Clifton Laboratories 7236 Clifton Road  Clifton VA 20124 tel: (703) 830 0368 fax: (703) 830 0711

E-mail: Jack.Smith@cliftonlaboratories.com

Answer:
Yes, one practical limit to sweep width is set by the bandwidth of the receiver circuits ahead of the IF connection point. That's why is is desirable to make the IF connection ahead of the receiver's selective filters, early in the RF chain. For example, the 455 KHz IF output in my Racal RA6790/GM receiver is after the IF filtering, so listening in the SSB mode limits the usable part of the  Z90's span to 3 KHz or so, regardless of whatever span setting I've entered.

The 250 KHz sweep limit is set be the number of pixels available, the maximum panadapter selective filter bandwidth and the desire to keep the display as "lively" as reasonably possible.

With 1 KHz maximum bandwidth and 240 available pixels for display, the actual usable span is 240 KHz, and I probably will make that the maximum acceptable value.

Even that means there is a 3 dB error potential in amplitude, with regard for other types of error (where the spectral line is half-way between the two tuned frequencies). For ham purposes as a band activity display, that error is not critical and certainly acceptable (and much better than available than in my SM220 with BS-8 adapter card, for example) And, there are things I could do in software to improve that, such as scanning in smaller steps and taking the peak reading or average or whatever, but that's really pushing the design beyond its intended purpose.

Since the command interface is open, you could, of course, write your own BASIC program to command the frequency to a specific point and grab the reading. (That specific command is not in the current firmware load but it's on my list of things to add to it.) If you have sufficient time, therefore, it would be possible to scan as many MHz as you wish, in as fine a frequency step as is reasonable (1 Hz increments).

For a 1 KHz filter, the minimum dwell time should be somewhat over 1 ms, so with a 200 KHz span, the actual refresh is around 3 traces / second when the rest of the overhead is factored in.

If you are interested in filter analysis, you should really look into the N2PK VNA. There's a Canadian ham selling PCBs for it. I have one (one of the W8WWV group purchase) and it's an excellent piece of gear--within its frequency range fully as accurate as any of my HP network analyzers.

Reference links:

N2PK's VNA home page: http://users.adelphia.net/~n2pk/
N2PK VNA PCB set: www.makarov.ca/vna_htm

Warning--this is a complex project. I bought mine as an assembled unit when Greg, W8WWV, had a small quantity of the VNAs professionally assembled. Looking at the assembled PCB, I seriously doubt my ability to construct one.

Question:
My preference would be for a black enclosure...just my vote

What size is the cabinet?

Answer:
Both the Z90 and Z91 use TenTec's BU/BK series enclosures, the Z90 uses a BU or BK-959 and the Z91 uses a BU or BK-929 enclosure. BU indicates a blue top and bottom and BK indicates a black top and bottom.

I will have custom front panels, laser cut, powder coated and silk screened, but the basic enclosures are from TenTec. It may turn out that the initial build is so small that there is no quantity discount for all cabinets of a common color. If that's the case (no pun intended), I should be able to give purchasers a choice of black or blue, assuming TenTec has your color choice in stock. (They run the cabinets in a batch and if they sell out of a particular color/style you may have to wait until the next run.) Otherwise, my preference is for the large cabinet to be blue and the small cabinet black, but if there's a consensus one way or the other, I'll follow suit.

I've measured the cabinet dimensions as follows. Note that there are screws on the side that stick out a small distance. Also, suitable clearance at the back is necessary to provide access to the connections and to select the input attenuation switches, if necessary. I've shown the figures to 3 decimal places, but I made the measurements with a standard machinist's scale, so the actual accuracy is less.

Question:
Will a Z10000 Buffer Board work with a <add your favorite radio make and model here> to provide the necessary
signal for the Z90? [This question was asked concerning an FT-920, with a 68.9 MHz 1st IF, but because it is of general applicability, I've intentionally changed the question.

Answer:
I've added an extensive discussion to the draft Z10000 Buffer Amplifier Assembly and Operating Manual addressing how one might connect to a generic receiver or transceiver. This Manual will be available at the Documents page when it's a bit closer to completion, likely around August 10th.

