Converting the FT847 to a more stable Frequency with GPSDO

 

As it is still giving drift even with the Crystal heater module.

you can see the rapid drift here on the signals due to the oscillator drifting like crazy.

I was on the Moon and one station mentioned i had drift , i noticed this when powering on the FT847 , which requires time to heat up the crystal.

but still the drift was to high even  after warmed up ,

I found a Radio ham that could supply a module to fit the FT847 , this then accepts a 10 MHz input and then applies 22.625 MHz to the oscillator circuit 

here is the modification requirements kindly provided by PA0BAT

I have reproduced it here , correcting some errors .

 

Xtal MODIFICATION FOR YEASU FT847with 10 MHz Ref

This Modification Instruction briefly describes how to install a DF9NP made oscillator (see Fig. 1) into a Yeasu FT847 transceiver.

 

 

Fig. 2 shows where the Oscillator Board will be placed.

PROCEDURE:

1. Remove top cover and bottom cover of the transceiver, and remove the protection plate with loudspeaker.

2. On the component side of the Oscillator Board are a number of pins.
   Cut the upper half of the pins, to prevent that they later get in contact to the top cover of the transceiver.

3. Prepare a distance keeper for the Oscillator Board. It will be placed underneath the Board.

   This can be done as follows (see Fig. 3):
   Take a piece of cardboard, thickness about 1.5 mm. Cut three pieces in the size of the Oscillator Board. Then cut holes in it, corresponding to the protuberances at the rear side of the Board.
   Stack the three card board pieces and glue them together, to form a 4.5 mm thick distance keeper.

   Fig. 3 Distance keeper of card board

 

4. Install an SMA female connector (or an SMA F/F feed-through) into the vent slot at the rear of the transceiver as shown in Fig. 4.

REAR VIEW 

 

TOP VIEW

Fig. 4 Installing SMA connector or feed-through

5. Turn the transceiver upside down. Remove the large PCB. Do not forget to label the electrical connections and/or to make pictures, in order to put it all together later again.

6. Locate the reference quartz XT1001, small trimmer TC1001 next to it, and small capacitor C1109 (at soldering side of PCB). See Fig. 5 and Fig. 6.

Fig. 5 Location of XT1001 and TC1001 

 

 

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Fig. 6 Principle diagram of reference oscillator

7. Remove XT1001, TC1001 and C1109 from the PCB.

8. Via a ceramic capacitor (22 pF or so) the signal from the new Oscillator Board is applied to the base of Q1034.
   Solder a ceramic capacitor to the correct soldering hole of XT1001 (see Fig. 7).

   Fig. 7 Placing ceramic capacitor and connect coaxial cable 

    

   
   
    

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9. Replace the large PCB.

10.Scratch away some lacquer to get access to the earth plane. This is to connect the shielding of the coaxial cable to the Oscillator Board (see Fig. 7).
Connect the coaxial cable and lead the other end to the installation position of the Oscillator Board.

11.Take a length of wire and solder it to the point shown in Fig. 8.
This is the DC supply for the Oscillator Board.
Lead the other end of the wire to the installation position of the Oscillator Board.

Fig. 8 DC supply point 

 

Now the Oscillator Board is to be placed. It is kept in position by three pieces of wire, which are soldered to surrounding coil housings.

12.Take the Oscillator Board, and solder three pieces of wire to its earth leads as shown in Fig. 9.

Fig. 9 Soldering wire pieces to Oscillator Board 

 

 

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13.Bring the Oscillator Board in its position. Put the carbon board distance keeper underneath.

Solder the three wire pieces to surrounding coil housings (see Fig. 10).

Fig. 10 Position and attaching the Oscillator Board

14.Connect the two coaxial cables and the supply wire to the Oscillator Board (see Fig. 11).

Fig. 11 Oscillator Board placed and wiring connected 

 

 

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15.Apply and/or replace tie wraps where applicable.

16.Check that the Oscillator Board does not touch the cover plate with loudspeaker, when that is placed.
For safety/insulation, a piece of carbon board or other suitable material could be glued to the underside of the plate.

17.Apply cover plate with loudspeaker, bottom cover and top cover. Ready we are! 

 

__________________________________

 

after carrying out this mod , here are some images .

 

 

 Afer all the work done i had problems getting this to work,

I got an accurate freq counter and measured the output from the board , it did show the 22.6250 MHz initially but still we had no functioning radio , no sound , no S meter readings .

 

 A calibrated freq counter do 10 milli hertz

 comparing the 10 MHz to a rubidium standard

This was a puzzle ?. i removed the connection to the input at the base of the transistor and re installed the crystal , things then came back to normal , so we haven't killed anything .....

I had purchased the Leo Bodnar SPSDO and this was going to be used to inject the 10 MHz locked signal to the board, after checking the board again i found the freq was anything but 22.6250 MHZ at the oiutput.

so i ended up removing the board altogether , and since the leo Bodnar GPSDO can go up to 800MHz , i programmed it with the USB interface and the provided software supplied , then checked it on the Counter , SPOT ON,  the levels were to high so i inserted a 6 dB SMA attenuator in the line and feed the output direct to the Crystal oscillator transistor via a 22pf capacitor , also set the output on the interface to 12MA as it was adjustable, with the attenuator and levels set this was we had a decent drive the the FT847.

put everything back together and VIOLA all working !! .

Later in the week i had some of the big guns check me off the moon , rock solid now !!!.

so if you thinking of getting a stable lock with e FT847 or any other radio i would recomemnd the Leo Bodnar interface and a simple attenuator and blocking capacitor , simple and easy.

 

 here is me working a station you can see the strait signals , unlike before

here are two station working , you can see the clear traces , dead strait traces now.