A Blow-By-Blow Account of the 1992 TAPR Annual Meeting
======================================================
The following is based on the notes I took during the TAPR annual
meeting. Any mistakes are mine. On no account should you assume
that this account represents the official position of TAPR or anybody
else. But I hope you find it interesting. You may publish parts or
all of this document if you wish, but if you do please credit the
SANDPAC Newsletter. Sorry it took so long for me to get these notes
published this time.
73 -Paul Williamson, KB5MU
The 1992 TAPR Annual Meeting was called to order by TAPR President
Bob Nielsen, W6SWE, on March 7 at 9:41AM at the Inn At the Airport in
scenic Tucson. He introduced Master of Ceremonies "Packet" Pete
Eaton, WB9FLW, who introduced TAPR Office Manager Heather Johnson,
N7DZU.
Heather welcomed everybody to Tucson. TAPR office hours are Tuesday
to Friday, 10 AM to 3 PM. Thanks to Bob Nielsen, W6SWE, for his work
as President of TAPR. Thanks to Pete Eaton, WB9FLW, for taking care
of TAPR's presence at the Dayton Hamvention. Thanks to Ron Bates,
AG7H, for fielding technical questions. Thanks to Dave Medley,
KI6QE, for fielding questions on the PK-232 DCD mod and the PSK
modem. Everybody hates not to have the latest version of software,
so thanks to the new librarian, Lou Nigro, KW7H, for updating all the
software in the TAPR library. Anybody who has software that should
be in the TAPR library, contact Lou. And of course, thanks to Lyle
Johnson, WA7GXD, for fielding the daily barrage of miscellaneous
questions. The new TAPR 9600 baud modem is available now at $70, and
the Trakbox is available now at $185. Thanks to everybody associated
with TAPR for being fun to work with.
Bob Nielsen, W6SWE, took the microphone again, and asked everybody to
introduce themselves. 112 of the usual suspects from all over the
place were present. Nielsen then announced that the TAPR Board of
Directors had been resized to 9 positions. The new officers are:
President: Bob Nielsen, W6SWE
Vice President: Dave Toth, VE3GYQ
Secretary: (open, volunteers?)
Directors: Tom Clark, W3IWI
Jerry Crawford, K7UPJ
Jack Davis, WA4EJR
Pete Eaton, WB9FLW
Greg Jones, WD5IVD
Dan Morrison, KV7B
Harold Price, NK6K
Bob Hansen, N2GDE, will continue to serve as editor of the Packet
Status Register. Lou Nigro, KW7H, will take over as software
librarian.
Pete Eaton, WB9FLW, took the microphone at 10:00 AM. For the first
time, this year's TAPR meeting is recorded by a printed Proceedings.
Thanks to the several speakers who managed to submit papers for the
Proceedings. He then introduced the first speaker:
==================
Lyle Johnson, WA7GXD
TAPR's New 9600 Baud Modem - What It Is, What It Isn't
TAPR's new 9600 baud modem is compatible with existing K9NG and G3RUH
9600 baud modems. It's an inexpensive kit, capable of full duplex
operation (like the G3RUH but unlike the K9NG), with improved DCD
(data carrier detect) performance and clock recovery. It looks up
the transmit waveform in ROM, like the G3RUH, and has a frequency
response compensation adjustment on the receive side. The board is
designed to mount internally in a TNC-2 (where it's a tight squeeze)
or a PK-232. The board includes provisions for bit regeneration
(parts optional) for use in a full duplex digipeater.
There are about 5000 G3RUH modems in service overall. Heathkit is
mostly out of the kit business, so one of the goals of the 9600 baud
modem project was to leverage TAPR's expertise at packaging kits to
make available a 9600 baud modem with better performance than the
K9NG at a reasonable price. The design address problems with the
K9NG modem (like its half duplex design) and adds features for
network builders (like the bit regenerator). The state machine in
the K9NG could mistake silence (like a squelched radio or a weak
carrier) for a data carrier, thus holding off transmission
indefinitely. The new state machine design cures that problem, and
also gives better clock recovery.
A block diagram of the modulator portion of the modem was displayed.
The modem disconnect header (TAPR standard or PacComm extended) goes
into a data scrambler, to the transmit waveform ROM lookup table, to
a digital to analog converter, through a filter, and out to the
radio. The clock can be obtained from the modem disconnect, or
generated on the 9600 baud modem board. RTS from the TNC controls
PTT through a watchdog and an LED indicator. Programmable logic
provides switching from the 9600 baud modem to the TNC's internal
modem. It is still necessary to hook up the modem directly to the
discriminator and modulator inside the radio, not to the speaker and
microphone jacks.
