The KA7OEI FT-817 pages
Circuit Description

Front panel view of my FT-817
A Front-panel view of my FT-817.

Detailed circuit description of the FT-817

Note:  This is not a copy of the circuit description in the FT-817's manual.  The "flow" of this document may have been suggested by portions of the description in the service manual, but it is (hopefully) presented in more detail that the original document.  Any similarities between this document and any Yeasu document, living or dead, is purely coincidental.

While reasonable efforts have been made to assure the accuracy of this document, I have no doubt whatsoever that I may have made some mistakes.  If you find one (or more) please let me know so that I may correct it.


The FT-817 is completely controlled by its microprocessor.  The majority of its "personality" is the direct result of its programming and as such, many of its capabilities and features are a direct result of what the microprocessor instructs the hardware to do, and how it should do it.

Receive paths:

All receive signals may be input via either the Front BNC connector (J1001) or the Rear UHF-type connector (J1002) using relay RL3016 on the PA unit.  The selection of this is make "per band" (i.e. HF, 6 meters, 2 meters, and 70cm) using menu selection 7.  It should be noted that front BNC connector is the antenna connector chosen when the relay is de-energized.

The 70cm receive path:

After relay RL3016, the 70cm signal path goes through a high-pass filter network consisting of C3252, L3075, C3243, L3071, and C3234.  The signal then flows through the RF directional coupler/power detector (not used on receive) and gets to the lowpass filter consisting of C3093, L3035, C3088, L3032, C3082, L3028, and C3076.

The receive signal then goes to a PIN-diode TR switch consisting mainly of D3004 and D3035, and D3006- all HSU277's.  In receive mode, all of these diodes are turned off.  With D3004 turned off, the receive signal does not backfeed relay RL3001 and enter the transmitter circuitry.  Note that PIN diodes D3035 and D3036 and related components form a quarter-wave network which, when activated, prevent transmit power from entering the receiver's front end.  The receive signal then passes through D3002, a DAN235U.  This is a dual diode and when in UHF receive mode, the appropriate diode is turned on, passing the 70cm signal through to JP3002 and the signal then leaves the PA board.

On the MAIN UNIT board the 70cm receive signal enters through J1001 and goes to D1001, a DAP236U.  This is a dual diode and when the 70cm receive mode is active one of these diodes is turned on (getting its current from the PA Unit.)  The receive signal goes through C1004, passes "over" D1005 - a device consisting of two back-to-back diodes which provide protection for the receiver's front end.  L1006 and TC1001 form a simple bandpass filter/matching network for Q1005, a 2SK2685, the 70cm preamplifier.  The output of this preamplifier is sent to CV1001, a three-section helical resonator filter.  The output of this now-filtered and amplified 70cm path is passed through D1033 (which is turned on during 70cm receive) and coupled into T1015, the receive mixer.

For 70cm receive, PIN diode bias is provided to D3002 (on the PA Unit) through D1001 (on the MAIN Unit) and then through an RF-decoupling network consisting of L1001, R1004, and R1005 from Q3003 (on the PA Unit) - a parallel-output shift register.  Bias for D1033 comes from R1127 near the receive mixer.  The "sink" current for these diode paths is sunk through the NPN portion of Q1012, a UMD3N.  This transistor array also provides power for Q1005, the UHF preamplifier, through its PNP portion, when the UHF receiver is active.

 The 2 meter receive path:

After relay RL3016, the signals are diplexed, with 2 meters and below going to the lowpass filter consisting of L3082, C3265, L3081, and C3264.    The 2 meter signal then gets diplexed again using a highpass filter consisting of L3079, C3252, L3075, C3242, L3071, and C3234, thereby separating out the 2 meter signal from the HF-6 meter signal path.

The receive signal then passes through the VHF directional coupler/power detector (not used in receive) to a lowpass filter consisting of C3092, L3034, C3087, L3031, C3081, L3027 and C3075.  The receive signal then passes by PIN diodes D3003 and D3005, both HSU277's.  These diodes (and related components) form T/R isolation switches that operate in a manner similar to that of the 70cm front end:  D3003 is turned OFF in receive mode, isolating the receive signal from the transmit circuitry and D3035, when turned on in transmit mode, prevent TX power from getting past the quarter-wave network consisting of L3022 and related components.  The receive signal passes through the half of D3002 not used for 70cm and then to JP3002, the RX RF output and is then passes to the MAIN Unit.

