Raspberry Sundae
Our ice cream sundae is a perfect metaphor for today's blog. If you love to homebrew, then you likely have a penchant for ice cream. Afterall, who in their right mind would turn down a taste of a Raspberry Sundae.
But to take a bite, does involve a calculated decision. Afterall with the average age of our ham being way above 30 then it is not a simple decision as concerns for health such as lactose intolerance, adding to an already bulging waistline, cholesterol impacts and then there is that leaking filing that rapidly responds to sugar shock on the nerve endings. When you are 16, none of these issues matter for at that age it is YL's and not ice cream that are in the PFC (Pre-Frontal Cortex) and causes sensations in other parts of the anatomy.
But those factors are in the process when it comes to a radical decision such as completely removing the analog VFO from the Project X radio and replacing it with some modern digital electronics.
Let us ponder some of the considerations that would enter our decision process.
The very 1st question is the technology and that is not a science project as the Arduino / Si5351 are mature and easily implemented. We must ask can the fix be done and can it result in a seamless operation that not only replaces the original circuit but adds a better readout and a more stable frequency generation.
Another consideration is how to switch bands without adding more controls on the front panel. Fortunately, there are three switch positions on the original band switch that are sequentially grounded. These can be used to selectively ground three inputs on the Arduino to change the LO frequency. Project X used the same carrier oscillator frequency for the three bands and by shifting the LO (and sideband inversion) results in LSB on 80 and 40M and USB on 20M. The Si5351 would only supply the LO for the bands as the original Carrier Oscillator in the rig would not be disturbed.
In one similar project where I took the Hallicrafters FPM 300 and added a Digital LO the code for that project is the sourdough starter and could be lifted and easily modified for Project X.
Another consideration is space in the radio for the digital electronics. Removing the original VFO would provide an adequate area and the Frequency window on the front panel would easily accommodate a ST7735 Color TFT.
The decision should also provide a capability to return Project X VFO to stock and the capability to fully test the digital solution before the J and P (Jerk and Pull) of the existing VFO.
This last consideration gives rise to a two digital VFO solution and one that enables a stepped approach. About two years ago I built a remote VFO for a Ten Tec Triton II as the dial string slide rule dial was real crap.
That remote VFO had a 12 Key keypad where band selection was made and some of the keys enabled selection of step tuning rates. In addition to the rotary encoder two keys provided up/down tuning of the frequency and two keys could provide a +10 or -10 kHz split for the DX pileups.
There were but two connections to the Triton II, one being power and the other the LO output. There I used the internal carrier oscillator of the Triton II.
This remote VFO could be easily adapted to the Project X radio by simply disconnecting the internal VFO at one location in the radio and using an existing hole in the rear panel apron install an RCA jack for the remote LO connection. Rewriting the code is some simple number changes to accommodate the change in IF frequency.
This would enable a full evaluation of the digital LO and provide a modicum of confidence if my solution would work. Then and only then add the internal Digital LO similar to that use in the FPM-300 reincarnation.
Them that know can make things go.
73's
Pete N6QW