Farhan,
Your doing what I tried back in June/July time frame, it failed then.
Reason first series traps good enough to suck out the spur at a given frequency
are narrow enough? to be only a spot frequency fix.? The 2IF-LO spur for 28mhz
BAND is between 17 to 16 mhz for 10M alone.? So you need a series trap that
can not do a band.
The other issue is the power amp.? At 80M and 10W out the gain is about 60db
but as you go up, at 20M the gain is down to ~56db, and at 10M the gain is maybe
~52DB.? ?So at the spur frequency you have more gain available than the desired
output frequency and the differential gain is enough to put that spur as shown at
-45db at more like -37db below 2W.
The fix has to be more comprehensive.? Also it must be field verifiable or factory
set to allow for 1 or 5% parts.
The 45mhz section needs:
? 45mhz filter inductors shielded or better that section relocated.
? Amplifier distortion clean up.
? Swap the 45mhz port and LO ports as IF ports are most sensitive to mismatch.
A thought to look into...
? Replace the TIA amp at 45mhz with a more common resistive feedback amp (typical 2n5109 amp)
? with 20db gain.? Here is the hint:? Often when that amp is shown due to the fact that changes at either
? port impact the opposing port they often have a 6db pad at the output.? However for the TX case that
? same pad can be at the input and it insures the 45mhz filter will have a good match for the network
? and the transistor with its input impedance stable will have output stability going to the mixer.
Allison
