SST design changes, round 1 (and thanks for the input!)

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From: L.Svec,W.Burdick (svecbrdk@well.com)
Date: Wed Oct 09 1996 - 04:50:09 EDT


Thanks everyone for many great suggestions on the SST. Based on these and
on discussions with Doug and other club members, I've modified the design
as follows:

1. The board will be laid out for controls and connectors, just like a
'40A or Sierra, except with smaller pots. I'll also design a custom case
for the rig. There may in fact be TWO kits:

        (1) the SST itself, with no controls, connectors, knobs or case;
        (2) the controls, connectors, knobs and case.

So, those who want to roll their own case and user interface will benefit
from a very inexpensive kit, while those who want the finished look of the
'40A or Sierra can have it their way, too! I just couldn't bring myself to
abandon my trademark, if not necessary, no-wires construction approach....

2. I've tossed out the VXO idea because Doug convinced me that some people
will have trouble finding a suitable air-variable cap. Instead, the rig
will use essentially the same tuning scheme as the '40A, with a
varactor-controlled VFO covering 20kHz nominally. You'll be able to set it
to any range you want with one resistor change, but I recommend staying at
20kHz to maintain good stability with the small VFO pot. At Walt Thomas's
recommendation, I'm going to use a small, conductive-plastic pot with
decent life expectancy. Finally, the VFO will use a slug-tuned inductor
(!)--no toroid, and no air-variable cap. I've found a combination of
components that gives very respectable stability, and this will be easy to
build as well as taking up minimum real-estate.

3. The SST will come stock with the parts to put it on 40 meters. The
same exact circuit will work on 80, 30, and 20 as well, but I can't predict
at this point which bands the club will have mod kits available for. One
possibility is that the mod kit would contain all the parts necessary to
put the rig on any of these other bands. It's too much work to maintain a
zillion different versions of the rig, especially with volunteer labor and
no coffee breaks. :)

4. Many people have asked for the PC board to be larger or smaller than
what I proposed. But the mean of the requests equals about what I wanted
anyway. Problem solved.

5. Many people have a suggested "Trail-Friendly Radio" (TFR) format for
the rig, as well as the ability to use the KC1 with it. Can't promise
either one of these, but I'll have alternatives ready.

*** TFR NOTE! ***

I'm hoping someone will help me out here by volunteering to design a
simple, small bracket that can be used to set the SST on the ground and aim
it up. The antenna connector should end up elevated enough to get an L
adapter onto it, which is then connected to the antenna coax (etc.). I
believe this is a reasonable compromise: I get to design a simple case in
the style that works best for the rig, and TFR advocates get a portable
bracket that puts it into TFR position. Perhaps the TFR bracket for the
SST can also have some other features, like a keyer paddle hang-on or a
place to store a log and pencils. Volunteers? Mechanical drawing skills
and access to a shop are required.

6. The antenna jack will be a BNC, by popular demand.

7. The custom case is likely to be around 1" tall, 2.5" wide, and 4.5"
deep--about the size of a medium-small HT. In fact I plan to use mine like
an HT in the field, with the possible addition of dot and dash buttons on
the top and bottom of the case. (If I make an accomodation for these
buttons, I'll make it reversible so lefties won't be left out.) The front
panel will have headphone jack, AF gain, and VXO pot. The rear panel will
have the BNC connector for the antenna, a small slide switch for on/off,
and a key jack. If you want an external DC power connector or RF gain
control, you'll have to add it yourself. There will be some room on the
rear panel for such things, but not a whole lot!

8. The PC board will have a cutout on one side into which you can nestle a
9V lithium battery. The power switch will be a SPDT type (on-on): in one
position it will enable the internal 9V battery, and the other position
will be OFF unless you opt to connect an external DC jack and wire it to
this side of the switch. In this case, you could also go with a
rechargeable 9V alkaline (from Radio Shack) or NiCad and add OR-ing diodes
to turn the external power supply into a battery charger.

As you can see from the above list, I'm trying to make the SST a pretty
classy little rig despite its simplicity. It will be great for first-time
kit builders and new NorCal members, but also for those who want a
hand-held rig for serious light-weight operation such as the Spartan Sprint
(or for QSO breaks when running marathons :).

But note that all of the frills can be left off or left up to you, keeping
the cost low and the component count down to around 60 parts--again, half
as many as a '40A or NE40-40. It's an update to the 40-9er, and not
intended to supplant any existing product.

73,
Wayne

P.S. Please note that I'd like to have all e-mail about the SST and other
QRP topics sent to the return address on this posting, NOT to my work
e-mail address. Thanks!


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