Softrock Lite 6.2
Adventures in Electronics and Radio
Elecraft K2 and K3 Transceivers
27 February 2007
Yesterday, I received the prototype printed circuit boards
for my new project, the Z100 CW tuning aid. I assembled one board today and
tested it. I found a couple of small errors, but nothing that can't be fixed
with an Xacto knife and a piece of wire for the test boards. I hope to send two
prototype kits to a couple of volunteer builders by Monday. The Z100 will
be a two or three hour kit, with most of the time being installing the LEDs so
that they align with the board edge and are equally spaced. (Spacing is set
during assembly with temporary 0.009" paper spacers.)
The boards look good:
The front of the PCB has 24 LEDs. The frequency step for
each LED is 25 or 50 Hz, depending on an option switch setting.
The bottom of the PCB has option switches and a center
frequency tuning potentiometer. These are on the bottom as I plan access holes
in the case bottom.
I've also worked today on Z90-Display version 2.0. I can now read parameters
from the Z90 and set parameters on the Z90, as well as display a standard trace
and a waterfall display. The standard trace has the same three line
status/title/date-time display found in version 1.0.
The waterfall image below shows all the controls populated
with data linked from the Z90. The signals displayed are from connecting an
antenna to the Z90, set for 10 MHz. I hope to provide a selection of palettes,
not just the gray scale shown.
There's still a lot of work to be done, but I hope to get
an alpha test version out next week.
26 February 2007
I've started re-writing the Z90-Display program in Delphi
2006. The current version is written with Liberty Basic v 4.03, and although it
works, some limitations have recently surfaced. At the request of a Z91 owner,
I've decided to offer Z91 owners a new firmware load with considerably faster
sweep speeds. The speed increase is a consequence of splitting the Z90 and Z91
firmware and deleting code associated with LCD control from the Z91 firmware. I
do not plan to make a general release of the revised Z91 firmware until Z90
Control version 2.0 is ready, as the current release produces objectionable
flicker when running with the increased sweep speed permitted by the new Z91
At the moment, I have an engineering version of version
2.0 running but it's a long way from even a test release. Assuming other things
do not get in the way, I hope to have a test release in a couple of weeks.
Version 2.0 will add a waterfall display option and may add other features as
well. Of course, the waterfall display will work with either a Z90 or Z91.
A preliminary view of the version 2.0 screen is shown
below. The main differences from version 1.0 are:
- Tab selection of amplitude / frequency display and
- Vertical position is set via a slider control.
- Progress bar shows incoming data receipt.
The extra buttons and display window at the bottom of the
display are for program development and will not be in the release software.
When is a 0.1uF capacitor not a 0.1uF capacitor? I've also added a
new page Capacitor Voltage Change (click
here to read it) presenting data I collected showing the variation in
measured capacitance versus applied DC voltage for six capacitor types. Some
high dielectric capacitors show major variation in capacitance with applied DC
polarizing voltage. If these capacitors are used for coupling signals with large
voltage excursions, harmonics and intermodulation distortion can be generated by
these "passive" components.
I also note that Andy,
G4OEP, has newly revised pages on the effect of turns spacing on toroidal
http://g4oep.atspace.com/coil/coil.htm as well as his analysis of the
G3UUP crystal oscillator method of measuring motional parameters.
Andy's home page is
http://g4oep.atspace.com/index.htm and you will find many interesting topics
21 February 2007
I've worked more with reading output from my Advantest
signal generator, and have a waterfall display working. In testing the code this
afternoon, I looked at the frequency range 144-154 MHz, using my 2 meter 6 dB
gain omni-directional antenna, at 120 ft above ground. To improve the noise
figure, I've added a Minicircuits ZFL-500LN preamplifier ahead of the spectrum
There's an interesting occurrence in the data. Here's a
Even in the small image, the diagonal line is quite visible.
Here's the full scale image of that part of the data.
The center white line is 147 MHz, and the lines at either
side are 146 and 148 MHz. The diagonal trace represents the sequential keying of
repeaters, with their outputs in the 146.6 - 147.39 MHz range. I can identify
repeaters at 146.79, 146.91, 146.97, 147.24 and a couple others.
If you look carefully, three "blips" on the repeater input
range below 146.6 MHz can be seen, and a weaker, but similar sequence on the
input side of the repeaters operating above 147.39 MHz is also visible. I've
marked these signals in the next illustration.
