Glossary of HAM Radio Terms

Alphabetical search:

[A] [B] [C] [D] [E] [F] [G] [H] [I] [J] [K] [L] [M] [N] [O] [P] [R] [S] [T] [U] [V] [X]


A

ACK

Abbreviation for acknowledgement. Sent by the destination station back to the originating station to indicate the successful reception of a frame. (See NAK.)

Address 1

The specific designation given to each station on the net>

Acronym for Audio Frequency Shift Keying. A method of modulation in which the RF carrier frequency remains constant and an audio modulation tone is shifted in frequency. When used on a SSB transmitter, cannot be differentiated from FSK.

ALOHA

Also ALOHANET. An early packet radio network set up at the University of Hawaii in 1970 for research and development on packet radio communications. (See menehune.)

Alpha Testing

The first stage of product testing after the prototype development. The sequence is: conception, design, prototype, alpha testing, beta testing, and production.

AMRAD

Amateur Radio Research And Development Corporation. A non-profit organization involved in amateur packet radio development.

AMSAT

The AMateur SATellite Corporation. A United States-based non-profit organization committed to the development and encouragement of amateur satellite activity.

AMTOR

AMateur Teletype Over Radio. An advanced form of RTTY usually operated on the HF bands.

Analog

A signal that varies in a continuous manner (e.g., voice, music, and voltage and currents that vary in a continuous manner). (See digital.)

ANSI

Acronym for American National Standards Institute. The principal standards development organization in the United States. (See CCITT, EIA, ISO.)

Application Layer

Level 7 of the OSI/RM. Contains user software.

Argument A

variable expression that follows a command.

ARRL

Acronym for American Radio Relay League.

ASCII

Acronym for American Standard Code for Information Interchange. Also USASCII. A seven bit code established by ANSI to achieve compatibility between digital devices.

Assembly Language

A low level, high-speed computer language consisting of mnemonics and operands which are converted, or assembled, to machine code. (See machine code, BASIC, C.)

Asynchronous

Also called Start-Stop transmission. Digital signals which are sent as groups of a specified length with start and stop bit indicators at the beginning and end of each group. Usually used when time intervals between transmitted groups may be uneven. (See synchronous.)

AX.25

Amateur packet radio protocol version of the X.25 protocol. Usually used in reference to the data link layer protocol in use by most amateur packet stations.

 


B

BASIC

Acronym for Beginner's All-purpose Symbolic Instruction Code. A high level computer language included with most microcomputers. (See C, assembly language, machine code.)

Baud

A unit of signaling speed equal to the number of discrete signal events per second. Baud is the same as BPS only if each signal event represents exactly one bit.

Baudot

Also called Murray code. A five level code for the transmission of data in digital form. Named for Emile Baudot. Baudot code is usually found in older teleprinters.

BBS

Also called CBBS, PBBS, Mailbox. Acronyrn for Bulletin Board System. An automated computer system which can be controlled from a remote location. Usually capable of sending and receiving messages and files.

Bell 103

A modem standard with a 200 Hz shift (1070 Hz, 1270 Hz) operating at 300 baud. Used for HF amateur packet radio operation.

Bell 202

A modem standard with a 1000 Hz shift (1200 Hz, 2200 Hz) operating at 1200 baud. Used for VHF FM amateur packet radio operation.

BER

Acronym for Bit Error Rate.

Beta testing

The fifth and usually final stage of product development before general production and release. The sequence is: conception, design, prototype, alpha testing, beta testing, and production.

Binary

A number system based on the powers of 2. The only characters are a "0" and a "1." Binary digits are easily transmitted and stored in electronic equipment. (See bit, hex, octal.)

Bipolar Keying

A technique in which a binary "1" is represented by a positive pulse and a binary "0" is represented by a negative pulse. Bipolar keying is the system used by NRZI on amateur packet radio. (See NRZ, Manchester, encoding technique.)

Bit

Abbreviation for BInary DigiT; either a "0" or a "1."

Bit Stuffing

The addition of a binary "0" following all sequences of five binary "1"s in the data transmission to avoid the accidental occurrence of a flag. The added binary "0" is removed by the receiving station.

BOP

Acronym for Bit Oriented Protocol. Control and data consume only as many bits as needed. No minimum binary grouping. (See COP.)

