Modifications for the Yaesu FT-920
 

Expanded Digital Mode Operating Instructions

  Application Note

Yaesu U.S.A - Amateur Products Division - Technical Support

File No.: AN-97xx Date: August 6, 1997
Model: FT-920 Serial No. Range: All

Expanded Digital Mode Operating Instructions

This document provides expanded operating instructions for the FT-920 when operating on RTTY, HF Packet, and/or other Digital modes.

Digital Mode Operation

While setting up your equipment for digital operation, however, it is important that you understand the differences between the two keying methods provided on the FT-920 for digital mode operation, so that the controls and switches may be set correctly.

  • Most operation is accomplished using Audio Frequency-Shifted Keying (AFSK), whereby the Terminal Node Controller (TNC) generates audio tones to be transmitted as data by the FT-920. To activate this mode of operation, the front panel Mode selection must be set to DATA-USB (even though "USB" may not be the actual sideband utilized in operation), and the rear panel [AFSK-FSK] switch must be set to AFSK.

     

  • The FT-920 can also accept input from a TNC or Terminal Unit (TU) operating in the FSK (Frequency-Shifted Keying) mode, whereby a closure to ground of the FSK keying line causes the transmitted carrier to be shifted in frequency; no audio tones are produced by the TNC or TU.

AFSK RTTY or Packet Operation

The AFSK configuration environment may be the easiest for you to use, as the TNC then has total control of the tone frequencies, Mark/Space relationship (normal/inverted), and other aspects of digital operation which are critical to successful operation.

  1. Connect your TNC to the FT-920's Data jack per the instructions on page 16. Pin 1 of the Data jack should be connected to the TNC's "Mic Audio" or "Tx Audio" line. Be sure to set the [AFSK-FSK] switch to AFSK.

     

  2. For AFSK RTTY (Baudot) or 300 bps HF Packet operation, press the [Data] mode key until [Data] and [USB] appear on the display. Now enter the Menu system, and select Menu #U-46; set this Menu Item for the frequency appropriate for your operating mode:

     

    • For typical RTTY operation, select 2125-L; this sets the carrier injection up for an offset of 2.125 kHz in a pseudo-LSB mode, so that the transceiver actually is operating in the "LSB" mode (even though the display still indicates Data-USB).

       

    • For Packet operation, you may leave Menu #U-46 in its default 2125-U (pseudo-USB mode), or set it to 1700-U or some other value as required by the configuration of your TNC. See the documentation provided with your TNC's communication software for details regarding defining the transmitted tones.

     

  3. The packet frequency display (offset) may also be modified via Menu #U-45, allowing you to have the radio's display indicate either Mark or Space frequency, or the center frequency of the two tones.

     

  4. At this point, you are ready to utilize your TNC's software to begin operation. After loading the software, tune in an RTTY station so that it is properly decoded on your computer screen. When solid copy is obtained, you may press the appropriate key on your computer's keyboard to activate the transmitter, and begin typing. See your TNC's instruction manual for further details regarding actual operation.

     

  5. The DSP High- and Low-Cut filters are particularly beneficial in reducing interference in RTTY pile-up situations. A typical setting of the High Cut control is at approximately 1 o'clock, while the Low Cut control may be set approximately to 11 o'clock.

     

  6. The "CW" Narrow filter may also be used for AFSK operation. Just press the Narrow key, then rotate the IF Shift control to peak the signal in the narrowed IF passband.

     

  7. Via Menu #U-10, the Enhanced Tuning Scale may be engaged so as to allow a visual representation of precise tuning pursuant to the tone frequency selected via Menu #U-46. However, since your TNC may also have such a facility, and because the TNC is ultimately in control of the tone generation and decoding, you may wish to rely on the TNC's tuning indicator, and use the Enhanced Tuning Scale of your FT-920 for other purposes.

     

  8. For 1200 bps FM packet, press the [Data] key until Data and FM appear on the display.

FSK RTTY Operation

This mode utilizes the tone generator in the FT-920 for production of the required Mark and Space tones used for RTTY operation.