The three input blips for repeaters operating in the range
146.6-147.0 MHz are inside the left ellipse, and the input signals for the
repeaters operating in the range 147.0-147.39 MHz are parallel to the yellow
line. The spacing matches the standard 600 KHz VHF repeater offset, -600 KHz for
repeaters below 147 MHz and +600 KHz for repeaters above 147 MHz.
My first thought was this is the result of a sweeping
spurious signal hitting repeater inputs. However, if it is a true spurious,
however, there should be a dead band in time, where the spur sweeps the repeater
output frequencies, but I don't see that, which says this is most likely
the result of someone going through the various repeater input frequencies and
keying them up in sequence.
When I have the waterfall display software completed, I'll
probably do a simple version for the Z90/91. The main problem with general
release of a Z90/91 version of the program is that writing individual pixels to
a computer screen is very CPU-intensive in Liberty Basic and the program does
not coexist well with other programs. My development computer is a Gateway
duo-core machine, and the program grabs 100% of one core, or 50% of total CPU
resources. On a single core computer, almost all resources will be grabbed,
unfortunately. I can throttle back the resource grabbing, but the paint speed
becomes painfully slow.
19 February 2007
Emachineshop says that the Z91 front panel job will be
re-made again, starting from scratch. Based on past history, this process will
run about 75 days, which places delivery around the end of April.
I'll contact the customers awaiting Z91 deliveries and
advise them of the delay and again offer to deliver the kits with interim front
panels and final rear panels.
I've also added a new page with measurements of various
bypassing strategies. It can be found via the index at the top left of the page
or by clicking here.
I've also added a power rating update to the
dummy load page based on Celwave catalog information
provided by Tom, N0SS.
18 February 2007
I've cleaned up the quick and dirty program I wrote
several days ago to capture data from my Advantest R3463 spectrum analyzer, and
looked at an hour's signal strength data from CHU at 7335 KHz. The data was
taken about 30 minutes either side of noon here in Northern Virginia. The R3463
was connected to an M2 log periodic antenna at 100 ft above ground. The spectrum
analyzer was set for 200 Hz resolution bandwidth and 10 Hz video bandwidth, with
a 20 second sweep, 1001 points per sweep, corresponding to 50 ms per data point.
The raw data is shown below. Of course, all 180,000 data
samples can't be shown at this resolution. The red line is a 60-second moving
average to show the longer term trends. The data shows at least two superimposed
fading patterns. One of relatively short duration, with deep fades of 20 to 40
dB and the second a slower trend, over the space of tens of minutes, although
rather sharp excursions in the moving average are also visible
Plotting the relative distribution signal strength
probabilities shows, as expected, a non-Gaussian distribution.
The two references I rely upon in HF progagation matters
are both by Kenneth Davies. They are Ionospheric Radio Propagation
(National Bureau of Standards Monograph 80, April 1, 1965) and Ionospheric
Radio Waves (Blaisdell Publishing, Waltham MA, 1969) If you are seriously
interested in HF propagation, these books should be in your library.
Before discussing fading statistics, it's important to
know that we are not considering slow variations in signal strength, e.g.,
measured over the space of hours as the ionosphere changes state from night to
sunlight or vice versa. Rather, by limiting our data to the space of an hour,
during a time when both ends of the radio path (Ottawa Ontario and Northern
Virginia) have been in sunlight for several hours, we examine the relatively
fine variation in signal strength, fades measured in terms of a few milliseconds
to a few seconds. Mixed in with this fast fading data is, of course, the longer
term changes in signal level, as evidenced by the red moving average line in the
first graph. A better analysis would remove these longer term trends, but we
will content ourselves with noting that the total slow variation in signal
strength is approximately 10 dB, and for the most part the the variation is
Prof. Davies states that HF signals, looked at over a
short time frame exhibit generally fading that can be described by one of two
- Rayleigh fading�the signal that arrives at the
destination is the sum of a large number signals, each with a time changing
path so that their vector sum increases and decreases as the individual
components phase and amplitude relationship changes.
- Ricean fading�the signal is dominated by a single path,
with several other signals also present, but with the other signals being
weaker. Again, the receiver detects the vector sum of these multiple signals.
The names Rayleigh and Rician derive from the names of the
scientists that developed the statistics, Lord Rayleigh and Stephen Rice. Rice
worked at Bell Laboratories and studied random noise processes and Lord
Rayleigh, of course, was one of the foremost 20th century physicists.
A later extension by Weibull generalized the statistics
developed by Rayleigh.
