Toshiba Linear Microwave Amplifier for 3400 MHz


by John Jaminet, W3HMS



 Updated from 13 Dec 2001 on 14 Dec 2004

Introduction. This paper was created from several messages received on the Internet Lists in September/October 2001 by Steve at DEMI, and K1DS. Important new info was received from Owen, K6LEW in November 2001 on the importance of voltage regulation and it is now incorporated in the text.  Other refs are cited in the text.


2. Checklist for Putting the New 3.456 GHz Toshiba
Amplifiers on the Air.

 There are two model:

a. 20 Watts output @ 3.456 GHz with 1 mW input.

b. 40 Watts output @ 3.456 GHz with 1 mW input.

Voltage: + 12.6 VDC (exactly)

 3. Vendor Info on the 20 Watt Amplifier

This is a Toshiba 20W Linear Microwave Amplifier for use in the
3.44 to 3.68 GHz range. It is sold in the original manufacturers packaging.

Heat sinking: Required…it gets hot..

Size: 5" x 8" x 1 ".

Weight: About 2 pounds.

Input power: For full output, this is about 1 milliwatt or 0dBm.

Specifications: The specs on these amps are very "tight" and are typically as follows:

Linear Gain = 42.5dB; Gain: Ripple = .1dB

Linearity is -45dB; Return Loss (in and out)= 25dB;

DC Power Supply current: Typically +12 VDC at 10.6 amps.

Power Jack: The DC power and control connector is a DB-15 male.

 DB-15 Pinout.  There are 3 rows of 5 pins each.

The ground is made from pins 3,7,10,11 connected together.
The +12VDC lead is made from pins 1,2,12,13 connected together

All VCC and ground pins need to be connected to handle the 10.6 amps.

Pin 9 is the enable pin (TTL) which must be connected to ground in transmit to switch the internal power supply on.

When pin 9 is not grounded, the 12 VDC supply draws about 15 ma. and the
amp is in stand-by mode.

This is a  Class A amp and as a linear amp, it will draw
about 10.6 amps with no signal input.

Pins 4,5,8,15 are assorted alarm output pins low true….no more is known..

4. The 40 Watt Amplifier

This is a new Toshiba UM2683A 40W Linear Microwave Amplifier for
use in the 3.4 to 3.6GHz range. It is sold in the original manufacturers packaging.

This amplifier differs from the "2683B" "20W" version on other auctions
because there is a TMD0305-2 MMIC instead of the discrete circuitry in
the front end. The TMD305-2 part is a 3400 MHz to 3510 MHz amp with 2 watt
output and 22dB Power Gain. Turning the two pot's at the far left on
the lower board in the photo fully clockwise (shutting down the
attenuator) and peaking the power with the third pot (2nd and 3rd
stage bias) yielded 46dBm, 40 watts @ 3.456GHz using 12.0 -12.6vdc
(as measured at the connector) with about 0dBm input power .

Power supply requirement is 12.6VDC @ 15amps after readjusting gain and

Heat sinking is required. The size of these units is 5 x 8 x 1 inch
and weight is almost 2 pounds. Input power required for full output
is about 0dBm. DC power and control connector is a DB-15 male. Pinout
is as follows: Ground are pins 3,7,10,11; +12VDC are pins 1,2,12,13;
All VCC and ground pins need to be connected to handle the 15 amps.
Pin 9 is the enable pin (TTL) which must be grounded to switch the internal supply on.

When not grounded, the 12 VDC supply draws only about 15 ma. and the amp is in a stand-by mode. Since this is a linear amp, is will draw about 14-15 amps without signal input.

Pins 4,5,8,15 are assorted alarm output pins low true…no more is known.
Only new amps are being shipped.


5. Overall System View

When the amplifier is integrated into a system such that relays, etc. are involved, the TX mode requires that the amplifier Pin 9, the PTT, be grounded for the amplifier to amplify, i.e. turns on the power supply built into the amplifier.  For RX, removing ground from Pin 9 places the amplifier into standby, drawing perhaps as much as 15 ma, while the T/R relays all reposition for receive.  There is no feed-through via the amp. Changing from RX to TX involves just grounding Pin 9.

There are no relays internal to the amplifier for switching RF between RX and TX, hence, external relays for switching between RX and TX are required.  

6. Critical Voltage Levels

Please refer to Step 14 (below) which is VERY critical. These amplifiers, especially the 40 W version, will go into "foldback" and be hard to recognize in so doing.  The 12.6 VDC +/- 0.2 is critical because the output FET regulator has an extremely narrow window due to the heavy current drain.

If you allow your primary voltage to get outside of this window, the FET bias voltage , as adjusted by R 150 as measured on Pin 1 of the regulator interconnect to the amp section, you will note the need for drive in excess of 0 dbm for 40 dbm output (40 W). ( W3HMS used about 950 microwatts drive for 40 watts output). Excess drive is not good and indicates foldback which generates excess heat causing the "final" to generate more heat than it should.  