A block diagram of the demodulator portion of the 9600 baud modem was
displayed. The input buffer has a high input impedance, 100 kohm or
more. A Butterworth 6kHz filter is tweakable to compensate for the
frequency response of the receiver, which is especially useful with
rigs with LC filters like Mitreks. The data slicer feeds a
descrambler, state machine and DCD circuit, with an output for a bit
error rate test. The DCD detects synchronous transitions, rather
than the lack of asynchronous transitions as before.
Block diagram of the bit regenerator. It consists of a PAL and a
FIFO chip. The FIFO inserts a nominal delay of 8 bits, and is
required to eliminate bit jitter and timing errors in the received
signal. The result is that if the repeater can copy the input signal
at all, it will transmit a perfect signal. A diagram of the
switching configuration shows how the bit regen is connected with the
TNC, so that the TNC can transmit on the channel instead of the bit
regenerator.
A sample of the 9600 baud modem was passed around the room. It's a
four layer PC board, which helps cut the RF noise. It's relatively
compact, but it has a lot of parts on it. The documentation shipping
today is preliminary, and needs more information on hookup to various
TNCs and radios. Updated documentation will be sent to early buyers.
Question: I'm interested in higher speeds than 9600. Is this modem
planned to be scalable to higher baud rates?
Answer: It hasn't been tested, but it should work. The op amps and the
ROM lookups are plenty fast. The input analog filter would have to be
adjusted. The transmit lookup table might help at higher speeds to
compensate for the nonlinearities of a wider filter. We should try that
experiment.
Question: Has it been tested on the satellite? How does its
performance compare to the G3RUH?
Answer: It hasn't been tested on the satellite yet. Lab bench tests
aren't realistic, but they show that the new modem is no better than
the G3RUH, and 1 to 2 dB worse under some conditions.
Question: The PK232 limits the TBAUD (computer to TNC) rate to 9600.
Does this cause a problem when using the PK232 with a 9600 baud
modem?
Answer: We haven't noticed any problems in testing. Probably the
worst thing is that you won't be able to keep the pipe completely
full on transmit, resulting in dead time.
On the PK232, the ALTMODEM 1 command permits the user to switch to
the 9600 baud modem from the keyboard. This means you effectively
have a third radio port, because you can leave the PK232's two
existing ports hooked up to other radios.
TXD (delay between PTT and first data) is another issue. If you have
the state machine DCD mod kit in your PK232, there's a small extra
delay that requires increased DCD at the other end. With a TNC-2 or
a Kantronics DataEngine we could run TXD of 1 or 2.
Question: Has the modem been tried at 4800 baud on the 6m backbone?
Answer: No.
==================
Dewayne Hendricks, WA8DZP
Use of CDMA Spread Spectrum in the Amateur Service
Last year at the TAPR meeting, we talked about Part 15 spread spectrum
(SS) communications systems, and displayed a low-cost commercial
product capable of high data rates. The year before that, N3FCT
presented a paper on license-free spread spectrum. Folks in the San
Francisco Bay area were inspired to look at the Part 15 market. The
results of a field test of units from Proxim was posted on Usenet.
One watt into a 6 dBi antenna gave 2 miles LOS tested and 8 miles LOS
predicted at 121 kbps. There's been lots of activity in the wireless
LAN market and at the FCC since then. We wanted to find out why the
amateur radio service isn't using SS techniques, and approach the FCC
for whatever rule changes are needed. An STA (Special Temporary
Authority) for testing was sought and obtained.
A second generation Proxim unit was passed around. It is a 121 kbps
data radio (data in, antenna out) in a very tiny box. In the OEM
package for laptops, it costs $50. The internal modules of the
Proxim radio were displayed - all very tiny. Computer manufacturers
are starting to put these directly into laptops for wireless LAN
use. Challenge to ham radio: get coordinated with the computer BBS
folks and build a wireless Internet.
The ARRL Spread Spectrum Handbook is good for a basic tutorial and
for historical information on SS. AMRAD did the experiments that led
to the current rules permitting SS. The present rules are like
handcuffs. In particular, they mean that amateurs won't be able to
use commercial SS products, because they don't happen to use one of
the few spreading sequences permitted by the rules. We decided to
seek a rules change. This turned into a long process. It turns out
to be important to use connections in rulemaking matters. After last
year's meeting, Paul Rinaldo, W4RI, at ARRL HQ was approached for,
and arranged, ARRL cooperation for an STA submission. After several
months, and polishing by the League lawyers, the STA application was
submitted to the FCC, which promptly sat on it and did nothing.
