Newbie - Trying to simulae 3.5MHz Xmtr - LTSpice

[Talion]

Greetings,

I have never used a schematic capture program before and I am just getting back
into electronics after many years, so I'm a bit rusty. Please bear with me.

I am trying to simulate a low-power transmitter in the 3.5 MHz range in LTSpice.
I would like to look at a plot of the emissions at ANT to see what my frequency
output looks Like. Effectively, a frequency spectrum plot. I understand I should
use an FFT plot after running a transient simulation, but I seem to be having no
luck.

I'm at a loss as to whether my schematic is faulty, I don't understand how to
properly use LTSpice or both. In particular, I wonder if I have configured the
crystal properly (a colorburst crystal) and whether I need a 50 Ohm load instead
of the ANT output?

Any insight would be appreciated, and I thank you in advance.

My LTSpice circuit follows:

----- snip 3.5MHZ xmtr.asc -----

Version 4
SHEET 1 892 680
WIRE 96 144 48 144
WIRE -16 144 -16 208
WIRE -80 272 -80 288
WIRE -80 288 -16 288
WIRE -80 208 -16 208
WIRE -16 288 -16 336
WIRE 48 224 48 144
WIRE 48 144 -16 144
WIRE 48 304 48 400
WIRE 48 400 336 400
WIRE 112 240 112 224
WIRE 112 224 160 224
WIRE 160 192 160 224
WIRE 160 224 192 224
WIRE 192 288 192 320
WIRE 192 320 112 320
WIRE 112 320 112 336
WIRE 48 144 48 32
WIRE 112 32 144 32
WIRE 160 96 208 96
WIRE 432 400 464 400
WIRE 464 400 464 416
WIRE 256 128 256 96
WIRE 256 96 336 96
WIRE 432 96 464 96
WIRE 336 128 336 96
WIRE 336 96 368 96
WIRE 336 208 336 400
WIRE 336 400 368 400
WIRE 336 400 336 448
WIRE 256 192 256 336
WIRE 288 448 336 448
WIRE 208 448 160 448
WIRE 160 448 160 464
WIRE 208 32 208 96
WIRE 208 96 256 96
WIRE 464 96 464 16
WIRE 464 16 560 16
FLAG -16 336 0
FLAG 112 336 0
FLAG 464 416 0
FLAG 256 336 0
FLAG 160 464 0
FLAG 560 16 ANT
IOPIN 560 16 Out
SYMBOL polcap -96 208 R0
WINDOW 3 24 64 Left 0
SYMATTR Value 33µ
SYMATTR InstName C1
SYMATTR Description Capacitor
SYMATTR Type cap
SYMATTR SpiceLine V=10 Irms=60m Rser=2.3 MTBF=1000 Lser=0 mfg="Nichicon"
pn="UPR1A330MAH" type="Al electrolytic" ppPkg=1
SYMBOL res -32 192 R0
SYMATTR InstName R1
SYMATTR Value 5.6k
SYMBOL res 32 208 R0
SYMATTR InstName R2
SYMATTR Value 15k
SYMBOL res 96 224 R0
SYMATTR InstName R3
SYMATTR Value 470
SYMBOL npn 96 96 R0
SYMATTR InstName Q1
SYMATTR Value 2N2222
SYMBOL Misc\\xtal 112 16 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C3
SYMATTR Value 3.56169600e-014
SYMATTR SpiceLine Rser=3.56169600e-014 Lser=0.0555779237 Cpar=8.90424001e-012
SYMBOL ind 320 112 R0
SYMATTR InstName L1
SYMATTR Value 2.5µh
SYMATTR SpiceLine Ipk=1
SYMBOL voltage 304 448 R90
WINDOW 0 -32 56 VBottom 0
WINDOW 3 32 56 VTop 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 9
SYMBOL polcap 144 48 R270
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C4
SYMATTR Value 0.01µ
SYMATTR Description Capacitor
SYMATTR Type cap
SYMATTR SpiceLine V=10 Irms=60m Rser=2.3 MTBF=1000 Lser=0 ppPkg=1
SYMBOL polcap 176 224 R0
WINDOW 3 24 64 Left 0
SYMATTR Value 0.01µ
SYMATTR InstName C2
SYMATTR Description Capacitor
SYMATTR Type cap
SYMATTR SpiceLine V=10 Irms=60m Rser=2.3 MTBF=1000 Lser=0 ppPkg=1
SYMBOL polcap 240 128 R0
WINDOW 3 24 64 Left 0
SYMATTR Value 100µ
SYMATTR InstName C5
SYMATTR Description Capacitor
SYMATTR Type cap
SYMATTR SpiceLine V=10 Irms=60m Rser=2.3 MTBF=1000 Lser=0 ppPkg=1
SYMBOL polcap 368 112 R270
WINDOW 3 24 64 Left 0
SYMATTR Value 100µ
SYMATTR InstName C6
SYMATTR Description Capacitor
SYMATTR Type cap
SYMATTR SpiceLine V=10 Irms=60m Rser=2.3 MTBF=1000 Lser=0 ppPkg=1
SYMBOL polcap 368 416 R270
WINDOW 3 24 64 Left 0
SYMATTR Value 0.01µ
SYMATTR InstName C7
SYMATTR Description Capacitor
SYMATTR Type cap
SYMATTR SpiceLine V=10 Irms=60m Rser=2.3 MTBF=1000 Lser=0 ppPkg=1
TEXT -98 514 Left 0 !.tran 0 10m 0 startup
TEXT -128 464 Left 0 !.option plotwinsize=0

