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Software Updates
Softrock Lite 6.2
Adventures in Electronics and Radio
Elecraft K2 and K3 Transceivers

Z90 & Z91 SpectraScreen Panadapters
and Z90 Control Software 

The Z90 and Z91 are planned receiver panadapters, to allow amateur radio and short wave listeners to see a visual display of signals. Both the Z90 and Z91 are currently in prototype stage and and were shown at the 2006 Dayton Hamvention at the Telepostinc table (table no. 517, across the aisle from SteppIR.)

Update � for the current status of the Z90 project go to Updates.

To see modulation samples displayed on the Z91, go to Modulation.

What is it? Z90/91 Differences Z90 with LCD Z91 Computer Only Z90/91 Display Software Specifications Status Contact

 Click on any image to view a large version

What is a Panadapter?

A "panadapter" is a specialized device connected to a receiver's intermediate frequency auxiliary output displaying signals near those to which the receiver is tuned. The horizontal axis is frequency (centered on the receiver's current frequency) and the vertical axis is signal strength, in decibels. 

 (Screen resolution issues may cause the illustration to show only some of  the 8 x 10 grid lines.) 

Z90 and Z91 Differences

I've designed the SpectraScreen panadapter in two versions�the Z90 with both a data output and an integrated 5.6 inch (diagonal) liquid crystal display, and the Z91, with data only output, to be used with display software such as the Windows® compatible Z90 Display software. The Z90 Display software offers interactive control of both the Z90 and Z91 models. 


Z90 - With LCD Screen

Front view of the Z90, with no signal received.

All control functions are exercised through the six "soft keys" to the left of the screen.


Z90 Rear:

From left to right:

 - Auxiliary signal generator output
 - RS-232 control\DC Power in (13.5 VDC @ 1 A)
 - Attenuator 20 dB
 - Attenuator 10 dB
 - Signal Input
 - Power Switch


Entering the custom (user-determined) IF frequencies from one of the Z90's setup screens.


Screen image of WWV during the 500 Hz modulation interval. WWV's tone modulation is at 50%, so each sideband should be down approximately 12 dB below the carrier.

The two sidebands are not equal due to selective fading.

This image is from the first PCB prototype.

The LCD is backlighted with a CCFL.


An early Z90 prototype printed circuit board, without silk screen and solder mask. Later units 
have a separate DDS daughter board. Production units will have both solder mask and silk screen.

The same PCB and microcontroller firmware is used in the Z90 and Z91, permitting a later upgrade to the Z90 version by adding the omitted components and installing it in a new cabinet.


Z91 - Computer Only - No LCD

The Z91 is identical with the Z90 in all performance specifications, except that it does not have an LCD screen. Rather, the received data is sent over an RS-232 serial line to your Windows 2000 or Windows XP equipped computer, where it is displayed in the Z90 Display Program.


The Z91, front view.

Production units will have a status LED on the front panel that alternates red/green to show scan starts.


The rear of the Z91 is identical with the Z90.

From left to right:

 - Auxiliary signal generator output
 - RS-232 control
 - DC Power in (13.5 VDC @ 0.5 A)
 - Attenuator 20 dB
 - Attenuator 10 dB
 - Signal Input
 - Power Switch

Most recent prototype board, late prototype board, with DDS Daughter board visible at left center of photography.


Z90 Display Software

The Z90 Display software operates with either the Z90 or the Z91 SpectraScreen units. If used with the Z90, control is interactive, i.e., if you change a parameter via the Z90's soft keys, the Z90 Display software changes to match your soft key selection. Likewise, changing a parameter using Z90 Display software correspondingly changes the LCD display.

Z90 Display is known compatible with Windows 2000 and Windows XP. It requires a serial port capable of operation at 115200 b/s. It is known to work with direct hardware ports and the Keyspan USB-serial adapter. Other adapters may work as well.

The interface mimics the soft keys but with a Windows flavor.


Z90 Display software supports copy (image is copied to clipboard to be pasted into other programs), print to printer, save image as bitmap or JPG and save data.


Condensed Specifications

Condensed Specifications � Applies to both Z90 and Z91, except as noted




Horizontal (cont)

Input Impedance

50 ohms

User-definable span

3, may be set to any value between 2.5 KHz and 250 KHz

Minimum Discernible Signal

-100 dBm (1 KHz RBW) (approx 2uV)
-94 dBm (200 Hz RBW)
(approx 4uV)

Time Per Sweep

Typically approximately 3 sweeps per second; in maximum resolution mode, approx 1.2 seconds/sweep.

Max Recommended Level

-30 dBm/span>

Frequency Accuracy

After user calibration typically 10 PPM over normal temperature excursion

Frequency Range


Frequency Range

50 KHz to 50 MHz

Dynamic Range

> 55 dB

Pre-defined Standard IF frequencies

450, 455, 500 KHz, 4914, 8215,
8830, 10700 & 21400 KHz

Third Order Intermod

With two equal signals of -43 dBm, third order products are > 55 dB below carrier; with two equal signals of -33 dBm,  third order products are 42 dB below carrier

User-definable IF frequencies

3, may be set to any frequencies within the 50 KHz � 60 MHz range. Less than 3 dB loss in sensitivity for IF up through 73.62 MHz. 


10 dB or 2 dB/div

Data Port and Control


± 1 dB typical, ±2 dB over 60 dB range

Data port

RS232 serial, two-way, permits control of Z90 and data capture from Z90. Speed fixed at 115,200 b/s/


200 Hz or 1000 Hz, user selectable or automatic selection via firmware



Filter Type

8 MHz, 4 pole crystal filters, Gaussian response

Power Required

13.6V nominal, 12V minimum, 15V maximum (never exceed) at 1.0 Ampere (Z90) or 450 mA (Z91)

Z90 only

240 x 320 (quarter VGA) blue/white LCD display with CCFL illumination.  Active area 5.6 inches diagonal.


Signal Generator Mode

Pre-defined Span (sweep width)

5, 10, 20, 50, 100 & 200 KHz

Signal Output

Buffered output from DDS available at rear panel. Approx. level +5 dBm between 100 KHz and 60 MHz. Usable outside these frequencies with reduced output.



Project Status

In late June, I submitted two draft articles to the American Radio Relay League to consider for QEX:

Here's how I described them in the cover letter:

The main article, The Z90 and Z91 Digital Panadapters, describes two micro-controller based panadapters that I�ve recently constructed�one with a liquid crystal graphic display and the other intended for computer control via a Windows display program that can also be used with the graphical display unit.

The second article, Designing the Z90�s Gaussian Crystal Filter, is an in-depth examination of one part of the Z90�s design, the crystal filter. It covers measuring motional parameters as well as the filter�s design, matching and testing.

My plans are to continue developing the Z90, Z91 and Z90 Display software and to offer both units as both kits and fully assembled units around September or Octover 2006. 

Pricing will depend upon the level of interest, as significant economies of scale are possible for major components, such as the LCD and cabinets. Both the Z90 and Z91 use some surface mount components, and the most difficult component for kit building, the AD9851 DDS, will be available as an optional "assembled and tested" module to plug into a user-assembled board.

Please let me know if you are interested in the Z90/Z91 and I will add your name and E-mail address for periodic updates.

You can also check the Updates page for the project's current status.



E-mail me at

The 18F4620 PIC Microcontroller in the Z90 and Z91 SpectraScreen is programmed with Mecanique's Swordfish compiler