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- Blow-by-blow Report of the 1989 TAPR Annual Meeting
-
- by Paul Williamson, KB5MU
- from the SANDPAC Newsletter
-
-
- On Saturday and Sunday February 25 and 26, 1989, the Tucson
- Amateur Packet Radio Corporation (TAPR) held their annual
- meeting. Approximately 75 people were in attendance from around
- the US, plus one each from Canada and Brazil. TAPR President
- Andy Freeborn, N0CCZ, opened the meeting promptly at 9:00 AM on
- Saturday. He announced the results of the Board of Directors
- election. The following were elected to serve a three-year term
- on the Board: Franklin Antonio, N6NKF; Bdale Garbee, N3EUA; Steve
- Goode, K9NG; Eric Gustafson, N7CL; and Lyle Johnson, WA7GXD.
-
- A discussion of the possibility of a new Amateur license class
- not requiring a Morse Code examination was on the agenda for
- Sunday morning. In preparation for that discussion, N0CCZ took a
- poll of those present. 35 were in favor of a codeless license,
- 13 opposed, 7 uncommitted.
-
- Harold Price, NK6K, served as program chairman for the meeting.
- He introduced Phil Karn, KA9Q, who spoke about "Recent
- Developments in TCP/IP".
-
- Phil Karn, KA9Q: TCP/IP
-
- Karn showed a diagram of the Internet protocol hierarchy to
- remind the audience of the general structure of the protocols.
- Since he has given the introductory talk at previous TAPR
- meetings, he gave only a quick overview of the protocols. He
- then showed a very long list of companies that sell or support
- TCP/IP-based products, to show that TCP/IP is a widespread de
- facto standard. He then listed the software modules that are
- currently a part of the KA9Q TCP/IP implementation:
-
- IP Applications: FTP, Telnet, SMTP, Finger
-
- AX.25 Applications: Mailbox, BBS/Internet Gateway
-
- Protocols: TCP, UDP, IP, ICMP, RIP, NET/ROM, Ethernet, AX.25,
- SLIP, AppleTalk
-
- Drivers: drivers for many Ethernet cards
-
- Karn went on to point out that NET's capability to use a NET/ROM
- network to carry IP packets is perfectly in keeping with the
- Internet concept of tying existing facilities together into a
- working network. However, link layer protocols cannot patch over
- physical layer problems. That is, the radios and modems must be
- able to communicate bits from one station to the next reliably
- before the protocols, no matter how well designed, can do a good
- job.
-
- An industry standard for Ethernet device drivers has been agreed
- upon, and Wollongong (a major TCP/IP vendor) has agreed to
- release their device drivers to the public domain as they are
- converted to the new standard. The NET software has been
- converted to work with the Packet Driver standard, so it can take
- advantage of this working base of driver software. In addition,
- drivers already exist for the Eagle board, HAPN (Hamilton Area
- Packet Network) board, the DRSI PC-Packet Adapter, and the
- Pac-Comm PC-100 board. KISS TNC firmware exists for almost all
- TNC's, including the TAPR TNC-1 and TNC-2, the VADCG board, the
- AEA PK-232 and PK-87, and various Kantronics models.
-
- The major work in progress on the KA9Q NET software involves an
- extensive rewrite of the internal structure of the software.
- Karn has implemented a simple multitasking kernel (referred to as
- "NOS") to replace the awkward up-call interface of the existing
- software. It uses lightweight processes and the Berkeley sockets
- interface. The main idea is to make it easier to integrate
- applications software with the basic networking software. Other
- work in progress includes automatic routing, possibly including
- the experimental SPF protocols currently being tested on NSFNet,
- and intelligent host interfaces for use with computers without
- plug-in adapters.
-
- Karn has switched compilers from Aztec C to Turbo C version 2.0.
- This is good news for many who are interested in making
- modifications to the NET software, since Turbo is much less
- expensive, more available, and faster than Aztec.
-
- Karn has also been working on various performance enhancements in
- the NET package. The amateur packet environment has unique
- problems due to the very low speed of the radio channel, so it
- presents an opportunity for original research in protocol design.
- Some of the ideas Karn is working on include round trip time
- variance estimation, slow start, congestion window thresholding,
- and retry timeout clamping. He is also adding the capability to
- fragment IP packets over multiple AX.25 frames, allowing the use
- of shorter frames for better performance over poor channels.
-
- Greg Jones, WD5IVD: TexNet
-
- The next speaker was Greg Jones, WD5IVD, of the Texas Packet
- Radio Society, which designed, installed, and operates TexNet.
