wescott●July 12, 20162016-07-12
On Tue, 12 Jul 2016 11:56:29 -0400, Phil Hobbs wrote:
> On 07/12/2016 09:51 AM, piglet wrote:
>> On 12/07/2016 06:47, Kevin Foster wrote:
>>> Would it be possible to build a single transistor Hartley oscillator
>>> by substituting a pancake (spiral) coil for each leg of the
>>> center-tapped inductor, and then placing one coil flat on top of the
>>> other so the insulation between them takes the place of the cap?
>>>
>>> If the current in each coil is made to flow opposite to the other,
>>> could their proximity to each other also be used to vary the overall
>>> inductance?
>>>
>>> Kevin Foster
>>
>> I don't see why not. I have built such one transistor oscillators using
>> two axial dogbone ferrite inductors side-by-side. Mine had an external
>> capacitor but coil self capacitances might do. I found I could get
>> suprisingly big separations like 1cm before oscillation ceased.
>>
>> piglet
>>
>>
> The mutual inductance of a Hartley reduces the impedance seen at the
> base, but otherwise it's just like a Colpitts. The k factor of an
> air-core solenoid is no better than 0.7 or so which is pretty poor for
> an autotransformer.
>
> You can build an oscillator by just hanging an emitter follower on the
> right tank circuit. The resistance in the emitter circuit makes the
> input resistance negative.
In fact, circuit designers have been doing this inadvertently for
decades, if not a century or so (I think the same thing can happen with a
cathode follower in a toob circuit).
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
I'm looking for work -- see my website!
Reply by Tim Wescott●July 12, 20162016-07-12
On Tue, 12 Jul 2016 09:45:18 +0300, Tauno Voipio wrote:
> On 12.7.16 08:47, Kevin Foster wrote:
>> Would it be possible to build a single transistor Hartley oscillator by
>> substituting a pancake (spiral) coil for each leg of the center-tapped
>> inductor, and then placing one coil flat on top of the other so the
>> insulation between them takes the place of the cap?
>>
>> If the current in each coil is made to flow opposite to the other,
>> could their proximity to each other also be used to vary the overall
>> inductance?
>>
>> Kevin Foster
>
>
> Hardly.
>
> The tapped coil (tap is usually lower than center) is an
> auto-transformer. You need considerable mutual inductance between the
> parts.
>
> You need a lumped capacitor to make a tuned circuit of the coil and
> capacitor. I doubt that there is an useful resonance with your idea.
(A) You do not need a tapped coil to make a Hartley. You do not need any
mutual inductance. You can argue about calling it a Hartley, but a two-
coil one-cap oscillator still perks along just fine.
(B) You do not need a lumped cap. That's not to say that the OP's idea
will work, but anything that gives the right amount of phase shift will
work. Stepping away from Hartley oscillators, there's plenty of
oscillators out there that use tuned circuits made of microstrip or coax.
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--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
I'm looking for work -- see my website!
Reply by John S●July 12, 20162016-07-12
On 7/12/2016 12:47 AM, Kevin Foster wrote:
> Would it be possible to build a single transistor Hartley oscillator by
> substituting a pancake (spiral) coil for each leg of the center-tapped
> inductor, and then placing one coil flat on top of the other so the
> insulation between them takes the place of the cap?
>
> If the current in each coil is made to flow opposite to the other, could
> their proximity to each other also be used to vary the overall inductance?
>
> Kevin Foster
A tapped inductor is not required. Two uncoupled inductors will suffice
just as two uncoupled capacitors does with the Colpitts.
See figure 4.7 in Experimental Methods in RF Design by Wes Hayard, Rick
Cambell, and Bob Larkin. ISBN # 0-87259-879-9.