------ snip end of file ------

 

[Rich Grise]

Greetings,

I have never used a schematic capture program before and I am just getting back
into electronics after many years, so I'm a bit rusty. Please bear with me.

I am trying to simulate a low-power transmitter in the 3.5 MHz range in LTSpice.
I would like to look at a plot of the emissions at ANT to see what my frequency
output looks Like. Effectively, a frequency spectrum plot. I understand I should
use an FFT plot after running a transient simulation, but I seem to be having no
luck.

I'm at a loss as to whether my schematic is faulty, I don't understand how to
properly use LTSpice or both. In particular, I wonder if I have configured the
crystal properly (a colorburst crystal) and whether I need a 50 Ohm load instead
of the ANT output?

Any insight would be appreciated, and I thank you in advance.

SYMBOL Misc\\xtal 112 16 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C3
SYMATTR Value 3.56169600e-014

I'd like to know where you expect to get a 35.61696 femtoHertz crystal. ;-)

Cheers!
Rich

 

[Andrew Holme]

Greetings,

I have never used a schematic capture program before and I am just
getting back into electronics after many years, so I'm a bit rusty.
Please bear with me.

I am trying to simulate a low-power transmitter in the 3.5 MHz range
in LTSpice. I would like to look at a plot of the emissions at ANT to
see what my frequency output looks Like. Effectively, a frequency
spectrum plot. I understand I should use an FFT plot after running a
transient simulation, but I seem to be having no luck.

I'm at a loss as to whether my schematic is faulty, I don't
understand how to properly use LTSpice or both. In particular, I
wonder if I have configured the crystal properly (a colorburst
crystal) and whether I need a 50 Ohm load instead of the ANT output?

Any insight would be appreciated, and I thank you in advance.

My LTSpice circuit follows:

[snip]

It'll never oscillate with 33uF and 100uF capacitors grounding the base and
collector. After reducing these, and increasing L1, I got it to oscillate
but not at 3.5MHz. I haven't checked the crystal model. I tried the
crystal parameters from the LTSpice "Pierce.asc" demo in your circuit but
that didn't work either.

Most people seem to make Pierce oscillators with a JFET.

I read that simulating high-Q resonators is difficult in Spice.

 

[dd]

Greetings,

I have never used a schematic capture program before and I am just getting back
into electronics after many years, so I'm a bit rusty. Please bear with me.

I am trying to simulate a low-power transmitter in the 3.5 MHz range in
LTSpice.

I have not run your listing on LT spice but have experience of crystal
oscillators in LT.
The crystal oscillator regenerates narrow band noise every cycle to
build oscillation a crystal with Q 1 million may take 100 milliseconds
to start to full amplitude i.e. 100000cycles. Depends on degree of
excess loop gain)
Spice under transient conditions calculates many times for each cycle
hence the start up difficulty. LT has fiddle factors that you can change
but the results are iffy.