Norcal 20 Progress Report

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From: Dave Fifield (fifield@pacbell.net)
Date: Sat Dec 12 1998 - 08:26:07 EST


Hi Folks,

Just thought I'd update you all with the latest news on the
Norcal 20 front. As you can guess, things have been moving
fairly slowly, for a variety of reasons.

I can announce that the development of the circuitry is now
complete!!! We have had, in addition to myself, three other
well known competent QRP'ers building/testing/pulling to bits/
using on air/etc. (beta testing) the final prototypes for the
last month and a bit.

I'd really like to recognize these folks publicly, for without
them, the NC20 would have had several design anomalies/foibles
that you guys would not have wanted, that's for sure! The fine
upstanding NC20 beta testers are (in no particular order):

   Mike Gipe, K1MG
   Dave Meacham, W6EMD
   Gary Surrency, AB7MY

In particular, these gentlemen found and cured two (what I would
consider) major problems with the radio as well as lots of smaller,
well worthwhile changes.

The two major issues were a) the transmitter had a tendency to
be a bit unstable at certain power level settings and b) the VFO
drifted too much for all our tastes! We solved a) by first hunting
down what stage was responsible for the problem (no mean feat) and
then applying some subtle design changes to cure the instability
tendencies.

The VFO drift cure, b), was a looooooooonnnnnnngggggg process!
It involved many, many hours of tests with various ratios
of different types of capacitors to get the right combination that
would work best. Initially, the drift was in the order of over a KHz
in the first half hour, then several more over the next hour or so.
After Dave M. had applied his magic to it, we had a combination of
polystyrene and C0G capacitance that gave us drift in the low 100's
of Hz for the first half-hour, the 30-50Hz drift per hour thereafter.

My particular rig now has imperceptible drift after the initial
warm-up. Ahhh, yes, the warm-up...well, since the RX is designed
to handle large signals properly, it has to dissipate some heat, that
heat slowly warms the rig by several degrees over the first half-hour.
There's no stopping it - we just had to minimize its effect on the
VFO, which we have done, and all is well.

I won't bore you with all the small changes we have made, just mention
a few - pads to allow an ON/OFF switch to be added, an "idiot" diode
is now built-in, volume change, paddle swapover....the list goes on...

I took my proto into work today and put it on the mega-machine
($65K HP spectrum analyzer!) It tells the brutal truth! Well, I
was very pleased with the results, and I'm sure you all will be too.
This is just about the cleanest QRP radio I've ever seen....no joking.
All the harmonics are 70dB or more below the fundamental and all the
other spurs are 53dB or more below the carrier. This was at 5.75W
output. At 5W output, everything is just a bit cleaner than this.

I have put the analyzer plots on my www site for you to peruse if
you want to. They are at http://home.pacbell.net/fifield/NC20.html
(my pages start at http://home.pacbell.net/fifield - there are a
few other ham things on there as well....take a look if you like).

Now we have a complete design/bill-of-materials, we have to order
the final boards and components and then we're done! Phew!! That
doesn't sound like much, but really, there's quite a lot to do
still. I'm anxiously awaiting the final metalwork to come through
too....should be fine...the previous version had all the holes in
exactly the right places, but the metal was the wrong thickness.

More later....Doug et al, do you want to add anything?

Cheers,
Dave Fifield, AD6A


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