Equipment Options for Medium to High-Speed Packet Radio

Compiled by Barry McLarnon, VE3JF (Last update: 14 Nov 95)

The purpose of the following is to summarize the hardware options available for constructing medium- to high-speed packet radio links. The speed range in question is 9600 bps and up. This material is intended to be a useful reference, but I make no claims as to its accuracy or completeness. Some details concerning model numbers and prices are missing, and I have very little information concerning equipment sources outside North America. If you have corrections, or suggestions on additional information to include in this survey, please send them to bm@hydra.carleton.ca.

This material is released to the public domain. You can do what you want with it - all I ask is that you retain this notice and attribution if you reprint it in whole or in part.

Note: unless otherwise noted, prices given are in $US. They should be considered only as approximate.

Equipment for 9600 bps

9600 bps Modems

The G3RUH modem is available from several sources:

PacComm MC-NB96 internal modem card ($115)

fits on disconnect header of most TNCs.

PacComm EM-NB96 external modem ($149)

standalone version of above.

Kantronics DE9600 modem card

similar to the PacComm MC-NB96.

MFJ MFJ-9600 9600 bps modem card ($110)

similar to the others.

The TAPR 9600 bps modem kit ($80).

The new design has all of the features of the G3RUH, plus a few enhancements. It is attractive for repeater use, since it includes provision on the board for bit regeneration/FIFO buffering ($15 extra for the parts). The first rev of the board in 1992 had a few problems, and some mods were needed for best performance. A new rev which incorporates the fixes became available in early 1993. TAPR members get a 10% discount on purchases.

DRSI DPK-9600 ($250).

This is a G3RUH-compatible modem and TNC-2 clone (10 MHz clock) housed in one box (no longer available from DRSI).

The G3RUH and TAPR modems can plug directly into a TNC modem disconnect header as a daughter board, or be connected externally via a ribbon cable.

Data Interfaces for 9600 bps

Ottawa PI2 card ($125 plus shipping).

It provides a DMA port which handles 56 kbps with ease, even with a 4.77 MHz XT-class machine. All you need to add is the cable to the modem. The main limitation of the card is that it does not support full-duplex operation, but full-duplex operation is rare (especially amongst end users). The PI2 also has a low-speed port and can be populated with an on-board 1200 bps modem (kit available for $30). The board can be used with any DOS version of KA9Q NOS, or with Linux. For more information about the PI2 Card, check the PI2 Web Page.

Gracilis PackeTwin-PC card ($229), now marketed by PacComm.

Like the PI2, it provides a DMA port for the 56 kbps modem and an interrupt-driven port for lower-speed modems. The DMA port supports full-duplex operation. The Kantronics 9600 bps modem can be piggybacked on the card.

DRSI PCPA Type 1296 ($290).

An interrupt-driven PC-plug-in card with onboard 9600 bps and 1200 bps modems.

Radios for 9600 bps

A standard NBFM radio is typically used. To interface to the modem, the radio must have a direct FSK modulator, discriminator output, an IF with sufficient bandwidth and reasonable phase characteristics, and fast t/r switching. Some radios are usable with just a few modifications to bring out the required signals, others may need more extensive mods such as adding a varactor FM modulator, and still others are almost completely unusable due to their IF characteristics or slow t/r switching. There are a few radios designed specifically for digital service which require no mods:

2m:

Alinco DR-1200TH2 (approx. $300).

This is a version of the DR-1200T 25W synthesized radio which has been modified for 9600 bps operation. It is reputed to be a mediocre performer, due to slow turnaround time.

MFJ MFJ-8621 VHF Data Radio ($120, crystals other than 145.01 extra),

5W crystal-controlled transceiver for 9600 bps or less. I have only heard one report about it, but it seemed to give it a good rating.

70cm:

Tekk KS900L Data Radio ($120, plus $25 for custom crystals [note: this was special pricing and may not be current]),

2W output, one channel, crystal controlled (430-450 MHz). Available directly from Tekk, and in packages from PacComm and other sources. Tekk has a more expensive model called the KS960 (in a larger, chrome case) which apparently does not work as well at 9600 bps as the KS900L, and thus should be avoided.

PacComm is another source of the Tekk radios, and they also sell modified versions with new filters installed (e.g., KS-900L-D96 for 9600 bps, $230) which they say provide improved performance. The filter upgrade kits are also sold separately ($35).

PacComm IPR-NB96 ($499)

This package includes a Tekk radio, modem, and Tiny-2 MK-2 TNC housed in one box.

