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Main receiver with 2 outputs — Jupiter Modular Receiver

Main receiver with 2 outputs — Jupiter Modular Receiver

SECTION 5  —  Main receiver with 2 outputs

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I crafted a simple DC receiver.  At some point, I might design and build a phasing ( ZIF receiver ) to supplant this module.

Above — I placed addition low-pass filtration on the input to allow receiver use with lesser grade preamp/filters than shown in Section 2 — and to scrub off any remaining VHF-UHF garbage at the input. I chose an SBL-1 mixer from MiniCircuits labs because I’ve got many left over from an estate sale purchase many years ago.

A “poor mans” AF diplexer terminates the IF port. Designed by Wes, W7ZOI for me in 2000, I like this diplexer because it employs only 1 value of cap + inductor and works OK.
  Main receiver with 2 outputs -- Jupiter Modular Receiver 6

Above — Simulation of the ideal diplexer using high Q caps + inductors. In reality, the L & C parts aren’t high Q and performance will fall short of ideal. But considering its parts count and simplicity, this diplexer seems practical.

Main receiver with 2 outputs -- Jupiter Modular Receiver 7

Above —GPLA simulation of the input low-pass filter. It delivers a good input match to the RF port of the diode ring mixer all the way up to 26.4 MHz


I spent much bench time on the feedback amp [ FBA ]. With a AF return loss bridge I tweaked the feedback and current to realize a input return loss of 25.8 dB at 1 KHz. The low noise
BC337 for Q2 and Q3 adds very little noise to the Johnson noise incurred in the bias + feedback resistors. Measured gain of the feedback pair = 28 dB with only 11.6 mA current. I designed a lower noise version, although current draw was over 35 mA so opted for the FBA shown.

A ripple filter + careful AF bypass & RF bypass removed any hum and RF from the output.

Main receiver with 2 outputs -- Jupiter Modular Receiver 8

Above — Audio amp and splitter schematic. 2 LM4562 op-amps make up the virtual ground plus 3 stages of low-pass filtered amplification. Measured gain = 24 dB. A Butterworth response employing low Q filter poles helps keeps ringing down. Low value resistors throughout keep Johnson noise down.

U3 serves as an active splitter/buffer to provide low impedance output to 2 panel mounted RCA jacks.  The output 22K resistor is normally in parallel with the load and serves to discharge the 3.3 µF caps when its port is unplugged.

Main receiver with 2 outputs -- Jupiter Modular Receiver 9

Above — I connected the receiver [ with cover off  ] to some bench modules ( left to right ) AF power amp + speaker; homebrew VFO/signal source; 7 MHz band-pass filter to coax and an 1/4 wave 40M band vertical antenna with 43 radials.

The band conditions were good and I listened to this receiver for 3 nights. Pleased, I boxed it up and moved onto the next module.