[HBR] HBR - BFO progress

[Chris Howard w0ep]

Mr Smith, your BFO page and your other HBR pages have been
very helpful to me.  That's what prompted me to get started
with the BFO.

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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