RF PA oscillator.

If you are focusing on the PA, then buy the oscillator or use sig gen to develop the PA.

"John Lee"

** Errr - I guess you are thinking of using a third overtone crystal in here somewhere ?? ** Not possible without one or two stages of RF amplification.

BTW:

80 MHz is not a free for all frequency with that kind of RF power.

Think licences, certification etc.

.... Phil

l in

In the US, 80.36 MHz is allocated for TV-5 and amateur use.

I suspect you're thinking of the 80 meter band, not 80.36 MHz.

80.36 MHz is not allocated for amateur use in the US.

Ed

The oscillator type is almost completely immaterial to the power amplifier design.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

Pick one out of the textbook, or ask the teacher for clarification of the assignment.

Good Luck! Rich

"mpm" "Phil Allison"

In the US, 80.36 MHz is allocated for TV-5 and amateur use.

** 75 watts of RF on 80.36 MHz would blot out TV sets on Ch 5 for many miles around.

..... Phil

I don't know what the oscillator has to do with the PA.

If you don't need a wide-range VFO, any oscillator will work. Just keep the harmonics more than 15dB down, and apply a good packaged filter device. My interest is mainly in the 2m band, where Minicircuits make a 7 stage low-pass filter in 1206 size!

You'll need to keep the PA very clean too - resonant or LPF at least.

However, I've been learning how to design clean RF oscillators, and have a few comments on Colpitts vs Hartley. When the active device turns on, the Hartley pumps energy into an inductor, whereas Colpitts dumps it into a capacitor. That means that the Hartley amplitude-limits on current (the resistance in the on-state circuit) whereas the Colpitts is voltage-limited. Distortion in the pure-sine waveform is cause by this asymmetric pumping action, so, assuming you have just enough gain, it depends on how smoothly the device turns on and off. This is easier to get right with a Colpitts than with a Hartley.

The tank voltage in a Hartley may be several times the supply voltage, so you need to avoid zenering any BE junctions, b/c that will cause more distortion and harm the device.

I'd use a Colpitts, and add AGC if I wanted a clean wide-range VFO. The following LTSpice circuit is the best I've been able to do around 150MHz with 2 transistors. The output should be buffered with an emitter follower coupled by 1pF to the tank. I'd appreciate comments from Jim Thomson and others on how to improve it.

Clifford Heath.

-------- Cut here for ColpittsEL_AGC.asc ------------- Version 4 SHEET 1 880 708 WIRE 304 -160 80 -160 WIRE 640 -160 304 -160 WIRE 80 -128 80 -160 WIRE 80 0 80 -48 WIRE 80 0 -80 0 WIRE 448 0 80 0 WIRE 528 0 448 0 WIRE 80 32 80 0 WIRE 448 64 448 0 WIRE 304 80 304 -160 WIRE 640 80 640 -160 WIRE -48 128 -80 128 WIRE 80 128 80 112 WIRE 80 128 -48 128 WIRE 240 128 80 128 WIRE 80 160 80 128 WIRE -48 176 -48 128 WIRE 448 224 448 144 WIRE 528 240 528 0 WIRE 80 272 80 224 WIRE 304 272 304 256 WIRE 304 272 80 272 WIRE 384 272 304 272 WIRE 304 304 304 272 WIRE -48 320 -48 256 WIRE 80 320 80 272 WIRE -48 432 -48 384 WIRE 80 432 80 384 WIRE 80 432 -48 432 WIRE 304 432 304 384 WIRE 304 432 80 432 WIRE 448 432 448 320 WIRE 448 432 304 432 WIRE 528 432 528 304 WIRE 528 432 448 432 WIRE 640 432 640 160 WIRE 640 432 528 432 WIRE 640 448 640 432 FLAG 640 448 0 FLAG -80 128 Vosc IOPIN -80 128 Out FLAG -80 0 Vbias IOPIN -80 0 Out SYMBOL ind 288 288 R0 SYMATTR InstName L1 SYMATTR Value 0.2uH SYMBOL voltage 640 64 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 9v SYMBOL cap 64 160 R0 SYMATTR InstName C1 SYMATTR Value 10pf SYMBOL cap 64 320 R0 SYMATTR InstName C2 SYMATTR Value 47pF SYMBOL ind -64 160 R0 SYMATTR InstName L3 SYMATTR Value 120nH SYMBOL cap -64 320 R0 SYMATTR InstName C3 SYMATTR Value 220pF SYMBOL npn 240 80 R0 SYMATTR InstName Q1 SYMATTR Value CA3046 SYMBOL res 64 16 R0 SYMATTR InstName R4 SYMATTR Value 10k SYMBOL npn 384 224 R0 SYMATTR InstName Q2 SYMATTR Value CA3046 SYMBOL res 64 -144 R0 SYMATTR InstName R2 SYMATTR Value 100k SYMBOL cap 512 240 R0 SYMATTR InstName C4 SYMATTR Value 1nF SYMBOL res 432 48 R0 SYMATTR InstName R3 SYMATTR Value 4.7k SYMBOL res 288 160 R0 SYMATTR InstName R5 SYMATTR Value 100R TEXT -272 -8 Left 0 !.tran 0 40uS 0 1nS TEXT -248 464 Left 0 !.inc "C:\\Program Files\\LTC\\LTspiceIV\\lib\\custom\\Transistors\\ca3000.lib" TEXT -336 -144 Left 0 ;Using an inductive emitter load roughly halves current\nusage for the same amplitude and harmonic performance

m\\Transistors\\ca3000.lib"

rent\nusage for the same amplitude and harmonic performance

So far I am learning. I prepare from the SMPS to the VSWR protection from directional coupler. I even don't know where to put the protection output to where? oscillator? or amplifier stage modulator? I have one oscillator, one driver stage, one amplifier stage. On amplifier stage, I will use collector modulation. This is much like for ISM band use like 13.56, 27.12, 40.68. 80MHz has its own advantages.

I will use collector modulated, class E amps. The oscillator is important because a good sine wave will save a lot work on the load. load is 50ohm. So far I know people use colpitts from S-band, hartley for high voltage (kV) RF as well as for 27.12MHz 50Watt amplifier.

I just need a single frequency. VCO is for future development only.

Then use any oscillator, but low-pass filter the output well, and don't under-drive it, since that tends to give subharmonics.

Clifford Heath.