Gift to

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RTTY LOOP
J
Marc I. Leave y, M.D. WA3AJR
4006 Win lee Road
Randallstown MD 21133
Okay, now, how many of you
out there have heard of iRL?
Come on, raise your hand s.
Tha t's o ne , t wo, three . . .
hmmm, not too many. I guess
this goes along wi th what one of
the guys from the company told
me. You see, they have a new
RTTY demodulator, the FSK
1000, and, in his words, "Whi le
we haven't expected the FSK
1000 to stu n the free wo rld and
enrich us overnight, we stil l
can't quite see wh y people
would want to spend almost two
hundred bucks more for something
else." We ll, after looking at
the FSK 10Cl0, I don 't know what
the problem is either.
Over the past few months, we
have covered many dem odul a­
tor design s and considered
what makes a good dem odul a­
to r. A common desi gn point of
many of these was the inc lusion
of a limiter stage in the front
end. What the limiter does is
boost the sig nal inp ut to a
c lipped or limited level so that ­
in theory - all sig nals present
are processed to the same arnpli
tude . In practice, however,
this only works for signals tha t
are in the clear or reasonab ly
noi se-tree . The ability to work
without a limiter, in true limiterless
(often called AM) mode , is a
distinct advan tag e on our ofte n
crowded ham band s.
Unfortunately, most of the demodulator
s marketed to th e
Any amat eur have not featured
true limiterless operati on. While
a fro nt-panel switc h may be
marked " LIMITER ON/OFF" or
"AMIFM", there is usua lly no
way to vary the input level to
best take advantage of what sig ­
nal the re is. Further, selective
fading without adequate logi c to
allo w insta ntaneous reception
on mark or space can be equally
disastrous . The FSK 1000
changes all that.
A front-panel inp ut level contro
l and an LED which lights
upon clipping, th us exc eeding
the li near range, make limit erless
operation of the FSK 1000
easy. By adjusting the imput so
tha t th e LED is just extf n-
guished, maximum capability is
ensu red. By increasing the input
level, any degree of clipping
fro m co ntrolled to hard limiting
may be achieved. Clearly, all sig ­
nals are not alike. Now there is
no reason that the demodulator
needs to sta y the same, eit her.
Another bugaboo of demod u­
lator design has been the filters.
Through the years, filters have
ranged, as we have seen, from
TV-width coils to toroids to coilless
acti ve filte rs. The problem
has alw ays been to maintain
adequate selectivity, gain , and
bandwidth at reasonable cos t
vs. perf ormance trade- off. Well ,
iRL has come through , again, by
using modern, six th-order active
filters in the FSK 1000. This permits
selectable bandwidth and
tunable peaks to cov er any shift
fro m 50 to 1000 Hz, wi th switch
selection of 850 Hz, 425 Hz, and
170 Hz. The shift change is accomplis
hed by tuning a multipole
bandpass filter of consta nt
bandwidth, rather tha n using
audio frequency mixe rs in a heterodyning
process. Thus, audio
image probl ems, bird ies, and
spurio us frequen cies are min i­
mized.
Now, as if the guts were not
impressive enough, the boys at
iRL have also wor ked hard to
provide a heck of a box. The circuit
board is a hefty 3132·inch
glass epo xy number, and the
pots and other components are
name brands. Full -sized, sta n­
dard connect ors are used on the
rear skirt; no scrounging for
mole x plug s here. The who le
thing is encl osed in an anodized
aluminum bo x that unscrews for
service but looks like it will support
a TO on top of it. (I said
"looks li ke it will " - 1 have not
do ne it !)
There are even a bunch of options,
as if the bas ic unit weren't
enough . You can get a video
board mount ed in side and make
a full term inal. ASCII-to-Baudot
conversions go wi th that One.
Some of the standard feature s
are even more imp ressive , how ­
ever. A RS·232 keyboard can be
hooked into the back to key the
loop, and RS-232 outputs are
available also . That means the
thing will work with our computer
terminal, without a 50·mA
loop at all. There is a keyboardacti
vat ed sw itch (hitting any key
turns on your transmitter) and a
CW 10 key jack. Tuni ng meters ,
scope outputs . . . 1even think it
makes a pretty good cup of cottee.
There are a few gripes, however.
First off , look at the picture
. I seriously co nsidered having
a contest to see how many
of you could tell which push-but ­
ton on the front pane l was
pushed . You see, even in real
life, it is hard as the devil to tell
what shi ft you are on, whet her
autost art is on or off, or whatever.
Som e form of indicator,
LED, or whatever, or changing to
tog gle swi tches is needed to
clear up that front panel. Speaking
of clarity, abou t mid way between
th e delta-tune and input
knobs is a small knob labeled
"THRESHOLD." This knob was
added to late produ cti on runs,
and allows you to adjust the autosta
rt threshold (tha t is, the level
at which the autost art will
start) from the front panel. Fine,
but the re is no calibration ,
sca le, or logging on the knob.
No way to know where it is set
nor return it to a previous setting.
Bad news, fell as. And one
last note: tne autostart. When I
fir st sta rted playing with this
thing, about a minute or two into
the session, the front lights died
and the printer went off . Now, if
ju st the prin ter and loop had
gone off, I would have known
the autostart disengaged. But
killing the front-panel li ghts
made me think I'd blown a fuse.
Only a fortuitous signal brought
fife to the machine and saved
the day. Really, now, why not
leave the light s alon e? Other-
The FSK 1000 from iRL.
wi se, when ki lling equipment at
the end of the day, there is no
qui ck way to know the thing is
on.
All in all, howe ver, I have to
commend the fol ks at iRL. They
have turned out a solid demodulator
that well sho uld stun the
free world. The FSK 1000 currentl
y sells for $449.00, and you
can see their ads here in 73 or
write to iRL, 700 Tayl or Road,
Columbus, Ohio 43230.
I received a lett er recently
from Tom Waarvik of Indiana polis,
Indiana, who related that he
was a begi nner, with a Teletype
Model KSR-35 and a modem,
and that he wan ted to be able to
receive Morse, Baud ot, and
ASCII on tha t setup. He notes
tha t much of the commercial
gear is over his budg et, and he is
looking for cheap way s of code
co nversion. Well, Tom, this is
where the co mput er in the shack
co mes in handy. There are
reams of publ ished programs
fo r receiving any or all of these
modes with just about any of the
popular computer chips. You
might c heck back issues of 73
and Microcomputing magazines.
In September and December,
1979, t listed many of these
articles in this columm. See if
you can scrounge a copy in your
area, or chec k with 73's back
issue department. Which computer?
Well, I am partia l to the
6800 and have written some fa irly
sophisti cated progr ams to
work RTTY on one. But whic h­
ever you can get within your
budget , 6800 , 8080, Z·80, Apple,
Pet, or TRS·BO, they can be made
to work on RTTY and Morse.
That is probably the best way to
go.
18 73 Magazine. October, 1980