On the MAIN Unit the signal enters through J1001 and then passes through a portion of D1001, through half of D1004 and then to T1002.  This transformer, along with varactor D1015 and related components, forms an electrically-tuned filter/matching network for Q1006, the 2 meter preamplifier.  The output of the preamplifier goes through T1004 and T1008 - both of which are also electronically tuned.  Finally, the output goes through a portion of D1030 and then part of D1031 to get to the receive mixer.

For 2 meter receive, the PIN diode bias is provided by Q3003 (on the PA Unit) which flows through part of D3002 (also on the PA Unit) and then through part of D1001 and D1004.  The current then flows through the primary of T1002 and then to the NPN portion of Q1013.   The PIN diode bias for the 2 meter preamplifier output is provided by R1127 (near the receive mixer) and flows through portions of D1031, D1030, and then through the secondary of T1008 - and is also through the same NPN portion of Q1013.  The PNP portion of Q1013 provides power for Q1006, the 2 meter preamplifier.

The Aircraft Band Receive Path (108-136 MHz:)

The aircraft band receiver path is the same as that of the 2 meter path on the PA Unit.  On the MAIN unit, it goes through the same part of D1001 as the 2 meter signal, but it then goes through the portion of D1004 that wasn't used for 2 meters and into T1001.  This circuit is nearly identical to that of the 2 meter preamplifier:  T1001 and D1013 form an electronically tuned bandpass filter, Q1003 is a preamplifier, and T1003 and T1007 and its varactors form an electronically tuned filter.  The output of is passes through the portion of D1030 not used for 2 meters and then through D1031, and then to the receive mixer.

The PIN diode bias is provided by Q3003 (on the PA Unit) and flows through part of D3002 (also on the PA Unit) and then through the relevant portions of D1001 and D1004, through the primary of T1001.  On the output, current is provided by R1127 (near the receive mixer) and then through the secondary of T1007.  Both current paths are completed using the NPN portion of Q1011.  The PNP portion of Q1011 provides power for Q1003, the Aircraft band receive preamplifier.

The FM Broadcast Band (WFM) Receive Path (76-108 MHz:)

This receiver path is identical to that of the 2 meter path on the PA Unit.  On the MAIN unit it passes through the same portion of D1001 as the 2 meter signal, then through D1002, a HSC277 diode.  This signal then goes into pin 10 of Q1025, a Sony CXA1611 FM Receiver IC.   This IC has a front end, mixer, IF, and demodulation and provides received audio.  In order to suppress LO leakage and provide a (slight) amount of image rejection, D1034 (a varactor) and L1024 provide one stage of tracking bandpass filtering.

It should be noted that as is typical of single-chip receivers, the dynamic range of this receiver (within-a-reciever) is rather poor:  When using a large antenna, expect significant overload/intermod problems.

The HF and 6 meter receive path:

After relay RL3016 the signal is diplexed via a lowpass filter consisting L3082, C3265, L3081, and C3264.  At this point the 2 meter, aircraft, and WFM are diplexed.  Continuing onward, the signal passes through a lowpass filter consisting of L3077, C3248, L3074, C3242, L3070, C3239, L3069, and C3257.  The signal path then continues through the RF Directional Coupler/Power Detector (not used in receive) through the lowpass filters selected by relays RL3009-RL3015 - the lowpass filter being selected as appropriate for the current receive frequency.

Relays RL3002-RL3008 are on the other side of the lowpass filters (correlating with relays RL3009-RL3015) and when in a de-energized state connect the lowpass filter in series with a highpass filter.  The combination of lowpass and highpass filters provide broadband bandpass filtering to the receiver front end.  For 6 meters, the highpass filter includes a preamplifier consisting of Q3019.  It should be noted that the Q3019 preamplifier is always used when receiving on 6 meters and is not affected by the IPO menu setting - that menu item operates another preamplifier.

