YAESU FT-7 MODIFICATIONS Improved noise blanker. Solution to this problem is found in FT-7B. With a noise simulator connected S-meter reading was S-9+ on 40M. With NB it was still S-5. With the modification the simulated ignition noise fall into the receiver noise. PB-1626 FILTER UNIT. Connect a 0.33uF capacitor from Q303 MPSA13, emitter to collector. C304 may be reduced to 10nF (sri I cannot remember). Variable CW-drive level. FILTER UNIT PB-1626. Isolate the source (Q304) from ground, see FT-7B. Connect a 10nF small disc ceramic capacitor from source to ground, and a 10uH choke from source to an available pin on PCB. You have to cut with a sharp knife to isolate a pin to connect to the connector. Remove ground connection from this pin, and connect a wire to the TXGAIN potmeter. Change the MIKE GAIN potm to a 2x10K or similar, logarithmic is best, but better to use what is. +12V ------10K-------------------- I I 1N4148 POTMETER I ----------------------------- TO PB-1626 GROUND POTMETER I I I 1N4148 100uF I I I GND GND GND Also connect an 1K resistor from source of Q304 to ground, and a 10nF capacitor from board connector to ground, under socket. The CW level control uses pin 12 on PB-1626. To switch the function out for SSB the following arrangement can be used PIN12 PB-1626 I +8V SSB C ------------10K--------------B BC547/BC238B I E 2K2 I I I GND GND Personally I use a single 10K potmeter linear for either SSB/CW gain and I use a fixed trimpot for SSB-MIKE GAIN, connected under motherboard. This was a later version, first I used the circuit as described, but later I decided to change this because I use FT-7 with transverter, and in order to keep equal power output for SSB and CW, and keep the carrier suppression high for reduced power output, I changed the thing to have variable TX-gain for SSB as well as CW. I take the output from the driver, and leave the power amplifier module without drive, RF output on 14/28MHz is about 5 mW, variable 40dB down. ----- Changing xtal in CW-oscillatos. PB-1625 IF UNIT Q403/Q404. Xtal X401 8999.3KHz require use of sidebands for CW 80/40M USB, 20/15/10M LSB. Apart from 40M this is the opposite of normal sideband for SSB. Situation is that you listen on 20M USB, and you will go CW to call a station, perhaps you operate CW to SSB, which is used much on VHF/UHF with transverter. It is then very little practical to change to lower sideband to operate CW. Therefore I have changed the xtal frequency for CW to 9000.7 and rewired the CW/LSB/USB switch for opposite sideband on CW mode. Now I operate: 80M LSB 40M USB 20/15/10M USB. The 40M USB is an acceptable compromise (((Above was mentioned 40M was originally USB, sri it is LSB))) FT-7: PROPOSAL CHANGE OF CALIBRATOR Proposed change of calibrator to avoid intermodulation distortion in the diode D101. RF MARK UNIT PB-1633. This proposal is based on an article in CQ-DL about 1975 about how to improve FT-250, unfortunately I have not kept this article. CD4024 PIN 3 100KHz OUTPUT I I C108 10p I GND---R106------- 1M ohm I 1N60 D101 MARK OUT I PIN 4---10nF-------------68K------I----------22K--------RX8V I-----10nF-------GND I C MARK SW PIN 5-----33K-----------B BC547/TUN (+8V) E I ---- GND Cathode of D101 goes to the 10nF/68K Added components, all written below D101/1N60 ------- Similar arrangement is made for FT-902, but this is more complicated. ------- FT-7 IMPROVED KEYING This modification is testes by LA8AK and LA9DL. It sounds perfect and it has been used with transverter for 6M meteorscatter QSO at 1000LPM. For first QSO's between United Kingdom and Norway with several HAM's. The original circuit seems not possible to work, whatever you try to do, it must be re-arranged! I never understand why YAESU keep on presenting such circuits all the time...(?). Personally I do not. Like key-clicks, and I am convinced about the fact that key-clicks always limit the signal intelligibility of a CW signal. ----- PB-1632 PRE-DRIVE. Note: power output from this PCB in FT-7 and FT-7B seems to be different, but the cards are the same. ---- In some, but not most of FT-7 there are a ground connection to MC14011 (CD-4011) pin 4. This must be cleared off (no connection) otherwise the 9V zener diode regulator will not work properly! --- In order to prevent accidental destruction of the IC by static discharges - insert a resistor between 'key-input' -pin 9 on edge connector (and R1013) and the IC pin 12-13-8. Suitable value is 100K. Change R1013 to 4K7 for better keyer operation. ---- Output from MC14011 to transistor was pin 10, you must now use pin 9 or 3, since a PNP transistor is used instead of NPN. A high gain germanium PNP low power general purpose transistor must be used, AC125, AC126 are good, I used AC162 but this has almost too low current gain, some american or japanese substitutes may be used. Change: R1003= 100 ohm R1010= 100 ohm R1012=3900 ohm R1014= 10K ohm C1012= 1uF bead tantalum New components: 1N4148, 3K9 resistor (3900 ohm) from R1014 to GND. The diode is inserted in series with R1003. Otherwise nothing changed for the circuit in series with Q1001 and Q1002 -------- Q1001 Q1003 SOURCE EMITTER I I I--C1003--GND I--------I I C1006 R1004 I I--------I----------I R1003 100 R1010 100 C1005 C1007 I I I I I---->I-------------------I GND GND 1N4148 I +9V---R1012 3K9----I I E AC125 MC14011 ---R1014-I----I--B AC126 or equivalent PIN 9(3) I I C PNP germanium general purpose LF 3K9 C1012 I transistor for low saturation I 1uF I voltage in this circuit as I I I linear 'emitter follower' GND GND GND KEY DRIVER ----- Similar circuits has also been tested for FT-726, IC-202E and other transceivers, but other values of components. It is important that keying voltage is only operated in 'linear range' of transistors, such that key-clicks will not occur. Good keying on/off ratio: abt 60dB ----- 73 de Jan-Martin LA8AK - 1982 FREQUENCY RESPONSE FT-7/902 Frequency response using marker frequency and adjusting RF gain down for out of AGC control (at least 6-10dB). Measured at input to audio output amplified FT-902 FT-7 USB LSB USB LSB -20 -18 -2 -1.5 200Hz - 4.2 - 3.4 +2.4 +2.4 500Hz -0.1 - 1.1 +.8 +.2 800Hz audio tone 0 0 0 0 1000Hz -0.8 - 1.2 -2.3 -2.3 1500Hz -1.3 - 1.6 -4.7 -4.9 2000Hz -4.5 - 4 -7.6 -7.8 2400Hz -8 -9.5 -9.8 -10.1 2700Hz -10.2 -20 -12.6 -13.3 3000Hz Levels are realtive to level at 1000Hz tone in audio. Measured with HP 4936A transmission impairment measuring set. I have modified my FT-7 such that CW is USB for all bands except 80/40M Frequency relations for FT-902(901) measured: LSB USB CW (CW-WIDE) or (NARROW) 1000 2145 1040Hz 1145 2000 2145 1000 Audio level in FT-7 is somewhat lower than in FT-902/901 so if you wish to use FT-7 with upconverter and independent audio line output you need some audio gain. Measured maximum audio level on line output (modifications published by LA8AK): FT-7 -26dBu (35mV RMS 10Kohm) FT-902 -7dBu(300mV RMS 10K or higher impedance) 73 de Jan-Martin LA8AK@LA9K EOF