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Re: Extra coil



Original poster: "rheidlebaugh by way of Terry Fritz <twftesla-at-qwest-dot-net>" <rheidlebaugh-at-zialink-dot-com>

NOT correct:  the crystal set used the natural resonant frequency of the
coil with no capacitor. The tap slide on the coil was the only tuning for
phase 1 crystal sets. Capacitor tuning came later and was much more
convinent than the coil tuning. Coil tuning was a trial and error play every
time you wanted to change and every day you started to recieve.1/2 to 1 hr..
   Robert  H

> From: "Tesla list" <tesla-at-pupman-dot-com>
> Date: Fri, 08 Feb 2002 16:40:08 -0700
> To: tesla-at-pupman-dot-com
> Subject: Re: Extra coil
> Resent-From: tesla-at-pupman-dot-com
> Resent-Date: Fri, 8 Feb 2002 17:16:07 -0700
> 
> Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <m.j.watts-at-massey.ac.nz>
> 
> Hi Robert,
> Thanks for the details........
> 
> On 8 Feb 2002, at 11:51, Tesla list wrote:
> 
>> Original poster: "rheidlebaugh by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <rheidlebaugh-at-zialink-dot-com>
>> 
>> The original crystal set was made with a 100 T coil with a sliding tap for
>> tuning. The coil was placed between earth ground and an antenna. A diode in
>> series witk a high impedance earphone was shunt across the coil. The load
>> reduced the Q of the coil and caused broad banding. A second version added a
>> capacitor (variable ) in series with the coil and a seperate output winding
>> of about 25 turns to the load. This improved the Q and tunability. A later
>> version added an extra winding between the two. About 75 turns with a 600 pf
>> capacitor across it forming a parallel tuned circuit between the input coil
>> and the output coil.The volume encreased enough to drive a high impedance
>> speaker( no longer made) with enough volume for a small room of people to
>> hear.The extra tuned coil was connected to nothing,Just a hi-Q coil between
>> input and output. No one moved the transmitter or the antenna to add volume.
> 
> V1 sounds as if you had a fixed capacitor for tuning and it was
> tapped across varying portions of the coil. Correct? The change in
> tap point alone would have caused the Q of the circuit to vary.
> V2 sounds as if it had a degree of antenna matching introduced
> by the variable cap between the antenna and coil. Also, a reduction
> in circuit loading.
> Without knowing the station/s frequency/s and inductance of the
> 75 turn coil it's difficult to know what action what is essentially a
> bandstop filter between input tuned circuit and output coil was doing
> but I bet that with 600pF across it, the Q wasn't all that high. But
> that isn't quite the same thing as having an unshunted resonator in
> series with the antenna and main tuned circuit. I'm having difficulty
> relating that to Tesla's magnifying system (my problem, not yours ;).
> 
> The little setup in my study uses a single resonator with no
> tuning cap between the aerial wire and ground. I designed it to be
> self-resonant in conjunction with the antenna to a station
> transmitting around 1.2MHz so the short antenna was used more
> effectively (just a few feet of wire arranged as a short top-hat
> vertical running up the wall and part-way across the ceiling). Even
> with a load, the circuit is very selective. The higher power
> transmitter I mentioned transmits on 567kHz.
> 
> I guess I will have to put another branch for experimentation
> into the in-tray. I see at least a degree of antenna matching in your
> setup.
> 
> Regards,
> Malcolm
> 
>> Robert  H 
>>> From: "Tesla list" <tesla-at-pupman-dot-com>
>>> Date: Thu, 07 Feb 2002 18:32:44 -0700
>>> To: tesla-at-pupman-dot-com
>>> Subject: Re: Extra coil
>>> Resent-From: tesla-at-pupman-dot-com
>>> Resent-Date: Thu, 7 Feb 2002 18:53:54 -0700
>>> 
>>> Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>"
>>> <m.j.watts-at-massey.ac.nz>
>>> 
>>> Hi Robert,
>>> 
>>> On 7 Feb 2002, at 12:06, Tesla list wrote:
>>> 
>>>> Original poster: "rheidlebaugh by way of Terry Fritz
>>> <twftesla-at-qwest-dot-net>" <rheidlebaugh-at-zialink-dot-com>
>>>> 
>>>> Just a thought as you 2 are discussing the extra coil. Before we had a
> tube
>>>> radio we had crystal sets that, at best, tuned 2 stations at once with low
>>>> volume. When we added an extra coil (3 coil system) the volume went up and
>>>> we tuned only one station at a time. The extra coil increased the total Q
>>>> and made the tuning narrow. Is it not likely that a similar effect is seen
>>>> in the TC with the extra coil?  More power going into one frequency
> band and
>>>> less power into the unwanted harmonic losses.
>>>> Robert  H 
>>> 
>>> Good question. First question from me: what was the exact arrangement
>>> of the crystal set before and after the extra coil was added? I
>>> suggest that in the first case, the load was coupled too tightly to
>>> the tuned circuit. In the second, the coupling was rendered looser by
>>> virtue of less total inductance under the influence of the coupling
>>> loop. Is there any reason that couldn't have been done with the
>>> single circuit? Presumably, the aerial was the same in both cases so
>>> no more power was available to the circuit.
msnip...