VFO Controlled Micro-Mountaineer (uM)
This uM is built into an enclosure that measures 3" (deep) x 8" (long) x 2.5" (high). Extensive shielding is incorporated into the enclosure to shield the VFO from the transmitter. Both shields can be seen at the ends of the enclosure. These shields were made with double-sided pcb and then bolted into place. I took extra care to cut and place the shields so that there were no visible gaps between the top, side and bottom of the enclosure. The receiver and audio bandpass filter are built in the center (the filter is stacked on top of the receiver board which is not visible in the photo). The transmitter (on the right) is actually built onto the outside of the shield. This shield is held in place by the BNC connector and key jack on the rear of the enclosure and bolted to the front panel. The shielding was necessary to keep the transmitter from "pulling" the VFO frequency. Having used this rig in a recent homebrew sprint and in other QSOs all signal reports are very good, indicating that the shielding is doing it's job.
Radio design by W7ZOI; W3TS suggested that I try the audio bandpass filter.
VFO Coverage - 6.999-7.102 MHz (with a 3:1 reduction drive).
Output Power - exactly 700mW into a 50 ohm dummy load.
Front Panel - (from left to right) Tuning knob, AIT switch, RF gain control.
Rear Panel - Power and key jacks and BNC antenna connector.
Audio Bandpass Filter
Centered very close to 750 Hz.
Input and Output impedances about 100 ohms.
This filter works perfectly, removing hiss and noises.
It uses Toko 92mH coils and standard mylar capacitors.
It inserts some loss into the audio chain, but there is so much gain there already, the loss is actually an asset.
Best DX QSO so far is with S51OI, about 6300 miles / watt.
For DX on 40 meters using only 700mW, I am quite pleased.