EMRFD Message Archive 6583
Message Date From Subject 6583 2011-09-05 13:37:13 Tim Full break in transceiver In a little portable rig, my latest iteration of full break in QSK, designed to feel the most like separate transmitter and receiver in the traditional sense:
17M transceiver rig.
Receiver is a simplistic superhet with an IF at 4.43MHz (6 pole equiripple crystal filter) and VFO (J310 Hartley) runs in the 13.6MHz ballpark to tune 17M.
Transmitter lives in the same box and shares no components except the VFO. There is a unkeyed 17.73 MHz crystal oscillator and divide by 4 in HCTTL to make 4.43MHz only on key down or spot, with front panel variable cap for tweaking up and down by about 2 kHz. Essentially this knob is the "XIT" (transmitter offset). This transmit BFO is mixed with the VFO to produce the transmit carrier which then goes through two low level stages (2N7000, then 2N7000's in push pull) and drives a RRD16HHF1 for about 15W out.
Receiver IF (simplified hycas without the AGC... I might add AGC in later) is muted in transmit, but the product detector and audio processing is not.
When in spotting mode or key-down the transmit BFO is loosely coupled to the receiver's product detector. Thus generating a sidetone which is exactly the note heard on the band. The transmit BFO does not go through the crystal filter but is injected right into the receiver's product detector at about -45dBm.
TR switching is no relay, ala EMRFD fig 6.125.
This works out very well. The sidetone is a pure sine wave, I get single knob tuning, there is no RIT offset network in the VFO. And it achieves my ideal QSK: I hear my transmitted signal exactly as it sounds on the band.
Is this reminiscent of any other rigs out there? I see some hints on page 6.59 and figure 6.106 of EMRFD that I'm not the first to go this way.