Simple spur fix

 


This fix reduced the spurs by up to 10 db  and requires ONLY ONE part to be added.
There is big change above 10MHz in the board. There is some improvement below also.

The way I did it, CW may not work anymore will need some more mods for CW:

1. T2 - desolder the transformer wires that go to pin 3 and 5. Pin 1 has a square pad.
2. Bring out the two wires above board and join them together and solder.
3. Take a 45Mhz filter- 45M15 or  similar 2 pole - one xtal only. Solder one end of filter
to the wires of T2 pulled out. The center filter wire to ground at one end of R26. You will
see a ground via there.
4. Solder the third wire of filter to C10/R27 junction.

Thats it! This prevents the leaked TX signal that gets amplified by the 1st BiDi from getting into
the first mixer and creating havoc.

Farhan method of the same..much simpler and CW will work.

1. Remove R27
2. Solder the 45Mhz filter two extreme ends to the pads of the resistor.
3. Solder the center lead of the filter to the nearest ground. R13 is very near with a ground via.

The first method the extra filter will work in RX mode also and may help! In the second the
filter is only in the TX path..

Folks with DSA815 or better please share your feed back. The filter may work better properly
terminated etc.

Have fun!

--
Raj, vu2zap
Bengaluru, South India.

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