From qrp-l@lehigh.edu Thu Sep 28 22:24:57 1995 Received: from fidoii.CC.Lehigh.EDU (fidoii.CC.Lehigh.EDU [128.180.1.4]) by oucsace.cs.ohiou.edu (8.7.Beta.11/8.7.Beta.11) with ESMTP id WAA09314 for ; Thu, 28 Sep 1995 22:24:55 -0400 (EDT) Received: from fidoii.cc.lehigh.edu ([127.0.0.1]) by fidoii.cc.lehigh.edu with SMTP id <8609-1>; Thu, 28 Sep 1995 22:24:06 EDT Message-Id: Reply-To: sbuxton@ccf.health.nsw.gov.au Originator: qrp-l@lehigh.edu Sender: qrp-l@lehigh.edu Precedence: bulk From: Simon Buxton To: Multiple recipients of list Subject: QRP with IC735 X-Listprocessor-Version: 6.0c -- ListProcessor by Anastasios Kotsikonas X-Comment: Low Power Amateur Radio Discussion Date: Thu, 28 Sep 1995 22:24:03 EDT Status: RO Hi gang, Some of you may be interested in the following which shows how to run an IC735/731 for QRP operation. ---------------------------- Cut here ---------------------------- Use of IC735 H/F Transceiver for QRP operation Others may be interested in this simple project to use IC735 or IC731 H/F transceivers for QRP work as it took a fair amount of investigation to find out what to do and then to make it work. These rigs normally operate with power output in the range 10 - 100 watts which is controlled by means of a slider on the front panel . There is also an internal switch which halves the power output. I had heard of these rigs being used for QRP and after enquiries to ICOM Australia and other sources, who could offer no help beyond what was in the manual, was finally advised by ICOM Support in the U.S., via the Compuserve network what to do. They suggested using the external ALC connection on the ACC(2) socket at the rear of the set where a voltage from -4 to 0 would control output from zero to the power level set on the front panel. ACC(2) is a 7 pin socket used to connect to an automatic ATU (the 8 pin ACC(1) socket could also be used as it contains similar connections but note that the pins are different). My first attempt at this using only a potentiometer across an external battery gave either full power or nothing. A later attempt got it right. The voltage controlling the power is very sensitive and on my IC731 only a small change of around 0.1 volt or so in the 1.5 volt region changes the output from zero to the set amount. The circuit is shown below. 3 volts seems OK to supply the voltage (as polarity is reversed, the internal supply can't readily be used), and the 12k resistors allow the 5k linear pot to cover only a small voltage range. You may need to experiment with the resistor values to ensure that the pot. covers the control range on your rig. This circuit allows smooth control of power from 0 to 10 watts, with the front panel setting at minimum power. The output power can be read from either the P/O range on the rig's meter or from an external SWL/PWR meter in the antenna lead. The unit may be built into a small PCB box and left connected to the rear socket, switching on as needed. You may like to include an LED plus resistor across the 3v after the switch to remind you to turn off (I forgot once when QRO and wondered why no power was getting out!). IC735 ACC(2) -------------------- Grnd Pin 2 + | 12k v 12k -----/\/\/\----/\/\/\----/\/\/\------- ALC Pin 5 - | 5k linear | | | ----- 3v | --- 2 x AA cells | ----- | --- on/off | | / | --------/ -------------------------- ------------------------- Cut here ------------------------------ **************************************************************** Simon Buxton VK2EII Sydney, Australia E-mail : sbuxton@ccf.health.nsw.gov.au Compuserve :100352,1612 **************************************************************** From qrp-l@lehigh.edu Fri Sep 29 11:37:30 1995 Received: from fidoii.CC.Lehigh.EDU (fidoii.CC.Lehigh.EDU [128.180.1.4]) by oucsace.cs.ohiou.edu (8.7.Beta.11/8.7.Beta.11) with ESMTP id LAA19069 for ; Fri, 29 Sep 1995 11:35:00 -0400 (EDT) Received: from fidoii.cc.lehigh.edu ([127.0.0.1]) by fidoii.cc.lehigh.edu with SMTP id <9011-2>; Fri, 29 Sep 1995 11:33:04 EDT Message-Id: <"17135 Fri Sep 29 10:16:10 1995"@nt.com> Reply-To: william.redfearn.cmwdr01@nt.com Originator: qrp-l@lehigh.edu Sender: qrp-l@lehigh.edu Precedence: bulk From: william.redfearn.cmwdr01@nt.com To: Multiple recipients of list Subject: re:QRP with IC735 X-Listprocessor-Version: 6.0c -- ListProcessor by Anastasios Kotsikonas X-Comment: Low Power Amateur Radio Discussion Date: Fri, 29 Sep 1995 11:32:52 EDT Status: RO ****** start message ***** subject: QRP with IC735 These rigs normally operate with power output in the range 10 - 100 watts which is controlled by means of a slider on the front panel . There is also an internal switch which halves the power output. I had heard of these rigs being used for QRP and after enquiries to ICOM Australia and other sources, who could offer no help beyond what was in the manual, was finally advised by ICOM Support in the U.S., via the Compuserve network what to do. ***** end message ***** On my IC-735, I just adjusted the LOW RF Power pot so that with the front panel panel RF POWER control at minimum, the actual RF output was 4.5 watts. This pot is on the PC board near the 50/100 watt switch and can adjust the power output down to 0. I don't remember the actual designation without the schematic in front of me but it is part of the TX ALC circuit and is on the schematic (but not the picture showing the adjustment points). There is also a HIGH Power for setting the maximum power output (you may not want to adjust that one). 73 - Dave. ============================================================= Dave Redfearn, Sr RF Systems Engineer NORTEL RTP, NC. ph.(919) 992-3925 email: cmwdr01@nt.com qrl? de N4ELM/qrp All opinions are my own, no one else wants them. From qrp-l@lehigh.edu Fri Sep 29 15:43:32 1995 Received: from fidoii.CC.Lehigh.EDU (fidoii.CC.Lehigh.EDU [128.180.1.4]) by oucsace.cs.ohiou.edu (8.7.Beta.11/8.7.Beta.11) with ESMTP id PAA12613 for ; Fri, 29 Sep 1995 15:43:29 -0400 (EDT) Received: from fidoii.cc.lehigh.edu ([127.0.0.1]) by fidoii.cc.lehigh.edu with SMTP id <9007-1>; Fri, 29 Sep 1995 15:40:21 EDT Message-Id: <9509291931.AA04696@clark.dgim.doc.ca> Reply-To: jcumming@clark.dgim.doc.ca Originator: qrp-l@lehigh.edu Sender: qrp-l@lehigh.edu Precedence: bulk From: jcumming@clark.dgim.doc.ca (Jim Cummings) To: Multiple recipients of list Subject: Re: QRP with IC735 X-Listprocessor-Version: 6.0c -- ListProcessor by Anastasios Kotsikonas X-Comment: Low Power Amateur Radio Discussion Date: Fri, 29 Sep 1995 15:40:03 EDT Status: RO >Hi gang, > >Some of you may be interested in the following which shows how to run an >IC735/731 for QRP operation. > > >---------------------------- Cut here ---------------------------- > > Use of IC735 H/F Transceiver for QRP operation > > >Others may be interested in this simple project to use IC735 or >IC731 H/F transceivers for QRP work as it took a fair amount of >investigation to find out what to do and then to make it work. > >These rigs normally operate with power output in the range 10 - 100 >watts which is controlled by means of a slider on the front panel . >There is also an internal switch which halves the power output. I had >heard of these rigs being used for QRP and after enquiries to ICOM >Australia and other sources, who could offer no help beyond what was >in the manual, was finally advised by ICOM Support in the U.S., via >the Compuserve network what to do. > >They suggested using the external ALC connection on the ACC(2) socket >at the rear of the set where a voltage from -4 to 0 would control >output from zero to the power level set on the front panel. ACC(2) is >a 7 pin socket used to connect to an automatic ATU (the 8 pin ACC(1) >socket could also be used as it contains similar connections but note >that the pins are different). > >My first attempt at this using only a potentiometer across an external >battery gave either full power or nothing. A later attempt got it >right. The voltage controlling the power is very sensitive and on my >IC731 only a small change of around 0.1 volt or so in the 1.5 volt >region changes the output from zero to the set amount. > >The circuit is shown below. 