I've plotted a typical Rayleigh distribution using Excel. The
blue probability curve shows a definite resemblance to the fading data. (The
curves need to be flipped left-to-right to match the scale). Altering the
parameters used to define the Rayleigh distribution will tighten or loosen the
curve and alter the tail.
The Excel spreadsheet actually uses Weibull statistics,
but with the parameters set to reduce to a Rayleigh distribution.
The last plot shows a cumulative distribution of the
measured data. As with the earlier data taken, the fades provide an almost
perfectly linear plot over a 40 dB range.
16 February 2007
I finished the last fixes in the Z100 tuning aid PCB
layout and ordered three prototype board this afternoon. I have two volunteers
for build verification and user experience feedback.
The Z90 PCB set was done with ExpressPCB. While I had no
problems with the schematic capture software, the associated board layout
software is short several useful features, such as design rule checking for
missing connections or short circuits between nets, and it does not have an
auto-router, although autorouters are about equally useful and dangerous. And,
of course, the ExpressPCB software is proprietary and can only be used with
their manufacturing service. (I understand they will generate standard Gerber
files for an extra fee.) Larry, N8LP, has also used ExpressPCB for his LP100
wattmeter and other projects.
Both of us decided to shift to a different schematic
capture and layout software package. After looking over the reasonably priced
alternatives, and downloading and trying several demo versions, we've selected
DIPTrace, whose home page may be found at
http://www.diptrace.com/. I have previously used layout software from Ivex
(now out of business) and Electronics Workbench (worked, but expensive and
buggy) and Eagle (either you will love it or hate its quirky user interface and
I'm, in the dislike category). I also looked at a couple of the freeware
schematic capture and layout packages.
After doing the Z100 schematic and layout with DIPTrace, I
can give it a qualified OK. It's relatively easy to learn and use, and it
follows normal Windows conventions. I did not find any major bugs, and the
program seems to have responsive user support. (The developers are in The
Ukraine and are active on the DIPtrace forum.) DIPTrace is missing a few useful
features that are scheduled to be implemented over the next few months. It has a
reasonable pricing schedule and an upgrade path that lets you purchase capacity
as necessary. I bought a "DIPTrace Lite" license, which works for double sided
boards, up to 500 pins for $145. The Z100 board has about 194 pins. I don't know
how many pins the Z90 PCB would have under DIPTrace's computation mechansim, but
I'm sure it would be well over 500.
No response from Emachineshop on the Z91 front panel
problems. I'll have a telephone chat Monday and see what they propose to do for
the most recent problems.
15 February 2007
I've added a note to the
Construction Notes page providing a
trouble shooting methodology for mixer, crystal filter and log amp problems. I
developed this approach when running down a problem with the 1 KHz filter in a
Z91 and it worked well. You might wish to print this note and add it to the
troubleshooting section of your manual.
14 February 2007
I've taken a short break from Z90/91 work today and worked on
a Liberty Basic program to read and
control my Advantest R3463 spectrum analyzer via a
Prologix USB-GPIB interface card. I spent
several hours trying to understand why a code sequence would work well when sent
using the keyboard and Terminal program to the R3463, but would fail when sent
from inside the program.
After solving the mystery, I realize that I should have
found it earlier. After running a sweep, the R3463 responds by returning a 0
value when a status register is queried. When set to 0 span to look at signal
strength, a useful sweep period typically runs between 10 and 100 seconds.
During the sweep period, the R3463 holds the CTS/RTS line but does not send
data. Hence, it's necessary when initializing the COM port to set a CTS/RTS time
out of longer duration than the sweep period. The default timeout in Liberty
Basic is 1 second. After increasing that to 30 seconds for a 20 second sweep
period, things finally made sense.
In case you are wondering why all this serial com port
discussion for a device controlled over a GPIB port (IEEE-488/HPIB are other
terms for the GPIB port), the Prologix adapter can be run as a serial com port
interface over the USB port. This lets you use Terminal for debugging and also
avoids specialized DLL calls for GPIB communications. Rather, the GPIB device
may be addressed just as if it were a serial communications port in your
The graph below shows received signal strength levels for
a period of 400 seconds. The signal measured is the strong shortwave broadcast
station at 9975 KHz, WWCR, and the R3463 was set for 200 Hz resolution
bandwidth, 30 Hz video bandwidth. These settings wash out almost all the AM
modulation. The R3463 was connected to an 80 meter inverted vee antenna with an
apex 80 feet above ground level.
