Direct FM receive questions
pedward
Posts: 1,642
So I had an idea of how to do Direct FM reception. I'm generating a carrier on one counter, then gating it in A&B or A==B mode into the second counter. I then sample the counter at the desired sample rate, which is bufsize samples per second.
I'm getting something recognizable, but not legible.
Perhaps someone could give me some ideas?
--Perry
I'm getting something recognizable, but not legible.
Perhaps someone could give me some ideas?
--Perry
CON
_clkmode = XTAL1 + PLL16X
_xinfreq = 5_000_000
' magicnum = 491_715_550
magicnum = 491_740_200
bufsize = 7680
OBJ
pst: "Parallax Serial Terminal"
VAR
long buffer[bufsize]
PUB Main | p, time, x
pst.Start(115_200)
pst.Clear
DIRA[0]~~
FRQA:= magicnum
CTRA:=010_111 << 23 + 0
FRQB:= 1
CTRB:=001_000 << 23 + 2 << 9 + 1
x:=clkfreq/bufsize
time := cnt
p:=0
repeat bufsize
buffer[p++] := PHSB
PHSB:=0
'pst.Bin(p,32)
'pst.Newline
waitcnt(time += x)
CTRB:=0
CTRA:=0
FRQA:=0
DIRA[3]~~
CTRA:=110 << 26 + 3
repeat
time := cnt
repeat p from 0 to bufsize-1
FRQA:=buffer[p] << 16
waitcnt(time += x)
' waitcnt(clkfreq + x)
Comments
I think this method might work on an IF, but not directly demodulating a 100 MHz broadcast. What prevents all the other stations from interfering?