- TexNet is a 9600 bps statewide network running on custom
- hardware. It uses RCA 700 transceivers in the 440 MHz band.
- Jones showed a diagram of the network, which currently includes
- three links via leased telephone lines. Linked lines are used as
- a stopgap to help build network connectivity, which helps to
- build interest in the network in the newly-connected areas. The
- leased lines can then be replaced with amateur radio links.
-
- TexNet includes a Network Management System, which performs
- several functions for the network. The network keepalive
- function of the NMS polls each network node every eight minutes.
- If any node fails to respond to several consecutive polls, the
- NMS issues a reset command to that node. The poll responses
- contain various information about the operational status of the
- node, which is used by the Report Collection and Analysis
- function of the NMS. The information is collected into reports,
- which are made available on the network PMS message system for
- users to download. The data collection is also used for network
- engineering, permitting the network managers to detect and
- correct nodes that have failed or have become isolated from the
- network.
-
- Some sample network statistics were presented. In one 14-day
- period, the network recorded 674 connections, of which 137 were
- to the network Packet Message Systems (there are three), 403 were
- connections through the network to another station, and 5 were to
- a node's Conference Bridge facility. (They consider the
- Conference Bridge to be underutilized, and are considering making
- the conference network-wide to increase interest.) An average
- weekday sees 2 megabytes of data pass through the network; on a
- weekend day the figure is 9 megabytes.
-
- Other networks based on the TexNet hardware and software exist in
- Oklahoma and Michigan. Maps of these networks were shown. The
- Texas group currently has 300 members, and supports three active
- working groups: the TexNet Support Group, the Texas Networks
- Group, and the Mailbox/BBS Group. They are currently working on
- several projects: a protocol converter/gateway to other networks,
- such as TCP/IP or NET/ROM; a new version of their weather
- information server, required to interface with the National
- Weather Service's new distribution system; software enhancements;
- and backbone radio improvements.
-
- Tom Clark, W3IWI: MicroSat
-
- Tom Clark, W3IWI, took the podium to speak about the MicroSat
- project. The first Ariane 4 launch, currently scheduled for July
- 15, will carry four MicroSats and two UoSATs of similar design.
- The MicroSats will be Pacsat/NA (North American packet
- satellite), Pacsat/LU (Argentine packet satellite), DOVE (Digital
- Orbiting Voice Encoder), and a satellite from Weber State College
- containing a CCD video camera. All of these satellites will
- carry a BBS-in-the-sky system for worldwide store and forward
- mail and bulletin transmission. They will ride on a platform
- installed atop the top stage of the Ariane 4 rocket, in the
- otherwise-unused corners around the base of the primary payload.
- This space provides an inexpensive opportunity to launch several
- small satellites.
-
- More opportunities to launch small satellites may be afforded by
- Pegasus, a commercial rocket plane being developed by American
- Technologies. Pegasus is a solid-fuel rocket with a small wing,
- which can be dropped from a B-52 like the X-15 experimental
- rocket plane. Since the solid-fuel rocket has no throttle, the
- main way to control the final orbit is by adding ballast to the
- payload. The Pegasus has been configured so that small
- satellites can be used for this ballast. This may provide a
- stream of cheap launch opportunities for MicroSats
-
- The satellites are quite small, only 7 inches on a side. They
- are constructed from five modules, which are stacked up and
- bolted together to make the satellite's structure. Each of the
- modules has a different function. The basic four modules contain
- the transmitter, receiver, CPU, and power systems. The fifth
- module contains whatever special application is desired, such as
- the CCD camera on the Weber satellite. All six sides of the cube
- are covered with solar panels, which together provide an average
- of 6 to 8 watts.
-
- This slim power budget forces the design to be very frugal with
- power. YT3MV has designed a transmitter for the MicroSats that
- is 80% efficient from DC to RF. The CPU is a low-power design by
- WA7GXD inspired by the PS-186 and based on an NEC V40 processor.
- It contains a 2K boot ROM, 256 kilobytes
- error-detecting-and-correcting (EDAC) program RAM, and 8
- megabytes of static RAM, and consumes approximately 1.5 watts.
- The receiver is a high-performance design by W3IWI. It makes
- remarkable use of low-cost commercial components, such as a
- Motorola receiver chip designed for cordless telephones and
- inexpensive Toko coils from Digikey. Clark displayed a prototype
- receiver in the flight configuration. Power budget calculations
- indicate that the MicroSats will be capable of continuous
- operation.
