I've completed measuring my K2's performance "before and after" installing the most recent IF buffer amplifier. I've posted a brief summary of the test methodology and a sample before and after photo at a new web page, K2 Measurements. I found no significant differences after installing the buffer amplifier.

In the next day or two, I'll also update the K2 Interface page to show the most recent board and cable installation, and to discuss BFO leakage issues.

My K2 has arrived at the local FedEx distribution center, so I should receive it sometime today.

I've made measurements of the typical output spectrum from the Z90's auxiliary signal generator output port, and also the Z90's signal input port. I also had an opportunity to examine the audio output versus signal level input for my Racal RA6790/GM receiver with AGC enabled.

In order to improve signal to noise ratio, it's common for AGC to be "delayed" or to allow the receiver to operate at maximum gain up to a certain, defined, input signal level. At that threshold point, AGC is applied and maintains the audio output more or less constant over a wide range of signal input.

AGC operation is often tested by plotting audio output versus RF input signal level. Rather than manually stepping a signal generator though a variety of levels and recording the audio output, I automated the process with a simple Liberty Basic program to control my Panasonic VP8191 signal generator via an IEEE-488 (GPIB) interface and to read the receiver's audio output with my Fluke 189 digital multimeter over an RS-232 interface. The computer program then saved the RF signal generator level and resulting audio output level to a disk file for later analysis and plotting.

I set the receiver to 14.025 MHz, CW mode, 300 Hz bandwidth, AGC = On, fast attack/decay, AGC threshold = default.

My K2 has been shipped, and should be in my hands Tuesday the 29th. Frank, W6NEK, received the replacement LCD diffuser assembly from Elecraft and has fitted it in place. I'm looking forward to receiving the K2 for both testing with the Z90 but also to make some real contacts with. It will likely reside in the basement shop area, but my antenna feedlines are accessible from the shop area through a jumper panel.

I've also received the second revision to the K2 interface PCB and should be able to assemble one later today. Assuming no errors in the layout--or at least no errors that can't be fixed with an X-Acto knife and jumper wires!--I'll send a kit to Stan for an independent assembly and test in his K2.

I've also had time to add the call sign customization hooks in the Z90 firmware and in the Z90-Display software. This allows you to enter your callsign (maximum 10 characters) into the Z90 (or Z91) EEPROM memory. Thereafter, whenever you power up the Z90, your callsign will be displayed on the LCD, and for both the Z90 and Z91, when used with the Z90-Display software, your callsign will appear at the upper left of the graticule.

Still on my "to do" list is a button or check-box to reverse the scan sense. That is a bit more complicated, as the Z90 LCD display routines are only distantly related to the Z90-Control windows software. But, it will be done.

I ordered the longest lead time items today, the front and rear panels for the Z90 and Z91. Delivery time is estimated at 50 days, consistent with my planned October shipment date. My supplier quotes the delivery quantity as +/- 4 units. I've ordered enough panels to meet the order requirements assuming the shipped quantity is -4 units, so if the actual delivery is +4, I can fill a few more orders. Hence, if you missed the original cutoff date, there's still a fairly good chance that I can accommodate a few more purchasers.

The panel color is gray, with white lettering (red for cautions).

I've also sent off a final prototype DDS board to my assembler for an independent test.

It looks as if I won't receive my K2 until early next week, as Frank, W6NEK, has not yet received the replacement part from Elecraft.

The order window closed Friday, 18 August. I plan to place the cabinet orders tomorrow and will order enough front and rear panels to meet the orders in hand as of tomorrow morning, a few extras for spares plus ones I will use in my shack. My supplier quotes the volume as "+ or - 2" so to ensure that I have enough on hand, I will order front and rear panels to meet the current order list assuming the delivery is -2 of the ordered quantity., If it's on the +2 side, I may well have enough parts to provide a few extra kits. So, I'll accept orders for the next couple of weeks on a contingent basis, with the contingency being enough extra parts being delivered to me by the supplier and receiving the orders in the next two or three weeks, at which time I must order some expensive electronic components.

I've reconsidered the color scheme and am now leaning toward black cabinet covers with gray front/rear panels, white lettering (and red lettering on the rear for the caution warnings). I'll make a final color decision tomorrow morning but that's where I', heading now.

Reminder - the Z90/Z91 order window closes Friday, 18 August 2006.

I've made a few changes to the Z90-Control software.

To obtain a sense of signal levels on the east coast of the US, near Washington DC, I connected my HP8558B spectrum analyzer to my main HF antenna. It's an M2 "skip band" log periodic, with coverage of 7.0 - 7.2 MHz and 10-30 MHz continuous. The antenna is at 100 feet above ground and was pointed at Europe (roughly 045 degrees) during the measurements. The measurements were made earlier this week, at around 8 PM, which is in medium twilight. The path over the North Atlantic, of course, has been in darkness for several hours at this hour.

Stan, W5EWA, is a beta tester and reports that his Keyspan model USA-19HS USB-to-serial adapter works well with the Z90 prototype. I've added this model to the FAQ. I also found Keyspan makes a USB adapter with four serial ports. This may be useful for controlling multiple devices with a single adapter unit. I've added a link to Keyspan's site at the FAQ.

I've added a new page describing how to measure (a) carrier suppression, (b) unwanted sideband suppression and (c) transmitted intermodulation distortion using the Z90, a coupler (such as Telepostinc's LP100 wattmeter coupler) and a two-tone generator. Click here to go to the page. In addition, you should read the related page IMD Measurements.

I've been asked to explain why, when using an Elecraft K2, some bands result in an "inverted" display, where higher frequencies display to the left of the center line. I've added a lengthy FAQ to address this point. I've mentioned it in the Operations Manual, but additional information may be helpful in understanding why this occurs.

Incidentally, inversion is not limited to the K2; the high IF output (40.455 MHz and 45 MHz, for example) of many commercial and military grade receivers is also inverted.

I've considered adding a "normal/inverted" option to the Z90-Control software, and I may do so. However, since the K2's normal/inverted status changes band-to-band, a switch may be less useful.

I've also made two more illustrative screen captures from my HP8558B spectrum analyzer.

I wanted to update both the firmware and display software so that I can capture and publish spectrum analyzer sweeps when I work with the K2 buffer amplifier performance verification work I plan to undertake in September. Rather than revise my old work, I decided to start fresh with an 18F2420 PIC and Swordfish and write a new Windows display program based on the Z90-Control software.

The Swordfish compiler continues to impress me with its speed. With an 18F2420 running at 40 MHz (10 MHz resonator and 4X multiplier engaged), Swordfish will execute a 10-bit ADC read and store the result into a 256 element word array in about 27 microseconds. Swordfish's speed means that I did not need any assembler code as a 100% Swordfish version more than meets my speed requirements.

Here are a few images captured with my HP 8558B spectrum analyzer using the 18F2420 PIC and the new Windows display software. It's connected to a 25-1300 MHz discone antenna at 75 feet above ground. To improve the spectrum analyzer's noise figure, I've added a Gali-74 broadband amplifier between the discone and the HP8558B. The 18F2420 firmware captures 256 samples with 10-bit resolution and outputs the data via a serial port. The firmware automatically adjusts the sample interval as the user changes the span control and adjusts the analog video filter control.