September 2007 Archives

I've been working on improved Z100 firmware and have a releasable version today. The main changes are:

• New "single tone" mode. This new mode allows the Z100 to act similarly to the PLL-type single tone detector. When tuned to the desired frequency, one of the green center LEDs will flash in sequence with the incoming CW. When incorrectly tuned, the LEDs stay blank. The detection bandwidth is 50 Hz, but you can change this, if you wish to modify the firmware code. This mode is engaged when the Memory Address switch is set to position "0."
• Slightly narrowed low pass filter for the normal multi-LED mode.
• Off-frequency display will not illuminate the far right LED. When listening with a wide bandwidth, such as LSB or USB mode, most of the audio energy is above the maximum displayable frequency, and will cause the Z100 to illuminate the rightmost LED, as a visual cue. I've received requests from a couple of Z100 users to change this display operation. Now, an out-of-range audio signal will not illuminate an LED.
• The start-up sequence now blinks the current software revision number, with the major release (2) being shown to the left of center and the minor release number (1) being shown to the right of center.

The plot below shows the new single tone's selectivity curve. The on/off threshold point is set in the stock software at a level that provides about 50 Hz bandwidth. The decoder is fast enough to follow keyed Morse dots at 25 WPM or so.

There are several ways you can update your Z100 to the new firmware:

1. If you have purchased the programming cable (available from Mouser Electronics for $20.00, part number 626-DLP-TTL-232R) you can download the free Swordfish SE compiler and compile and load the new release 2.1 firmware. This process is covered in more detail at Section 5 "Programming the Z100" of the Z100's Operating Manual. The free Swordfish SE compiler can be downloaded at http://www.sfcompiler.co.uk/swordfish/download/index.html. The Z100 code, version 2.1 source code can be found here or via my Software page.
2. I will program the new firmware into your PIC and return it to you. Remove the 18F2620 PIC from your Z100 and mail it to me at the address shown at the top of this page, along with $3.00 for return postage, and I'll put the new code into your PIC. If you can't be without your Z100 for the week or so it will take for back and forth mailing, I'll send you a programmed 18F2620. When you receive it, return your current 18F2620 to me, along with $3.00 for postage.
3. If you have access to a PIC programmer, drop me an E-mail message and I'll send you a HEX file of the new code.
4. If you want to keep your old 18F2620 PIC, I'll sell you a new one, programmed with version 2.1 for $15, including shipping.

I have not yet revised the Z100 documentation, but will do so tomorrow.

My Z93 RF/IF prototype PCB powers three AD8007 amplifiers with Texas Instruments TL750L12 12 volt low dropout regulators. These devices are similar to the familiar 78L12 TO-92 packaged regulators, but will maintain a stabilized 12V output with an input only 0.6V greater than the output voltage. The 78L12, has a 1.7 V dropout voltage, which makes the TL750L12 an attractive choice as it permits stabilized 12 V with only 12.6 V input.

Working with the prototype board, however, shows that the TL750L12 is not a direct "drop in" replacement for a 78L12 regulator, and unless the output is properly bypassed, the TL750L12 will oscillate.

The image below shows the problem; when used with the typical 0.1 µF output bypass capacitor, the TL750L12 has a nasty oscillation. For more information, see my new page TL750L Low Dropout Regulator.
 

I finished building the Z93 RF/IF board this afternoon, after several days work. It went slower than anticipated due to a couple of layout errors on my part. The photo below shows the completed board, with all shields off.
 

I started assembling and testing the Z93 RF/IF board yesterday and have the microcontroller and local oscillator buffer amplifier working. So far, all I've found wrong are a couple of mechanical errors, such as not placing the DDS module's mounting hole in  the correct location. This board, however, has a number of extra debugging features and test points so conversion to a finished board will likely require layout revisions beyond those needed to fix these small errors.
 

Photo below shows the DDS module in place (the smaller PCB without solder masking.) Ths is the same DDS module used in my Z90/91 design. It could be replaced with a higher performance DDS.
 

DDS buffer amplifier uses an AD8007 instead of the Gali 74 I used in my Z90/91 design. The AD8007 has about 10 dB better harmonic suppression and also can be tweaked to provide the exact gain required via feedback resistor selection, which is not possible with the Gali 74.

As usual, August's Updates have been moved to an archive page, reachable by links at the top of this page, or by clicking here.

I received prototype PCBs for the next generation digital panadapter RF/IF section today. The board is approximately 7" x 7" and is pictured in the photo below. I'll assemble the board over the next few days, and check out each section as built. More details as I work on the board.