Yaesu FT-290R Conversion to Four Metres (70Mc/s)
"FT-490"
"FT-490"
The Completed Rig
This is my second FT-290R conversion to four metres, the first version was made dual band 4/2m and runs 2.5 watts output on both bands, the switching was however very complicated so I decided to convert another to single band 4m operation.
This new conversion covers all of the four metre band only and produces a clean 20 watts output on SSB/CW and 10 watts on FM.
All of the new circuitry is contained within the original battery holder compartment and the PA stage is cooled with the help of two additional fans one of which is on the rear apron and the other on the bottom panel directly below the PA module.
Various modifications have been made to the rig prior to the addition of this transverter including LED back lighting to the METER and LCD digital display, new uprated 2.5mm power socket (re wired as per normal convention, positive to inner pin), removal of the "notched" tuning arrangement, the tuning dial is now smooth which is much better for SSB/CW, plus various other mods to improve the received audio and squelch operation.
This new conversion covers all of the four metre band only and produces a clean 20 watts output on SSB/CW and 10 watts on FM.
All of the new circuitry is contained within the original battery holder compartment and the PA stage is cooled with the help of two additional fans one of which is on the rear apron and the other on the bottom panel directly below the PA module.
Various modifications have been made to the rig prior to the addition of this transverter including LED back lighting to the METER and LCD digital display, new uprated 2.5mm power socket (re wired as per normal convention, positive to inner pin), removal of the "notched" tuning arrangement, the tuning dial is now smooth which is much better for SSB/CW, plus various other mods to improve the received audio and squelch operation.
The board below can be regarded as the heart of the transverter and contains the 12 and 5 volt regulators, 75Mc/s local oscillator module, mixer module and double band pass filters.
The pictures below show the completed unit.
The low pass filter can be seen on the top right below which is the 145Mc/s Mutec front end board.
The Mitsubishi PA module can be seen at the top of this picture, to the right is the fuse link LK1 which is where the meter is connected in order to set up the standing current of the module.
To say that the circuit I have used is unconventional would be something of an understatement.
In order to reduce the component count I have used relays at the input and output of the stage responsible for r/f amplification on receive and voltage amplification on transmit, the stage therefore has two functions. On receive the stage itself has a fixed gain but has a 6dB attenuator at its output, on transmit the stage gain can be varied by setting the G2 voltage (R11) on the dual gate mosfet, this is used to set the output of the rig to 20watts on ssb/cw, the reduced output on fm is set by reducing the bias on the pa module (R10).
Apart from the inductor in the low pass filter all the rest are Toko MC111 types which are Ideal for this purpose, they exhibit a very high Q which is needed to prevent the local oscillator signal which is only 5Mc/s away from reaching the output stage, the LO signal is more than 60dB down at the output which is very respectable.
Each pair of the inductors used in the band pass filters are screened with double Toko screening cans which can be seen in the pictures. A link in the form of a 20mm fuse holder is fitted close to the pa module for inserting an ammeter in order to check the PA standing current on each mode. The drive to the PA module is in the order of 75mV peak to peak on fm or key down on cw. As all of the tuned circuits are used on transmit and receive this means it is very easy to align the transverter and to "stagger tune" the inductors to cover the whole of the band and yet have a sharp attenuation both above and below the required parameters.
It will be noted that the only pre set trimmers used are in the low pass filter, these trimmers are rather expensive now which is why I have used fixed capacitors to tune all of the other inductors, BUT they must be silver mica types as thermal stability is required due to the aforementioned Q of these circuits.
All of the connections are shown to the right of the circuit which come from the FT-290, the 13.8v supply to the PA stage MUST be connected directly to the power input socket, the other connections including the 6.8v on transmit voltage, meter line, 145Mc/s if and fm power down ground are fed from their respective points within the rig. The fans have been connected to the transmit12v line, no fan delay circuit was found to be required here.
Ensure that the output from the FT-290 is permanently set to the low power output position (I disconnected the HI/LO switch which is highly recommended here) and properly terminated in a 50 ohm resistor and capacitively coupled to the SBL-1 mixer, the correct drive can now be set with the low power output pre set pot in the rig, this will normally be with the pre set pot at or near minimum output.
A scope is all that is required to resonate all of the tuned circuits and about 75mV should be seen at the input of the PA module, this should be done with the link LK1 removed. Final alignment can be made with the link LK1 in situ and a suitable power meter and 50ohm dummy load connected to the output, a spectrum analyser should be employed at this point in order to set up the low pass filter and to check the purity of the output signal.
Here the "pull" fan can be seen on the rear apron, the "push" fan is mounted on the base plate directly above the PA module.
All three slide switches have been removed from the rear panel, only three sockets remain which are for the aerial, key and 13.8vdc power which is an uprated 2.5mm coaxial dc socket. The new power lead must contain a 3 Amp quick blow fuse.
Complete Circuit
NB, all of the relays are shown in the TRANSMIT position. The IF input pins for the SBL1 mixer are 3 and 4.