Buffer

Memory space set aside for the temporary storage of data until recalled, processed, or permanently stored.

Bus Network

A network configuration in which all nodes are on the same channel and may communicate with each other directly providing they are within range.

Byte

A grouping of eight bits. (See nybble, octet.)



C

C

A high-speed, high level computer language. (See BASIC, machine code, assembly language.) CCITT

Comite Consultatif Internationale de Telegraphique et Telephonie. An international committee that establishes international communications standards. (See ANSI, EIA, ISO.)

Checksum

The numeric result of a CRC. Sent within a frame as the FCS.

Collision

When two or more stations transmit at the same time, or when one or more stations transmit while another station is transmitting. A collision may destroy one or more of the transmissions depending on the relative strength of the signals and the sensitivity of the receivers.

Command

A string of characters recognized and acted upon by a device.

Command Set

A subset of the user interface consisting of all available commands and parameters. May be organized by group, function, or alphabetically.

Connection

The condition of having established commnunications between two stations via a preset path.

Contention

A condition in which two or more stations try to transmit at the same time.

Control Character

A special character recognized by the receiver (usually a computer) as having a special meaning. Usually sent by pressing a control key and the appropriate character on the keyboard. Control characters are written in the abbreviated form as CTRL or CTL. For example, CTRL-C: break, CTRL-M: carriage return.

COP

Acronym for Character Oriented Protocol. All information must be sent as characters of a specified length. COPs are usually less efficient and less flexible than BOPs. (See BOP.)

CPU

Acronym for Central Processing Unit. The "brains" of a computer. Responsible for directing the flow of data throughout the computer.

CRC

Acronym for Cyclic Redundancy Check. An error detection scheme in which a check character is generated by dividing the entire numeric binary value of a block of data by a generator polynomial expression. The CRC value is sent along with the data, and at the destination station, the CRC is recomputed from the received data. If the received CRC value matches the one generated from the received data, the data is considered error free. (See FCS, checksum.)

CRRL

Acronym for Canadian Radio Relay League.

CSMA/CD

Acronym for Carrier Sense Multiple Access with Collision Detection. The system used in amateur packet radio to handle TDM of the channel and contention. Each station monitors the channel and only transmits when the channel is clear.The absence of an ACK from the destination station indicates that a collision may have occurred, and the transmission is resent after waiting a random time interval.

CTS

Acronym for Clear To Send in the RS-232 standard. Also referred to as Pin 5, CB by the EIA, and 106 by the CCITT.

 


D

Data

The digital information which is being transmitted or received.

Data Link

layer Level 2 of the OSI/RM. Arranges bits into frames, establishes and maintains a link, and performs error detection and recovery. ISO HDLC is the most common level 2 protocol.

Datagram

A type of packet networking in which each packet contains complete and extensive addressing and control information. This allows for variable routing at the expense of greater overhead. (See virtual circuit.)

DB-25

A series of 25-pin connectors which are commonly used in RS-232 interfacing applications.

DCD 1

An indicator which signals the presence of a signal. 2. Acronym for Data Carrier Detect in the RS-232 standard. Also referred to as Pin 8, CF by the EIA, and 109 by the CCITT.

DCE

Acronym for Data Communication Equipment. A device capable of establishing, maintaining, and terminating a connection. Also may have to handle signal conversion and coding. (See DTE.)

Demodulation

The process of retrieving data from a modulated signal. (See modulation, modem.)

Digipeater

A simplex packet repeater which stores an incoming packet, and, if so instructed, re-transmits it. The digipeater does not retain a copy of the packet once sent or wait for an acknowledgement from the next node.

Digital

A discrete or discontinuous signal whose various states are identified with specified values. (See analog, RS-232, 7'TL.)

DOS

Acronym for Disk Operating System. A program which handles all disk access by the computer system. May be loaded into memory or permanently stored in firmware.

Downlink

A radio link originating at a satellite and terminating at a ground station.

DSR

Acronym for Data Set Ready in the RS-232 standard. Also referred to as Pin 6, CC by the EIA, and 107 by the CCITT.

DTE

Acronym for Data Terminal Equipment. A device capable of I/O. (See DCE.)

DTR

Acronym for Data Terminal Ready in the RS-232 standard. Also referred to as Pin 20, CD by the EIA, and 108/2 by the CCITT.

