[HBR] HBR - BFO progress

[B. Smith]

Hi Chris
  Please

On 1/5/2014 8:06 PM, Chris Howard w0ep wrote:
>
> I decided to investigate
> the Hartley to see what the inductor tap requirements were.
> I figured that the Hartley was an old-time circuit and
> if those guys could wind one maybe I could too as long as
> I could get the specifications.  I have an inductance/capacitance
> meter, an o-scope, frequency counter, generator... I ought
> to be able to do it if those guys could :-)
>
> I looked around and found one statement that the Hartley
> tap needed to be 1/5th to 1/3rd from the cold end.The other thing was to go through some inductance/capacitance
> combinations on the assumption that the 50 pF BFO control
> was enough to move the frequency X amount either way.
>
> I did end up rewinding my coil today.  I take the
> tuning slug out and use a long thin machine screw as an
> axle.  I wrapped the screw with some blue masking tape
> to get it to run in the middle of the coil form; a couple
> of washers and a nut put a clamping action from each
> end of the coil form.  Then I put
> the tail end of the machine screw in a hand drill which
> has a little handle bob on the side.  I can mount the drill
> horizontal in the bench vice and crank the drill with one
> hand while guiding the wire with the other hand.  I upped my
> turns count about 10% and the new coil is looking better.
>
> Just for posterity, a coil of about 8k-9k mH with a tap
> at 25% up from the cold end is what I was aiming for.
> It didn't seem to matter if the cold end went on the
> form first or last.
>
> My plan is to get the inductance in the neighborhood, then put
> on the right amount of capacitance + 1/2 of the control capacitance
> to get things at the desired frequency. I can fiddle with the
> tuning slug in the coil to trim things up.
>
> Chris
> w0ep
>
>
> On 1/5/2014 10:36 AM, B. Smith wrote:
>> I highly recommend that the builder do the BFO first. You will get your feet wet and solve a major problem with construction.  My best luck has been with a colpits oscillator but others were tried See:
>> (http://k4che.com/HBR/BFO%20Coil%20Page%201and%20photos/BFO%20Coil%20Page%20%201.htm)
>> k4che
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