The data shows two periods of strong fading, with a center period of
As interesting as this sort of plot is, a much more informative analysis
looks at the probability of signal levels. Strictly speaking, this should be
done as the probability of a fade of X dB above or below the mean signal level.
I did not take the time to compute the mean signal level and subtract the value
from the individual data readings, but this adjustment only shifts the curve up
or down. Its main usefulness is that it allows one to compare data with
different means, of course. If I have the time, I'll do more data capture and
analysis using the fade from mean methodology and add a page with the
The graph below shows on the vertical axis the percentage probability that
the received signal is at least as strong as the corresponding X axis value.
For example, 1% of the time, the received signal level was at least -68 dBm. If
we compute the mean of the data set (20,200 data points) we find it to be -51.06
dBm. This means that there's a 1% chance that the signal will experience a fade
of at least 17 dB from the mean.
Looking at the probability of fade distribution, the fit to a
log distribution is remarkable. In fact, the R value is 0.99, an excellent fit.
The fade probability data can tell us a great deal about
the path over which the signal arrives. I've been extensively involved in signal
strength measurement and analysis for VHF and UHF paths over the last 30 years
but this is my first detailed excursion into HF fading. In the VHF/UHF
mobile radio world, almost all propagation is via scatter as the mobile station
seldom has a direct line of sight path to the serving base station. A scattering
path is best described by Rayleigh statistics. If the mobile station has a line
of sight to the base station, Rician statistics may provide a better fit to the
HF propagation, as I understand it after a cursory reading
of the literature, is often described via a two-ray model, i.e., a dominant
skywave path and a second skywave path, with the receiver detecting the sum of
the two paths. As the relative strength and phase relationship of the two paths
change, the sum of the two signals will differ. If we think about it, it's also
apparent why signals fade down far more than they fade up. Assuming each path
has 50% of the signal power (not necessarily realistic, of course) if the
two paths arrive with 180 degree phase shift, the result is cancellation and no
received signal. If the two paths arrive with 0 degree phase shift and thus
mutually reinforce each other, the net power increase is only 3 dB over
receiving one path only. Hence, on the up-side we see 3 dB and on the down side,
infinite dB, so it's obvious that fades will be biased to reduced signals.
When I have the time, I'll sort through a bit of the HF
fading literature and gain a better understanding of the data I'm capturing.
13 February 2007
The latest installment in the Z91 panels from Emachineshop
has arrived. To recap, the re-done order resulted in the front panel silk screen
being applied upside down. After some discussion with Emachineshop, we agreed
they would have the front panel paint removed, chemically or sandblasted, and
then repaint and re-silk screen the bare metal panels.
UPS delivered the Z91 panels today. Here's the result.
The photos show a "ghost image" of the old, upside
down, silk screening. A ghost image of the white line is visible in both images
and in person, I can read the old text as well. If you look carefully in the top
photograph, you can see the Clifton Laboratories logo under the paint as well.
In my opinion, the panels were not taken down to bare metal, but rather a second
coat of black paint was applied. (The white dots are from the Styrofoam packing
I've sent Emachineshop an Email asking what we are to do
next. To say that I am disappointed is a major understatement.
09 February 2007
I've been intrigued by the "Luxembourg Effect" since first
hearing about it many years ago. The "Luxembourg Effect" is named after the
early high power LF broadcast station in Luxembourg where the effect was first
noticed in the 1930's. The LE is cross modulation caused by a high power
transmission due to non-linearity in the ionosphere. In other words, one
station's modulation is superimposed on other stations (albeit at a rather low
level) as a result of the ionosphere's non-linearity.
Outside of specialty literature, little is available on
the LE, but with the BBC scanning copies of their Research Department Reports
from the 1960's onward, a pair of papers on the Luxembourg Effect are now
available over the internet. The more interesting paper is BBC Research
Department Paper 1972/23 and may be downloaded at
A complete list of the BBC's older research department
papers can be found at
http://downloads.bbc.co.uk/rd/pubs/reports/rpt60s_70to96.pdf. The actual
papers are linked in this document and can easily be downloaded.
Speaking of BBC research, there are several BBC White
Papers worth reading, including those on dipole antennas and coaxial cables.
Both of these White Papers are fairly mathematically, but it's possible to skip
the math bits and still benefit from reading the white papers.
The White Paper index may be found at
http://www.bbc.co.uk/rd/pubs/whp/index.shtml and is worth perusing for other
worthwhile reads, including several studies on Broadband over Power LIne (BPL)
and their potention for harm to shortwave reception.