Kantronics D4-10 ($359),

10W output, two channel, crystal controlled (430-450 MHz). Can go to at least 19.2 kbps.

A large number of amateur VHF and UHF transceivers have been successfully used for 9600 bps work. Many commercial FM radios are also suitable; ironically, the IF filters in these radios are typically 'better' (narrower bandwidth, steeper skirts) than in amateur-grade equipment, which leads to inferior performance at 9600 bps (on the other hand, they also tend to have superior intermod immunity compared to amateur rigs). The IF stages of most receivers can be broadbanded successfully, but the degree of difficulty and expense involved varies considerably.

A good source of information on radio interfacing and other topics related to 9600 bps operation is the 9600 Baud Packet Handbook by Mike Curtis, WD6EHR. Hard copies are distributed with the TAPR modem, and it can also be found in electronic form on some BBS's and on the Internet. The latest version seems to 2.0 (June 94).

Tests of a number of recent "9600 ready" synthesized radios were reported in the May 1995 issue of QST. Most were poor performers. The only two which delivered acceptable 9600 bps performance were the Icom IC-820H 2m/70cm multimode and the Azden PCS-9600D 70cm voice/data transceiver. Both are very expensive, however. Another expensive radio which performs well at 9600 bps is the Kenwood TM-255A 2m multimode tranceiver (QST, June 1995).

Summary: 9600 bps

Equipment for 19.2 kbps

Until recently, operation at 19.2 kbps had not received much attention. A major reason for this is that binary FSK at 19.2 kbps cannot be accommodated by the IF stages of NBFM receivers, nor is it compatible with the 20 or 25 kHz channel spacing used for FM in the amateur VHF/UHF bands. On the other hand, it makes relatively poor use of the 100 kHz channels typically allocated for 'wideband' digital modes. However, interest in 19.2 kbps operation has been spurred by the appearance of the Kantronics D4-10 radio. Since it contains a varactor modulator, plus a data slicer following the discriminator, it can be operated in 'raw FSK' mode at 19.2 kbps without additional modem hardware. All that is needed in addition to the radio is the computer interface. A 'souped-up' TNC might work fairly well, but one of the PC DMA interface boards (or maybe a DataEngine) would be better. Running 'modemless' FSK entails some loss of performance, most notably from the lack of data scrambling, which results in more jitter in the recovered clock signal and thus higher bit error rates.

Kantronics also offers a 19.2 kbps modem, similar to the DE9600. The performance difference between the 'barebones' D4-10 radios and that which you could realize with the more sophisticated modem has not, to my knowledge, been quantified. The GRAPES modem (see below) could also be run at 19.2 kbps, but it would not be compatible with the Kantronics equipment (and why would you want to throttle back a modem that can do 56 kbps and more, to only 19.2?).

Some experiences with using the D4-10's at 19.2 kbps, using Ottawa PI cards and DataEngines as interfaces, appear in an article by John Ackermann, AG9V in the 11th ARRL Computer Networking Conference Proceedings (available from TAPR).

PacComm offers Tekk radios which have been modified for 19.2 kbps operation (KS-900L-D192, $235). The filter upgrade kits are also sold separately ($39).

Equipment for 56 kbps

56 kbps Modem

GRAPES (WA4DSY) modem, $250 in kit form. You also need to provide a box for it, plus a few interconnecting cables and connectors. It requires +/-5V power (about 0.5A @ +5V, 0.1A @ -5V). This is an RF modem with input and output (about 1 mW) in the 28-30 MHz band, designed for use in the bands above 220 MHz (occupied bandwidth is about 70 kHz at 56 kbps), using standard receive and transmit converters. The receive and transmit portions of the modem are separately crystal-controlled , and it can run full-duplex. It is not limited to 56 kbps - with suitable modifications, it can be made to work at 128 kbps or more.

Dale Heatherington WA4DSY has come up with a complete redesign of his modem, substantially reducing the parts count and size (now fits on one board instead of three). The new modem is fully compatible with the old one at 56 kbps, but it will not work at other bit rates. The big news is that it will be sold in assembled and tested form by PacComm. Availability is said to be "late 1995", and the price has been announced as $349.

Data Interface for 56 kbps

• Ottawa PI2 card ($125)
• Gracilis PackeTwin card ($229) from PacComm

Both of these cards (see descriptions above) will handle 56 kbps with ease.

Kantronics DataEngine (~$350?).

This is essentially a higher-speed TNC with two HDLC ports that can reportedly run at 56 kbps, and an RS-232 port that can run at up to 19.2 kbps. The standard firmware is KA-Node or G8BPQ, but there is now also a port of JNOS (JNOS40) by WG7J available. The DE appears to be more useful as a small standalone packet switch than as an interface for end users.