The appropriate highpass filter output is selected with a PIN diode D3025-D3028 (some of which are dual PIN diodes) with logic levels supplied by Q3003.  The output from the PIN diodes are then routed to D3043 and then to JP3002 and sent to the MAIN Unit.

On the MAIN Unit, the receive signal is applied to dual PIN diode modules (type DAP236U) D1003 and D1011.  One path routes the signal directly between the two modules and the other path passes the signal through a 10 db pad - the pad that is switched in as a menu item.

The output from D1011 is then passes through a simple lowpass filter consisting of C1021, L1005, and C1022, and then to D1018, another DAP236U.  One of the outputs is applied to a preamplifier consisting of Q1008 and the other is applied to D1029, bypassing the preamplifier.

The output of D1029 is applied to an IF trap consisting of T1014, C1119, C1120, and R1103, the purpose of which is to prevent 68.33 MHz energy from the antenna from getting into the 1st IF.  The HF receive signal is routed via D1031 to the receive mixer.

IF signal path:

The filtered/amplified signals are applied to the receive mixer consisting of T1015, D1047 and T1019.  D1047 is a quad MESFET mixer module.

The output of the mixer is sent to D1058, a DAN235U dual PIN diode switch.  The output of D1058 is applied to XF1001, a 68.330 MHz Monolithic crystal filter and the output of the filter is then applied to D1059, another dial diode switch, and then the signal is applied to T1025, an IF transformer.

Note:  D1058 and D1059 are used to steer either the receive or transmit signals through XF1001, the crystal filter.   The description above describes the PIN diodes in selected for the receive function.

The output of T1025 goes to Q1051, a dual-gate FET.  The output of this amplifier is filtered via T1026 and applied to diode D1063, and then to T1030.  D1063 is fed current via Q1077, a multiple-output D/A converter and used to adjust the gain of the IF amplifier, a parameter set via the software-driven configuration menu (i.e. the "RXG" settings.)

T1030, Q1060, Q1062 and T1034 comprise a singly-balanced mixer.  The IF signal at 68.330 MHz is mixed with a 67.875 MHz signal produced from triple the 22.625 MHz master reference oscillator.  The difference frequency of 455 Khz is amplified by Q1110 and filtered via transformer T1034.

D1074 is used to steer either the receive signal or transmit signal through the IF filters.  D1075 and D1076 select which filters are used.  Additionally, one portion of D1076 routes the 455 KHz signal to the narrowband FM demodulator section.

Following the filter selection matrix, the IF signal is applied to T1033, another IF transformer, and then amplified by Q1075, Q1065, and Q1054.

AGC circuit:

A sample of RF is taken from the output of Q1054 and applied to D1064 for rectification.  This signal is the amplified by Q1066 and Q1067.  The AGC voltage is then applied to Q1068, a silicon bilateral switch, which provides selection of AGC time constant (fast or slow.)   The output of the AGC circuit is applied to the second gates of Q1051, Q1075 and Q1065 to provide gain control.

AM Demodulation:

The output from the last IF stage (Q1054) is applied to D1060 and Q1048, resulting in demodulated audio.  This audio is passed to Q1049, a quad analog switch used to select among the various receive audio demodulators.

SSB Demodulation:

A sample of signal from Q1054 is passed to Q1055, a balanced mixer.  The IF signal is mixed with a BFO  signal from Q1031, an AD9835 DDS (Direct Digital Frequency) synthesizer.  The resulting audio output is applied to Q1049.

FM demodulation:

A portion of the 455 KHz IF is switched from D1076 (one of the IF filter PIN diode switches) and applied to Q1080 for amplification.  The output of this amplifier is applied to Q1079, a dual PIN diode switch, to select one of two IF filters.  The output of the selected filter is then applied to D1069.  The filtered IF signal is then sent to Q1069, a Rohm BA4116 IC which performs demodulation  of the FM signal.  An voltage for S-meter reading is generated with Q1056 amplifying the RF and being rectified by D1065.  It should be noted that this voltage has quite good logarithmic conversion properties:  The ratio of input signal in db has quite a good correlation with the linear voltage output by this device.

Audio Stages:

The audio from one of the demodulators is sent to a summing junction consisting of R1264-R1267 and applied to Q1057, another quad analog switch.  This switch provides additional selection of audio sources.  Audio buffering/amplification is provided by Q1094 and final audio amplification is provided by Q1070, a TDA7233.

