Info

Ml

• Frequency accuracy, ± . 1 Hz maximum - 40°C to + 85DC

• Frequencies to 250 Hz available on special order

• Continuous tone

• Frequency accuracy, ± . 1 Hz maximum - 40°C to + 85DC

• Frequencies to 250 Hz available on special order

• Continuous tone

Group B

TEST- TONES: 600 1000 1500 2175 2805

TOUCH-TONES:

697 1209

770 J 3 36

852 1477

941 1633

BURST TONES: 1600 1850 2150 2400 1650 1900 2200 2450 1700 1950 2250 2500 ]750 2000 2300 2550 1800 2100 2350

• Frequency accuracy, ± 1 Hz maximum - 40 C to + 85't

• Tone length approximately 300ms. May be lengthened, shortened or eliminated by changing value of resistor

426 West i àft Avenue, Orange, California 9266" (800) 854-0547/ California: (714) 998-3021

RTTY Loop

Marc I. Leavey, M.D. WA3AJB 4006 Win tee Road Randallstown MD 21133

Last month, I indicated that we were going to investigate the demodulator situation. Well, as the old saying goes, there is more than one way to lead a horse to water (or something equally non-violent). In this case, demodulators can be acquired from at least three sources. In this month's column, we will start to ]ook at one of them.

To begin with, where can you get a demodulator and why do you need one, anyway? For those of you who just came in, a demodulator, sometimes referred to as a "terminal unit" or <lTU," is a device which converts receiver output, either at audio or i-f (intermediate frequency) frequencies, into 7 FY compatible loop levels. Historically, there have been three waves of demodulators available. Follow ing World War If and the Korean "conflict," large quantities of surplus Teletype® equipment found a final resting place in an amateur's shack, These beasts were usually large, power hungry, and possessed less than ideal weak signal qualities, But the price was right, and the surplus market started many of us on the Road to RTTY {apologies to B and 8). As the surplus market started to dry up and as many of the defects in the "boat anchors" became apparent, more and more demodulators

multitude of designs were published ranging in complexity from simple one-tube affairs to rack panels full of shack heaters. Now, many of us find ourselves returning to commercial units, this time made for amateurs, with ail of the features one could desire, at a price to match!

This month, I will start an overview of various published home-brew designs. What I will

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