-
- Another innovative cost-reduction feature of the MicroSat design
- is the interconnection scheme. Instead of an elaborate handmade
- wiring harness connecting signals every which way (construction
- time: 2 months), the MicroSat is connected largely by a single
- ribbon cable between the modules (construction time: 20 minutes).
- Each modules contains a Motorola 14469 AART chip, which enables
- the modules to communicate serially over a miniature local area
- network.
-
- Clark then discussed the uplink bandplan of the two Pacsats.
- Their uplink passbands are divided into four 16 kHz channels
- each, spaced at 20 kHz. Since the satellite band on 2 meters is
- only 140 kHz wide, the highest channel of one satellite coincides
- with the lowest channel of the other. Two different modulation
- schemes are planned. 1200 baud Manchester FSK, compatible with
- existing Fuji-OSCAR 12 modems, will be used by less sophisticated
- stations. These stations need not track their uplink frequency
- according to the satellite's Doppler shift, since the passband of
- each channel is wide enough to accommodate Doppler plus the
- narrow 1200 baud waveform. 4800 baud FSK, however, requires more
- bandwidth, so users of this waveform must precompensate their
- uplink frequency to remove the Doppler shift. It is expected
- that this waveform will be used primarily by gateway and mail
- forwarding stations.
-
- Clark explained the choice of Manchester FSK at 1200 baud and
- straight FSK at 4800 baud. The use of HDLC on the baseband data
- ensures (through bit-stuffing) that the fundamental frequencies
- in the baseband data are 75 Hz to 600 Hz for a 1200 baud data
- stream. These frequencies do not pass through a normal SSB
- filter. Manchester encoding amounts to a DSB modulation around a
- 1200 Hz carrier, shifting the spectrum right into the center of
- the SSB filter. With four times the data rate at 4800 baud, the
- baseband frequencies are four times greater: 300 to 2400 Hz.
- This is exactly the passband of an SSB filter, so no Manchester
- encoding in necessary or desired.
-
- The choice of waveform is made on a per-channel basis under
- software control. The Harris chip used for demodulation provides
- an appropriate matched filter for either waveform on command.
- This will permit some channels to be operated at 4800 baud for
- the use of gateways while others are operated at 1200 baud for
- user stations.
-
- Clark responded to several questions from the audience. Q: Where
- are the bar magnets? A: The satellites are stabilized by four
- bar magnets, which are mounted in the corner edges of the
- satellite. The magnets also provide some additional structural
- support to the satellite frame. Q: How does TAPR fit in? A:
- TAPR and AMSAT have a heavy overlap of personnel. In addition,
- TAPR has funded much of the hardware for Pacsat/NA, for a total
- contribution of $21,300. Q: What about thermal considerations?
- A: A detailed thermal model shows that everything runs cold. The
- temperature is predicted to be 0 C plus or minus 5 degrees C.
- This is a good temperature for the NiCad batteries.
-
- Jon Bloom, KE3Z: MicroSat Power Module
-
- Jon Bloom, KE3Z, of the ARRL Laboratory, described ARRL Labs
- contribution to the MicroSat project. He has designed the power
- module, including the batteries and battery charge regulator.
- The solar cells are arranged in clips of 20 cells in series,
- providing about 22 volts when illuminated. The power control
- system provides 10V unregulated and 5V and 8.5V regulated to the
- rest of the satellite. The power control system is heavily
- instrumented with telemetry sensors. A clever circuit based on a
- saturated toroidal core is used to measure current without
- dissipating much power.
-
- Harold Price, NK6K: MicroSat Software
-
- Harold Price, NK6K, described the MicroSat software design.
- Since the processor in MicroSat is a V40-based system, software
- development can rely heavily on standard IBM PC compilers and
- tools. MicroSat software is written in assembler and Microsoft
- C, linked with Microsoft LINK. It is then loaded into the
- satellite's processor by a cooperative process between the
- satellite's bootstrap ROM loader and the ground station PC.
-
- A primary goal of the software design is ease of implementation
- for new satellite applications. A small multitasking operating
- system has been implemented, along with an operating system
- services library that emulates the standard "stdio" C library
- interface. It provides the application with a disk-like
- interface to the 8 MB bulk memory. This operating system is a
- port of QCF, a product developed by NK6K's company and donated to
- AMSAT for satellite use. WB6YMH is implementing all the low
- level I/O routines that communicate directly with the satellite's
- hardware. With these facilities, the applications developer need
- only program in portable C and link with the provided libraries
- to develop satellite software. This design enables the software
- team to be divided between the operating system and applications
- developers, which has never been possible in previous amateur
- satellite software development efforts.