The audio output is sent to a speaker, or to the earphone jack.  The earphone jack is a 3-conductor stereo type, and switch S1001 switches in some 100 ohm series resistors to limit power that may be applied through the earphone jack to prevent excess power from being output to the headphones and resulting in possible hearing damage.

Transmit circuitry - Audio processing:

The low-level audio from microphone jack J1014 is amplified by Q1092 and routed to Q1071, a multichannel electronic attenuator providing SSB, AM and FM microphone gain adjustability.  From this point audio is distributed to the FM and SSB audio chains.

For SSB, the audio is amplified and lowpass filtered by Q1096 and applied to Q1087, an SSB balanced modulator.  For FM, the audio is pre-emphasized, clipped, and filtered by sections of Q1095 and Q1096.  Subaudible tone and DCS modulation is applied via C1384 at Q1095 having been generated by the main CPU (see below.)  The audio is then re-introduced to Q1071 for deviation adjustment, buffered and amplified by another section of Q1095, and applied to the frequency modulator.

SSB Modulator:

The audio from the audio processing circuitry is applied to Q1087, a balanced modulator.  VF1001 provides an adjustment for carrier nulling, and the carrier is supplied by Q1031, the AD9835 DDS unit.

The double-sideband output is fed through D1080 to the IF filtering matrix.  From this point, it is routed through the appropriate sideband filter - which could be the standard ceramic filter (CF1004) or the optional filter at U1003 if it is an SSB-type filter.  The now-filtered SSB signal is steered through D1075 and D1074 and out to the upconverter circuitry.

Frequency Modulator:

To generate FM the output from Q1095 is applied to D1056, a varactor associated with crystal X1001 and Q1033.  These components comprise a frequency-modulated crystal oscillator operating at a center frequency of approximately 22.7785 MHz.  The audio from Q1095 modulates the frequency of this oscillator.

This signal is amplified by Q1023, limited by D1042, and amplified and frequency-multiplied by Q1015.  The tripled carrier frequency (68.3355 MHz) is then filtered by T1013 and T1012 and then amplified by Q1007 - a dual gate MOSFET - which also provides electronic gain adjustment for power control by the ALC and VSWR protection circuitry.  It should be mentioned that Q1007 is also used on the SSB/AM/CW modes as well.

Note that although the frequency modulator is "off" frequency, this is (apparently) taken into account by the microprocessor and the synthesizer is used to put the transmitter on frequency.

Amplitude Modulator:

To generate AM the amplitude modulation is created in a manner similar to that of SSB except that Q1079 applies a voltage to Q1087 via D1077, unbalancing the balance modulator.  This produces a DSB signal without a suppressed carrier - essentially AM.

CW Keying:

CW is generated via a voltage from D/A converter Q1077.  It is generated in much the same way as AM (except no audio) by disrupting the balance of Q1087, the balanced modulator.

Transmitter upconversion:

For SSB, CW, and AM, the transmit IF signal is routed to Q1040 to be buffered.  The signal is then mixed with the a signal that is 3 times the main reference oscillator (67.875 MHz) resulting in a signal at 68.33 MHz - the first IF.  Diodes then steer this signal through XF1001 - the main 68.33 MHz IF crystal filter.  After passing through this filter it is then routed to Q1007 - a dual gate MOSFET (also used in the FM transmit chain) for electronic gain adjustment for power control in the ALC and VSWR protection functions.  More dynamic range for transmit power control is provided by D1017 (a PIN diode) and Q1002:  This gain control is provided by the microprocessor and is related to the "TXG" settings in the "Soft Calibration" menu.

Final upconversion is performed by D1049 - a quad diode array that, along with T1022 and T1017 (both quadrifilar transformers)  mixes the 68.33 MHz transmit IF with the output of the synthesizer.  The result is (among other signals) the final transmit frequency.

Transmit bandpass filtering:


For UHF, the output of the mixer is steered by D1040 to a filter array consisting of tuning capacitors TC1005, TC1002, TC1004, diodes D1037-D1039,  and inductors L1013, L1019, and L1020 and associated components.  This bandpass filter is sufficiently broad enough to pass signals for the 70cm amateur band while rejecting the LO and image frequencies.  The output of this filter is selected by D1009 and passed to one half of D1010.