Parts List
R1 68r
R2 15k
R3 150r
R4 150r
R5 39r
R6 15k
R7 82r
R8 18k
R9 2k2
R10 100k min pre set (set fm power)
R11 25k min multi turn pre set (set tot power ssb/cw)
C1 47pF disc cer
C2 104 disc cer
C3 2.2mfd tant
C4 2.2mfd tant
C5 2.2mfd tant
C6 103 disc cer
C7 2.2mfd tant
C8 2.2mfd tant
C9 33pF disc cer
C10 1pF disc cer
C11 1pF disc cer
C12 33pF s/m
C13 33pF s/m
C14 33pF s/m
C15 33pF s/m
C16 103 disc cer
C17 103 disc cer
C18 103 disc cer
C19 33pF s/m
C20 103 disc cer
C21 33pF s/m
C22 1pF s/m
C23 33pF s/m
C24 33pF s/m
C25 102 disc cer
C26 65pF min trimmer
C27 65pF min trimmer
C28 22mfd tant
C29 22mfd tant
C30 472 disc cer
C31 472 disc cer
RL1 to RL3 12v min dpdt relay
L1 5T 18swg enam
L2 to L10 Toko MC111 pink (see text below)
IC1 UA7805
IC2 UA7805
IC3 UA7812
Mod 1 75Mc/s oscillator module, JCO 14-3-B or equiv
Mod 2 SBL-1 or ADE-1 double balanced mixer
Mod 3 Mitsubishi RA35H1516M, modified for 4m operation
D1 1N4148
D2 1N4148
TR1 BF961/BF981/3N201 or equiv
TR2 BC337 or equiv
NB, The relays RL1 and RL2 should be the metal cased variety or a snug earthed screen fitted over them, the double Toko screening cans used on the band pass filter inductors are Ideal for this purpose. The Toko MC111 inductors used here have a primary winding of 6.25 turns and a secondary of 1.25 turns and have a Q of 118. As a matter of interest these inductors can be used from about 28 to 160Mc/s using the appropriate value of tuning capacitor ranging from 3 to 120pF.
As the TR1 stage performs a dual function, RX RF amplifier with post amp resistive attenuator and variable gain TX voltage amplifier the relay switching is rather complicated and may be a bit hard to follow so below are three re drawn diagrams showing the operation and signal flow in both transmit and receive modes, tx in red and rx in green, I hope that this will make it easier to follow.
The modified Mitsubishi output module was found to be about 60% efficient after its conversion to 70Mc/s, details of this conversion can be found elsewhere on this site.
Various dual gate mosfets have been tried in the TR1 location and all performed well. No heat-sinking is required on any of the regulator IC's.
Although not shown in the circuit diagram, screened leads are used for the input and output of the PA module and any inter-stage r/f links if separate boards are used. large rubber feet have been fitted on the base of the rig at the front and shorter ones at the rear which gives it a pleasant slope when sitting on the operating bench, also needed in order to give airflow to the "push" fan on the base.
These modifications provide a very versatile and small 20watt multi mode four metre transceiver which is Ideal for home or portable use.
R2 15k
R3 150r
R4 150r
R5 39r
R6 15k
R7 82r
R8 18k
R9 2k2
R10 100k min pre set (set fm power)
R11 25k min multi turn pre set (set tot power ssb/cw)
C1 47pF disc cer
C2 104 disc cer
C3 2.2mfd tant
C4 2.2mfd tant
C5 2.2mfd tant
C6 103 disc cer
C7 2.2mfd tant
C8 2.2mfd tant
C9 33pF disc cer
C10 1pF disc cer
C11 1pF disc cer
C12 33pF s/m
C13 33pF s/m
C14 33pF s/m
C15 33pF s/m
C16 103 disc cer
C17 103 disc cer
C18 103 disc cer
C19 33pF s/m
C20 103 disc cer
C21 33pF s/m
C22 1pF s/m
C23 33pF s/m
C24 33pF s/m
C25 102 disc cer
C26 65pF min trimmer
C27 65pF min trimmer
C28 22mfd tant
C29 22mfd tant
C30 472 disc cer
C31 472 disc cer
RL1 to RL3 12v min dpdt relay
L1 5T 18swg enam
L2 to L10 Toko MC111 pink (see text below)
IC1 UA7805
IC2 UA7805
IC3 UA7812
Mod 1 75Mc/s oscillator module, JCO 14-3-B or equiv
Mod 2 SBL-1 or ADE-1 double balanced mixer
Mod 3 Mitsubishi RA35H1516M, modified for 4m operation
D1 1N4148
D2 1N4148
TR1 BF961/BF981/3N201 or equiv
TR2 BC337 or equiv
NB, The relays RL1 and RL2 should be the metal cased variety or a snug earthed screen fitted over them, the double Toko screening cans used on the band pass filter inductors are Ideal for this purpose. The Toko MC111 inductors used here have a primary winding of 6.25 turns and a secondary of 1.25 turns and have a Q of 118. As a matter of interest these inductors can be used from about 28 to 160Mc/s using the appropriate value of tuning capacitor ranging from 3 to 120pF.
As the TR1 stage performs a dual function, RX RF amplifier with post amp resistive attenuator and variable gain TX voltage amplifier the relay switching is rather complicated and may be a bit hard to follow so below are three re drawn diagrams showing the operation and signal flow in both transmit and receive modes, tx in red and rx in green, I hope that this will make it easier to follow.
The modified Mitsubishi output module was found to be about 60% efficient after its conversion to 70Mc/s, details of this conversion can be found elsewhere on this site.
Various dual gate mosfets have been tried in the TR1 location and all performed well. No heat-sinking is required on any of the regulator IC's.
Although not shown in the circuit diagram, screened leads are used for the input and output of the PA module and any inter-stage r/f links if separate boards are used. large rubber feet have been fitted on the base of the rig at the front and shorter ones at the rear which gives it a pleasant slope when sitting on the operating bench, also needed in order to give airflow to the "push" fan on the base.
These modifications provide a very versatile and small 20watt multi mode four metre transceiver which is Ideal for home or portable use.
The yellow shows the RX signal path and the red shows the TX signal path.