From a technical prospective, the Buffer Amplifier works well beyond 68.9 MHz and is thus compatible with your Yeasu. Likewise, the Z90 will work with an IF of 68.9 MHz, although the technical specifications are very slightly degraded from operations at lower frequencies. (I've successfully tested it with simulated IF frequencies up to 73 MHz.)

The more difficult questions relate to whether there is enough room inside the Yeasu to install the board (it's about 1.25 inches x 1.5 inches) and whether there's a place to attach the buffer board to that will not disturb the Yeasu's operation.

I'm confident that the answer to these two questions is yes, but since I don't own an FT-920 I can't provide you an answer with 100% certainty. It's also the case that it might be necessary add a couple of impedance matching parts to the buffer amplifier, depending on where inside the FT-920 you make the connection. I've tried to address these topics in the Z10000 Manual and I can provide more specific information if necessary.

Also, I can provide an assembled buffer amplifier for a test installation before you decide to purchase a Z90, but in order to make an assessment of whether the buffer amplifier is correctly installed and working you will need some test equipment. [This offer is open to anyone; you pay the postage to return the buffer amplifier and agree to return it within 10 days or so. Contact me via E-mail at Jack.Smith@cliftonlaboratories.com if you wish to borrow a buffer amplifier for this test.]

Question:
How complicated is the kit; does it require special tools or test equipment to build or align and how long does it take to construct?

Answer:
I've designed the Z90 and Z91 to be simple to build and not to require test equipment beyond a digital voltmeter and ohmmeter.

Based on the time it has taken me to assemble prototype boards, and Dario's experience as an independent prototype board assembler (see N5QVF Build page for his experience) I believe than an experienced kit builder should be able to assemble a Z91 in about 8 to 9 hours, and a Z90 in about 9 to 10 hours. This time is from opening the box until checkout completion.

These estimates are likely on the generous side, as the board Dario assembled was not silk screened and solder masked, and he had an extra module to assemble that not required in the release version, as the DDS Daughter board will be provided as a wired and tested module. This removes an hour or so assembly time, as well as simplifying the construction.

The Z90/91 have about 25 surface mount components and the rest through-hole parts. All the passive (resistors and capacitors) surface mount components are 1206 size or larger. Although small in comparison to most through-hole parts, these are considered "large" in the surface mount world. I've also designed the PCB to be significantly larger than necessary in areas around the surface mount components to make assembly easier. For suggestions on the tools and techniques I use to work with surface mount components see my Surface Mount Assembly page.

The test equipment required during construction is simple -- a digital voltmeter and ohmmeter. During calibration stage the ADC reference voltage may be set using either a digital voltmeter, or the Z90's built-in facilities. It is also desirable (not strictly necessary, but certainly useful) to calibrate the DDS time base. This can be accomplished with a frequency counter or by zero beating against WWV at 10 MHz using a receiver.

As far as complexity is concerned, I'll rank it as "moderate." I would not recommend it as the first kit to give a complete beginner, but previous kit builders should have no problems.

Question:
How do the span, RBW, skip, dwell, video averaging relate to each other? What should I see on the screen?

Answer:
This is far too complex to be part of the FAQ, so I've added a new page Display to address these questions.

Question:
My computer does not have a serial port. Can I use the Z90 or Z91 with a USB-to-serial adapter?

Answer:
Yes. The first six months I worked on the Z90 hardware and software, I used an older 500 MHz Gateway laptop computer running Windows 2000. That computer had one hardware RS232 port and USB ports.. I found no difference in performance using either the built-in hardware port or a Belkin F5U109 USB-to-serial adapter. (But see later comments on the F5U109.)

A couple months ago, I updated to a Gateway Duo-core laptop equipped with Windows XP MultiMedia Edition with no "legacy hardware" ports -- it has only four USB ports and no RS-232 or Centronics printer port. I use a Keyspan UPR-112  USB "port replicator" that provides an RS-232 serial port, a Centronics parallel printer port and two USB expansion ports to communicate with the Z91 I use for firmware development.

