Sunday, October 16, 2011

Base Bias Tuned VFO

VE7BPO describes the interesting article called Base Bias Tuned VFO. The VFO is based on the common base colpitt's oscillator and tries to change the bias voltage. The 2N3904 transistor is used for the VFO.
I made the VFO with this schematics but the capacitor 220pF is not good for my built VFO. Therefore, the capacitor 220pF and L1 have been changed to make the oscillation. My VFO has got the 7MHz band. Since the VFO is the L/C oscillator, the stability should be managed with the L/C value.

Monday, October 03, 2011

BS170 is used for the QRP rig PA.

The 2N7000 PA was described in my blog message sometime ago. The BS170 by Fairchild can be also used for QRP rig PA. It is N-Channel Enhancement Mode FET. The Maximum Power Dissipation Pd is 830mW, therefore it can be suitable for QRP rig PA. The transmitter section of ADC-40 is the dual BS170 and it generates about 4watts with 13.8V power supply. The small heatsink is required to use BS170s for PA because it will be hot and drops the power. The PFR-3A is the triple BS170 for PA and generates 5 Watts with 12V power supply.