Softrock Lite 6.2
Adventures in Electronics and Radio
Elecraft K2 and K3 Transceivers
June 2008 Updates Archive Page
29 June 2008 (PM)
I've had the Weather Envoy remote wireless
transceiver running for more than a day receiving signals from the Integrated
Sensor Suite via the console repeater. (See 28 June 2008 for details on what
this means.) The plot below shows the percentage of transmitted packets
received. I made the change to repeater mode around 7 AM yesterday, which is
roughly the middle of the data set in the three day plot below. The result is
highly consistent reception, with 80% of packets received and relatively few and
This lead me to wonder more about the transmission mode. From the Vantage Pro
manual, I found that the wireless link operates on a center frequency of
916.5 MHz at an output power of 1 milliwatt or less. Digging through the
technical specifications associated with the packet plot indicates that data
packets are sent at a rate of one packet every 2.3 seconds or so.
This afternoon, while I have the use of a WJ 8617B
receiver, I dialed up 916.5 MHz, 100 KHz bandwidth and sure enough, there's a
data burst every couple of seconds. With the 8617B connected to my discone
antenna, there's plenty of received signal strength, perhaps 30 to 40 db over
the noise level. But, that's (a) with an antenna that is relatively close to the
weather station transmitter and (b) with a reasonably sensitive receiver
that cost the US government as much as a new Cadillac when purchased 20 years
I then tuned the Advantest R3463 spectrum analyzer to
916.5 MHz, added a broadband preamplifier and connected it to the discone
antenna. By operating the spectrum analyzer in zero span mode, we get a plot of
signal amplitude versus time. Unfortunately, the choice of sweep speeds is
limited, and the fastest speed is 5 ms/division or 50 ms for the entire 10
A typical data burst is shown below. I didn't want to drag
my TDS430 digital oscilloscope across the basement, so we'll use just the R3463
images for the analysis.
First, the visible databurst is about 11.4 ms long.
(Marker 1 is at the trailing edge of the burst.) I don't know how much of
the burst's leading edge is lost, but probably not too much. (This can be looked
at with the TDS430 digital scope if I have some idle time.) The modulation
mode appears to be OOK or ASK or "on/off keying" or "amplitude shift keying"
which are fancy terms for keying the 916.5 MHz carrier on/off to transmit
The shortest data elements look to be on the order of a
few hundred microseconds (really need the TDS430 connected to see this type of
detail). Let's say 250 microseconds as a rough estimate. This means 4 bits per
millisecond or 46 bits in 11.4 ms. If I had to guess, my money would be on 48
total data bits and a burst length of 12 ms if the 250 us number is correct.
There could well be a synchronization preamble lead-in as well that is lost to
the left of the trace.
Every now and then, I would head what sounded like a double
burst. The image below captures one of the double bursts.
First, assuming the second burst is of equal length to the
first burst, it seems that the 12 ms figure is reasonable. Both bursts also
start with a similar length high followed by a short low. This might well be a
synchronization lead-in. (Something similar can be found in IR remote controller
transmissions.) Second, the data transmitted in the two bursts is not identical.
There's also a "channel ID" somewhere in the data burst as well as a checksum to
help weed out corrupted data.
The second burst could be the console's repeater signal.
There's a slight amplitude difference between the two bursts, with the second
burst being a couple dB weaker than the first burst. This supports the two
signals being from different sources.
If one wanted a project to keep their idle hands busy for
a while, the data format looks to be slow enough and simple enough to be decoded
with an 18F PIC with time to spare. However, the current production Vantage Pro
II uses frequency hopping transmission, which means that you will also have to
build a frequency agile receiver and program it to track the hopping
transmission. Frequency hopping is mostly an anti-interference measure as allows
several similar weather stations to operate without mutually interfering, or at
least statistically spreading the interference. It has a perhaps not so
accidental side benefit of making it more difficult to build a compatible
receiver as one must know the hopping sequence. In this case�where it is
unlikely that the hopping sequence is intended to provide military grade
security�one could likely deduce the hopping sequence with a series of
Since the older Vantage Pro equipment I have uses a single
RF channel, sharing amongst multiple weather stations uses a different approach.
(The ISS transmitter has a "channel set" DIP switch, whilst the console and
Weather Envoy set channels via software. These are logical channels, as all the
gear operates on a single frequency, 916.5 MHz.) With a short burst transmisison,
12 ms or so every 2.3 seconds, there's a good chance that transmissions from two
ISS units will not overlap. However, Davis has added an additional
anti-interference measure. Each logical channel has a slightly different frame
rate, i.e., the data bursts are transmitted at slightly different
intervals. Logical Channel 1 bursts are, say, 2.3 seconds apart, whilst logical
channel 2's bursts are 2.4 seconds apart. (not the actual values). This avoids
the statistical chance that if two Vantage Pros are nearby, and both have the
same burst rate, they could be in perfect synchronization so that every data
burst from one transmitter interfered with the second. Given component tolerance
and temperature drift, that's not likely, but it does mean that there could be
longish periods where the two were close enough in synchronization to have the
bursts overlap, at least in part. If the two transmitters, in contrast, start in
synchronization but with intentionally slightly different burst periods, they
will drift in and out of mutual interference. If the burst periods are selected
with sufficient care, this may provide quite useful periods of interference free
operation compared with the "all transmitters use the same burst rate" approach.
29 June 2008
Rick, VE7TK, has written a tutorial on using a Z10000-U
buffer amplifier to extract a wideband 9 MHz IF sample from a Ten-Tec Orion
(model 565), available from Rick's web site at
http://www3.telus.net/ve7tk/9MHz_IF.pdf (the document contents are still subject to change, Rick says).
