amateur radio license required to operate on the air!


Cost estimate: $65

More ambitious, versatile, and powerful than the 500mW Transmitter is this enjoyable unit that originally appeared June 1967 in QST. A two-stage crystal-controlled rig for 80- and 40-meter CW operation, it puts out a clean and very stable 3 watts for some challenging QSO's and can drive an external power amplifier if more power is desired. Switching operating bands is accomplished by changing plug-in coils.

Variations of this circuit were used to demonstrate basic solid-state CW transmitter Oscillator/Power Amplifier design in many editions of the annual ARRL Handbook - indication of its classic elegance. Although a "vintage" project, all parts are readily available and affordable. This is a great rig that's fun to use and a perfect match for the Receiver, which also operates on the 80- and 40-meter bands.

Unless otherwise noted, decimal capacitance values are in microfarads (uF);
whole-number values are in picofarads (pF or uuF).

Suppliers for this: check current catalogs of especially Antique Electronics Supply, Dan's Small Parts, and Ocean State Electronics. See the suppliers page for links to these and other sources.

C1,C2 - 100pF variable capacitors. OK to use somewhat higher-value units.
I1 - 250ma. pilot lamp, bayonet-base "No. 44".
I2 - 150ma. pilot lamp, bayonet-base "No. 47".
Use insulated bayonet bulb holders for I1 & I2. I use holders with different-colored lenses for I1 & I2: spiffy!
J1 - open circuit jack for matching key-plug of choice, also appropriate jacks for antennna and 12-14V DC power supply plugs.
L1,L2,L3,L4 - see table below; use 5-pin coil forms with corresponding 5-pin tube sockets.
L1 = 36 turns #24 AWG enam. on 1-inch dia. form, close-wound. Tap 15-3/4 turns from C1 end. L2 = 6 turns #24 AWG enam. close-wound over cold end of L1. L3 = 36 turns #24 AWG enam. close-wound on 1-inch dia. form. Tap 12 turns from cold end. L4 = 5 turns #24 AWG enam. close-wound over cold end of L3.
L1 = 18 turns #20 AWG enam. on 1-inch dia. form, close-wound. Tap 5-3/4 turns from C1 end. L2 = 4 turns #20 AWG enam. close-wound over cold end of L1. L3 = 18 turns #20 AWG enam. close-wound on 1-inch dia. form. Tap 6 turns from cold end. L4 = 4 turns #20 AWG enam. close-wound over cold end of L3.
S1 - DPST switch, or use 1/2 of DPDT switch.
Q1,Q2 - 2N2102 or 2N3053 NPN transistors. Use socket & heatsink for Q2; socket for Q1 is optional.
Y1 - 80/40 meter band fundamental-cut crystal.
For FT-243 or HC17/U crystals, an octal tube socket can be used for Y1.
Misc. - Chassis Box (approx 3"x5"x7" aluminum suggested), terminal strips, knobs, hookup wire, solder, mounting hardware, etc.

Parts layout is not critical. My version's guts are an inefficient-looking mess, but it still works great. I built this project the old-fashioned way, wiring components point-to-point inside the chassis. Drill or cut holes for sockets to hold L1/L2, L3/L4, Q2, Y1, I1 & I2; drill holes for C1, C2, S1, J1 and the antenna and power jacks. Mount all, then wire and solder the other components together inside the chassis. Mounting a 5-point terminal strip with each of the coil sockets greatly simplifies wiring.

Next comes the really fun part: winding the coils. Pulling out more than you need for each winding,tying an end to a dooknob, and winding toward the door is one way to do it... I found that running the leads along the outside of the forms and holding them in place with tape while winding - and wrapping the leads around the pin bases before soldering them - works much better than drilling holes in the coil forms to pass the leads inside. Do whatever works for you, but take care when making the coils that all the windings go in the same direction and the wiring to the pins is correct! Finish the coils with tape, Q-dope, or even scale model-type sanding sealer (!) to secure the turns.

Since 1967 FCC spectral purity laws have been tightened, which is why a harmonic filter module section is included on the business end of the transmitter in the schematic diagram. Homebrew low-pass filter information using standard components can be looked up in filter tables in the ARRL Handbook and very easily assembled, so option choices are left to the builders' discretion. My filters use capacitors available everywhere and miniature inductors which are availiable almost everywhere - EXCEPT Radio Shack.

Tuneup and Operation
With S1 in the OPEN (tune) position, attach a 50-ohm dummy load, insert a crystal, apply 12-14 volts, and close the key. Adjust C1 and C2 for maximum brightness of I2. Tune C2 to the point that I2 shows maximum brightness with the least amount of brightness at I1. The point of this is to get the maximum output indicated by I2 with minimum-current conditions at I1. Now flip switch S1 to the OPERATE position and adjust C1 for best tone as monitored by your receiver. THAT'S IT! If all is working well, replace the dummy load with a 50-ohm antenna and repeat the tuneup procedure. Always tune the transmitter with S1 in the OPEN (tune) position or risk blowing output transistor Q2! With S1 is in the OPERATE position and supplied with 13 volts my transmitter draws 250mA on 80 meters and 350mA on 40 meters. Other models may vary.

Approximate RF Power output can be determined by using a common multitester with a very simple RF wattmeter circuit. Confirm that the signal is "getting out" by using a field strength meter at the antenna - and do yourself a favor by using a half-wave dipole to avoid antenna tuners and assure good results. Output power is about 3 watts with a 12-14 volt power supply. More than 17 volts tends to blow the output transistor in my version, but go ahead and experiment if you don't mind frying some transistors. Go get 'em!

Sources: American Radio Relay League, "A Transistor 5-Watter for 80 and 40," THE ARRL HANDBOOK, 46th edition, (Newington, 1969) pp.177-180 American Radio Relay League, "Circuit example of a simple, solid-state CW transmitter" (schematic diagram), THE ARRL HANDBOOK, 70th edition, (Newington, 1993) p.11-2

WHAT NEXT?-- Try a station controller that frees you from switching the antenna from transmitter to receiver and back again. I use the one described in "How To Build A Simple QRP Transmitter Control System" by Pat Bunn, N4LTA (CQ, Feb 1992, p 40). It provides semi-QSK operation, electronic keying with keying filter, and optional sidetone and receiver muting features. (To make it go with the transmitter described above, just delete the transmitter's KEY jack and connect the OSC and AMP +V together. The keying is then provided by the controller via the +V input...)
***2-BAND VFO***