Gracilis PackeTen ($1595?) from PacComm.

This is a full-blown packet switch that runs a custom version of KA9Q NOS. It is available in both standalone and PC bus versions. This is the Rolls Royce of packet switch hardware. The name is a bit of a misnomer, since one PackeTen provides five ports - you must add another one to get ten ports. All of the ports will handle synchronous or asynchronous rates of 1200 to 19200 bps, and three of them will do synchronous rates up to T1 or more.

PacComm has also announced that they are working on a scaled-down version of the PackeTen (PackeTen Junior?) which will run the same code as the big one and have two RF ports and one serial port... in other words, like the DataEngine, only better. :-) According to PacComm, it will be "available mid-winter at a price well below that of the PackeTen".

RF Equipment for 56 kbps

(1) Half-duplex point-to-point links

An example is the Georgia backbone network. The usual RF equipment is a Microwave Modules (220, 430 MHz) or Sinclabs (220 MHz) transverter.

(2) Full-duplex point-to-point links

Full duplex operation is significantly more complicated, but it is also highly desirable if you want to maximize the throughput of a backbone link. The GRAPES modem is inherently full-duplex, so it is only necessary to provide separate RF up- and down-converters. The two channels may be in-band or cross-band, using either separate antennas or duplexers. The only full-duplex point-to-point link I'm aware of is in Chicago - it uses PackeTen switches and operates in-band in the 70 cm band.

(3) Multiple-access networks with full-duplex repeater

In this case, an in-band or cross-band 56 kbps repeater provides hidden transmitter-free access to a channel (or rather, a pair of channels) by multiple 56 kbps stations. This might just be a LAN for the power users, but it also is an attractive means of linking a number of network nodes together, with less complexity than multiple point-to-point links. See the 10th ARRL Computer Networking Conference proceedings (available from TAPR)for more details. As in the preceding case, separate receive and transmit converters are used, usually with separate antennas (in principle, a transverter with "split" frequency operation could be used, but such things are hard to come by). The stations in this network do not require full-duplex computer interfaces, but since the RF portions have full-duplex capability, it allows smaller txdelays to be used than in the half-duplex case. It also allows users to observe the quality of their signals coming back from the repeater.

The first 56 kbps full-duplex repeater went on the air in Ottawa in January 1990. The repeater is cross-band (220.55 MHz in, 433.55 MHz out), so users must up-convert the modem's 28-30 MHz IF output to 220 MHz, and down-convert 432 MHz to the 28-30 MHz IF input. The new WA4DSY modem will have the bit-regenerator repeater capability built-in.

220 MHz (219 or 222 MHz in the US!)

Transverters and up-converters:

Sinclabs ST220-28 transverter ($329 CDN),

15W output. Sinclabs has recently withdrawn from this business, but transverters may still be available from Bob Morton, VE3BFM (Maple Leaf Communications).

Microwave Modules MMT220/28S transverter,

10W output. The company no longer sells to the amateur market, but its remaining stock of transverters was bought up by Advanced Radio Technology in the UK. Prices are in the $300 range ($272 plus $25 shipping to the US). Used units show up quite frequently at flea markets, etc. You may also come across some MM clones produced by Hans Peters VE3CRU ("Transverters Unlimited") - they are good quality, and produce higher output (~15W).

Down East Microwave DEM222 no-tune transverter,

20W output, 1-100 mw input:

• DEM222-28CK complete kit (PC board, board-mounted parts, enclosure, connectors, heat sink, hardware, $295)
• DEM222-28K board-level kit (PC board, board-mounted parts, $225)
• DEM222B assembled and tested unit ($395)

SSB Electronic TV 28-220/01 transverter ($380),

100 mW output. These units have no T/R switching, so that would have to be added externally for single-channel half-duplex operation. On the other hand, there are separate local oscillators provided for the receive and transmit converters, so this looks like a good choice for in-band full-duplex or half-duplex split operation.

Hamtronics XV4 transmit converter (kit, $79),

0.5 - 1W output. The cheapest alternative, and the power level is adequate if you aren't too far from the repeater and have a reasonable transmitting antenna. But you do need to find someone with a spectrum analyzer to get it tuned up properly, and some people have had problems taming this unit.

PacComm has announced that they will be selling assembled and tested transverters for 219 MHz (from dB Microwave - see below) in early 1996, prices TBA.

Down-converters:

Microwave Modules MMc220 (current price/availability unknown),

2.8 dB NF.