-
- The software in the satellite is constantly collecting data from
- many sensors throughout all the modules of the satellite. This
- telemetry data is transmitted (at low power) on the downlink
- whenever the downlink is not otherwise occupied. It is also
- accumulated into files, which are made available to users as
- downloadable files. In the case of the Weber satellite, some of
- the CCD pictures will also be made available for downloading.
-
- The satellite is protected against software bugs. The only
- software which is burned into PROM is a small simple bootstrap
- loader. The actual operating software is uploaded (after launch
- if necessary) into EDAC RAM, where it is protected against most
- radiation upsets by the EDAC circuitry. A watchdog timer resets
- the processor if the CPU fails to kick it periodically. A
- hardware "Fire code" circuit allows a ground station to reset the
- satellite's processor even if it is totally crashed.
-
- The satellite is expected to be easy to access. The downlink
- signal should be quite loud, comparable to the signals from the
- Space Shuttle SAREX transmissions. Omnidirectional antennas
- should be adequate, except when the satellite is in view of
- heavily populated areas. An FO-12 modem is the only special
- hardware needed to communicate with the satellite.
-
- Jan King, W3GEY: MicroSat
-
- MicroSat program manager Jan King, W3GEY, displayed the MicroSat
- chassis that was used for vibration tests. It was subjected to
- 15 G's RMS. He said that all the solar panels (which were once
- believed to be the critical-path items)had been received from the
- vendor. Each satellite has two transmitters; it is possible (but
- not currently intended) to operate both at once. It is yet to be
- determined whether the two transmitters will be placed on the
- same frequency or two different ones. The satellite is expected
- to have a long service life. Its lifetime will probably be
- limited by radiation damage to the large RAM array. The
- batteries are 6 Ah GE aviation NiCads, which have functioned
- flawlessly on UoSAT for over five years. The total materials cost
- for a MicroSat is approximately $43,500.
-
- Dave Toth, VE3GYQ: HF BBS Network
-
- Dave Toth, VE3GYQ, discussed the HF network of coordinated BBS
- systems. This system is designed exclusively for mail
- forwarding. No users are permitted to use the system directly,
- and users are discouraged from transmitting on the network
- frequencies. Several frequencies on various bands are used,
- depending on propagation and the required range. 40 meters is
- used for intrastate forwarding, 20 meters for interstate
- forwarding, and 15 meters for intercontinental forwarding. 30
- meters is also used, sometimes in night/day alternation with 10
- meters. Each frequency has an assigned manager, and Toth
- provides central coordination for all frequencies.
-
- The network has several deficiencies. It has low throughput, due
- to low data rate and difficult conditions on HF. It is subject
- to the vagaries of HF propagation. And, it is subject to the
- hazard of new or inconsiderate packet operators. They sometimes
- operate on the network frequencies, causing drastic reductions in
- network throughput.
-
- In December 1988, the HF network experienced a congestion
- collapse. Throughput remained near zero for several days. It is
- believed that the problem was caused by network operators raising
- the retry limit in response to poor conditions. As more and more
- stations retried more and more times, the network approached a
- state in which the channel was saturated with retransmissions.
- When all stations backed off the retry limit to the original
- value and held back mail transmissions for a few days, the
- network returned to normal operation.
-
- The HF network plans to test a variation on the AX.25 protocol
- called "prioritized ACK". The idea of this scheme is to give
- acknowledgments effective priority on the channel over other
- transmissions. This is thought to reduce the performance
- degradation due to the hidden terminal problem. Suppose station
- A is transmitting to station B, and station C has a packet for
- station D that it is ready to transmit. Station C hears station
- A, so it is waiting for the end of A's transmission. In AX.25
- Version 2.0, station C would transmit its data as soon as A's
- transmission ended (allowing for DWAIT and possibly random
- backoff time). In the prioritized ACK version, station C is
- required to wait long enough for station B to send a RR frame to
- station A before transmitting. This permits the RR from B to
- arrive at A without collision, even if C cannot hear B. The HF
- network will attempt to determine if this modification actually
- leads to increased throughput.
-
- Mike Lamb, N7ML: No-Code License
-
- After lunch, Mike Lamb, N7ML, of AEA spoke about the code-free license
- proposal. Lamb is on the ARRL committee to study the possibility
- of proposing a no-code license to the FCC. He pointed out that
- the early days of packet radio were marked by not only technical
- accomplishments, but also impressive salesmanship by the likes of
- Pete Eaton. He asked if TAPR members would be willing to act as
- salesmen for a no-code proposal; 15 to 20 hands were raised.