We live in a part of Fairfax County VA that is reasonably
undeveloped, due to watershed conservation zoning. Consequently, we have a large
wildlife population including fox, deer, raccoon, woodchucks and the like. The
deer, in particular, are quite common. I took the two photographs below two days
Her two young. Old enough to have lost their spots but
still together as a family group.
08 February 2007
My Z90 QEX article is wrapped up, with the last edits
submitted. It will appear in the March/April edition, and should be in your
mailbox�what, you are not a QEX subscriber? Sign up now, it's a great magazine
for the technically oriented ham�in a few weeks.
I've also finished breadboarding a CW zero beating aid,
the Z100. The concept is not original, and dates back at least to HAL
Communications' SpectraTune sold 25 years ago, but advances in electronics make
the design much simpler. My plan is to offer this as a simple kit, that can be
assembled in a couple of hours. It requires +12V and has two 3.5 mm (1/8")
stereo jacks in the back. You plug a jumper from one into the K2 speaker or
headphone output and the second jack is paralleled for your headphones or
The Z100 has 24 LEDs, with each LED corresponding to 25 Hz
in frequency. To correctly match your transmit and receive frequency, you tune
until the two green LEDs in the center flash. If you are a bit off in frequency,
the yellow LEDs on either side of center will flash, and if you are way off, the
red LEDs will illuminate.
Breadboard model on top of K2, with a CW signal correctly
tuned for zero beat on transmit. I had to hand hold the camera with a slow
exposure to make the LEDs and K2 display show up, and I did not hold it
The rubber band holds the top and bottom
case together and let me have easy access for measurements and software
Breadboard version. The final kit will have a printed
circuit board, of course, but will use the same Hammond 1553B plastic
The trim pot lets you set the center
frequency to match your CW tone choice. It's settable from 400 Hz to 3000 Hz,
so that it can be used for RTTY or other tuning purposes, although the days of
requiring a separate RTTY tuning aid have largely dispappeared.
Displaying a 170 Hz shift RTTY signal. When properly tuned
in, the two red LEDs on either side of the two yellow LEDs are illuminated.
The LEDs are not in very evenly, of course, which is a
function of (a) lack of craftsmanship on my part; and (b) using a pre-made
prototype board instead of a custom made PCB.
It's way too early for anything definitive on
delivery or pricing, but my hope is to have a price point similar to Elecraft's
mini-kits. The Z100 kit, however, will include the enclosure. I'm working on a
PCB layout now and hope to have a first prototype PCB version running in a
couple of weeks.
If you are a CW operator and would like to build a
prototype and provide feedback on its usefulness, please contact me via E-mail.
There's nothing K2-specific about the Z100, of course.
January 2007 is now in the archives and may be read by
clicking here or via the link at the top of this
My QEX article The Z90 and Z91 Digital Panadapters
is now on its second revision, and I believe that the errors have been fixed,
but I have not yet had a chance to go through the second proof copy in detail.
I'm caught up on all orders for which payment has been
received. To recap:
- Z91 orders for customers electing not to take
interim enclosures�I'm waiting on Emachineshop to re-make the re-made
front panel. It's out for refinishing and re-silk screening, but I do not have
a estimated delivery date. However, I believe these should be in my hands
before the end of February.
- Z90 orders for customers electing not to take
interim enclosures�I've notified all customers that their kits are ready
to ship upon receipt of payment and have shipped half a dozen or so Z90 kits
in the last week. Several customers have not responded to this notice,
however. I will make one more contact and if there is no response, I will
start releasing kits to those customers on the waiting list.
- Z90 replacement panels�All Z90 customers that
received interim panels should have received replacement panels a couple of
weeks ago. Any Z90 customer not receiving a replacement panel should contact
me via E-mail.
- Z91 replacement panels�As reflected in (1), I am
still awaiting acceptable Z91 front panels. As soon as I receive them, all
existing Z91 customers will receive replacement front and rear panels.
Buffer Amplifiers�I made 50 buffer amplifier kits,
and I am nearly out of stock. If you do not really need two buffer amplifiers, I
would greatly appreciate it if you do not order two. The economics of scale make
it very difficult for me to make 10 or 15 more buffer amplifier kits at the
current price. I will meet orders as long as I have remaining stock, but when
these are gone, that's likely to be it. Or, if I make a run of 10 or 15
additional buffer amplifiers, the price will increase to $35 each.