“Is it time to ban the 458?” or: Transceive Operation with the Central Electronics 20A By Robert Nickels W9RAN © 2017 RAN Technology Inc.

Single-conversion SSB exciter: Develop SSB signal at 9 Mhz Use external VFO or crystal to mix 9 Mhz SSB to desired frequency Central Electronics 20A Speech Amp 90° AF Phase Shift Network Diode Modulator 9 Mhz Osc. 90° RF Phase Shift Network Mixer Driver PA Xtal or VFO

“-” indicates SB reversal CE 20A Mixing Scheme “-” indicates SB reversal Injection to the mixer can be either above (high side) or below (low side) Sidebands will be reversed (SB1 vs SB2) Mixing products and spurs will be different for each Norgaard “5 +/- 9” scheme is easiest and most efficiently produced with converted command set transmitter as VFO, reduced output on other bands Short version: Operating Freq. plus or minus 9 Mhz into the 20A

Double-conversion superhet receiver: VFO and heterodyne crystals are “premixed” to produce injection signal that is 5.645 Mhz above the desired signal. Crystal filter at 5.645 Mhz 2nd conversion and LC filter at 50 Khz. Drake R4 series

Desirable Characteristics Excellent SSB receiver Injection output (premix system) Drake premix internally mixes the VFO with a crystal oscillator to produce a first LO injection signal that is always 5.645 Mhz above the desired operating frequency Simplifies operation with a transmitter in transceive mode Drake’s choice of INJ frequencies is fairly compatible with the 20A requirements

Drake R4 series analysis Nominal LO of 14.645 Mhz works for 80 and 20 meters and is reasonably clear from image frequency 14645-9395 = 5250 (SB1) 14645-19945 = -5300 (SB2) Others may require additional filtering or amplification or both Spurs and spectral purity TBD (look at how many traps Wes had to use)

Sources of Frequency error, drift, etc All crystals age differently and unpredictably Different errors to begin with Not high precision Temperature effects depend on operating conditions

Solution: Frequency agility NE-602 Mixer Class A Amp R4 INJ OUTPUT 20A VFO Input ~20V P-P Si5351 Clk Gen Up/Down switches Arduino Nano 12VDC

Results (so far) GOOD LESS GOOD Provides the essential ability to set frequency and compensate for drift Simple, easy to build, low-cost (~<$50) Freq. increment can be set as desired (20Hz steps presently) Non volatile memory holds last-programmed value Drives 20A to full output on 80 and 20 meters LESS GOOD Range of INJ and required LO frequencies make covering some bands challenging with the R4 series The same is true for most other receivers 20A has reduced efficiency on bands other than 80 and 20 Solving the above issues is probably possible but spectral purity is unknown

Conclusion A modern Arduino-controlled digital frequency generator provides excellent transceive operation with the CE 20A and Drake R4 series receiver on 80/20 meters, and is easily reproducible. Let’s get more 20As on the air! Remember – if Wes hadn’t been willing to incorporate new technology into his products it would have been: AM