About this time, the League managed to get FCC Chief Engineer Stanley
to speak at the Computer Networking Conference. Stanley is a
proponent of spread spectrum, and he was interested in the amateur
proposal. He assigned a staffer to the STA. The STA requested a two
year authorization for any spreading code on any VHF or higher band.
Before the STA could be approved, the staffer had to get every agency
involved with the use of any of those bands to accept the proposal.
It was a lot of work, but with support for Stanley and the League is
was done. The STA was granted.
There are plans for tests in at least the Northern and Southern
California areas. People interested in serious experimentation with
SS can be added to the STA. The intention is to eventually submit a
Petition for rulemaking to get a better set of SS rules. The
restrictions on spreading codes and the requirement for narrowband
station ID are particularly onerous.
One test is starting in San Diego, under the California State Library
project for packet radio. Using radios produced by SRI, the project
will interconnect libraries to the wide variety of online databases
available via the Internet, without the cost of a 56kbps landline
connection to the Internet. The pilot project in San Diego is
sponsored by Apple Computer, and radios have been donated by
Tetherless Access (Hendricks's company) and by hams. Parts of the
network are operated under Part 15 (license free), Part 97 (amateur),
and Part 5 (experimental).
Funding has been allocated in the Bay area to connect 100 libraries
from San Jose to Roseville, San Francisco to Sacramento, all in one
WAN. Part 97 (amateur) radios are to be used for long haul links,
and Part 15 radios for intra-city links. This experiment will last
through the end of the year. Phase II will involve redesigned 1.5
Mbps radios and associated networking software. Currently the
project supports only Macintosh computers, partly because any Mac off
the shelf can handle up to 900 kbps data links. Hams in northern and
southern California will be seeded with equipment to try out Phase
II.
There's a lot of work to do. First, get the FCC rules changed. That
will take 1 to 1.5 years, on the fast track. It is hoped that the
rules will be changed before the STA ends. Then hope that
manufacturers will go after the ham market. We haven't done a good
job of keeping the FCC up to date. We need to tell the FCC where the
public interest lies. The FCC wants to help, but we have to play the
game: STAs, Part 15, waivers, and so forth.
Question: Is all the Part 15 activity at 900 MHz?
Answer: No, we're not using 900 MHz at all. We are currently working at
2.4 GHz, and have plans for 5.7 GHz.
====================
Fried Heyn, WA6WZO, ARRL Southwestern Division Director
Read the Division newsletter for more about what's going on. Some high
points:
There's a bill in Congress that can protect amateur frequencies from
further erosion.
A big effort funded by the ARRL membership was directed to preserving
amateur spectrum at WARC-92. The results are not final yet, but it
appears that no amateur spectrum was lost at the conference!
The 1992 ARRL National Convention is at the Los Angeles Airport Marriott.
====================
Jon Bloom, KE3Z
TAPR DSP Project Report
KE3Z received one of the first set of beta test DSP boards from the
hardware designer, Lyle Johnson. Procrastination set in: the board
has over 2000 holes, so assembling it is a bit of work. Finally, got
it assembled. The next step was to learn about how to do DSP
programming. Highly recommended: the Computer Literacy Bookstores in
and around San Jose. Good books for techno-weenies, including some
on DSP.
Some preliminary DSP applications are already written and working. A
Bell 202 (1200 bps AFSK, like on 2m packet) modem is up and working,
with a driver for KA9Q NOS for packet use. A RTTY modem (2125/2295
Hz AFSK) with a RTTY driver and receive-only AMTOR driver is working.
Dave Hershberger, W9GR, has written two audio-in/audio-out filter
programs. One notches out tone interferers from the audio channel,
and works great. The other tries to remove noise from an SSB signal,
and needs more work. These filters were originally written for a
TMS32010 board of his own design, and have been mechanically ported
to the TMS320C20 on the TAPR DSP board (so they aren't optimized for
it).
The lesson is that DSP software isn't necessarily magic anymore. It
is quite possible to write working modem software, for instance,
without getting heavily into sophisticated mathematics. The basic
building blocks are simple, and design tools exist to handle filter
design.
Coming attractions:
Bell 103 modem (HF packet)
1200 baud PSK for Pacsats
9600 baud FSK (K9NG/G3RUH/TAPR compatible)
Spectrum display
4800 baud PSK for Pacsat - the satellite has never been in this
mode, since no user modems have ever been built.
