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| 7038.5 — 7039.5 kHz | Norcal SMK-1 |
650 milliwatts transmit power 0.178 μV MDS receive sensitivity |
Exterior view. A consulting client was throwing away a whole box of unused plastic cases... I just needed to shear sheet aluminum to make a bunch of appropriately sized panels, and find some long 4-40 screws to hold the case halves together. |
Top cover removed — it's mostly empty space! Bridge rectifier, 7809 regulator, and capacitors at rear so it can be fed with 9-15 V AC or DC. |
My first surface-mount transceiver. But with the relatively large 1206 surface-mount devices (0.12 x 0.06 inches) it's not too hard. |
The circuit board mounts to the front panel by its three pots for RX gain and RX and TX frequency. I did the "high-power modification" to boost power from about 360 mW to 650 mW, so the final amplifier transistor is up off the board with a finned heat sink. |
I added a TiCK keyer — also surface-mount on a small board. |
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The SMK-1 was a kit sold by the Norcal QRP Club.
It's no longer offered, but for details see:
http://www.amqrp.org/kits/smk1/index.html
For a good presentation of the construction, see:
http://www.qsl.net/wb8rcr/SMK1.html
| 10100 — 10150 kHz | NorCal NC2030 |
4.0 watts transmit power 0.178 μV MDS receive sensitivity |
(Still undergoing final alignment...)
| 14000 — 14110 kHz | Small Wonder Labs SW20+ |
1.6 watts transmit power 0.251 μV MDS receive sensitivity |
Exterior view. Yes, I put everything in those cases. |
The front panel is just a Postscript file printed out and photocopied onto colored cardstock. There's more inside than in the SMK-1. |
I added a larger heat sink to the final amplifier, and added a power filter capacitor. |
For the switch (blue, at left), RG-174 coax (black "C" shape), and the two tuning pots, joined by resistors with purple wire insulation pulled over their leads, see the frequency coverage modification below. |
The SW+ series of transceivers are designed and sold as kits
by Dave Benson, K1SWL.
See:
http://www.smallwonderlabs.com/
Modifying the SW20+ for expanded frequency coverage:
First, replace C8 with a 47 pF NPO/C0G capacitor.
Second, replace C7 with a short piece of RG-174 coax running to a SPDT switch selecting between two capacitors:
15 pF
high | |
O---------| |----------+
/ | | |
switch/ |
+------O |
| 27 pF |
| | | |
| O---------| |----------+
| low | | |
| |
| +---------------------------+
| |
| | RG-174 to original
| | C7 position
| |
O --O--
---
-
Third, replace the VCO tuning potentiometer. The original design uses a 50-100 kohm potentiometer from regulated +8V to ground, with the VCO input taken from the wiper. Replace that with this:
regulated <---+------------------+
+8V DC | |
[ ] |
100 kohm [ ] |
[ ] |
| |
| |
300 kohm [ ] [ ] 100 kohm
fine tuning[ ]<-------+------>[ ]coarse tuning
pot [ ] | [ ] pot
| | |
| | |
[ ] | -----
100 kohm [ ] | ---
[ ] | -
| |
| +---------------> to VCO input
-----
---
-
My result was a range of 13990 - 14059 kHz in the low range, and 14039 - 14110 in the high range, with fine tuning available across the total frequency range.
| Straight Key | Paddle |
A military surplus J-38, cleaned up and back in service. Fully adjustable for travel and tension. |
Norcal also put out a mechanical construction kit. The heavy steel base was ready to go, but the brass and plexiglass parts all took some finishing work. Adjustable for travel, the tension is magnetic. I had some issues with contact oxidation on both of these, and tried burnishing the contacts and then rubbing on some Ox-Gard conductive grease. Not enough to call it a layer, more that I rubbed it onto the surface and wiped it off, leaving only a very thin film. So far that seems to have helped the problem. |
Click here for Morse Code tables
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| Cut a hole in an Altoids tin with a Dremel tool, install a BNC jack so the lid can still close. A screw in the bottom floor holds a wire lug, connected to about 2m of wire with an alligator clip. The BNC center conductor goes to a quarter-wavelength of wire, the far end of which is tied in a small loop around a large nut. Attach the alligator clip to some handy ground / counterpoise, throw the other end into a tree or over some shrubbery. Separate models for 7040, 10106, and 14060 kHz, flavor-coded by frequency. | |
This can make for a very high performance HF system. Rick Campbell, KK7B, has written a series of articles in QST magazine starting in the early 1990s, see below for a bibliography.
More recently, Dan Tayloe, N7VE, has designed some systems that do I/Q quadrature conversion using switching rather than traditional mixers. See the NC2030 design above.
Also see some articles describing the technology as an "H-mode mixer", named after the circuit topology. Sergio Cartoceti, IK4AUY, wrote an article in QEX: http://xoomer.alice.it/sergiocartoceti/pdf files/IK4AUY_ qex_07-2004.pdf
Siniša Tasić, YU1LM, has also used it in some interesting designs that combine sample-and-hold quadrature modulation and demodulation with software-defined radio technology: http://www.qsl.net/yu1lm/
Here's one way of doing it digitally. Use a VFO running at 4 times the desired LO frequency, and use high-speed D flip-flops to generate the quadrature signals:
+--------------------------- Q ( 90 degrees)
| _
| +------------------------ Q (270 degrees)
| |
+-------+ | | +-------+
+-----+ +---+D Q+--+-)|(-----+D Q+--------- I ( 0 degrees)
| | | | _| | | _| _
| VFO +--+--)|(--+clk Q+-----+ +--+clk Q+---+----- I (180 degrees)
| | | | +-------+ | +-------+ |
+-----+ | | | |
| +--------------------)|(-------------+
| |
+-------------------------+
The resulting four LO signals will be square waves,
which are in fact preferred assuming (as with everything
else) you do it right and provide:
— A low-pass filter on the mixer RF port
— Broadband 50-ohm termination on all mixer ports
This approach is used in the designs by Dan Tayloe, N7VE. See:
A bibliography on the topic includes:
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