Dumb Terminal

A communications terminal with only the basic capabilities necessary for communications such as an input device, an output device, and a predefined I/O port. (See smart terminal.)

 


E

EBCDIC

Acronym for Extended Binary Coded Decimal Interchange Code. An eight-level character code developed by IBM and used primarily in their equipment. (See ASCII, Baudot.)

EIA

Acronym for Electronic Industries Association. A standards organization specializing in interface equipment. (See ANSI, CCITT.)

Encoding Technique

Also called line coding, channel coding, and data format. The system utilized to encode the digital data for transmission. (See NRZ, NRZI, Manchester.)

 


F

FAD

Acronym for Frame Assembler/Disassembler. Often used interchangeably with PAD and TNC.

FADCA

Acronym for Florida Amateur Digital Communications Association. Published the FADCA > BEACON newsletter; now publishes Packet Radio Magazine.

FCS

Acronym for Frame Check Sequence. A CRC for a frame.

FDM

Acronym for Frequency Division Multiplexing. A technique for distributing users over a number of separate channels; each channel may have different characteristics. (See TDM, SDM.)

Flag

A unique binary sequence used to delimit frames at the data link layer. In HDLC, the flag is 01111110. (See bit stuffing.)

Flow Control

The process of stopping and starting the flow of data between devices.

Frame

A group of bits delimited by flags. May contain control information and data.

FSK

Acronym for Frequency Shift Keying. A method of frequency modulation in which the frequency varies. (See AFSK, PSK.)

Full Duplex

Simultaneous two way independent transmission in both directions on separate channels. (See simplexs, half duplex.)

 


G

Gateway 1

The amateur packet radio newsletter published biweekly by the ARRL. 2. A device which re-transmits received data in another format or on another channel

 


H

Half Duplex

A circuit designed for transmission in either direction on two separate channels but not both directions simultaneously. (See full duplex, simplex.)

Hard Drive

Also called Winchester dnve. A rigid disk magnetic storage device permanently sealed in a herrnetic container which can store large amounts of data; usually (for microcomputers) 5 to 20 megabytes.

Hardware

Physical equipment as opposed to a program or protocol; for example, TNC board, computer, printer. (See software.)

HDLC

Acronym for High-level Data Link Controller. An ISO standard for the data link layer of the OSI/RM. (See protocol.)

Header

The collective components of a frame preceding the information component. The header of an AX.25 frame consists of an opening flag, the address field, and control information.

HEX

Abbreviation for hexidecimal. A number system based on powers of 16. Characters are 0-9 and A-F. (See binary, octal.)

 


I

IBM

Acronym for International Business Machines Corporation.

IC

Acronym for Integrated Circuit.

I/O

Acronym for InputlOutput. Used in reference to any system or function that deals with sending and receiving data.

ISO

Acronym for International Standards Organization. (See CCITT, EIA, ANSI.)

 


J

JAMSAT

The Japanese AMSAT affiliate.

JAS-1

A packet radio satellite designed by JAMSAT which features a flying mailbox and digipeater capabilities. (See RUDAK, Pacsat.)

 


K

Kludge

A temporary "quick and dirty" solution to a problem. Often used to imply that a system is inefficient, ill-designed, and in need of improvement.

 


L

Landline

Common expression for a terrestrial cable link between two stations. Usually used in reference to the telephone system.

LAPB

Acronym for Link Access Procedure Balanced. A subset of HDLC in which each node is treated on an equivalent basis with each able to send both commands and responses.

LCD

Acronym for Liquid Crystal Display. A display device commonly used in portable computers. Contains a crystalline liquid whose optical properties change in the presence of an electric field to appear either light or dark. Must have an external light source to be visible.

Level 1-7

Numerical designators for the OSI/RM levels as follows; level 1: physisal layer, level 2: data-link layer, level 3: network layer, level 4: transport layer, level 5: session layer, level 6: presentation layer, and level 7: application layer.

 


M

Machine Code

A low-level, high-speed computer language consisting of the actual binary instructions acted upon by the computer. (See assembly language, BASIC, C.)

Mailbox

(See BBS.)

Manchester

Two types are Manchester I and Manchester II. An encoding technique similar to NRZI, but differs because the transition from positive to negative or negative to posi digital devices.

Modulation

The process of adding a signal to a carrier to transmit information. Can be used in reference to voice communications, but refers to digital data in the context of packet radio. (See demodulation, modem.)