- Lamb pointed out that six MHz of spectrum at 800 MHz was
- estimated by the FCC to be worth $1,200,000,000, and that the
- amateur UHF-and-up spectrum is extremely valuable to commercial
- interests. He stated that bands like 902-928 MHz will be as
- important to the Amateur Radio Service in a few years as 144-148
- MHz is now, and that we should seek to populate these bands now
- to avoid losing them to commercial interests.
-
- Bdale Garbee, N3EUA: N6GN 1200 MHz Transverter
-
- Bdale Garbee, N3EUA, had several projects to discuss. The WA4DSY
- 56 kbps modems have a 28 MHz IF interface, and thus require a
- transverter to 220 MHz or higher. These transverters are quite
- expensive and not very available. Also, spectrum space on 220
- and 450 MHz is scarce. To solve this problem, N6GN is working on
- a transverter from 28 MHz to 1200 MHz for use with the DSY
- modems. Spectrum is still available on 1200 MHz, omnidirectional
- antennas are practical, and Japanese RF building blocks are
- available inexpensively. The design can also be used at 900 MHz.
- The N6GN design, which is currently in prototype, provides 1 watt
- or 18 watts if a final Mitsubishi brick is installed. It has
- either a 28 MHz or a 144 MHz IF, permitting use with the DSY
- modems or with a 2m satellite station. It provides fast T/R
- switching using PIN diodes, and can be run full duplex by
- splitting the LO. The materials cost is estimated at $150 to
- $200. Garbee asks that potential users of this design contact
- him with comments.
-
- Bdale Garbee, N3EUA: Microwave Ethernet
-
- Garbee is also working on a project to use 10 GHz or 24 GHz Gunn
- diode transceivers designed for police radar applications to
- transmit very high speed data. He uses standard Ethernet
- transceiver chips with the clock oscillator modified to produce
- 2.4 Mbps instead of the usual 10 Mbps. The reduced rate is
- necessary to permit use of a Motorola FSK demodulator chip on the
- receive side. He has a prototype working on the bench at 2.4
- Mbps. Operational concerns include stability over temperature
- and the validity of current path performance predictions. Garbee
- estimates that a 2 Mbps half-duplex system can be built for
- around $200, plus the cost of the computer and Ethernet interface
- card.
-
- Bdale Garbee, N3EUA: KA9Q NET Release
-
- Garbee is also handling the release of KA9Q's NET software. One
- final release of the current (122587.33 derived) software is
- planned before the initial release of KA9Q's new NOS NET. This
- last release will contain many changes submitted by many
- individuals. Garbee has been receiving about 100 electronic mail
- messages per day, about one third of which contain code
- fragments. Several HP and Apollo technical writers have
- volunteered to update and enhance the user documentation for the
- package. Garbee was unwilling to commit to a schedule for the
- release, but admitted that late March was a possibility.
-
- Mike Chepponis, K3MC: Awesome I/O Board
-
- Mike Chepponis, K3MC, described his development of the "Awesome
- I/O Board". The board is a smart I/O controller designed to plug
- into a slot on an IBM PC or AT computer. It contains an 85C30
- serial communications controller chip, connected by four DMA
- channels to an onboard NEC V40 processor running at 8 MHz. The
- 85C30 provides two full-duplex channels. The V40 shares 8K or
- 32K of dual-ported RAM with the host PC via the 8-bit XT bus.
- Chepponis displayed a wirewrap "not quite working" prototype
- board.
-
- Chepponis described two other configurations for similar designs.
- In one, the V40 stood alone with its own ROM and RAM, and was
- connected to multiple 85C30 SCC's. One SCC was connected for DMA
- and used for a high-speed channel, and the others were connected
- for interrupt-driven I/O and used for low and medium speed
- channels. In a second configuration, a stand-alone V40 was
- connected to a single 85C30 for DMA. One channel of the V40 is
- used for high-speed communications, and the other channel is
- connected to a Macintosh host computer's Appletalk network port.
-
- Chepponis listed a few of the applications he envisions for high
- data rate packet radio. At 56 kbps, "instant" mail delivery, six
- TDM digital voice signals, FAX at less than 10 seconds per page,
- digital SSTV, and multiperson realtime interactive services such
- as remote schematic drawing become possible. At 2.0 Mbps, file
- servers, compressed fast scan TV, 200 TDM digital voice signals,
- and various picture formats (even animated) are possible.
