开云体育

Chris,

A potential issue with the QDX is a spike at the end of a transmission over the 60-volt specified limit of the BS170.? The TN0110 is a possible solution, EXCEPT that it must be installed backward compared to the BS170.? This reduces the amount of heat that can transfer out of the device.? That would increase the potential for power-induced failures.

There are two alternatives to the QDX potential issue.? One is to install a diode across L14 as if it were a relay to reduce the magnetic field build-up.? The other is to install Zener diodes to take the surge at the end of transmission.? Both have been reported as helping solve the problem.

The QMX has key shaping (rise and fall) in the power supplied to the PA stage.? That eliminates the spike at the end of the FT4/8 transmission.? The Zener pads were added to allow installation later.? Hans did not have conclusive evidence that the Zeners were needed at the time of manufacture.? Several designs by other designers do include Zener protection, so it was added as an option for the constructor of the QMX.

I have chosen the Zener approach for my QDXs.? The more common is the diode across L14.? You could install both, though that might be a belts-and-suspenders type of overkill.? I have not done any implementations on the QMX.? I am waiting for the firmware to settle before I return to playing with it.

I also have a solder-sucking gun, a Hakko.? I also have a hot air rework station.? You can still damage the very fine traces on the QDX board.? That happened to me when I went to clean up the excess solder with some wick after an IC5 failure.??

There have been posts on steps to protect the BS170s from failure.? The most significant is not to use an ATU.? Many of the reported failures are when using an ATU.? I must use a tuner for some bands as my HOA limits me on the size and number of antennas.? I use an ATU connected to my Icom 7300 to tune the antenna tuner and switch to the QDX.? The QDX does not see the high SWR associated with the tuning process.? Since following that process and installing the Zeners, I have not seen a failure on any of my QDX.? As stated earlier, I am currently not actively using my QMX.

73
Evan
AC9TU