Mfj624 Phone Patch Circuit

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Fig. 5 Digital access.

Fig. 5 Digital access.

took less than one hour to make the conversion and get the ten-meter rig on frequency

A few modifications are available in the conversion kit that can be left out — mainly, the frequency expansion switches that allow a full one-megacycle coverage. By selecting the correct set of crystals in the kit, the Pace can be put on the frequency you have selected without the addition of the switches and cabling. American Crystal also recommends a modification that allows the "clarifier" to move the transmitter as welf as the receiver. As long as you check the two frequencies very carefully and do not plan to move the ten-meter frequency, this modification also can be left out

The COR pick-off point is taken from Q28 Fig 2 shows the very simple, but very effective, COR circuit used to key up the two-meter transmitter, Spare contacts on this relay can be used for various other applications which may suit your particular needs. 1 his one connection is the only connection that has to be made inside the Pace. Everything else is done from the speaker jack and microphone jack- Should you desire local audio from the Pace, you may want to install a switch {or wire the speaker jack permanently) to keep the speaker operational with a plug inserted into the speaker jack Normally, the speaker wire is disconnected when a jack is plugged in Since we will pull the ten-meter audio from this jack, you will not have any local speaker audio unless you make this change.

Two-Meter COR

The Pace will need on!y a ground to transmit for the PTT circuit, which will be tapped off at the microphone front-panel plug. If you do not have any spare contacts on your two-meter COR, parallel another relay across the main COR and away you go You also could use electronic switching here to save you the problems of installing a separate relay. Look over this auxiliary circuit in Fig, 3 Fig. 4 shows the actual audio patching in and out of the two-meter repeater. It is very important to use good shielded cable with proper rf bypassing to keep the audio lines free of any stray rf that may occur when installing the addi tionat equipment.

Access Equipment

Access to the ten-meter link can be accomplished in many ways. The simplest method is to use a telephone line with proper equipment to allow a control operator (or operators) to dial up the proper codes to complete the access link in the two COR circuits. (See Fig. 4.)

With digital circuitry today, it is very simple to come up with an easy access system for the ten-meter link, The only thing that the access equipment has to do is connect the 12-voit dc line to the COR

circuits. With the 12 volts removed, power can be left on the Pace continuously, and even though there may be signals received on the ten-meter frequency, the COR will not bring up the two-meter system, or vice versa. By allowing the access equipment to connect the 12 volts to the COR, the ten-meter link then becomes active Fig 5 will give you a simple digital access to the system. We really don't need to go into great detail here because almost all of the repeater systems have some kind of access control for other functions and it should be easy to tie in the ten-meter access to this existing logic.

The only problem that your group may encounter, should you use ten-meter access, is that there is no really good foolproof access through ten meters. The MARC ten-meter group feels that the only access should be on two meters; a great man\ problems are eliminated while a tighter control can be kept on the system.

An Alternate Control System

Carlos T12CF has an Icom 701 linked to a Spectrum two-meter repeater via a regular phone patch system, like the Data Signal RAP 200. This system controls the audio of the 701 just as it would the telephone line. To use this system, a member of the group accesses ¡ust as he would if it were a phone patch, only when this occurs, the ten-meter Imk will come up. When the two-meter station transmits, the patch circuitry keys the PTT line of the ten-meter transmitter When the two-meter station listens, the ten-meter receiver audio is patched to the two-meter transmitter. The only problem with this system is that the two-meter transmitter would be keyed up con-

stantly (as it would when any patch logic is accessed). Should someone access the ten-meter link and not bring it down, the two-meter repeater stays on until someone brings it down.. This system does allow the two-meter operator to switch the ten-meter [ink audio by simply pushing his or her mic PTT button 1 he ten-meter station received would not contro! any relays or controls The system would work just like a phone patch but, of course, without the phone lines and actually substituting a ten-meter (or 20-, or 40-meter!) transceiver for the phone lines.

This system has some advantages but also needs additional equipment that groups may not have, nor could round up the finances to obtain, it also has some disadvantages for control, so your group wiu have to select the method that best suits its needs.

The Marissa system at WD9COE/R has been in use since March, and many excellent contacts have been made by many members of the group as well as by dozens of interested newcomers that the system has attracted. It becomes very exciting to work Venezuela from southern Illinois on a Tempo S-1 HT with the rubber ducky! It is also very exciting to foreign stations when they discover what they are working! The system has brought the entire St. Louis area to its feet, and, again, attention to amateur radio is gained through simple technology, some imagination, and a few hours of hard work. This is only the beginning. Let's a!l get to work and see where we can go from here. It's all for amateur radio! I


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Function switch: OFF lor normal operation ON connects your rig lo phone line for patching. NULL switches VU meter to let you ad|usi for Tiaximum null

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