-
- Chepponis compared the cost of a conventional 1200 bps packet
- station ($1000) to that of a 56 kbps packet station using his I/O
- board ($1700). In terms of bits/second/dollar, the 56 kbps
- station is about 25 times more cost effective.
-
- Phil Karn, KA9Q: WA4DSY 56 kbps Modem
-
- Phil Karn, KA9Q, took the podium again to discuss the design of
- the WA4DSY 56 kbps modem. He stated that this modem is not
- well-known in the amateur community. He has a network of three
- DSY modems working on 220 MHz in northern New Jersey. The DSY
- modem uses a modified form of MSK (minimum shift keying). In
- terms of phasor diagrams, MSK can be understood as a vector that
- rotates 90 degrees every bit time, at a constant amplitude and
- phase velocity. Thus, it traces out the unit circle on the
- phasor diagram. This modulation scheme has a constant envelope,
- but a wide spectrum. The DSY modem achieves a narrower spectrum
- by having the phasor cut the corners of the unit circle, tracing
- out a diamond on the phasor diagram. This results in sinusoidal
- phase velocity, and a non-constant envelope. The DSY modem
- generates a signal about 74 kHz wide at 56 kbps, or plus and
- minus 14 kHz deviation.
-
- The DSY modem consists of three circuit boards, available from
- GRAPES. The Transmit Encoder board contains a clock generator,
- data scrambler (to remove any low-frequency or DC components from
- the data), and a state machine waveform lookup table driving two
- DACs. The DAC outputs form the I and Q channel signals, which
- are lowpass filtered and passed to the Modem board. The
- modulator consists of a standard I/Q modulator with a 0 dBm 28
- MHz output and a receive chain based on a Motorola 3357 FM IF
- chip with a crystal controlled LO. The analog baseband data is
- sent to the Receive Decoder board, where a slicer and descrambler
- recovers the data and a PLL recovers the clock.
-
- Karn stated that he is a big fan of the DSY modem. He beleives
- that the user stations should be operating at least 56 kbps. The
- channel access problem is critical. He recommends crossband full
- duplex operation, so that collisions may be detected and aborted.
-
- Dan Morrison, KV7B: Modem Comparison
-
- Dan Morrison, KV7B, described his experiments in collaboration
- with Eric Gustafson, N7CL, comparing a phase detection
- demodulator for FSK with a simple filter demodulator. Their goal
- is to better understand how HF packet works and how to improve
- performance of HF modems. They used a Kenwood TS-440S and a
- Dalanco Spry DSP board together with a beta-test DSP signal
- analysis software package running on a PC. They used the DSP
- software to simulate the two demodulators.
-
- Morrison showed several graphs of power versus frequency that
- show a discrepancy between the theoretical power spectrum for
- random data and the spectrum of actual packet data. The actual
- spectrum shows an additional peak in the center of the main lobe,
- which Morrison attributes to the HDLC bit stuffing.
-
- Morrison modeled a naive discriminator, having a linear response
- over the frequency range of interest. This demod performed very
- poorly. Then he modeled a filter demod, whose graph resembles
- that of the discriminator to some extent. Integrating the
- frequency response of the filter demod results in a curve that
- matches the spectrum of the signal fairly well; a perfect match
- would imply an optimal demodulator. This demod generates good
- eye patterns. Next, he added limiters to the filter demod.
- Filters have a reputation as the bane of HF demodulator
- performance. It still generated good eye patterns. He then
- added noise, and still got good eye patterns. He concludes that
- the filter demod works just about as well as the phase detection
- demod as long as the signal is bandlimited before the
- demodulator.
-
- Morrison presented a graph of a signal before and during a severe
- multipath fade. The attenuation of one tone was clearly visible.
- These signals were demodulated, and both demods did well as long
- as the envelope of the signal was above the noise level. A
- member of the audience asked "why not demodulate just one tone?",
- and Morrison replied "That won't work very well. What if the
- multipath fade took out the tone you were demodulating?". Tom
- Clark, W3IWI, stated that the conceptual model of "tones" was a
- poor one for modulations with bit rates about as big as the
- shift. Perhaps the incidental amplitude modulation caused by
- selective fading could be used by a sufficiently smart
- demodulator.
