Msg Nr. : 40872 Da : EA5SP Per : MODS @EU Tipo/status : B$ Data/ora : 0914/1250 Dimensione : 8103 Titolo : Alcune modifiche per l'IC 275 . Bid (Mid) : 301_EA5SP De : EA5SP@EA5FDS.EAV.ESP.EU A : MODS@EU EA5SP/TPK 1.81 Msg #:301 La 30/08/93 y 14:58Z EA5SP/TPK 1.81 Msg #:300 La 30/08/93 y 14:52Z Dear Reader! Hello my name is Juan, this text talk about the mods for transceivers of Ham Radio... I hope you interest this... If you need mods for others tranceivers, ask me.... BE CAREFUL! Procede at your own risk. Dont forget that transmitting outside the amateur band is not allowed so please consult your local athorities for a special permit. THANKS EA5SP.EA5FDS.EAV.ESP.EU.WW IC275 29-Mar-90 01:44 EST Sb: IC275 Mods for FO20 After reading a FUJI-OSCAR-20-PRBBS message from James, G3RUH, regarding the modifications he made to his Yaesu FT736 to improve the PSK transmit audio, I decided to investigate the situation on my ICOM IC275H to see if the same problem existed. I was certainly less than satisfied with the results I was getting in the first few days with FO-20 Mode JD. I was feeding the TX audio in at the front microphone socket and results on the uplink were quite poor but my downlink copy was 100%. The first change I made was to move the Tx audio to the rear connector, ACC1. Results improved but I was still not satisfied. Some scoping around the Varicap diode, D40, revealed considerable distortion of the PSK audio. To prove if this was the cause of my problem I studied the IC275 circuit to see how I could feed the TX audio in as close to the Varicap modulator diode, D40, as possible. In the IC275H there are several Audio feeds to D40, including 3 via Q33, and in my unit one of these, the feed from the Tone Squelch is unused. P46 normally plugs into the Tone Sq card but as this option is not installed it is left unterminated inside the rug. I also found that Pin 1 on ACC1 was unused so a shielded wire from P46, pins TSTN and GND to ACC1, Pins 1 and 2 would give easy access from outside the rig to D40 and NOT alter any of the existing functions of the IC275H. The installation of the wiring is not as easy as it sounds however: (1) You have to find a way to connect P46. I stripped a small amount of insulation from the wires just behind the plug housing and soldered the extension wire there. CONTINUED IN IC275.1 IC275.1 (2) To gain access to ACC1 you must remove the PLL PCB that it is mounted on. With the board removed I soldered the extension wire to the underside of the board taking care not to short out any surrounding tracks. The whole exercise took about 30 minutes. You will probably need more audio level from you PSK modem (see changes recommended by G3RUH in his FT-736 discussion). You can then use the pot, F151, in the IC275H to set the TX modulation level. Results from making this change have been outstanding with many less retries on the uplink than previously. The waveform being applied to the Varicap diode is now identical to the output from the modem. Performance via LUSAT and PACSAT digipeaters have been equally pleasing. EXTRA hint: Use DWAIT=0 RESPTIME=0 and start TXDELAY=100 ms and reduce to as low as possible for your radio - I use 30 ms. A similar change could be performed on the ICOM IC271 by wiring to J12 on the Main Board. J12 is normally unused in Australian IC271's. Since the above article referred to G3RUH's FT-736 discussion, I sent a message to James Miller G3RUH on FO20 and asked him to repost it on the bird. I had lost the copy I downloaded since I did not anticipate any need for it. CONTINUED IN IC275.2 IC275.2 Jack - the notes about mods to the FT736R were specific to that machine, and won't be relevant to the IC735. 1. What you need to do is work out a way to belt the varactor directly. Then inject a square wave (1200 hz will do) and measure the deviation that results. 2. You can do this measurement with either a proper deviation instrument or more likely with a monitor RX, by looking at the output from it's discriminator. 