I changed the display from a 1.44" 128x128 TFT ti a 1.8" 160.x128 TFT. Unfortunately they use different driver chips so I had to make some changes to the software , mainly a different driver library and the position of text on the screen. While I was doing that I also added a couple of
functions to the system.
New circuit board layout moved parts around to make room for the larger display, and added a ERA-3 MMIC amplifier with attenuator to boost output and present 50 ohm to the DUT.
After I got the hardware working with the pickup coil to
use the SNA Jr. as a Dip Meter, I decided to add a DIP function to the
software. It does a sweep from 1 Mhz. to 50 Mhz. with 50 KHz steps, and
looks for the deepest dip in the signal from the RLB. After that sweep
it sets the range to 1 MHz. below and above the dip frequency and
then does a normalized sweep of that frequency range. Much faster than
sweeping through in several ranges.
In the existing sweep functions, they are a single sweep triggered by a short push on the encoder button. After the sweep is started pressing and holding the button down will enter a setup mode, where you can make adjustments to the gain pots for the sweep range you are using if desired. Because I added the normalizing function, I had to do a complete sweep and then display the data.
Moving the coil wound on the pen with parallel cap
in and out of the "Dip Meter" pickup coil
From comments on QRP-L, sometimes a continuous reoccurring sweep would be better. This would be useful for adjusting filters, and other alignment procedures.
I added a FAST sweep function that does sweeps at around 1 second per sweep. To get this rate I had to remove the setup functionality, and only did one reading at each point instead of using multiple readings to reduce noise. In this FAST mode I erase the old data point and draw the new datapoint as it is acquired.
Still waiting on some parts to arrive, before I can finish testing the updated circuit board layout. After the last local QRP club meeting I was asked about the possibility of making kits available. Still trying to decide if I want to go this route, or just make the design for boards and software available. If anyone would be interested in a kit of this project drop me a e-mail at firstname.lastname@example.org Depending on the response I will decide which way I will go.