2400 bps Kantronics-style
improved W9GR "de-noiser" filter
weather fax
slow-scan television
Some of these applications exist for other boards, and just need to
be ported to the TAPR board. Others need to be written from
scratch. Many of these applications will be implemented over this
spring and summer. PC software to support the applications is also
needed. NOS is nice for some packet applications, but other
applications need other PC software.
A virtual-hardware block diagram of the RTTY demodulator is shown.
It's just two bandpass filters running into detectors, followed by a
comparator and lowpass filter. Standard stuff.
DSP-oriented block diagram of the RTTY demodulator. The bandpass
filters are straight out of a manufacturer's application note. The
coefficients for the filters are computed by a computer program, so
no heavy math is needed. The filter design is an 80-tap FIR (finite
impulse response) linear phase filter. The detector is just absolute
value, then a peak detector followed by a decay. The comparator is
just a subtraction. The lowpass filter is another cookbook design.
That's it. Notice the absence of any higher math in this
description. This isn't the optimum demodulator, but it's as good as
most analog designs, and it works.
A similar approach was tried for the Bell 202 demodulator, but for
unknown reasons it didn't work very well. A Bell 103 modem was taken
from another ap note, based on a discriminator design: the audio is
delayed by 90 degrees and mixed with itself, then lowpass filtered
and compared to zero. The Bell 202 demodulator is just this design,
tweaked up for Bell 202 tones and bit rate.
The book _Digital Signal Processing Experiments_ by Alan Kamas and
Edward A. Lee contains a diskette with educational versions of
Burr-Brown DSP design tools, including the tool that generates
coefficients for FIR filters. The book is quite inexpensive (about
$21) for a DSP tool set. It's published by Prentice-Hall;
recommended.
Both DSP programmers and PC programmers are needed to work on
applications for the TAPR DSP project. The PC level programmer sees
an environment much like a DSRI board plugged into a PC. Contact Jon
Bloom if you're interested.
Tom Clark, W3IWI, spoke up:
The TAPR DSP project grew out of earlier development on the
Dalanco-Spry Model 10 DSP board. About 30 of these boards were
purchased, and probably some could be made available to new
interested people. Lots of applications were written for the
Dalanco-Spry board, and they're all available for the grabbing on
tomcat (Tom C's AT) by anonymous FTP via Internet, or by telephone,
or by floppy disk if necessary. Another application that's needed is
a good adaptive HF modem (along the lines of Clover II), and HF
protocols that can use them. AX.25 sucks on HF. AMTOR has problems,
too. Pacsat broadcast protocols are a bit like what's needed for an
HF protocol, but it needs changes for the HF environment.
Question: Who is doing satellite imaging?
Answer (W3IWI): The AEA box has it. The Dalanco-Spry board had it,
and that version will be ported (or rewritten) for the TAPR DSP
board. We may want to rewrite rather than porting Dalanco-Spry
applications, because the subset of instructions supported by that
processor was pretty brain-damaged compared to the instruction set of
the TMS320C20 used on the TAPR DSP. The AEA box contains a Motorola
56001 DSP processor. Its modems are superb compared to analog
modems.
Question: What sampling rate can DSPs handle?
Answer (W3IWI): The Dalanco-Spry board could do a spectral display at
50 KHz.
Answer (KE3Z): It's been suggested that we can just digitize the
antenna voltage.
Answer (W3IWI): Unintentional radiation can be a problem. The DSP
processors can generate a lot of crud.
Answer (KE3Z): The TAPR DSP board is pretty well decoupled.
======================
Bob Nielsen presented an award to Chuck Green, N0ADI, for his
outstanding contributions to the development of packet radio through
ten years of TAPR. Chuck accepted the award, but claimed that it
represents the teamwork that goes on behind the scenes everywhere.
Pete Eaton held the drawing for door prizes, then the meeting broke
for lunch.
======================
Mike Parker, KT7D
The Radio Workstation Concept
Block diagram: Antenna connected to analog radio, connected to a
digital sampling and output box, connected to a general purpose
workstation.
The problem with DSP software is that it's so difficult to write for
special-purpose DSP processors. By the time you've finished writing
the software, the special-purpose DSP processor you wrote it for is
obsolete. Worse, by that time your general-purpose workstation has
improved in performance to the point where it outperforms the old
special-purpose DSP! This whole problem can be bypassed by writing
the DSP application for the general purpose workstation in the first
place. Portable languages can be used, so it should be easy to take
advantage of improved workstation technology as it comes along.
