Irvin M. Hoff, K8DKC, W6FFC

Irv Hoff was the prolific designer of the "Mainline" FSK Demodulators. Hoff also wrote a series of RTTY related articles for QST in 1965 and 1966. Most of the QST articles are polished versions of earlier articles that he had originally written for the RTTY bulletin.

Mr. Hoff was a pilot with United Airlines. Irv became silent keyboard on April 3, 1991.

The "Mainline" series FSK Demodulators.

The Mainline TT/L is a highly optimized tube based demodulator. It includes both an ATC and a DTC circuit.

The ST series are solid state demodulators. The ST-1 was never published. The ST-2 was a demodulator targeted for VHF use.

The ST-3 uses a single op-amp stage as its limiter; the rest of the ST-3 consists of discrete component. The ST-4 was an ST-3 for 170 Hz shift.

The ST-5 is a further simplification of the ST-3, using two op-amps, one of them replaces the discrete-circuit slicer in the ST-3.

The ST-6 is finally a solid-state demodulator that outperforms its tube TT/L counterpart. All the pervious ST demodulators aimed at cutting the cost and complexity of the TT/L, rather than to out perform it.

"Getting Started On Radioteletype - The Mainline Converter." RTTY Bulletin January 1963.

"The Mainline TT/L FSK Demodulator." QST August 1965.
(Appeared earlier in November 1964, RTTY bulletin. with coauthor Keith Petersen, W8SDZ)

The Mainline TT/L is a widely duplicated TU which includes both a DTC and a ATC for limiterless demodulation.

"The Mainline TT/L-2 FSK Demodulator. Parts I and II." QST May and June 1969. Co-authored with Keith B. Petersen W8SDZ.
(Appeared earlier in September 1967, RTTY Journal, by W8SDZ)

This is an updated version of the TT/L.

"The Mainline ST-3 RTTY Demodulator." QST April 1970.
(Appeared earlier in September 1968, RTTY Journal.)

The stated goal of the ST-3 is to be a low-cost solid-state unit. It employs a simple first order filter as the input filter, with an op-amp as the limiter. It lacks an ATC circuit and will not copy Mark-only or Space-only signals. The ST-3 does not support limiterless operation.

"The Mainline ST-5 RTTY Demodulator." ham radio Magazine, September 1970.
(Appeared earlier in May 1970, RTTY Journal.)

The ST-5 is a further simplification of the ST-3. The active circuits in the signal path consist of just one 709 op-amp working as the limiter and a second op-amp working as the slicer.

"The Mainline ST-6 RTTY Demodulator." ham radio Magazine, January 1971.
(Appeared earlier in September and October 1970, RTTY Journal.)

This is a "solid state Mainline TT/L demodulator." It uses nine 709 op amps, compared to two that are used in the ST-5. Like the ST-5, the limiter has better than 90 dB of gain.

For limiterless operation, the gain of the limiter stage is reduced so that the demodulation chain operates in the linear region. The ST-6 has an ATC which allows it to print Mark-only and Space-only signals, but it has no DTC.

Parts cost is about $150 in 1970.

QST Series.

"The Teletype Machine."QST January 1965.

"Operating the Teleprinter." QST February 1965.

"Receiving Radioteletype." QST March 1965.

"Over-All Design Considerations for RTTY Demodulators." QST April 1965.

"Transmitting Radioteletype." QST May 1965.

"Checking RTTY Shifts." QST May 1965.

"Audio Frequency-Shift Keying for RTTY." QST June 1965.

"The Mainline TT/L FSK Demodulator." QST August 1965.

"RTTY Indicator Systems." QST October 1965.

"Operating the RTTY Station. QST November 1965.

"Fun with RTTY. QST December 1965.

"High-Performance RTTY Filters, Part I." QST August 1966.

"High-Performance RTTY Filters, Part II." QST September 1966.

Other Articles.

"Narrow Shift (or Reducing RTTY Error Rates)." RTTY Bulletin, March 1964.

"Current RTTY Receiving Techniques."
(coauthored with Keith B. Petersen, W8SDZ) RTTY Bulletin, December 1964.
(Reprinted in two parts in March and April 1970, RTTY Journal.)

Even in the era of the DSP, "Current RTTY Receiving Techniques" from 1964 is still a "must read" article.

"An Introduction to Amateur RadioTeletype." Frederick Electronics Booklet.