Monitor Mode

A mode in which the TNC is instructed to forward all received packets to the terminal. The user usually specifies categories of packets to be received (i.e., to or from certain stations, digipeated packets, control packets).

MSK

Acronym for Minimum Shift Keying. A modulation method similar to FSK in which the shift in hertz is equal to half the signaling rate in BPS. (See AFSK, FSK, PSK)

Multiconnect

The ability of a packet station to connect with more than one station simultaneously.

Multiplex

The process of dividing a communications medium so that many users can share it. ( See FDM, SDM, TDM.)

 


N

NAK

A negative acknowledgement. (See ACK.)

NEPRA

Acronym for New England Packet Radio Association.

Network

An interconnection of computer systems, terminals, and communications facilities.

Network Layer

Level 3 of the OSI/RM. Deals with addressing, routing, multiplexing, and flow control. Two types of networks are virtual circuit and datagram.

Network Node

Also called packet switch. A hardware system with a level 3 protocol designed to forward packets through the network to their destination. (See datagram, virtual circuit.)

Node

A general term used to indicate the different stations in a packet network. Nodes may be terminal nodes, network nodes, station nodes, and others. (See TNC, digipeater.)

NRZ

Acronym for NonReturn to Zero. An encoding technique for binary digital signals in which a binary " 1" is encoded as a positive pulse and a binary "0" as a negative pulse. When modulated, the positive pulse becomes the mark tone and the negative pulse the space tone. This is the encoding technique used in Baudot RTTY. (See Manchester.)

Null

A "blank"; a meaningless character usually used to consume extra bit space or time.

Null Modem

Also null modem adaptor and null modem cable. An RS-232 interfacing device which switches several pins to allow DTEs or DCEs to communicate with devices of the same designation.

Nybble

A group of four bits. One half of a byte. Represented by a single HEX character.

NZRI

Acronym for NonReturn to Zero Inverted. An encoding technique for binary digital signals in which a binary "0" causes a change in signal level while a binary "1" causes no change. This is the encoding technique in use in most amateur packet radio systems. (See Manchester.)

 


O

Octal

A number system based on powers of 8. Characters are 0-7. (See HEX binary.)

Octet

A group of eight bits. (See byte, nybble.)

OSCAR

Acronym for Orbital Satellite Carrying Amateur Radio.

OSI/RM

Acronym for Open Systems Interconnection Reference Model. A formal hierarchical identification of all network functions as established by the ISO.

Overhead

Any information other than the actual data that is transmitted. In packet radio, some overhead is necessary (i.e., addresses, control information), but it should be kept to a minimum.

 


P

PAC-COMM An abbreviation for Pac-Comm Packet Radio Systems, Inc.

Packet

A group of bits including data and control elements which is transmitted as a whole. Technically, a packet is not formed until the network layer; however, many refer to frame transmissions on the data link layer as packets. (See frame.)

Packet Controller

Term used for a hardware TNC with an on-board modem.

Packet Switch

A device which is used along with a network layer protocol to forward (switch) data sent on the network to the next node. Packet switches acknowledge data sent to them and then wait for an acknowledgment from the next node. In most cases, individual users are not involved in selecting the routing used by the packet switches. (See network node.)

PACSAT

Contraction of PACket SATellite. A packet satellite designed by AMSAT which will feature a flying mailbox similar to terrestrial BBSs. (See JAS-l, RUDAK.)

PAD

Acronym for Packet Assembler/Disassembler. May be used interchangeably with TNC. (See FAD.)

Padding

The addition of extra character to a group of characters in order to reach a predefined amount.

Parallel Transmission

A method of transmitting data in which all bits of each bit grouping are transmitted simultaneously on separate channels. (See serial transmission.)

Parameter

A variable stored for future reference.

Parity

The addition of a non-information bit to a group of bits making the total number of binary "1"s in the group either even or odd depending on the type of parity selected. This permits single bit error detection in each group.

Path

The sequence of channels, gateways, and repeaters used to transmit information from one node to another.

Peripheral

Any device which can be connected to a computer system to extend its operating capabilities.

Physical Layer

Level 1 of the OSI/RM. Concerned with electrical characteristics of the communications link. (See modem, RS-232C.)