When I tested the Belkin F5U109 with my new Gateway computer, I found that it worked normally with the Z90-Control software. However, I found that it failed when I used the Swordfish loader program to upload new firmware to the Z90. It's important that you have a way to update the Z90 firmware using the loader (supplied with the kit) and accordingly, I cannot recommend the Belkin F5U109. It might work for you, as it did with one of my computers, or it might fail in updating the Z90's flash firmware code, as it did my new computer. I do recommend Keyspan's UPR-112, based on actual use. I imagine--but have not tested--other Keyspan adapters should work as well as its UPR-112.

[16 Aug 2006] Stan, W5EWA, reports that his Keyspan USA-19H USB-to-serial adapter works well with the prototype Z90 he is testing. Stan says it cost about $40 at the local Fry's Electronics.

Incidentally, looking at Keyspan's product listing, I see a USB adapter with four RS-232 ports, model USA-49WLC. This could be a useful if you need multiple serial ports. I have not tested it with the Z90, but based on good results with two other Keyspan USB-to-serial adapters, it should be a good bet for Z90 compatibility.

Question:
I noticed your product on the Elecraft website and I have been looking at your website regarding the Z90/91.  I was wondering if the displays for both variants will contain your call letters or will you have the provision for blanking that.

Answer:
When I get around to it (next couple of weeks, I hope, but certainly before the kits ship) I will add code to allow users to program in their own call sign or name (or whatever, but not more than 10 characters). In the case of the Z90, this will have to be entered via the RS-232 interface using eitherZ90-Control software or a terminal program. The default entry will be something other than my call, maybe CALLSIGN or something like that.

I may also add callsign personalization  to the Z90-Control software, so that screen copies and prints will show the owner's callsign. Probably at the top left corner below the parameter string.

 

Question:
When connected to my K2, on the higher bands, signals below the tuned frequency display to the left of center, but on lower bands signals below the tuned frequency display to the right of center. Is this normal? [This topic is not limited to the K2. JRS]

Answer:
The short answer is "yes" this is normal. Let me provide some detail, however.

The Z90's current firmware always shows a lower input frequency to the left of center and higher input frequencies to the right of center. This is how a real spectrum analyzer works; the frequency sweeps left to right, with the starting, lower, frequency at the left.

However, the relationship between the RF input frequency and the IF frequency depends on the receiver architecture.

Let's look at an example with a double conversion, up-converting receiver design using the arrangement shown below.

The receiver is tuned to 14.100 MHz and there's a second, weaker, signal at 14.050 MHz. In this example, the receiver has two Z90's connected, one at the 1st (45 MHz) and one at the second IF (455 KHz).

The receiver architecture inverts the frequency band with each conversion stage. Thus, the 1st IF frequency band is a mirror image of the frequency to which the receiver is tuned; signals lower in frequency than that to which the receiver is tuned are translated to a higher 1st IF frequency. A Z90 connected to the 1st IF will therefore show the lower frequency (considered with respect to the 14 MHz band) as to the right of center.

If the Z90 is connected to the 2nd IF, the 2nd mixer's inversion cancels the 1st mixer's inversion so the Z90's display will have the correct display-to-frequency relationship.

Some receivers invert their IF output and others don't. For example, my Watkins Johnson HF-1000's 455 KHz IF output is inverted with respect to the original RF input. My Kenwood TS940's 8830 KHz IF output, however, provides correct sense; lower RF frequencies correspond to lower IF output frequencies. However, an upconverting receiver always inverts the 1st IF (A bit of working with the math will convince you this is necessary to avoid spurious signal problems,.)

Now, let's look at the K2, which is a single conversion receiver, with high side injection on some bands and low side injection on other bands.

We'll start with the 10 meter band. The K2's local oscillator runs below the tuned frequency (low side injection). The IF output tracks the RF input; frequencies below the one the receiver is tuned to are translated into lower IF frequencies and the Z90 displays the visual image of the signal correctly with respect to left/right of center.

Now, suppose we switch to the 80 meter band. Again, we'll suppose the K2's receiver is tuned to 3.6 MHz and there's one other signal on the band, a weaker one at 3.550 MHz.

On the 80 meter band, the K2's local oscillator runs above the received frequency (high side injection) and hence the IF frequencies are mirror imaged about the tuned frequency. Signals that are below the tuned frequency appear on the Z90 right of center.

