It's pretty easy to make a sorta decent sine wave generator. I can switch R1 with an HC analog mux to make FSK. Three resistors and two dual diodes bend the triangle into a sine.
R6 makes the sine look a little nicer, but doesn't affect the FFT much, so I could leave it out. The 3rd harmonic is about -26 dBc either way. The values are very un-scientifically fiddled.
Version 4 SHEET 1 1180 680 WIRE 528 32 224 32 WIRE 672 32 528 32 WIRE 720 32 672 32 WIRE 816 32 720 32 WIRE 976 32 896 32 WIRE 1024 32 976 32 WIRE 1056 32 1024 32 WIRE 224 48 224 32 WIRE 528 64 528 32 WIRE 976 80 976 32 WIRE 352 112 320 112 WIRE 368 112 352 112 WIRE 640 112 608 112 WIRE 656 112 640 112 WIRE 320 144 320 112 WIRE 288 160 144 160 WIRE 608 160 608 112 WIRE 400 176 352 176 WIRE 432 176 400 176 WIRE 528 176 528 128 WIRE 528 176 512 176 WIRE 576 176 528 176 WIRE 144 192 144 160 WIRE 224 192 224 128 WIRE 288 192 224 192 WIRE 720 192 720 32 WIRE 720 192 640 192 WIRE 976 192 976 160 WIRE 976 192 912 192 WIRE 1056 192 976 192 WIRE 576 208 528 208 WIRE 320 240 320 208 WIRE 352 240 320 240 WIRE 368 240 352 240 WIRE 608 240 608 224 WIRE 656 240 608 240 WIRE 672 240 656 240 WIRE 912 240 912 192 WIRE 1056 240 1056 192 WIRE 528 256 528 208 WIRE -320 288 -352 288 WIRE -288 288 -320 288 WIRE -112 288 -160 288 WIRE -80 288 -112 288 WIRE 64 304 16 304 WIRE 112 304 64 304 WIRE 224 304 224 192 WIRE 224 304 192 304 WIRE 272 304 224 304 WIRE 400 304 400 176 WIRE 400 304 352 304 WIRE -352 336 -352 288 WIRE -160 336 -160 288 WIRE 16 336 16 304 WIRE 912 352 912 304 WIRE 912 352 752 352 WIRE 1056 352 1056 304 WIRE 1056 352 912 352 WIRE 752 384 752 352 WIRE 912 400 912 352 WIRE 1056 400 1056 352 WIRE -352 448 -352 416 WIRE -160 448 -160 416 WIRE 16 448 16 416 WIRE 752 512 752 464 WIRE 912 512 912 464 WIRE 1056 512 1056 464 FLAG -352 448 0 FLAG -160 448 0 FLAG -320 288 +5 FLAG -112 288 -5 FLAG 528 256 0 FLAG 352 112 +5 FLAG 640 112 +5 FLAG 352 240 -5 FLAG 656 240 -5 FLAG 16 448 0 FLAG 672 32 OUT FLAG 144 192 0 FLAG 64 304 KICK FLAG 400 176 MID FLAG 1024 32 SINE FLAG 912 512 0 FLAG 1056 512 0 FLAG 752 512 0 SYMBOL voltage -352 320 R0 WINDOW 0 61 39 Left 2 WINDOW 3 64 76 Left 2 SYMATTR InstName V1 SYMATTR Value 5 SYMBOL Opamps\\UniversalOpamp 320 176 R0 SYMATTR InstName U1 SYMBOL Opamps\\UniversalOpamp 608 192 R0 SYMATTR InstName U2 SYMBOL voltage -160 320 R0 WINDOW 0 55 40 Left 2 WINDOW 3 57 76 Left 2 SYMATTR InstName V2 SYMATTR Value -5 SYMBOL res 528 160 R90 WINDOW 0 66 57 VBottom 2 WINDOW 3 68 56 VTop 2 SYMATTR InstName R1 SYMATTR Value 1K SYMBOL res 368 288 R90 WINDOW 0 68 58 VBottom 2 WINDOW 3 73 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 2K SYMBOL res 208 288 R90 WINDOW 0 70 58 VBottom 2 WINDOW 3 75 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 100K SYMBOL cap 512 64 R0 WINDOW 0 -44 2 Left 2 WINDOW 3 -50 33 Left 2 SYMATTR InstName C1 SYMATTR Value 10n SYMBOL voltage 16 320 R0 WINDOW 3 38 113 Left 2 SYMATTR InstName V3 SYMATTR Value PULSE(1 0 100u) SYMBOL res 208 32 R0 WINDOW 0 -53 36 Left 2 WINDOW 3 -52 66 Left 2 SYMATTR InstName R4 SYMATTR Value 1K SYMBOL res 912 16 R90 WINDOW 0 70 58 VBottom 2 WINDOW 3 70 59 VTop 2 SYMATTR InstName R5 SYMATTR Value 1K SYMBOL res 992 176 R180 WINDOW 0 -58 71 Left 2 WINDOW 3 -55 44 Left 2 SYMATTR InstName R6 SYMATTR Value 50 SYMBOL diode 896 240 R0 WINDOW 0 -75 9 Left 2 WINDOW 3 -101 47 Left 2 SYMATTR InstName D1 SYMATTR Value 1N4148 SYMBOL diode 1072 304 R180 WINDOW 0 -74 47 Left 2 WINDOW 3 -103 9 Left 2 SYMATTR InstName D2 SYMATTR Value 1N4148 SYMBOL diode 896 400 R0 WINDOW 0 -63 21 Left 2 WINDOW 3 -91 53 Left 2 SYMATTR InstName D3 SYMATTR Value 1N4148 SYMBOL diode 1072 464 R180 WINDOW 0 -71 48 Left 2 WINDOW 3 -103 9 Left 2 SYMATTR InstName D4 SYMATTR Value 1N4148 SYMBOL res 768 480 R180 WINDOW 0 52 64 Left 2 WINDOW 3 54 32 Left 2 SYMATTR InstName R7 SYMATTR Value 1K TEXT -208 176 Left 2 !.tran 400u TEXT -296 64 Left 2 ;FSK Modem Sine Generator TEXT -264 112 Left 2 ;J Larkin Dec 19 2012