================================================================ D A S (DTMF ACCESSORY SQUELCH) APPLICATION NOTE 5 SPECIAL REMOTE CONTROL APPLICATIONS AND OPERATIONS 951128/Iss-1 ================================================================ Paul Newland, ad7i Post Office Box 205 Holmdel, NJ 07733 ad7i@tapr.org ---------------------------------------------------------- | Copyright (c) 1995 by Paul Newland, P.E. | | All Rights Reserved. This guide may be reproduced | | by radio amateurs for their own personal use, provided | | this copyright notice is included in any reproduction. | ---------------------------------------------------------- ******************************************************************* * NOTES * * * * SPECIAL TYPESETTING FUNCTIONS (I.E., FOOTNOTES, ITALICS, * * ETC.) ARE MARKED WITHIN THE TEXT USING A DOUBLE SLASH (LIKE * * THIS //). * * * ******************************************************************* INTRODUCTION ------------------------------------ DAS (DTMF Accessory Squelch) acts like a switch connected in series between the speaker output of your VHF or UHF transceiver and an external speaker. DAS will monitor a radio channel for you, with the speaker switch open so the speaker remains silent, until someone sends one of the DTMF sequences you have selected. When DAS hears your personal Touch-Tone ID sequence on the radio channel it will light a LED, sound an buzzer and close the series speaker switch so that you can hear the audio of the calling station. An introductory discussion of DAS was published in //QST//, December, 1995, pages 25-31. The "DAS Configuration Reference Guide", available from the TAPR FTP file server as well as the ARRL BBS//1, provides a more complete description of each programming option, the purpose of the option and how the various options may interact. This document, DAS Application Note 5, "Special Remote Control Applications and Operations", describes how you can make use of DAS-AN5: SPECIAL REMOTE CONTROL -2- 951128/Iss-1 DAS for special remote control applications. One particular DAS application of interest to ham radio operators may be using DAS to control a remote radio transceiver. GENERAL PURPOSE REMOTE CONTROL ------------------------------------ General purpose remote control can be handled by means of the PER-PLUS commands. These commands allow you to set either of the two relays on DAS to either an "energized" or "de-energized" state. You can also use PER-PLUS commands to set any of the six open collector outputs of DAS to either a "floating" or "current sink to ground" state. Additionally, you can set three of the open collector outputs used to drive the LEDs (LED0/URG, LED1/PER and LED2/GRP) to any of the six LED flash codes. You can not set the state of the output used for LED3/STA since that's used to display internal DAS status conditions. A complete discussion on the use of the PER-PLUS commands is given in the in the "DAS Configuration Reference Guide" under the heading "General Purpose Controller Functions". RESET CONTROLLER FUNCTIONALITY ------------------------------------ DAS provides a capability to serve as a master reset controller. It's function is briefly described in the "DAS Configuration Reference Guide". If you haven't done so already, please review the "Reset Controller Functions" section in the Configuration Reference Guide. In general, when DAS is functioning as a Reset Controller, it looks for the special sequence followed by a configured PER ID sequence. When DAS has detected both sequences it then closes K1 for two seconds which can be used to reset all devices at a site. It's expected that K1 on DAS will control additional relays that are mounted physically within each piece of equipment at the mountain top (or other remote location) that is to be reset. Assuming that a small reed relay, similar to Radio Shack 275-233, is used within each device to be reset, then the coils of up to 50 relays can be safely paralleled together and driven by K1. Each relay should include a clamp diode across the coil. Relays are added within each piece of equipment because the "on-board" reset signal for each device should not leave the housing of that device. If a high impedance reset signal was routed outside the housing it may become susceptible to electrical noise in general and, electro-magnetic fields from radio transmitters specifically. As discussed above, a relay should be added within every device that is to be remotely reset and that relay should be within inches of the existing reset switch or within inches of the circuit board where the switch is wired. The contacts of that relay should be connected to the reset circuit of that device and the low impedance coil windings are brought out of DAS-AN5: SPECIAL REMOTE CONTROL -3- 951128/Iss-1 the box, with suitable RFI filtering as may be needed, and are wired in parallel with any other similar purpose relays. These paralleled relay coils would then be connected to a series circuit consisting of the paralleled relays, K1's normally open contacts and a 12 volt DC power source. REMOTE RADIO CONTROL ------------------------------------ DAS provides a capability to control a remote radio transceiver. The DAS feature is called "K2 Control Mode". It's function is briefly described in the "DAS Configuration Reference Guide". If you haven't done so already, please review the "K2 Control Mode" section in the Configuration Reference Guide. In the remote radio control application (like a remote base) it's assumed that there is an audio path between the user and the remote radio. That audio path might be implemented with a "4-wire" radio link, a 4-wire audio link or a 2-wire audio link//2. A dial up telephone line is an example of a 2-wire audio link. Once the user has established a communications link to the remote transceiver, he can access that transceiver by entering a multi-digit access code (PER+33 in this case). When the PER+33 command is detected by DAS it will activate K1. The remote transceiver system should