-
- Morrison then presented graphs of eye patterns for a very noisy
- signal received with a 2.4 kHz SSB filter. This generated a
- hopelessly bad eye pattern on the phase demod, and a pretty good
- eye pattern on the filter demod. This is a result of the
- narrower frequency response of the filter demod. Narrowing the
- input filtering to the phase demod to 500 Hz produced similar
- performance to that of the filter demod. Morrison concluded that
- a well-designed filter demod works very much like an ideal
- noncoherent demodulator. Either modem needs a narrow bandpass
- filter before its first nonlinear stage for good performance.
-
- A member of the audience asked if increasing the shift from 200
- Hz to 600 Hz would help performance. His intuition was that it
- would. Morrison stated that it would not, and Clark agreed.
- Both had run experiments verifying their conclusions.
-
- Eric Gustafson, N7CL: TAPR Hardware Projects
-
- Eric Gustafson, N7CL, described three new developments from
- TAPR's hardware designers. Two of them are tiny circuit boards
- designed to improve the DCD performance of a TNC's demodulator.
- These circuits were described in the last Networking Conference
- proceedings. One is for a TNC-2, and the other is for AM7910
- based modems. The other new development is a hardware upgrade
- path for TNC-1 owners. This board piggybacks on the TNC-1 board
- and permits the TNC-1 to run TNC-2 firmware. This allows TNC-1
- owners to keep up with the evolution of TNC firmware, even though
- TNC-1 firmware updates have not appeared. None of these items
- are priced or available yet.
-
- Gustafson described the prioritized ACK proposed modification to
- the AX.25 Level 2 protocol. He stated that code implementing
- this version of the protocol for TNC-2 will be available for
- testing on TOMCAT and CompuServe soon. The code is based on TAPR
- version 1.1.6.
-
- Jim Vogler, WA7CJO: 10 GHz EME
-
- Jim Vogler, WA7CJO, was introduced by coworker Tom Clark, W3IWI.
- Vogler was the first to succeed at 10 GHz EME. He showed us
- pictures of his EME station. He has a 15' dish with a moving
- mass of one ton and a half-power beamwidth of 0.5 degrees. He
- points the antenna at the moon by listening for the noise
- reflected from it at 10 GHz, and tracks by means of a video
- camera mounted on the edge of the dish. He can control antenna
- pointing to 30 seconds of arc, and frequency to a few hundred
- Hertz. He uses a surplus 100W TWT amplifier with a scalar ring
- feed for about 20 MW EIRP. The TWT beam was defocused, so he
- used permanent magnets to refocus the beam. He was able to hear
- his echoes from the moon with 15-20 dB S/N.
-
- Vogler said a few words about the problems of creating a power
- amplifier for 1.2 MHz and up. Transistors for 20W at 1.2 GHz are
- $50 and falling. Amplifiers can be built, but commercial ones
- are very costly. Kits can be a problem, since considerable test
- equipment is required to align the amplifier, and mistakes that
- destroy the device are costly.
-
- Jon Bloom, KE3Z: ARRL and Packet
-
- The STA authorizing automatic control of certain stations on HF
- has been renewed for another year. The League hopes to have a
- permanent rules change in place by the time it expires. The
- Digital Committee and Membership Services Committee will examine
- the results of the testing and propose new rules.
-
- ARRL has established a Technology Grants program, whereby
- developers of amateur radio technology can apply for funding from
- the League. This is partially a result of Paul Rinaldo, W4RI,
- pushing for improved HF modems and protocols.
-
- Expect a MicroSat article in an upcoming issue of QST.
-
- TNC's are being integrated with the SAREX transceivers in
- anticipation of the next ham in space, schedule for STS-35 in
- spring of 1990. The request for prioritization has been
- submitted to NASA HQ for the experiment.
-
- TAPR Business Meeting
-
- President Andy Freeborn, N0CCZ, resumed the chair and conducted
- the annual business meeting. He gave a summary of the year's
- activities. The office complex was closed, and Chris the office
- manager now operates the TAPR office from her home. TAPR had no
- booth at Dayton '88, but has requested a double booth in the new
- wing for Dayton '89. A rewrite of the TAPR Bylaws is in
- progress. The DSP Project is now an official joint project of
- TAPR and AMSAT. The two organizations will share the risks and
- benefits fully. Two AT-type computers outfitted for CAD work
- were purchased to support hardware design efforts. They are
- presently in use in Tucson and St. Louis. TAPR has contributed
- $21,300 for Pacsat/NA hardware, and is serving as the procuring
- agency for all Pacsat hardware purchases.
