开云体育

Adrian,

On the Bitx40, Q13 and R141 can get hot enough to fail on long transmissions,
especially if the rig is operating at over 12v..
If feeding it 14.5v, I suggest you add a 3 terminal regulator such as an LM2940CT-12 or LM7812
inside the rig to drive 12.0 volts into the PWR1 connector, which supplies most of the rig.
But make a direct connection from the 14.5v source into PA-PWR1 to power the IRF510 drain,
since that will want to draw an Amp or two.
The IRF510 is the only place where the extra voltage can be put to good use, giving more power out.
The IRF510 should be happy enough with PA-PWR1 of 20v or more if properly heatsinked.

During manufacture, the 12mhz crystals get sorted by frequency, and five crystals very near the same
frequency are used on any given rig.? That happens to give good alignment between BFO and crystal filter
in most cases (the parallel resonant frequency of the crystal in the BFO is a couple khz below the series
resonant frequency as used in the crystal filter).? Curious that yours did not work out so well.
If you want to pursue this, I suggest trying Allard's v2 instructions,?
This allows driving the BFO from the si5351, and the BFO freq is then easily set-able from the menu.
?
There are two ways to switch from LSB operation to USB operation:
1)? Move the BFO a few khz to the upper side of the crystal filter.
? ? ?This would require either adding a coil at L5 of the analog BFO,
? ? ?or must use Allards v2 firmware to drive the BFO from the si5351.
2)? The stock Bitx40 uses low side VFO injection, so 4.8mhz VFO + 7.2mhz signal mixes to a 12mhz IF.
? ? ?Putting the VFO above the IF (so now the VFO is at 12mhz + 7.2mhz = 19.2mhz) is an alternate way to flip the sidebands.
? ? ?Both versions of Allard's firmware allow this VFO method of sideband selection to be used.
? ? ?
Since you are using method two, for USB the VFO frequency is now 19.2mhz instead of 4.8mhz.
C91 and C92 (part of the feedback network in the old pre-Raduino analog VFO) must be removed or they will
suck away the available 19.2mhz energy and make the rig deaf.? Double check that you did this surgery correctly.
Note that when the Raduino sources the VFO, the old analog VFO coil L4 is removed, so Q9 is just a buffer and not an oscillator.
If you have a scope handy, would be interesting to see if the injection level into T2-pin6 is as strong on USB
as it is on LSB.? Your trouble of weak USB operation is probably somewhere between the DDS1 connector and T2-pin6.
If you can't get this to work, go with Allard's v2 firmware and move the BFO instead when you want USB operation.

These rigs usually arrive moderately well calibrated, but off by a khz is not just too unusual.
Perhaps this rig got skipped on final calibration at hfsignals.

Jerry, KE7ER