be configured such that when K1 is active the receiver audio will be coupled onto the communications link back to the user. When the user wants to activate the transmitter on that transceiver he sends a momentary DTMF 0 signal to DAS. When DAS detects this DTMF 0 and then sees that the DTMF 0 has been removed from the audio path, K2 will be activated for 30 seconds or until DAS detects DTMF *, which ever comes first. K2 would be wired to actuate the transmitter's PTT circuit. With PTT active, any audio on the link will be transmitted by that remote radio transmitter. Normally the user will end the transmission with a momentary DTMF * to deactivate the transmitter and return to the receive mode. The 30 second timer provides a watchdog function so that if the user fails to send the momentary DTMF * the remote transmitter will not be on the air for more than 30 seconds. To deselect that remote transceiver unit the user would send DTMF * * * (3 stars). In summary, use PER+33 to select a particular DAS unit controlling a particular remote transceiver. When a particular DAS unit has been selected its K1 remains active until that DAS unit is deselected. Use DTMF 0 to enable K2 and DTMF * to disable K2. Use DTMF * * * to disable both K1 and K2 and to deselect that DAS unit. Please note the following. When DAS is in the "K2 Control Mode" DAS doesn't change output states until the appropriate DTMF signal is REMOVED from the audio input of DAS. Thus, the DTMF 0 used to enable K2 (and the transmitter) does not get transmitted by the DAS-AN5: SPECIAL REMOTE CONTROL -4- 951128/Iss-1 remote transmitter. Additionally, the DTMF * used to disable K2 (and the transmitter) ALWAYS gets transmitted by the remote transmitter. Thus, to send a DTMF LiTZ signal via a remotely controlled transmitter the user will need to send a momentary DTMF 0 to activate the transmitter and then follow with the actual LiTZ signal. Note also that if a user makes brief transmissions on a radio channel via a remotely controlled transmitter that receivers of that signal will demodulate a DTMF * at the end of each transmission. If a receiver is connected to a DAS unit with the STAR IS WILD CARD CHARACTER option set to active, that DAS unit may respond to what appears to be a series of Wild Card characters. The two second "end of sequence" timer keeps this from being a problem. As long as the transmissions do not occur at a rate faster than one every 2 seconds, those DAS decoders should not respond to the DTMF * used to deactivate the remote transmitter. If the user has a need to transmit a DTMF * as part of a SELCAL sequence, the user will need to actually send DTMF * 0 on the link for each DTMF * actually transmitted by the remote transmitter. The DTMF * will be transmitted by the remote transmitter but it will also cause the remote transmitter to become deactivated. The DTMF 0 will reactivate the transmitter, but will not be transmitted over the air by the remote transmitter. For example, to send the DTMF sequence 1*34# via a remote transmitter the user would send the following DTMF sequence: 0 1 * 0 3 4 # * The first DTMF 0 enables the transmitter without that DTMF 0 signal being transmitted by the transmitter. The first DTMF * will be transmitted but it will also deactivate the transmitter at the end of the DTMF *. The second DTMF 0 will not be transmitted but it will reactivate the transmitter. The second DTMF * will be transmitted (and should have no effect on monitoring DAS units) and will deactivate the transmitter. NOTES ------------------------------------ 1. TAPR FTP File Server ftp.tapr.org, look in /tapr/das. TAPR on the Web at "http://www.tapr.org". ARRL BBS, +1 860 594 0306, 8-N-1, look in the FILES area, search on DAS. 2. The terms "4-wire" and "2-wire" are telephone system terms. They are derived from the number of "wires" needed to implement a particular circuit. The important considerations of these circuits are as follows. In a 4-wire circuit, the transmit and receive audio travels on totally independent circuits. The only cross-talk that exists in the 4-wire case is from the small capacitive and inductive coupling that may exist between the transmit and receive signal wires. DAS-AN5: SPECIAL REMOTE CONTROL -5- 951128/Iss-1 Cross-talk is typically non-existent in 4-wire audio circuits, for most practical purposes. In a 2-wire circuit, like the circuit between the telephones in your home and the telephone company's central office (the source of dial tone), the transmit and receive signals are carried on a 2-wire path. The transmit and receive signals travel on the same signal path -- that one pair of wires. The telephone instrument and the central office switching ports each include balance networks that attempt to cancel out, or balance out, their own transmit signals from their own receive signal ports. In practice, the balance circuits don't work well because of the unknown characteristics of the wire pairs (which usually include inductors called loading coils). The important consideration for 2-wire circuits is that the lack of balance from transmit port to receive port can cause problems in the case of a remotely controlled radio transceiver. For example, DTMF signals demodulated by a remote radio transceiver might be detected by the remote DTMF controller (DAS) that's used to control the transmitter associated with that transceiver. Thus, if a "K2 Control Mode" DAS unit was controlling a remote transceiver that used a 2-wire audio link, and that transceiver demodulated DTMF 0 from the radio channel, and that DTMF 0, perhaps because of poor balance, was coupled into the transmitter audio input port and was detected by the DAS unit monitoring that audio input, that remote transceiver will become active -- and that's a real world problem. The only practical way to avoid this problem is by using a 4-wire audio link. Fortunately, most all radio links have 4-wire TX/RX cross-talk characteristics (low cross-talk), although they are often half-duplex paths. ---ooOoo---