  1. Follow the interconnection guidelines on page 17 for details on how to hook up your terminal equipment to the transceiver. Be certain to set the [AFSK-FSK] switch on the rear panel of the transceiver to FSK. In this mode of operation, closing Pin 1 of the Data jack to ground causes the carrier to shift; the magnitude of the shift (170/425/850 Hz) is set via Menu #U-43, while the carrier's offset from zero beat and its sideband USB/LSB) can be set via Menu #U-42. Do not connect Pin 1 of the Data jack to any TNC/TU line which carries "Mic Audio" or "Tx Audio" as these lines are used for AFSK operation (see previous section).

     

  2. Press the front panel Data switch to select the [Data] [LSB] mode, which corresponds to "FSK" operation (remember, "Data USB" is used for "AFSK" operation).

     

  3. At this point, you are ready to utilize your TNC/TU's software to begin operation. After loading the software, tune in an RTTY station so that it is properly decoded on your computer screen or TU display. When solid copy is obtained, you may press the appropriate key on your computer's keyboard to activate the transmitter, and begin typing. See your TNC/TU instruction manual for further details regarding actual operation.

     

  4. As with AFSK operation, the "CW" filter may be engaged in the FSK mode by pressing the [Narrow] key, and the DSP filters may also be used to reduce interference in crowded digital operating situations.

Operating Tips

  • If you are hearing and decoding stations successfully in an AFSK environment, but stations cannot understand you, check to be certain that your TNC's software has not set a shift other than 170 Hz, and be sure that the tones have not been "inverted" in the software configuration.

     

  • If you are getting no shift (only a steady carrier) in RTTY FSK operation, be sure that you have not connected Pin 1 of the Data jack to an AFSK output line from your TNC (use only the "FSK" line provided by your TNC). If the FSK line has been properly connected, check to be sure that you have the "FSK" mode properly enabled on your TNC, if the software requires you to do so.

     

  • If you are having trouble decoding HF packet stations, be sure that you have set Menu #U-46 to one of the settings which ends with "U" (instead of "L"), and that you have chosen a tone frequency compatible with the tones for which your TNC is configured.

 

MARS/CAP modification for the American FT-920
 
  1. Remove top and bottom cover.

     
  2. Remove DSP unit and remove or cut green wire that connected between R2544 and Q2510. See the picture shown in below.

     
  3. Replace DSP unit.

     
  4. Press and hold STEP and LOCK buttons and POWER ON.

     
  5. Enter 1 9 8 4 1 2 9 then press ENT.

     
  6. Test the radio for correct operation.

     
  7. Turn the radio off and replace top and bottom cover.

     
  8. The modification is now completed.


 

Subject: Note
 

I purchased a FT-929 in Sept 2000. I would offer these suggestions to make it easy on the HAM doing the modifications.

  1. Remove only the bottom cover. There is no need to remove the top cover.

     
  2. The DSP Unit is the large (3 5/8" x 5 1/2") shiny metal box in the front left corner of the radio, bottom face up.
    Remove the three (3) screws, lift DSP Unit Box out , carefully.
    The Green wire is easily visible.

     
  3. Follow the instructions for cutting the green wire, etc.

     
  4. The ten (10)number key pad is superimposed with the HF buttons It is activated when you , " Press and hold STEP & LOCK and POWER ON".

 

Service menu for the ft-920

Download the service menu.

 

FT-920 Switch Board
The FT-920 Switch Board Mod allows the use of one filter or two in cascade. The switching is done by a mini toggle switch mounted on an L bracket under a screw in the bottom cover. Two of these boards may be mounted in the FT-920, providing filter selection from one switch for both CW and SSB. The boards are supplied pre-wired so the customer need do only a minimum of soldering. Please specify the mode when ordering. (Filters not included.)

One early customer of this mod wrote the following review:

"...the resulting performance improvement in the radio is dramatic... The two filters in cascade create an improvement in selectivity that really stuns the ear. It's so obvious to hear the skirt noise drop away and the voice in the middle of the passband jump in clarity. Flick the switch to cut out the cascade, and the radio returns to the full-sounding audio for casual rag-chewing... You have transformed the FT-920 into a super premium receiver..."

The FT-920 Switch Board Mod is pin compatible with our filters, so when ordering filters for this product please specifiy the "bare filter -- no board" option.

 For more details click on this link http://www.inrad.net/product.php?productid=3

ATTENTION
The KB2LJJ takes no responsibility for any damage during the modification or for any wrong information made on this modification.