Now to the user, all of these frequency conversion schemes are totally invisible--the K2's microprocessor adjusts the BFO and frequency readout and tuning steps to make the receiver act consistently, regardless of whether high-side or low-side injection is used for any particular frequency band.

But, the Z90 displays the actual IF frequency and hence will show a normal display on some bands and an inverted frequency sense on other bands.

I have on the list of things to do to add a software setting to the Z90 and Z91 to reverse the sense of the display, so that a frequency lower than the center will appear at the right side of the screen, not the left, so that someone with an inverting receiver can see the correct relationship on the screen. If  the relationship between input frequency and IF output frequency is consistent, such as for an up-converting receiver, this option makes sense.
 

Question:
When I try to generate an output signal in Signal Generate mode, the output drops off above 60 MHz. Is this correct?

Answer:
This is intentional. The Z90's Direct Digital Synthesis signal source uses a 60 MHz low pass filter as an anti-alias filter and will sharply roll off signals above 60 MHz. An anti-alias filter is essential in the digital-to-analog conversion process to control spurious signals.

Question:
As I exclusively use USB SSB for all my 50 through 1296 Mhz contacts, the BFO sits below the center of screen, but moves to around 1.5kHz Higher if I change to LSB. I note that you have 4916 kHz set as center frequency in your explanation of the leak through of the BFO...I'm trying to get my head around what I'm seeing, with my BFO leak through BELOW the center frequency of 4914 kHz...I think everythings right ??

Answer:
Yes, this is correct. The K2 has a single IF filter (by that I mean it does not have separate USB and LSB filters; I know it has two filters) and is a single conversion receiver, so in order to receive both USB and LSB, the BFO must shift a total of approximately 3 KHz. Ignoring inversion on some bands for simplicity, in USB mode, the BFO is positioned at the lower side of the filter passband, actually a bit below the passband is typical. In LSB mode, the BFO must be positioned at the upper edge (or a bit beyond) of the filter passband.

To avoid the cost and complexity of two SSB filters, the K2 designers use a single filter, and move the BFO from one side to the other—the K2's microprocessor takes care of this for us when the mode switch is pressed, so the process is transparent to the user. If you have a panadapter connected to the K2's IF, you will see the BFO leakage signal move. I believe the shift should be 2.5 to 3.0 KHz in theory (it should equal the bandwidth of the SSB receive filter, plus a bit if the BFO runs outside the filter bandpass as is commonly the case).

This then causes a question as to what the actual IF frequency of the K2 is. I started out setting the stock IF frequency setting to 4914 KHz, and then moved it to 4916 KHz at the suggestion of a K2 user who thought it would be closer to the actual IF frequency. That's one reason I added three "custom" IF frequencies, so feel free to define your own IF that matches your particular K2. The custom IF frequencies are settable to 1 Hz resolution. Depending on whether you have downloaded the Z90-Control program updates, your computer may show 4914, while the actual Z90 firmware sets it at 4916. If you have not already done so, upload the most recent file changes to the Z90-Control program.)

There's also a question about what is the "center" of the IF frequency. For example, in SSB mode, it should be half the filter bandwidth from the BFO frequency. In CW mode, it will be the same, but the BFO offset shifts as well as the filter bandwidth changes. So, there's really no single "center" frequency for all modes and filter bandwidths. Hence, I decided to set the stock frequency to 4916 and let users program in a custom IF frequency that will match their own favorite mode and filter. Finally, further complicating things, I believe that when the IF filter is tuned to different bandwidths via the varicaps, the center frequency of the filter also changes to some degree, and that is compensated for by shifting the BFO slightly, so as to maintain the same beat note and keep it centered in the filter passband. Again, this is done by the microprocessor so it is transparent to the user, but if you look at it with the Z90, there will be some changes.

Now back to your question as to why the BFO is below the center frequency for USB...I think that is normal; to receive USB, the BFO should be at the lower edge of the passband, if the K2 has not inverted the frequency response. On 28 MHz, the K2's local oscillator is on the low side, so there is no inversion. On 3.6 MHz, the K2's LO is on the high side, so there is frequency inversion and the BFO will be on the reverse side, i.e., on 3.6 MHz USB, the K2's BFO should be on the high side of the filter.