board QRP 20m transceiver. The
January 1991 issue deals with the transmitter part. These QST issues are now available
from the ARRL in CDROM format.20 METRE RECEIVER
This receiver was designed by Gary Breed, K9AY, and
described in the December 1990 issue of QST. The complete article outlines the building of
a two board QRP 20m transceiver. The
January 1991 issue deals with the transmitter part. These QST issues are now available
from the ARRL in CDROM format.
I built the receiver a couple of years ago and have been pleasantly surprised with its performance. Despite a fairly simplistic superhet design it delivers ample performance. Being compact allows me to easily take it with me on trips. By adding just a wall-psu and stringing up some wire for an antenna it gets me over any cw withdrawal symptoms.
Features include:
1. A simple superhet design based around a
Motorola MC3362, VHF FM receiver IC
2. Audio-derived AGC for listening comfort
3. Narrow IF cw fiter - about 400Hz
4. Signal meter
6. Low receiver noise
7. Stable VFO in normal conditions
8. Good receiver performance
9. Availability of components
10. Easily replicated
11 . Low cost
Although there was a kit of parts available at the time the article was printed in QST, its availabilty is now dubious. After building it from scratch it worked first time - no problems! The hardest parts were designing a pcb, winding coils and finding a stable vfo capacitor. This is worth careful cosideration as it will determine the finished receiver's frequency stability. Although Breed recommends a silver-mica or NPO capacitor here, I used an smd capacitor since these also exhibit a low temperature coefficient - in normal indoor use (ie: no sharp temperature changes) drift is negligible. The only other minor change made was to use a 10-turn potentiometer for tuning instead of two normal pots (coarse and fine) as suggested. A dearer choice but the resulting silky smooth tuning makes it worth it.
Receiver performance is promising - the article reports good sensitivity, with a minimum discernible signal of about -123 dBm. A third-order IMD dynamic range of 70 dB is not exceptional but good for the circuit's simplicity and the audio-derived AGC is reasonably smooth, and better than no AGC at all.
Adjustment is straightforward. Tune-up the frequency range you want - mine is set up for the bottom end of the band (until about 14.050MHz), peak the input coils for maximum signal at band centre, adjust the BFO trimmer to get a 750Hz tone and adjust a resistor to obtain the deflection you want on the S-meter. For more info ...read the article.