3 volts seems OK to supply the voltage (as >polarity is reversed, the internal supply can't readily be used), and >the 12k resistors allow the 5k linear pot to cover only a small >voltage range. You may need to experiment with the resistor values to >ensure that the pot. covers the control range on your rig. This >circuit allows smooth control of power from 0 to 10 watts, with the >front panel setting at minimum power. The output power can be read >from either the P/O range on the rig's meter or from an external >SWL/PWR meter in the antenna lead. > >The unit may be built into a small PCB box and left connected to the >rear socket, switching on as needed. You may like to include an LED >plus resistor across the 3v after the switch to remind you to turn >off (I forgot once when QRO and wondered why no power was getting >out!). > > IC735 ACC(2) > -------------------- Grnd Pin 2 + > | > 12k v 12k > -----/\/\/\----/\/\/\----/\/\/\------- ALC Pin 5 - > | 5k linear | > | | > ----- 3v | > --- 2 x AA cells | > ----- | > --- on/off | > | / | > --------/ -------------------------- > >------------------------- Cut here ------------------------------ > >**************************************************************** >Simon Buxton VK2EII Sydney, Australia >E-mail : sbuxton@ccf.health.nsw.gov.au Compuserve :100352,1612 >**************************************************************** > > > > The following is from the QRP column of June 1990 73 Magazine. The column was written by M. Bryce, WB8VGE on the adjustments of the Icom IC 735. I tried them and they work. First, a modification to convert the popular ICOM IC-735 to QRP operation. These modifications will let you operate the IC- 735 at QRP power levels down to one watt or less. DON'T ATTEMPT THIS IF YOU ARE NOT SURE OF WHAT YOU ARE DOING! Leave it for someone who feels secure working inside a modern transceiver. Start by removing the bottom cover. With the radio turned upside down, find the slide switch at the rear left center. This is the switch that selects either 50 of 100 watts as the maximum output available from the transmitter. Push the switch to the rear of the radio. This is the 50 watt position. Next, find the pot labeled (sic) R-267 at the right rear of the radio. Turn the pot to full clockwise position. This is the minimum output setting. You should now have about four watts output with the front panel control set at a minimum, and about 50 watts out at maximum. R-268, locate just to the of R-267, sets the maximum power output when the front panel control is advanced to the maximum position. Find the pot labeled (sic) R-361 at the front left of the radio. If you want lower power output, adjust this pot for the lower power setting desired. This adjustment is quite touchy at settings below two watts out but, if you are careful, you can get outputs down to approximately one watt. You can maintain this power level through a reasonable amount of vibration, such as while operating portable or mobile. Be aware that this adjustment will probably change the power output obtainable when the front panel control is advanced to the maximum position. For example, with the R-361 adjusted to 1.9 watts, the maximum that you get is 30 watts. Replace the bottom cover. You should now have a power control for the IC-735 while operating QRP. The newer IC-725 can be adjusted down to QRP levels via the front-mounted drive control. You won't need the get inside the radio to modify it for QRP use. End of instructions for the 735. If I may add, I would suggest that you find the mod which swaps the SQUELCH control with the RF DRIVE control. In the stock IC- 735, the SQUELCH is an outer ring pot control surrounding the VOLUME control, while the RF DRIVE control is one of those sliding pots in the front. The modification is quite simple and swapps the lines. As a result, the SQUELCH will adjust the power out, and do so more smoothly. As I can recall, the mod was described in a Hints and Kinks collection of QST. If you can't find it. let me know and I will see if I can look it up for you. ===================================== Jim Cummings eMail:jcumming@clark.dgim.doc.ca packet:VE3XJ@VE3JF.#EONT.ON.CA.NOAM 73 and live better digitally DON'T GET TOO EXCITED... because remember, today is the first day of the rest of your life. =====================================