These amps should draw 15 amps key down, not 14 amps, though some do vary.  The set-up is simple enough but it has been necessary for several amps to be readjusted. This is because some operators did not see the importance of the relationship between the primary voltage at 12.6 VDC and the 10.3 VDC from the regulator controlled by R 150 and measured at Pin 1. This 12.6 VDC should be measured inside the unit with the cover off while the amp is under load, i.e. key down or Pin 9 grounded on the subminiature DB 15.

NOTE: You do NOT need any RF drive for this set up as the amp runs in Class A.  If you have a power supply with remote sensing use it. If it does either voltage or current drain sensing, use voltage sensing.  The voltage MUST stay steady at 12.6 VDC or something will surely be damaged, most probably the regulator, to be followed shortly thereafter by the costly output FET.

It is not necessary to monitor the drive level if you have reliable and repeatable equipment for the "exciter". Once you establish 0 dbm at the input port to the amplifier it should stay adjusted. If somehow the equipment is not reliable as to its output, and there is time to adjust, then monitoring the input level would be necessary.  Most modern transmitting equipment of today is reliable such that once power levels are set, the input level to the amp should remain set.

One could easily think about installing two VDC measurement jacks and make R 150 an external pot so as to monitor and adjust both the 12.6 and 10.3 VDC (at the VR) levels. NO, the better choice is to monitor the output from a known and acceptable starting level.  If you see the output begin to vary, then it is time to check the input level.  To clarify this point, R 150 adjusts the output of the regulator BUT it does so in a very narrow window based on the primary input voltage of 12.6 VDC and the amount of current being drawn and R 138 will adjust this on the 40 W version.

In summary, this is to say that R 150 adjusts for 10.3 VDC ONLY when the primary voltage is 12.6 VDC with the amp under load (Pin 9 grounded) and the amp is drawing current.  If 12.6 VDC in either direction is exceeded by about 0.3 - 0.4 VDC, adjusting R 150 will NOT regain 10.3 VDC.

Thus, make absolutely certain you have sufficient heat sinking mounted to the amp for any tests or operation.  The devices in this amp are extremely expensive and will not accept much heat. This amp gets VERY hot very quickly without a heat sink attached.  One could also use a muffin fan blowing across the heat sink.  One of the "alarm" functions available on the subminiature DB 15 appears to provide a "temperature" alarm.  It is not known what the temperature should be when this function is energized but there is a voltage on one of the alarm lines that appears to relate to an increase in temperature. This amp does not self protect, i.e. shut down, so be very careful !!! Perhaps the voltage could be used to control a relay which would remove PTT-ON from pin 9 but we do not know how much current it can handle. It may not be enough to control a relay, but it might control a NPNB transistor which could in turn control a relay, but this is not sure.


7. Output Power Monitoring.  In an NTMS Feedpoint “article, also cited in MUD Proceedings  2003 on Page 66, Doug Robinson, WW2R, found a terminal in the amp which provides 5 VDC equal to 40 watts output. This terminal is in a 6- pin connector at the right end of the amp, 3rd pin from left, when the shielded amplifier box is above the connector.  This is the forward voltage. Doug connected a wire to an empty pin on the DB15 connector. I chose to drill a hole on the closest wall in a clear spot for a feed-through capacitor and then connected a 0-10 VDC meter via shielded cable.    




8.  Conversion Steps.

Obtain power plug DB-15 male at RS or other. RS # is 276-1502 for about $2.00_______

Find and install heat sink size about 5" by 8"(size of amp) or larger and muffin fan if desired __________

Calculate and obtain the attenuator value needed if you have more than 1 mw output from your rig. FYI, the DB6NT units have about 200+ mw output and I will use 24 db of attenuation. ___________

Connect DB 15 power plug pins # 3,7,10,11 to ground________.

Connect DB 15 power plug pins 1,2,12,13 as the + 12.6 VDC lead usable at 15 amps load__________.

Connect a switch or relay to ground pin #9 for XMT__________

7. Install antenna relay and necessary D.C. power_______________

Remove cover to see the 4 pots R217, R210, R136 on 20 watt model, R138 on the 40 watt model, and R150. These first 3 are the first 3 counting from the left and R 150 is directly to the right of the voltage regulator____

Counting from left, turn pots R217 and R 210 fully clockwise_______

Connect exactly + 12.6 VDC power and power up_______________

Measure +12.6 VDC at pin 4 on P6 to ground____________

Connect input signal on 3.456.1 GHz at the level of 1 mw or 0 DBM ___________

Monitor supply current and regulate to 15.0 amps with R138 on 40 W model and R136 on 20 W model_________

If needed, adjust R150 for 10.3 VDC (CRITICAL) on right hand pins of P3__________

Peak the power output with the third pot ( This is R 136 or R 138 ) to yield 40 watts output__________