PLL

Acronym for Phase Locked Loop. A circuit for synchronizing an oscillator with the phase of a signal.

Polling System

A method of TDM (Time Division Multiplexing) in which each station is asked (polled) to determine if it has any traffic to send. (See random access.)

PPRS

Acronym for Pacific Packet Radio Society.

Presentation Layer

Level 6 of the OSI/RM. Performs any code conversion, handles control data structure and display formats. Also manages data interchange with peripheral storage devices.

PRM

Acronym for Packet Radio Magazine. A monthly publication by FADCA.

Propagation Delay

The time lapse between transmission and reception of a signal on a radio link. Satellite delays tend to be longer than those of terrestrial links.

Protocol

A formal set of rules which dictate the format, timing, and other parameters of message exchange between two or more devices.

Prototype

A very early design of a product assembled in small quantities for initial testing and further development. Sequence is: conception, design, prototype, alpha testing, beta testing, and production.

PSK

Acronym for Phase Shift Keying. A method of transmitting digital information in which the phase of the carrier is varied in accordance with the digital signal.

PSR

Acronym for Packet Status Register. The newsleKer published by TAPR as part of PRM.

 


R

RAM

Acronym for Random Access Memory. Electronic memory which may be read from and written to. However, once power is removed, all stored data is lost. Some RAMs provide for battery backup to retain the data in case normal power is removed.

Random Access

A type of network in which stations may transmit at any time provided the channel is available. (See polling system.)

Ring Network

A network configuration in which each node is connected to two other adjacent nodes, one on each side. When the connections are complete, the path of connections will resemble a ring or circle. Each node may communicate directly only with the node immediately preceding and immediately following it. All nodes serve as relay stations to allow for communications throughout the network. (See star, Bus.)

ROM

Acronym for Read Only Memory. Electronic memory which may be read from but not written to. Data is perrnanently retained. Some ROMs allow for occasional programming and erasure (the EPROM--Erasable Programmable ROM). Most ROMs can be erased with W light, so the top of the ROM chip is covered with a label or sticker to block all light.

RS-232C 1

An EIA standard. The latest version is C. A common serial communications interface for computer peripherals.2. Defines the voltage signaling levels in electronic equipment. Range is -25 to -5 and +5 to +25volts; +/-12 and +/-15 volts are commonly used.

RTS

Acronym for Request To Send in the RS-232C standard. Also referred to as Pin 4, CA by the EIA, and 105 by the CCITT.

RTTY

Contraction of Radio TeleTYpe. Direct printing digital radio communications.

RUDAK

A packet experiment designed by the West German affiliate of AMSAT included on the Phase IIIC satellite. (See JAS-l, Pacsat.)

 


S

SDLC

Acronym for Synchronous Data Link Control. An IBM data link protocol very similar to HDLC.

SDM

Acronym for Space Division Multiplexing. A method of allowing multiple users to share a single communications channel by arranging the users so that they are not in each other's communications range. (See FDM, TDM.)

Serial transmission

A method of transmitting data in which each bit is sent sequentially on a single channel. (See parallel transmission.)

Session Layer

Level 5 of the OSI/RM. Initiates and terminates communications through the network; also handles network log-on and authentication.

Simplex

Operation over a single channel in one direction at a time. (See full duplex, half duplex.)

Smart Terminal

A communications terminal with advanced capabilities (such as X-on/X-off flow control, buffers, variable parameters, and echoing) in addition to those required for basic communications. (See dumb terminal.)

Software

The program and procedures that control the operation of hardware systems.

Standard

An established procedure, model, or design that has gained widespread recognition and conformity. Can be developed by committee, industry, or popular usage.

Star Network

A network in which all user nodes are situated about a central node. All communications between user nodes must take place through the central node. (See ring, bus.)

Start Bit

Used in asyncbronous serial communications. The first bit in each character which notifies the receiver that a bit group is coming.

Stop Bit

Used in asynchronous serial communications. The last bit in each bit group which notifies the receiver that the bit group is ended.

Synchronous

Transmission in which the data is transmitted at a fixed rate with the transmitter and receiver synchronized. This eliminates the need for start and stop elements used with asynchronous transmission. (See asynchronous.)

 


T

TAPR

Acronym for Tucson Amateur Packet Radio. A non-profit organization specializing in packet radio development.

