Hello, Here are some mods for the original G3RUH modem,write me if you want more info. Item: PWG Technical Note Issue 5 Date: 13/2/94 From: ON1AOT @ ON6AR Crauwels Walter Lode VissenAekenstraat 30 2600 Berchem ++32-3-440.34.95 To: All PWG Node SYSOPS Send to: PWGSYS via FWD and to MODEM @ WW. Total Pages: 1 Including this one. Today's Topics: - G3RUH TX Eyepattern improvements. Here are some improvements for the TX eyepattern on the original G3RUH modem. - Introduction: - First of all this modification improves 2 things: - the TX eye pattern comming out of your G3RUH - in RX,TX audio is switched off. - First we will do some measurements to prove the different. Let's have a look on the original schematic, there are "only" 2 address bits to make the wave ( U15 pin 9 and 10), that means that a sine wave is generated on 4 stairs. Take a scope and look on JMP7. Of course, the TX filters will make this signal clean. But if we use 2 more bits, we can get a sine wave build on 16 stairs, this signal is "cleaner" and looks "better" than the original one. And why should we do without, if everything is still on the board ? So the new eprom contains also the high definition pattern of the signal, you just need to add two wires. After this modification, have another look with the scope on JMP7, you will be surprised ! - One of the other problems often found in the BBS is how to mute the TX signal while we are in receiving. In fact when we are receiving WE MAY NOT MODULATE the PLL other wise the modulation shall be disturb the receiving signal and we will decode just nothing else than garbage. The solution is easy : as U15 contains the modulating signal, we can also change the content of the eprom so that it sends "nothing". That is what we do by using the high part of the eprom, and we switch between lower part (transmitting) to the higher part (receiving) by using pin 22 (A14) of U15 or JMP 8 - Parts needed: - 20 cm wire - 2764 RX eprom - 27256 TX eprom - Modifications: - Starting from an original G3RUH modem with no modifications. - Remove the original RX eprom (U2 2764) and replace it by the new RX eprom which is listed below in 7plus. - Remove the original TX eprom (U15 27128) and replace it by the new TX eprom also listed below in 7plus. - Remove jumper 1,2,3,4 and 8. - Add two new wires between: pin 21 of U15 (A10) and pin 13 of U8 (Qb) pin 23 of U15 (A11) and pin 14 of U8 (Qa) - Connect a wire between pin 27 of U15 and your PTT from your TNC (use the schematic below.) \ / R28 \ 4k7 / d1 JMP8 | +------------------+ +--|<-----o-----+---+ pin 22 (A14) | +--------------+ | o | eprom TX 27256 | | Your tnc2 | | | | from ON5ZS | | PTT +-----+ --- | | | | | /// +------------------+ +--------------+ | | d2 +------------------+ +--|<----------+ PTT | | your transceiver | | | +------------------+ d1 = d2 = 1N4148 (or better BAT 85) - You can add D2 in the connector to your TRX. - Eproms dumps: - New RX eprom U2 2764 go_7+. 001 of 001 RX-EPM.ZIP 0001603 0680 01A (7PLUS v2.0) ۘ |dg)ƨ"0G\"aC%$t!!!wkB=d6B29ϭ7e^b'! SI[#Ątdi=(AU'VRJ!ajƭ5ذ65W۳! t;8es[yTR{lr}~򜏦f^$omFyRZ{uN)Q8A^Il˨!U ib\kX5?u١zPFoHšJeFbڲulԉvżۋX$׮2Au(]"Yj nM~(Qp\:]jS8;˖5:%5ePVSI_:CTZO&" OJ#xoTξ6?H'ugQk|ľ]5\CA~tu427-@|>hu'#} ?ZZމ[xMɨ\xvW&گ?ˀ.`^u~BKfkB(5ll}:{#Β BbJ$T_2=B>Ǽ{/.h;|"[RUEȍD#?3))HBY=.#( YL&tYsGOmk~򛈛ҋEyK.,{yF`3ҚH;#[ 9b?vѨC)afZJ6k{o8l;NIAPoٜa)gǸKjv.ZnBT޸Z$6 >mnqnzֿQtWXkxXxJ@,I%qu`DXրR[6$zu \j4G?oW窨z\WM~ة&ἆʼ-'̄xbowks<%1 L>B@k%8PJ%Vag!\m\}0xBCAga_zw5+%Q>GQ%, NX|V&#/2߷-3hGoЗuRNI!q5i]Jl5=h^N2[E]d`מΔ0ҳ=hĀth:<{&U΍mYYgҹHT;CW5'% ZSXY)冶aEf{0!&bꖲ[2)b}\'Z6󴁐Od/SЪ~1(| ax9h>q3b?1qcчmJ!yGTd&.1-rlÙ+hi(B !Qe#[f$9mRZzډhƛ&IJV|˂[%+X4#;F_n(5 Q3=d8"ǶkP0gZ42dIKIQ);UEwĽg"oaR.^)X dv;؋DflASTħ.(; _ymAPREP/N}q1Cs,ZFA~ۂ([O7F}3/n~dq3]5POOx.Ƞ1R1>cWL("r wq^Y[Ö=mOd=/J0b֚??YR6@łDb:4:H:F'qVFVEΆD\#": U覶:!!!!!!!!!!!!Ş['r%^$%!!!U;D!%!!>!!!!!!!!!!5#Ɲ ŏ