Tuesday, June 27, 2017

A New Line of Transceivers ~ DifX

Transceiver Architecture 2.25

A Hint and a Clue

6/28/2017 ~ More on the Hint and Clue ---- Read ON

The above hint and clue is to show that I will be using a technique for USB/LSB selection where the BFO is at a fixed frequency and Upper and Lower Sideband filters are switched into the loop based on the mode selection of either Upper or Lower Sideband. R.L. Drake did this in the TR-4 transceivers and many commercial designs use this same approach. I actually had experience with a commercial Ten Tec transceiver which did this as well. It was the Model 100.
In my second filter architecture I use a pair of filters that were liberated from a commercial Kachina Transceiver and operate at 12.7 MHz and thus only need one BFO frequency in the Arduino Sketch. This is a good frequency as the 1st IF will be at 45 MHz and the second mixer frequency will be at 57.7 MHz and with a double sideband frequency inversion there will be no sideband inversion. I looked at any unwanted mixing products or harmonics and thus the 12.7 MHz is a clean frequency.
I have selected the ADE-1 for the Double Balanced Mixer as it is a 7 dBm device and for the IF stage I will use the standard Plessey developed 2N3904/2N3906 bilateral amplifiers. No Need to use the MMIC's for this stage as the upper limit for the Plessey is 40 MHz and it is loafing along at 12.7 MHz. The MMIC stage will be used in the bidirectional stage.
I have modified this circuit slightly with the insertion of a 22 resistor connected at the junction of the 680 Ohm resistor and 100 NF cap and that now connects to 8 Volts versus 6 volts. This gives a bit more "kick" to the circuit.
The board wiring has been completed and I will begin shakedown tests in the next couple of days. Power wiring, TR wiring and SSB Filter Select are all down on the underside of the board and coax is used to connect the bilateral amps to the filter matching transformers. This makes for a clean looking board. Initial tests of this board will be as a single conversion with a 12.7 MHz IF and once proven the 1st ADE-1 will have then have the  injection frequency of 57.7 MHz versus the tunable LO.

By the way the board can be replicated using Rex Harper's (W1REX) MePads and MeSquares and the only hiccup would be the ADE-1 but if you used a SBL-1 then "Bob's your Uncle." Most of the pads are 1/4 X 1/4 inch so lots of room and no crowding of parts.
Stay tuned for more exciting happenings.
Pete N6QW