Yaesu FT-817

FT-817

The Yaesu FT-817 is one of the smallest MF/HF/VHF/UHF multimode general-coverage amateur radio transceivers. The set is built by the Japanese Vertex Standard Corporation and is sold under the Yaesu brand.[1][2] With internal battery pack, on board keyer, its all mode/all band capability and flexible antenna, the set is particularly well suited for portable use. The FT-817 is based on the same main circuit board as Yaesu's FT-857 and FT-897, so it is a compromise transceiver and incorporates its features to its low price ($670.- at its 2001 release).[3]

The upgraded FT-817(N)D was launched in 2004. The difference between the two models is the addition of the 60 meter band coverage, other display lighting options, modifications in the RF stage, the included FNB-85 battery-pack and NC-72B charger.

The FT-817 is one of the most famous QRP transceivers[4][5] and there is a variety of modifications[6][7] ranging from frequency extensions to internal antenna tuners.[8]

Technical description

CAT Interface

A serial port with a wide range of commands is provided. While the specified interface[2] has little functionality, additional functionality has been reverse-engineered.[9]

Circuit description

The following circuit description is an extract from the service manual[10] and a detailed reverse-engineered analysis[11]

RX signals may be input via a front BNC connector or a rear UHF SO-239 connector (Yaesu calls it a type "M" connector) using a relay on the PA unit. The selection has to be made per band (HF, 6, 2 m or 70 cm) using menu selection. The BNC connector is the antenna connector chosen when the relay is bypassed.

A 70cm signal path goes through a high pass filter network, through the RF directional coupler/power detector (not on rx) to a low pass filter to a PIN-diode. In rx mode, these are turned off. The rx signal then passes through a DAN235U; this is a dual diode and when in UHF rx mode, the appropriate diode is turned on, passing the 70 cm signal through and the signal then leaves the PA board. On the MAIN circuit board the 70 cm rx signal enters a DAP236U. This dual diode get its current from the PA unit and when 70 cm rx mode is active one of the diodes is turned on. Rx signal goes through a device consisting of 2 back-to-back diodes providing protection for the receiver's front end. The output of the preamplifier is sent to a helical resonator filter. The output of the filtered and amplified 70 cm path is passed through and coupled into the receive mixer. For 70 cm receive, PIN diode bias is provided to the PA unit, through the MAIN unit and then through an RF-decoupler network, a parallel-output shift register.

A 2m signal goes to a relay and then the signals are diplexed, with 2m and < going to a lo-pass filter. The signal gets diplexed again using a hi-pass filter, separating out the 2 m signal from the HF-6 meter signal path. The rx signal passes through the VHF directional coupler/power detector (not used in rx) to a lo-pass filter and then passes by 2 PIN diodes (both HSU277). These diodes and related components form T/R isolation switches that operate similar to that of the 70 cm front end. Rx signal passes through the half which is not used for 70 cm and then to the RX RF output and is then passes to the MAIN unit. Here the signal enters and then passes through a transformer, along with a varactor and related components and forms an electrically-tuned filter/matching network, the 2 meter preamplifier. The output of the preamplifier goes through 2 electronically tuned transistors. Finally, the output goes through to get to the rx mixer. For 2 m rx, the PIN diode bias is provided by the PA unit to 2 m preamplifier.

Aircraft band Rx path (108-154 MHz) is the same as that of the 2 m path on the PA unit. On the MAIN unit, it goes through the same part as the 2 m signal, but it then goes through the diode portion that was not used for 2 m into an electronically tuned bandpass filter. The output passes through the rx mixer. The PIN diode bias is provided by the PA unit and flows through the primary transistor. On the output, current is provided and goes through the secondary transistor. Both current paths are completed using the aircraft band rx preamplifier.

WFM broadcast band rx path (76-108 MHz) is identical to the 2 m path on the PA unit. On the MAIN unit it passes through the same portion as the 2 m signal, then through a HSC277 diode. This signal then goes into pin 10 of a Sony CXA1611 FM Receiver IC. The IC has a front end, mixer, IF and demodulation and provides received audio. In order to suppress local oscillator leakage and provide a slight amount of image rejection, a varactor and a coil provide one stage of tracking bandpass filtering. Typical for single-chip receivers, the dynamic range of this receiver is poor. When using a large antenna, expect overload/intermod problems.

HF and 6 meter receive path. After relay the signal is diplexed via a low-pass filter. At this point 2 m, aircraft and WFM are diplexed. Continuing the signal passes through a low pass filter, continues through the RF Directional Coupler/Power Detector (not used in rx) through low pass filters selected by relays as appropriate for current rx frequency. The combination of lo- and hi-pass filters provide broadband bandpass filtering to the rx front end. For 6 m the hi-pass filter includes a preamplifier (always used on 6 m rx and not affected by the IPO menu setting). The appropriate high pass filter output is selected with a PIN diode with logic levels. The output from the PIN diodes are routed to the MAIN unit. Here the rx signal is applied to dual PIN diode modules (type DAP236U). 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 is then passed through a simple lo-pass filter to another DAP236U. One of the outputs is applied to a preamplifier and the other is applied to a diode, bypassing the preamplifier. The output of the diode is applied to an IF trap. 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 to the receive mixer.

Technical Specifications[2]

Accessories[2]

3rd Party

Suitable Antenna Tuners

Known Weaknesses

Vulnerable final transistors! The 2SK2975 FET's in the final stage are VERY sensitive and can easily be destroyed by high SWR, overheating, overvoltage or voltage peaks. In the ND model Vertex have replaced the FETs by RD07MVS1 devices but the problem still exists so the RF stage remains sensitive to damage.[13][14]

The internal battery should be removed if the radio is to be stored for an extended period. In the non-ND model, a failing battery can (and does) cause the finals to oscillate which destroys the FETs. This was corrected with the ND model though it is still recommended that the internal battery be removed for extended storage.

References

  1. ↑ Yaesu FT 817 http://www.yaesu.com/indexVS.cfm?cmd=DisplayProducts&ProdCatID=102&encProdID=06014CD0AFA0702B25B12AB4DC9C0D27
  2. 1 2 3 4 Yaesu FT-817 Operating Manual
  3. ↑ Testbericht Yaesu FT 817, Funkamateur http://www.funkamateur.de/testberichte.html?file=tl_files/downloads/testberichte/frei/FT-817_test.pdf
  4. ↑ WG0AT with FT-817 http://www.youtube.com/watch?v=pX2r0ddUqsw
  5. ↑ Review on eham http://www.eham.net/reviews/detail/1184
  6. ↑ FT 817 Modifications, KA7OEI: http://www.ka7oei.com/ft817_mods.html
  7. ↑ http://www.yaesuft817.com/wp
  8. 1 2 Elecraft T1 ATU in FT 817: G8IFF: http://www.ngunn.net/cyberworld/hamradio/t1/
  9. ↑ Undocumented Interface of the FT 817: http://www.ka7oei.com/ft817_meow.html
  10. ↑ Yaesu FT-817 Service Manual
  11. ↑ Detailed circuit description of the FT-817: http://www.ka7oei.com/ft817_desc.html
  12. ↑ Quick-Tune Dongle: http://www.huk-electronics.co.uk/quick-tune_dongle.html
  13. ↑ Blown finals: http://pages.cs.wisc.edu/~timc/e/ft817.html
  14. ↑ Replacing the FT 817 finals, KA7OEI: http://ka7oei.com/FT817-finals.pdf
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