Advanced Receiver ResearchR220VDA (current price/availability unknown).

This unit is in the $100 range and of high quality, but it really needs a front-end preamp. We use one of these converters on the Ottawa 56kb repeater, along with an ARR preamp.

Antennas:

You might get by with omni antennas, but multipath can cause poor performance even when signal levels are high. Small yagis provide more margin and help discriminate against multipath. A typical example is the Cushcraft A220-7 7-element yagi (about $50).

430 MHz

Transverters and up-converters:

Down East Microwave DEM432 no-tune transverter,

50-100mW output. This is a 3-board set, available in several forms, and there is an optional power amplifier that provides 15W output. The local oscillator board normally has a single oscillator for standard half-duplex operation, but a second oscillator can be added on the board for half-duplex split or full-duplex operation. Some options and prices:

• DEM432B assembled and tested unit, including case, $275
• DEM432BD as above, but set up for dual frequencies, $300
• DEM432K basic kit (no case or connectors), $155
• Second LO kit, $8
• 432PA 15W PA, assembled and tested, $180
• 432PACK 15W PA complete kit, $135
• 432PAK 15W PA basic kit (no case, connectors or heat sink), $75
• Enclosure to house both DEM432K and 432PA, $25
• DEM432-15S complete 15W dual-frequency transverter, $395

Microwave Modules MMT432/28S transverter,

10W output. The company no longer sells to the amateur market, but its remaining stock of transverters was bought up by Advanced Radio Technology in the UK. Prices are in the $300 range ($272 plus $25 shipping to the US). Used units show up quite frequently at flea markets, etc.

SSB Electronic TV 28-432 transverter ($310),

100mW output. These units have no T/R switching, so that would have to be added externally for single-channel half-duplex operation. On the other hand, there are separate local oscillators provided for the receive and transmit converters, so this looks like a good choice for in-band full-duplex or half-duplex split operation.

Hamtronics XV4 transmit converter (kit, $79),

0.5 - 1W output. The 432 MHz version of the unit described above.

PacComm has announced that they will be selling assembled and tested transverters for 420-450 MHz (28-30 MHz IF), made by dB Microwave in Vancouver, in "late 1995". In addition to up- and down-converters which are synthesized in 100 kHz steps (it is not known yet whether these will be available separately), optional preamps and 25W power amplifiers will be offered. No pricing available yet. The units may also be available in kit form direct from dB Microwave.

Down-converters:

Hamtronics ($49/$69/$99 for basic kit/kit with box/wired & tested).

Quality of this unit is uncertain.

Microwave Modules MMc435.2 ($115).

Current availability unknown.

SSB Electronic K7001-10 ($180).

High quality, with a price to match.

There are other sources for units in the $100-$150 range, such as Lunar.

1.2 GHz

Transverters and up-converters:

Down East Microwave SHF-1240(K) "No-tune" transverter board ($149 kit, $189 assembled):

144 MHz IF (10 mW drive required), 10 mW output. Also required is the separate SHF-LO local oscillator board ($50 kit, less crystal; $85 assembled). A complete transverter (transverter board, LO board, IF PIN diode switch, packaged in a metal box) is available for $265. Note that no RF switching is included, so if you wanted to run half-duplex, a suitable RF T/R switch or a circulator would be needed. NF of the down-converter is in the 4-5 dB range. Due to the 144 MHz IF, a separate 28 MHz to 144 MHz conversion stage would be needed.

SSB Electronic USM-3 transmit converter ($210).

1W out (20 mW in). Requires external LO source (10 mW). Although normally used with 144 MHz IF, it reportedly can be tuned for 28-30 MHz IF input. Housed in a metal box with BNC connectors.

Down-converters:

SSB Electronic UEK-3 receive converter ($200).

2.2 dB NF, 20 dB conversion gain. The nominal LO frequency is 1152 MHz, for conversion of the 1296-1298 range to 144-146 MHz. An LO output port is provided for driving the USM-3 transmit converter. Housed in a metal box with BNC connectors.

Power amplifiers:

Pauldon (kit, $165):

18W out for 1W in.

Down East Microwave 2318PAM ($205):

18W out for 1W in. Also available in kit form.

SSB Electronic PA 2310 ($250):

10W out for 0.5W in (a 20W out version is $300).

Advanced Radio Technology carries the Microwave Modules MMT line of linear amps, with outputs up to 100W.

Antennas:

Although loop yagis are commonly used at 1.2 GHz ($89 kit, $109 assembled for the 45-element loop yagi from Down East Microwave), a better choice for linking would probably be the Tonna 23-element yagi (about $70).

