In line with the yesterday's posting, how many of the ARRL newly minted Extra Class Licensees can understand this block diagram let alone create it. Likely not many. This is the block diagram for the CW transceiver. It was created 15 years ago and in hindsight I regret not formally publishing an article on the project and/or even creating a commercial product. It is really that good!
I intend to spend the next several blog postings covering the full design of this rig as there are various nuggets in the design that would be useful in any design created today. For those uninterested check the blog in a couple of days.
The first jack out of the box is to go to my website and click on the link for the 40M MMIC CW Transceiver. There is enough info there to replicate this FB CW Transceiver.
To clear up a misnomer this is not a Transceiver but a Trans-Receiver. There are only two blocks in the design that are common to both the Transmitter section and the Receiver section. Those blocks are the TR Switch, a NE555 (straight out of SSDRA) and the VTO. In fact, you could build just the Transmitter and VTO + NE555 and be on the air.
The next shocker is this was done without the use of an Arduino and Si5351. Wow, now this should get the attention of those who are weak in the knees when it comes to MCU's (Micro Controller Units = Arduino). But for those hams who would turn up their nose to anything that does not have those two elements then this is a design ripe for a conversion.
Because an MCU was not used the CW Crystal Filter frequency was chosen as 5.185MHz (avoiding the use of 5 MHz and WWV bleed through). That filter frequency was also purpose chosen to work with a low frequency VTO at 2MHz for frequency stability and that sum results in a 40M signal. Those choices also are good to eliminate harmonics slipping through a properly designed Band Pass Filter. A shift to an MCU opens up the possibility of higher frequency bands such as 20, 17 or 15M.
The next item that should jump out of the block diagram is the use of four MMIC devices with three in the Rx and one in the Tx. For those who can only think Bitx, this is a departure from that paradigm and yes, the MMIC's are Termination Insensitive so you have some part of your security blankie.
The MAR-6SM+ would work well in leu of the AG303-86G. MMICs were chosen because little supporting hardware is needed, no tuned circuits, 50 Ohms, termination insensitive, low cost and wide bandwidth + 20dB gain.
One of the ever-present problems with a CW transmitter is the offset frequency. You have to purposefully have some sort of offset otherwise you would always be zero beat. This design fixes that issue with a NE602. The transmit mixer stage has a separate oscillator crystal adjusted to be 700 hertz higher or lower than the BFO crystal. So, when transmitting the transmitted signal is automatically offset from zero beat by 700 Hz. This circuit is activated via the TR Switch to provide a constantly on signal during the timed CW transmit period. The actual CW keying is done in a subsequent Driver stage via a PNP keyer transistor. This eliminates chirps, clicks and burps riding along on the signal. The PNP keyer affords an opportunity for CW pulse shaping.
A good place to stop for today. For those who are not homebrewers -- set the snooze alarm for a couple of days hence. Exciting topics to be covered include how the sidetone monitoring was created.
This posting is aimed squarely at the ARRL. For the Newington Nerds, did you realize by creating a no knowledge Extra Class License that you created several generations of hams who could not pull off a project like this. That has a direct impact on advancing our hobby.
For those into POTA, SOTA and IOTA, this CW transceiver would be an ideal rig -- a small size and just enough power that would be heard. Updating with an MCU adds an order of magnitude of capabilities such as an LCD display, built in keyer and an uptown keyboard port for sending CW with a code mill. You could even have canned messages triggered from the keyboard.
In case you have some really old back issues of QRP Quarterly the keyboard keyer was a joint published article from N6QW and KK6FUT.
73's
Pete N6QW