For VHF, the output of the mixer is steered by the other half of D1040 to a bandpass filter consisting of T1009-T1011 and varactors D1025 and D1026.  These (and associated components) form an electronically tuned bandpass filter for the 2 meter amateur band.  The output of this filter is selected by the other half of D1009 and passed to the same half of D1010.

Note:   This filter does NOT provide coverage below the 2 meter band (i.e. the aircraft band.)

6 Meters and HF:

The 6 meter TX signal is passed to a highpass filter consisting of L1038, L1039, C1472 and related components via one half of D1041.  For HF, this highpass filter is bypassed.  In both cases, the signal then is applied to a lowpass filter consisting of L1002, L1008, L1009, C1011, C1043-C1046 and related components to remove Harmonic, LO and IF content.  The output of this filter is applied to the half of D1010 not used at VHF and UHF.

TX preamplifier:

The filtered TX signal from D1010 is amplified by Q1001 - an extremely broadband monolithic amplifier.  The output of this stage is then sent to the final amplifier board.

Final amplifier:

This is a separate, extremely broadband amplifier module capable of amplifying signals on all frequencies from 160 through 70 cm.  The first stage is a low-level broadband bipolar amplifier (Q3001) and is followed by Q3002 - a MOSFET amplifier, the bias of which is set by VR3001.  This signal is further amplified by a parallel (single-ended) amplifier consisting of Q3004 and Q3005 with bias for this stage being set by VR3002.  The output of this stage is passed through T3004, a bifilar broadband transformer (consisting of small coaxial cable wound on a toroid) to the "Final Unit."

The final amplifier is of a push-pull design, getting its bi-phase drive from T3004.  The signal is amplified in balanced fashion by Q5401 and Q5402.  The bias is set for each transistor by VR5401 and VR5402 (respectively) and the output signal is applied to T3005, another bifilar broadband transformer.  DC decoupling is provided by C3053 and transformer T3001.  The output of the amplifier is then routed (via RL3017) to either the HF filter network or the VHF/UHF filter network.

The HF and 6 meter signal path for transmit is the same as that for receive except that the lowpass filters are NOT used, being switched out with the relays in the associated filters.  The output of the filters then go to the Forward/Reverse Power detector consisting of T3003, D3032, D3033 and related components.

The VHF and UHF transmit signal are routed to the appropriate filter via RL3001.  There, they are lowpass filtered and applied to the appropriate Forward/Reverse Power detector consisting of a circuit board stripline and associated components (i.e. D3009 and D3017 for VHF, and D3007 and D3008 for UHF.)

The detected voltage from the Forward/Reverse Power detectors is sent to the main board to allow power control and VSWR protection/indication.

RF/VSWR power control circuitry:

The output of the Forward/Reverse Power detector  is routed to the main board.  Sections of Q1097 (a quad op amp) are used to buffer these voltages.  The reverse power voltage is made available to the CPU and is amplified by a portion of Q1098 (another op amp section) which also acts on a threshold from Q1077 - a multi-channel D/A converter under control of the CPU.  In the event of excess reflected power, the output of this section activates Q1024, which operates Q1007 and reduces transmit power.  This voltage is also activates part of the ALC circuit, relaying that information to the CPU.

Forward power voltage is made available to the CPU and applied to a section of Q1097 for amplification and threshold setting:  If the power exceeds that set by a threshold from Q1077 (the "PWR" line) power is cut back.  This is the basis of the power control and ALC action.  When in AM mode, a voltage divider is activated (by turning on Q1016 and Q1018) thus setting the output carrier power to approximately three-tenths that of the maximum power.

External control circuits interfaced at the ACC connector:

External ALC control is applied via the rear panel connector (through resistors) to a portion of Q1097.  When the transmitter is keyed, Q1045 is activated, providing a "ground" at the  "TX-GND" pin.  Note that there is no current limiting at this pin, so it is strongly recommended that the user provide some outboard protection at this point - such as a resistor.  The TX-INH pin prevents transmit output power from being produced when it is pulled high.