Block diagram of a sample application (not implemented): meteorology
satellite image reception and display. The software can be written
in manageable small modules, like orbit prediction or overlay
generation, and the resulting modules can be patched together readily
to make a complex application.
The SPARCstation currently used as the workstation costs about
$10,000 after discounts. Thus the TAPR DSP project and the Radio
Workstation approach address different (but overlapping) issues. The
TAPR DSP is cost effective, IF you can get the software working
quickly. Experimental applications written for the Radio Workstation
might serve as prototypes for DSP-board applications.
The current configuration uses a DAT (digital audio tape) machine
interfaced via SCSI to the SPARCstation or VAX, running Unix or VMS,
with signal processing software, an interactive display layer like X,
and FORTRAN with VMS extensions and C for widgets. This isn't a
cheap configuration, but it's off-the-shelf. The code developed for
this project is being made available free, on the condition that if
you add to it, you make your results available free also.
Why should TAPR get involved in this project?
- to help promote research
- to spend time doing research, not software development
- to develop and debug applications for the TAPR DSP board
- to help develop standards for file structures, datalink
structures, and so forth, before it's too late.
Question: How big is the publicly-available source code?
Answer: About 100,000 lines of code, comprising 300 processing primitives.
=====================
Tom Clark, W3IWI
Various Topics
Topic #1: 900 MHz
In 1985, Motorola and NEC were engaged in a battle to dominate the
market for cellular telephone base station equipment. In 1990, NEC
gave up on the market, and the hardware they had managed to sell was
orphaned. In 1991, the NEC hardware at cell sites in Richmond was
scrapped. A total of over 100 45W radios already outfitted for 19.2
kbps data were made available surplus for $20 each. The equipment
complement for a normal cell site was 16 transmitters and 16
receivers, all nicely racked up. Six cell sites plus spares were
scrapped. Each cluster weighs about 800 pounds and fills a pickup
truck. The salvaged radios are all spoken for, but similar
opportunities may become available in other areas.
The radios are set up for 19.2 kbps data, with a digital interface,
used originally for signaling for billing purposes. They are
designed for full duplex operation, and the receiver won't work
without the transmitter operating. An analysis of the filters
indicates that data scramblers will probably not be required. The
transmitters are a very simple, conservative design. They are
serviceable, understandable, and robust.
Block diagram of the receiver. A buffer amp feeds a
synthesizer-driven mixer, followed by a standard IF and
discriminator. A measurement of received signal strength goes to a
Z80 microprocessor. The audio and demodulated data go out. The 70
MHz IF filters are from the same line as those used in the Microsat
receiver. The RF filters will need to be replaced with ones that can
go up to the amateur 900 MHz frequencies. High-side injection will
be needed, because low-side injection puts the IF image in a crowded
spot in the band. The modification involves removing a chip
capacitor and trimming a microstrip. It remains to be seen whether
the Z80 processor part of the board is useful. Perhaps it could be
used for signal strength telemetry.
Block diagram of the transmitter. A 15.36 MHz oscillator drives a
synthesizer. A power controlled amplifier chain feeds the antenna.
The modulator frequency modulates the synthesizer. One bandpass
filter in the RF path needs to be replaced to reach the amateur 900
MHz band.
All this cost us $20 per unit. Be jealous.
Outstanding issues and problems:
* The transmit frequency isn't easily moved. Luckily, this is a
relatively simple radio so modifications are easy.
* Frequency stability. In the cell site, the radios were driven by one
common master oscillator at 15.36 MHz. To use the radios individually
and get 1 kHz error at 900 MHz, we need to provide an oscillator that's
good to one part in 1e6. Crystal manufacturers want $80 to $90 for
such an oscillator, despite the quantity price of around $7. If anybody
knows a source for small quantities of 15.36 MHz oscillators, please let
me know.
* Antennas and preamps. To use all 100 radios, we need to get 200 antennas
and 100 preamps. They have to be cheap and easy to replicate 100 times.
* The vehicle locator service has priority over the amateur service in the
900 MHz band. The AVL (automatic vehicle locator) folks have been very
aggressive about defending their allocation, even threatening civil suits
against retail stores using theft alarms in the band. The North Texas
Microwave Group is also looking into this problem.
* Network coordination and architecture. This is mainly a political
problem. It has practical implications, like what kind of antennas are
needed and where they have to be pointed. The biggest problem is how
get everyone to agree on something, anything.
