Msg Nr. : 87188 Da : G0TSG Per : PMR @WW Tipo/status : BF Data/ora : 1227/0107 Dimensione : 8516 Titolo : Alcune modifiche per il MOTOROLA MT700 Bid (Mid) : 18792_GB7BAD Hello fellow "hams", Due to the apparant release onto the suplus market of the Motorola MT700 hand held radio,may i offer this mod.file. All the 700's i have modded have been for the UHF bands,ideal for 70cms! They are a two channel set,with (usually) built in C.T.C.S.S. which can be defeated via the top panel switch marked as SPEAKER CANCEL (has a picture of a speaker,and a speaker with a bar through it!) Also on the top panel,you will find the on/off-vol,squelch and chan. switch marked "F1-F2" When running on 70cms,the rig will produce 1-2W,good enough for the local repeater,or for use on packet,and sensitivity is quite good too! OPENING THE SET........ First,remove the battery and cover by rotating the stud on the bat.cover with a pair of long nose pliers inserted into the two holes. Then undo the 4 captive phillips screws in the back case and remove. You can now see the 4 pillars,which the back case screwed into-these are also "screws" which can be "un-done" to remove the part of the casing which has the antenna socket on it (i recommend sawing away the molded ant.parts,and fitting a BNC socket) Under these studs are yet another four,which will release the front panel/speaker... SPLITTING THE RIG...... With the radio face up ie. topside will be the pcb with the hole in it for the speaker...undo the 4 slotted screws,then with a bit of jiggling and a finger in the speaker hole,the board should come away easily..... BEWARE,there are 2 wires links to the bottom board (coax) be carefull not to pull them off ! CRYSTALS..... Now locate the crystals which are both (or 4 if two chans.fitted) on the board still in the chassis,partened by 4 ferrite cores. With the rig on the table,vol/sq knobs at the top,the top/right hand crystal(s) are the "TRANSMIT"(left=chan 1)the "RECIEVE"(s) are located in the middle left (chan 1) and central (chan 2) The crystal formulae are : TXcrystal= freq/24 RXcrystal= (freq-17.9)/8 and are "short j" cases TUNING....... After fitting the crystals,plug the two boards back together,still speaker side up...and locate the 7 RX tuning slugs (these are at the bottom of the board,and are metal with hexagonal heads) Reading from left to right,number them 1..2..3 ect,either mentally or stick a lable on. With a suitable signal to recieve (i use my 70cms handie,into a dummy load gradually increasing the distance between the two rigs as tuning progresses) first (with sqelch "open") tune the ferrite core located just above and to the right of the 7 slugs,to obtain best quieting. You may have to "trim" the crystal to bring it onto frequency-this is located on the OTHER side of the rig (you will see 4 cores-the very top one is TX chan 1,below it-TX chan 2.....half way down the board are the RX pair chan 1 is the bottom one. "unscrew" the 7 slugs so they are about 6mm proud Now working in the order 8,7,1,2,4,3,5 tune the 7 slugs for best quieting- -reducing the recieved signal,to keep a "noisy" signal-which is easier to tune to ! and thats the RX done ! you might like to try the core above the slugs again,and ensure the freq is still ok. If you have a 2m (two metre) radio,you could use it as a "signal generator" by transmitting into a dummy load,and setting the freq. to ONE THIRD of the radio you're tuning! (ie if your MT700 is on 433.650,then your 2m rig will be set to 144.550...cos' 144.5 time three equals 433.65 !!!!!this uses the "third harmonic" which is (or should be!) a VERY low signal,ideal for our purpose. Now to the TX,on the same board as the 7 rx slugs,you will see 2 more in the top/left,lift these to 6mm,and with the "antenna" connected to a 50ohm load tune the bottom of the pair,then the top for best power output.you may find it easier to monitor the CURRENT drawn by the radio at first ! (feed 12v onto the battery contacts via an amp meter...the first contact is 0v,the third is 12v-the one with the miniature fuse in line) The antenna feed is on the OTHER board,in the extreme top/left corner. There is a convenient ground located directly under this.....for connection of the BNC socket (if required) If you look through the hole where the speaker fits,you will see a white pre-set resistor,this is "MIC GAIN" also there is a multi-turn resistor fitted to the top board,also accessable via the spkr hole,this is "POWER out" On the same side,below the main pcb,there is (if fitted) the CTCSS board, on which you will see a white pre-set-this controls the tone volume,so if you do not want ctcss,turn it fully anti-clockwise. Sorry about the endless rambling, Any ideas,comments,improvements most welcome. 73,Paul G0TSG @ GB7BAD