-
- PSR Editor Scott Loftesness, W3VS, has announced his intention to
- retire at the end of the calendar year. A new volunteer is
- sought. TNC-2 licensing fee income will be ending soon. A new
- project is necessary to provide a source of income. The Board
- has been in continuous session via CompuServe HamNet during the
- year; nine votes were taken during that time. An income
- statement and balance sheet were presented. With an income of
- about $61000, the total assets and liabilities of the
- organization are $122,500.
-
- A question and answer period followed. One member stated that
- the Board should keep the membership better informed about its
- day to day activities, and there was general agreement. A member
- asked about the status of the DSP project. W3IWI answered that
- Bob McGwier, N4HY, has been writing software for the Dalanco-Spry
- development system, including several new demodulators. Since
- there is no prototype hardware in the final configuration yet, he
- has not begun porting the software to the target system. W3IWI
- guessed that late summer would be earliest possible availability.
- The V40 hardware has been designed, but layout has not begun.
- The other boards are being fabricated in a prototype version.
- They have had problems finding satisfactory CAD software for PWB
- layout. There may be a problem with the V40 chip and interrupts.
- It appears that TAPR is standardizing on the V40; this is
- important so that we can build up a base of knowledge about its
- quirks. The DSP Project is personnel-limited; more qualified
- volunteers would be welcome.
-
- Another member asked if the DSP Project was the only new
- development under way. Freeborn answered that there was another
- project in the early design stages: a 9600 baud VHF radio/modem.
- This project was mentioned briefly in PSR. TAPR is wary of
- announcing products before they become real, so they try not to
- make a lot of noise about a project this early in the design
- phase.
-
- Pete Eaton, WB9FLW, led the membership in thanking Andy Freeborn,
- N0CCZ, for his outstanding efforts in the past year in
- reorganizing the organization. Applause.
-
- The meeting was adjourned for the day at 5:15 PM.
-
- An additional session was held on Sunday morning, with a single
- agenda item: the no-code license proposal. Harold Price, NK6K,
- led the discussion. He has been charged, along with other
- committee members, with creating a concrete proposal of some sort
- to provide to the ARRL committee. The discussion proceeded in
- stages: opening remarks, purposes, and specifics. An appropriate
- background was provided by sounds of hymn-singing from the church
- service being held next door.
-
- Your reporter will not attempt to reproduce all the arguments
- presented in this 3-hour discussion. Though the discussion
- remained intelligent and civil for the most part, there were
- diverging opinions. The following represents an attempt to
- summarize the semi-consensus that evolved during the meeting.
-
- TAPR's purpose in getting involved in the issue in the first
- place is to help the ARRL to lead the amateur community to accept
- some proposal. Last time no-code came up, the proposal was
- violently opposed by a large fraction of the community. The
- ARRL, being a political organization, will be reluctant to
- reverse this position unless it believes there is significant
- support for the proposal in the community. By presenting a
- workable proposal and standing behind it, TAPR may be able to
- encourage ARRL leadership to try again.
-
- Our purpose in seeking a license that does not require Morse Code
- proficiency is threefold:
- 1. To ensure that crucial spectrum allocations in VHF and up are
- utilized and remain available to the Amateur Radio Service,
-
- 2. To lure more technically competent people into Amateur Radio, and
-
- 3. To lure more young people into Amateur Radio to ensure the future
- of the Service.
-
- The specific proposal should have the following characteristics:
- o The existing licensing structure remains as it is. No privileges
- will be given to or taken from any existing licensee. To do so
- would be to invite controversy.
-
- o An addition licensing structure consisting of two license classes
- would be added. These classes would grant operating privileges
- above 30 MHz only. One license would be fairly easy to obtain,
- with a written exam similar in difficulty to the Technician exam.
- This license would have very limited privileges. The licensee
- might be prohibited from controlling repeaters, homebrewing
- transmitters, or operating high power; and/or the license could
- be made nonrenewable. The license would be limited to selected
- bands or subbands. The other license would be difficult to
- obtain, with a written exam more difficult than any now in use.
- This license would have full amateur privileges above 30 MHz.
-
- The group was unable to agree on the specifics of the
- restrictions to be placed on the beginning license class, or even
- on an appropriate name for it, in the time available. The
- Board's committee is charged with fleshing out the proposal based
- on the opinions stated during the meeting. At the end of the
- discussion, Freeborn asked how many opinions had been changed by
- the arguments. Several people in the anti-no-code and
- uncommitted camps admitted to being swayed toward no-code by the
- arguments they had heard.
-
- The TAPR Annual Meeting was adjourned at 12:28 PM.
-