Other Considerations (applies to all bands):

The receive converters have very broad front ends, and some additional bandpass filtering will often be needed. A single cavity (or helical resonator front-end filter, in the case of separate receive converters) should do the trick in most cases. There is also a design available for a home-brew 28-30 MHz bandpass filter for the modem front end. This might eliminate the need for a front-end filter, but it depends on your receiving environment.

56 kbps Summary

The Packet Frontier: Equipment for Speeds Greater than 56 kbps

The following is a very rough first cut at summarizing the current situation for packet at speeds greater than 56 kbps. Commercial availability of radio and modem equipment for these speeds is nil, so this is really the domain of the true experimenter!

Data Interface

• Ottawa PI2 card: up to 500 kbps, maybe more
• Gracilis PackeTwin: up to 1 Mbps claimed
• Gracilis PackeTen: up to 4 Mbps (aggregate)

RF Hardware for >56 kbps

GRAPES Modem

The original GRAPES Modem (not the new 1995 design) can run at higher speeds than 56 kbps. In his 1987 CNC article, Dale WA4DSY mentions rates up to 120 kbps. I've run a pair of modems back-to-back at 125 kbps. Most of the changes are straightforward (e.g., changing the baud rate generator crystal from 3.579 MHz to 8 MHz), but there are two problem areas. Standard 555 timer chips won't work reliably above 100 kHz, so the receiver clock recovery PLL circuit needs more than just a resistor or capacitor change. Replacement of the 555 with a TI TLC555 does the trick. The other problem is the 455 kHz IF filter: it can be retuned so that the modem works at 125 kbps, but the eye pattern isn't very satisfactory. A new filter design will be needed for decent on-the-air results.

N6GN 250-500 kbps RF Modem

Glenn Elmore N6GN (glenne@sr.hp.com) has designed an RF modem for the 902 MHz band which is intended for use at rates in the 250 to 500 kbps range. The modem is crystal-controlled, has about 12W output, and extremely fast turnaround time. Note that this is an FSK modem, and is not at all similar to the spread spectrum "wireless ethernet" systems which are available for this band. Glenn is currently running some of these units at 230.4 kbps, using Ottawa PI2 cards. No PC boards or construction plans are available at the moment. Units for 1.2 GHz have been mentioned, but I'm not sure if they exist. For more info on this work and the 10 GHz equipment described in the next section, check out Glenn's Higher Speed Packet Page on col.hp.com.

High-speed Packet at 10 GHz

Glenn Elmore and friends (Kevin Rowett N6RCE, Bdale Garbee N3EUA, etc) have also designed an X-band (10 GHz) full-duplex packet data link using inexpensive gunnplexor modules that runs at a nominal 2 Mbps rate. Details can be found in recent editions of the ARRL Handbook. I haven't heard of any such systems actually being put into service yet, but there is a source for the PC boards:

Date: Tue, 10 Aug 93 16:30:44 CDT
From: bob@lachman.com (Bob Van Valzah)
To: glenne@srlr12.sr.hp.com, bdale@col.hp.com, ron@chaos.eng.wayne.edu,
tcp-group@ucsd.edu
Subject: 2 MBPS 10 GHz Link Boards Available
Status: RO

Receiver boards are now (at last!) available for the n6gn designed, 
2 MBPS, 10 GHz microwave link as described in the ARRL Handbook and 
other places.  You'll still need to make the 1st IF board yourself, 
but trust me, that's easy.  I didn't believe Glenn at first, just 
follow the procedure in the article and it works!

The receiver board is 4-3/4 x 5-3/4", double sided, and drilled, 
*but not plated through* (hence you'll have to solder top and bottom 
leads in some cases).  This shouldn't be a big problem because there 
are no signal traces on the component side--it's all ground plane.

Folks who helped make these boards available (though they may not 
all want to admit it :-) are Glenn Elmore n6gn (of course), John 
Conner wd0fhg, Ron Atkinson n8fow, Fred Reimers kf9gx, Bdale Garbee 
n3eua, and Jon Bloom ke3z.

They're available from:

for $15.  Fred just shipped 8 to me for $5 postage, but I'm not sure 
what the rate would be for smaller quantities.

T1 Modem

Clint Turner KA7OEI (ka7oei@uugate.wa7slg.ampr.org) has designed a T1 rate (1.536 Mbps) modem, intended for use in the packet backbone network in Utah. This modem is designed for full-duplex operation and produces and demodulates a baseband-type signal. It was designed for FM transmitter/receiver systems with a baseband bandwidth of at least 1.5 MHz.

Sources