The TXD and RXD pins interface with data (via series protection resistors)  from the CPU.  These are TTL level pins of fairly high impedance.  The "Band Data" is provided by a D/A converter consisting of resistors R1216, R1217, R1224, and R1225 (from 4 data bits output by Q1022 - a 4094 shift register.)

Note:  The "13.8" volt output is UNSWITCHED (that is, it is there even when the radio is turned off) and is current limited by R1235 - a 10 ohm 1/2 watt resistor.  Note that this resistor will be destroyed if you short this line to ground - even momentarily!  To remain within the power-handling capability of this resistor, draw no more than approx. 224 mA from this connector - and keep in mind that this much current will result in a 2.24 volt drop.

Power input circuitry:

The rear panel input is RF bypassed and then goes through Shottky diode D1085 to provide reverse-polarity protection.    Voltage at this point also turns on Q1109 which signals to the CPU that power is being applied via the rear panel connector.  If power is applied via the battery connector, it arrives via D1084 - another Shottky diode.  Charge for internal batteries is activated by Q1099 - which is used to activate a current regulator consisting of Q1101 - Q1103, Q1105 and related components.

The so-called "green wire" is used to turn on Q1107.  When voltage appears on this wire it signals to the CPU that non-rechargable batteries are being used.  It also disables the charge regulator circuitry via hardware.

One of the less-obvious protection measures in the FT-817 is that of overcurrent protection.  This is used mostly to protect the final transistors from certain types of faults.  It operates by using the inherent resistance of T1035 - a bifilar transformer in series with the power supply of the '817.  Voltage drop is amplified by Q1108 - an op amp - and made available to the CPU for monitoring.

The "main power" switch is Q1104 - a P-Channel power MOSFET.  When instructed by the CPU, this transistor is turned on, providing power the '817's audio amplifier as well as the main regulators, which which consist of Q1088 (a 5 volt regulator) as well as the nearby components such as Q1090 (which provides a regulated 6 volt supply) and Q1082 - which provides a semi-regulated 9 volt supply for other components such as the relays.

PLL Unit:

The heart of this unit is Q2016 - a DDS Synthesizer.  This chip produces a fairly low-frequency sine wave signal ranging from 7.2 to 8.0 MHz.  While the output of this synthesizer is extremely accurate and low in phase noise, it has some low-level spurious signals associated with it.  Because of this, it cannot be used directly.  Instead, five VCOs (Voltage Controlled Oscillators) are used to create the local oscillator signals at the desired frequencies.  The output of the currently-operating VCO is sent to Q2021 - a combination programmable divider and PLL circuit.  This IC takes the output of the VCOs, divides it down to the 7.2-8.0 MHz area (I think) and then outputs a control voltage to force the VCO to track the output of the DDS chip.    With the "loop filtering" of the VCO/PLL system, the spurious signals from the DDS are removed while the ability to use a high "reference" frequency as well as the extremely fine frequency step resolution of the DDS provides the best of both the DDS and PLL worlds.

Panel Unit:

The heart of the '817 is Q4004 - A Hitachi 64F2345FA CPU.  This CPU contains 128 KB of flash ROM (yes - flash!) as well as 4 kb of RAM, a bunch of timers, an 8 channel multiplexed 10 bit A/D converter, a multiplexed 8 bit D/A converter, and two serial ports - one of which is used internally to "talk" to various circuits, and the other is used for the serial port.

In lieu of a lithium battery, nonvolatile data (such as memory, configuration, "soft calibration," etc.) a 24C64 EEPROM is used - a part that effectively contains 8 kbytes of storage.

The CPU generates and detects CTCSS and DCS tones/codes.   Detection is done by taking discriminator audio and applying it to a filter/detector consisting of Q4017.  The limited/detected tone/code is then applied to the CPU and it does the nasty job of figuring out what tone/code is used.

CTCSS/DCS tones/codes are generated directly by the CPU - and are filtered somewhat before being sent to the modulator circuitry.

The End.

Go to The KA7OEI FT-817 "Front Page" - This is, well, the "front" page of the '817 pages here...

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This page maintained by Clint Turner, KA7OEI and was last updated on 20020313.  (Copyright 2001-2002 by Clint Turner)

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