Re: UBITX V6 Q90 Pinouts on board
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Thanks David and Evan, Adding the protection is definitely my intention once?I get my current issues sorted also Q90 upgrade. I really appreciate your help and will give some updates. Just wish my Standard Exam results?would magically appear its taking?a ...
Regards Open?Vk5kov
On Sat, Jun 24, 2023 at 6:06?PM Evan Hand < elhandjr@...> wrote: Dave,
Good idea
Owen,
Dave refers to past discussions on causes for Q90 to fail.? Here is a link to one of the posts with a picture of how I did the protection on one of my v4 boards:
/g/BITX20/message/89267
Read through the entire thread to get the full value of the community discussion.? To summarize, high RF on the antenna input of the uBitx can cause a voltage pumping or doubling effect on the base-emitter junction of Q90, which leads to the device's failure.? Back-to-back diodes on the line to the receiver between the two T/R relays can short any RF above the .7 volts turn on of the diodes.? This is a much higher voltage than the signal received while operating (usually in the microvolt range).
Even with the diodes, it is best to disconnect or short the antenna input of the uBitx when operating another transmitter.? I use a shorting RF switch so that only one radio is connected to the antenna.? A single shorting selector switch would not work for two radios with two antennas.? You would need a separate switch for each radio (and the discipline to short the unused radio).? Powering off the radio will not protect Q90.
Q90 replacement brings up another thought of improving the overall power across all bands.? I have implemented Allison Parent's KB1GMX mod listed here:
All the radios I modded to level the power showed significant improvement.? I highly recommend the modification if you are up to the SMD work of adding and changing the SMD resistors and swapping out Q90 for a BSR106 device.? Well worth the effort.
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Let us know how it works out.
73
Evan
AC9TU
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