Arvid Evans <arvevans@...>
After reding over today's posts...here are a couple of thoughts and
1) The manufacturer and model number for the faucet washer used in
BITX20 coils is probably much ado about a triviality. The requirement
for air-core (or nylon core, to be more correct) toroid coils in your
BITX20 is a reference to the shape and to the absence of ferrite
material in the magnetic field. I suspect that if you wanted you
could use 'slices' from the body of a plastic ball-point pen. I used
1/4 inch wide slices from a piece of 1/2 inch PVC pipe (a bit larger
than the faucet washers, but also required a few less turns). No, I
don't know what effect the different dielectric constant of the PVC
had on the result.
2) Many years ago I obtained some PCB material that is quite thin
and flexible. My method for making the "pads" is to punch them out of
this material with a conventional paper punch (the pliers shaped type
you can buy for a couple of USD in many local stores). I sometimes
punch out a handfull when I have a few free minutes (it makes a great
distraction during those boring commercials on US Television), or if
none are immediately available I will punch out just what I need as I
build a circuit.
At times I have made pads from thicker PCB material by just punching
them out from PCB scrap(and from used boards when parts have all been
removed) by using the larger lever-operated paper punch on my desk.
Also, in the US Harbor Freight sells a compound-action pliers type
punch (about $10 USD) complete with different sized dies, see
<www.harborfreight.com> and search for "punch".
FYI: My "pads" using the thin PCB material measure 1.4 PF between the
circuit connection and underlying PCB substrata. I'm using "Super
Glue" to stick them down.
3) Yes, when I am in a hurry, like assembling my first BITX20, I
resort to point-to-point self-supported wiring...the UGLY method. It
is quick and effective, but nearly impossible to repair if the
defective part is two or three layers deep in the rats-nest of
4) My initial BITX20 effort did not use the LM-386 AF amp. Instead
I just used a 741 Op-Amp and relied on headphones-only for the audio
output. I guess I neatly sidstepped the schematic error regarding the
wrong pin being indicated for the + voltage! ;-) Since then I have
added an NPN (2N3904) driving an NPN-PNP (2N3904 & 2N3906) pair for
1/2 watt of audio to the speaker.
Maybe I am different but I see Farhan's elegant design as very
interesting because it allows the builder to match up his particular
incantation of the rig with the contents of his junk box.
My BITX40 is coming along quite well. Several modules have been
assembled and tested with just the IF filter, VFO, and the linear amp
left to finish. I am waiting for an order to be delivered from "Dan's
Small Parts" before I can continue. My junk box became severly
depleted of the more commonly used parts!