[HBQRP] Elmer 101 Part 2

[Darrel Swenson]

Hi Guys...

After a quick survey, I'm not sure where everyone is...  I know of 4 people
who are building along, 2 who are not, and ???  If you are building along
let me know (and let me know where you are so we don't get too far ahead of
anyone.)

Now for the VFO.  Remember the Elmer 101 material was written for the SW40+,
so a few of the parts are different for the SW30+ and SW20+...  The
component name (C4, etc) should stay the same for all the bands, but the
value may (or may not) change with the different bands.  I've listed the
changes below:

part     value
         SW40+    SW30+     SW20+
c2       47 pF
c3       10 pF
c4     2700 pF   3300 pF   1200 pF
c5     2700 pF   3300 pF   1200 pF
c6     3300 pF
c8       82 pF    120 pF     27 pF
c9       10 pF
c10     270 pF
c103    .01 mF
c105    .01 mF
D1      MV1662
D2      1N4148
L1     wind this
Q2      2N4401
R15     47K ohms
R16     22K ohms
R17    2.2K ohms (follow installation instructions on diagram instead of
silkscreen)
R18      1M ohms

Follow the directions on page 3 and page 12 of the manual for winding L1
(and the other toroids.)
For the SW40+ it's 25 turns on the larger yellow .50 inch diameter core.
~18 inches of wire.
For the SW30+ it's 29 turns on the larger yellow .50 inch diameter core.
~20 inches of wire.
For the SW20+ it's 23 turns on one of the yellow .37 inch diameter cores.
~14 inches of wire.

I've had a couple of questions about wire size and length.  IF I understand
toroid theory right, I think you can use the same number of TURNS of about
any wire size from about 20 to 30 gauge and get the SAME inductance on the
same core.

The question is many turns of a wire gauge will fit on a size toroid, and
how long of a chunk to start with for a wire size and toroid size.  The
SW30+ directions say 18" of 24 gauge wire.  (I think this may be a typo left
over from the SW40+ original manual.)  The 18" of the wire supplied with my
kit will only get 27 or 28 turns.  (At least one other SW30+ builder had the
same problem.)  Diz's toroid calculator says about 20" for 29 turns on a .50
diameter core.  I used 20" and it worked out fine.

A good source for toroid information is:
http://partsandkits.com/
http://partsandkits.com/xtoroids.html
http://partsandkits.com/ttoroids.html

A fun experiment would be to wind 29 turns of 22 gauge, 24 gauge, 26 gauge,
28 gauge, and 30 gauge on 5 different toroids and then measure the
inductance... (or resonant frequency of the same VFO circuit.)  I think they
will be within a few hertz of each other.  The spacing between turns will
probably alter the outcome more than the wire size.

To perform part of the tests on page 6 you will need an RF probe.  Here is
some information on them.  (If you don't want to take time to build one now,
that's OK.  RF Probes are a good troubleshooting tool.)
http://www.norcalqrp.org/phprint.php
http://www.io.com/~n5fc/rfprobe2.htm
http://www.io.com/~n5fc/rfprobe1.htm

OK... all the components are in... apply power and check for smoke!

When following the test, the wire end of R15, or R16 is the best place to
measure the base of Q2.  If you installed R17 according to the notes instead
of the silkscreen, it is the best place to measure the emitter of Q2.

Here is what I got on the tests:

My SW40+ VFO was running 2.89 MHz.
I measured 2.5V Peak-Peak on the base of Q2 with my Oscilloscope.  My RF
Probe measured 1.7V.
I measured 2.7V DC on the emitter of Q2 with the VFO running.
I measured 2.3V DC on the emitter of Q2 with the VFO running.
I measured 1.7V DC on the emitter of Q2 with L1 shorted.
I measured 2.3V DC on the emitter of Q2 with L1 shorted.  0.6V as predicted.

My SW30+ VFO was running 2.45 MHz.
I measured 3.2V Peak-Peak on the base of Q2 with my Oscilloscope.  My RF
Probe measured 2.0V.
I measured 3.0V DC on the emitter of Q2 with the VFO running.
I measured 2.3V DC on the emitter of Q2 with the VFO running.
I measured 1.7V DC on the emitter of Q2 with L1 shorted.
I measured 2.3V DC on the emitter of Q2 with L1 shorted.  0.6V as predicted.

My SW20+ VFO was running 5.03 MHz.
I measured 1.5V Peak-Peak on the base of Q2 with my Oscilloscope.  My RF
Probe measured 2.1V.
I measured 3.0V DC on the emitter of Q2 with the VFO running.
I measured 2.3V DC on the emitter of Q2 with the VFO running.
I measured 1.7V DC on the emitter of Q2 with L1 shorted.
I measured 2.3V DC on the emitter of Q2 with L1 shorted.  0.6V as predicted.

Take time to read the VFO description and questions on pages 7 to 14.  Glen
and Mike did an excellent job with this, probably more information than you
will ever need :)  I recommend reading this several times in small segments.
There is a lot of theory and if your brain works anything like mine, it will
overload fairly fast.  (I'm on my 6th or 7th reading, and I still don't get
all of it!!!)

If anyone has questions or is having problems... please post to the list and
we will try to find an answer.

Melt Solder...  Darrel... K0AWB