TDM

Acronym for Time Division Multiplexing. The sharing of a single communications channel between many users by allotting the channel to each user on a time basis. (See multiplexing, FDM, SDM.)

Teleport

A gateway between a terrestrial station or network and a satellite.

Teletype

A registered trademark of the Teletype Corporation. Generic term used is teleprinter. A typewriter like device with a mechanical system to change keypresses into electrical pulses for transmission. Received pulses are converted back to characters which are printed on paper.

Terminal

A dedicated communications device that usually has a keyboard, display device (s), and an VO port. (See dumb terminal, smart terminal.)

Throughput

The actual rate of transmission (usually in BPS) taking into account switching times, re-transmissions, and other delays.

TNC

Acronym for Terminal Node Controller. A device which assembles and disassembles frames. Usually includes some form of a user interface and command set. May be implemented in hardware or software. Used in conjunction with a radio, modem, and terminal for packet radio applications. (See node, PAD, FAD, packet controller.)

Toggle

To switch between one of two possible conditions.

Token Passing

A form of TDM in which a unique binary sequence is passed from node to node. Only the node with the token may transmit.

Transponder

A device that receives radio signals in one segment of the frequency spectrum and repeats them on another segment of the spectrum.

Transport Layer

Level 4 of the OSVRM. Arranges data in order in the event packets arrive out of order.

TTL

Acronym for Transistor Transistor Logic. A logic standard which represents a binary "1" as + 5 volts and a binary "0" as 0 volts. TTL logic is used in the internal operations of most computer circuits.

Turnaround Delay

The time period required for a station to switch between receive mode and transmit mode.

 


U

UART

Acronym for Universal Asynchronous Receiver Transmitter. A device, usually packaged as an IC, which transmits and receives asynchronous serial data. The transmitter accepts data in parallel format and outputs the data in serial format. The receiver accepts data in serial format and outputs the data in parallel format.

Unipolar Keying

A technique in which a binary "1" is represented by a pulse and a binary "0" by the absence of a pulse. Unipolar keying's poor performance led to the development of bipolar keying.

Uplink

A radio link originating at a ground station and terminating at a satellite. (See doumlink.)

User Interface

The interface between the user and the device being used. In packet radio, the procedures implemented to allow the user to communicate with the TNC. Usually consists of a computer program incorporating a variety of commands. (See command set.)

 


V

VADCG

Acryonym for Vancouver Amateur Digital Communications Group.

VADCG

Protocol An early level 2 protocol based on HDLC developed by Doug Lockhart VE7APU for use in packet radio development. No longer in widespread use. Now called the V-1

Protocol

(See AX.25.)

VDT

Acronym for Video Display Terrninal. A terminal with a video monitor.

Virtual Circuit

A type of packet networking in which a logical connection is established prior to the transfer of data. This allows for abbreviated addressing and lower overhead at the expense of routing flexibility. (See dataBram.)



X

X.25

A CCITT standard. "Interface Between DTE and DCE for Terminals Operating in the Packet Mode on Public Data Networks." Defines the architecture of three levels of protocols existing in the serial interface between a packet mode terminal and a gateway to a packet network. AX.25 level 2 is derived from the data link layer of X.25.

X.28

A CCITT standard. "DTE/DCE Interface for a Start-Stop Mode DTE accessing the PAD in a Public Data Network." Defines the protocol structure in a serial interface between an asynchronous terminal and X.3 PAD.

X.29

A CCITT standard. "Procedures for the Exchange of Control Information and User Data Between a PAD and a Packet Mode Terminal DTE or another PAD." Defines the protocol structure between two PADs or between a PAD and a Packet Mode Terminal.

X.3

A CCITT standard. "Packet Assembly/Disassembly Facility (PAD) in a Public Data Network." Describes the PAD which normally is used at a network gateway to allow connection of an asynchronous terminal to a packet network.

X.121

A CCITT standard. "International Numbering Plan for Public Data Networks." Defines an addressinf plan with code assignments for each nation.

Xerox 820

A single board Z-80 based microcomputer. Usually equipped with 64K memory, a parallel printer port, and two RS-232 serial ports. Often combined with a keyboard, monitor, and disk drives to form a complete system. The Xerox 820 is used in many amateur packet radio applications including the WORLI BBS, dualport digipeaters, and dedicated TNCs.

 

 


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