3. You can calibrate the monitor RX quite easily, Tune in a steady unmodulated carrier and note the discriminator DC output voltage Change the RX frequency by 1 Khz (knob on the RX front) and note the change in DC voltage. That gives you the monitor RX sensitivity in volts per Khz. 4. Now return to the TX, and adjust that driving square wave to give you approx +/- 3 kHz, you want to see about 6x volts peak to peak square wave on the monitor. (Somewhere between 4x and 6x will do, no more.) 5. Now return to the modem and juggle about with the TXAudio output components to achieve this level of drive signal, and look at the monitor RX too. 6. When you have done this, which should take you all of 30 minutes, you should be in business. If you can't get square waves TX to produce squarish waves out of the monitor RX, then the varactor dept. must be suspect, and so on. All is fairly logical. Hope useful. Let me know the results. 73'S For you and your family.... \\\\ (o^o) 縛컴컴컴컴컴컴컴컴컴컴컴횽Oo컴 (_) 컴oOO컴컴컴옜 납 EA5SP @EA5FDS.EAV.ESP.EU.WW � � Op. JUAN 납 응컴컴컴컴컴컴컴컴컴컴컴컴컴컴켸 읕컴컴컴컴컴켸� P.O.Box 169 � 46700 GANDIA (Valencia) � S P A I N 判判判判判判判 Msg Nr. : 72696 Da : IW7BLI Per : MODS @ITA Tipo/status : BF Data/ora : 1129/1425 Dimensione : 5255 Titolo : Alcune modifiche per l'IC 275 Bid (Mid) : 33767_IW7BLI **************************************************** ** MODIFICA HARDWARE PER IC 275 (E o H) de IW7BLI ** **************************************************** Questa modifica consente di espandere la gamma operativa dell'IC 275, sia esso nella versione E o H, da 138 MHZ a 174 MHZ. La modifica puo' riguardare sia la parte ricevente dell'apparato che la parte trasmittente. ********************************************* * ABILITAZIONE DELLA RICEZIONE DA 138 A 174 * ********************************************* 1 - Asportare la parte superiore dell'involucro dell'apparato avendo cura di provvedere a svitare anche le viti dell'altoparlante. 2 - Asportare il grosso involucro di alluminio contenente la ventola svitando le due viti poste a ridosso del visore e poi le due poste posteriormente all'apparato. 3 - Si raccomanda di asportare delicatamente l'involucro poiche' esso e' anche collegato al resto dell'apparato da molti fili tramite spinotti volanti. 4 - A questo punto localizzare una scatola in alluminio di forma rettangolare posta sulla scheda principale dell'apparato. -------------------------------------------------------- | ========================= | | | D43 e D44 ----> | | | | | | | | | | | | | | | | | | | | | | | | <---- D27 | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | ========================= | | | | | -------------------------------------------------------- | V F O | -------------- 5 - Con un cacciavite sollevare delicatamente il coperchio e come mostrato nella figura sopra, si possono localizzare i diodi D43 e D44 nell'angolo a destra in alto (sulla destra della batteria al litio) e D27 al centro verso sinistra. 6 - Per abilitare la ricezione estesa e sufficiente rimuovere il D44 e porre un diodo di egual valore in D43 (la cui posizione e' vuota). Lo stesso risultato lo si puo' ottenere semplicemente dissaldando il capo di D44 e spostarlo su D43 visto che l'altro capo e' in comune ai due diodi. ************************************************ * ABILITAZIONE DELLA TRASMISSIONE DA 138 A 174 * ************************************************ 1 - Localizzare D27 come da figura (e' a sinistra di IC4 e immediatamente sopra gli spinotti da stampato. 2 - A questo punto con delicatezza tagliare uno dei capi del diodo. Non e' infatti necessario asportarlo completamente. ****************************************************************** * CONSIDERAZIONI E CONCLUSIONI SULL'ESTENSIONE DI GAMMA OTTENUTA * ****************************************************************** Dopo le operazioni sopra descritte l'apparato avra' un'estensione di gamma da 138 MHZ a 174 MHZ sia in trasmissione che in ricezione. E' da notare che non vi sono perdite apprezzabili nonostante l'operazione eseguita. Auguri, buon lavoro e 73 de IW7BLI Maurizio.