He notes that the
suggestions likely apply to the Orion II as well, but can't confirm that.
I've also added a section to the Z10000 page linking to
the four radio-specific installation notes. These are, in addition to Rick's
28 June 2008
The last few days have seen me working on linking data
from my Davis Instrument's Vantage Pro weather station to the Internet. When
visiting Mike, W4XN, earlier this month, he demonstrated Davis's
WeatherLink software he uses with his Vantage Pro II. Both my Vantage Pro and
his Vantage Pro II are wireless stations, with an outdoor integrated sensor
suite (temperature, humidity, rain, wind speed and wind direction) linked back
to a display console via a low power 900 MHz packet radio link. (Davis employs
an interesting power mechanism with the ISS�a solar cell array charges a "super
capacitor" with a lithium battery for backup during extended cloudy
periods. During periods of reasonably daytime sunshine, the lithium battery
isn't used even at night.) The photo is of a Vantage Pro II, but there's little
difference in the console appearance between the VP and the VP II, save for the
In order to extract data from the ISS, Davis sells a "data
logger" that plugs into a port on the rear of the display console. The data
logger saves all data readings for several days and connects to (different
models) either a computer's serial port or a USB port.
In both Mike's case and mine, our display consoles are not near our computer
rooms. Fortunately, Davis has a solution�the "Weather Envoy," a stand-alone
transceiver that communicates with the ISS over the radio interface. The Weather
Envoy has no display, containing only the radio transceiver, local temperature
and humidity sensors and a connector for the data logger.
Mike gave me the Weather Envoy used with his
Vantage Pro before he upgraded to the incompatible Vantage Pro II weather
station. I ordered the separate data logger module and PC control
software, WeatherLink 5.8.0, from Davis and installed it Thursday.
Although other software compatible with Davis Vantage Pro
equipment is available, it all requires the data logger module, which Davis
sells only as a package with the Weather Link software.
Installing WeatherLInk starts with a multi-screen "Setup
Wizard" that is generally well thought through with useful help screens. When
completed and connected to the ISS, the main screen presents the indoor and
outdoor data, as shown below.
In addition, various graphs and text reports can be displayed. One such display
is the Strip Chart, where four plot panes are provided, with each plot pane
showing user-selected data variables. Clicking on the caption at the far left of
the Y axis steps through the variables and changes the Y axis for that plot pane
to match the selected variable. Likewise, the horizontal axis is settable over a
range of times from one hour to one year in a series of steps.
My ISS is in the back yard, about 100 feet from the house. I've had an
occasional problem with the console dropping communications with the ISS. The
console has a selectable "high gain" receiver option and I enabled that shortly
after purchasing the weather station several years ago. The computer room is on
the front side of the house and is therefore 25 feet further from the ISS and
has the extra loss of an interior wall.
What I found was that the signal, as measured by the ISS
Reception parameter, which measures percent of received packets, 0...100%,
showed long periods of good reception but with extended dropouts. Moving the
Weather Envoy to different locations made changes, but I could find no position
that would consistently ensure reliable communications. The data plot below
shows 24 hours of signal level with four periods of signal failure.
Fortunately, Davis has built-in repeater functionality in the display console.
The console receives packets from the ISS (ISS #1 in my case) and then
re-transmits the packets with a different ISS identification. This permits the
Weather Envoy to receive signals from the much closer display console instead of
trying to directly read the distant ISS.
The figure below shows the effect of switching to repeater
reception. I made the change at 7 AM just after the deep but narrow dropout. The
reduction at 9 AM is a result of experimenting with a different antenna
Although the direct reception mode shows some periods of
100% packet reception, it also shows periods of zero reception, with major
swings. In contrast, repeater reception fluctuates a limited amount, with 80%
reception the norm. Missing 20% of packets is not a serious matter, as the data
is repeated to account for this eventuality.
Now that the data was successfully being captured by my computer, I signed up
with Weather Underground and share my weather station data over the WU network.
You can see the results at
Look for the Clifton, Clifton VA site.
I've used WeatherLink's web server features to add a weather page to this site.
The graphics are a bit crude, but serviceable. I've also noted slow updating of
the scrolling display at the top of the page, which I believe is the browser not
refreshing its display and instead showing a cached out-of-date version of the
scrolling display data. You can see the page by clicking
here, or by using the navigation bar at
the top left of this page.
In experimenting with the
software and making changes, some of the weather data became corrupted. The peak
wind speed was not 175 MPH in June, regardless of what the weather station data
25 June 2008
I've made a couple of small changes in the Watkins Johnson
8617B page WJ-8617B Receiver
Impressions to correct the source for a couple of stories and to add
comments based upon using the NRT squelch system more.
21 June 2008
Mike, W4XN, loaned me his Watkins-Johnson WJ-8617B HF/VHF/UHF
receiver last week and asked me to use it and give him my opinion of it. I've
decided to memorialize my impressions of the WJ-8617B receiver at
this site as well. You may read it by clicking
here or via the navigation bar at
the top left margin of this page.
If you're not familiar with WJ products, they have been
widely used by the US military and by three letter agencies. This particular
8617B tunes from 2 MHz to 1100 MHz and receives AM, FM, CW, SSB and pulse
modulation, with a wide selection of IF bandwidths. It includes a panadapter
Oh, yes, I should mention that when new, this receiver
cost about as much a new Cadillac automobile. WJ's 1992 list price (without
options) shows the receiver starting at $24K, and Mike's receiver has at least
$12K in "options."
20 June 2008
As anyone who has read even small pieces of this site
understands, I like numbers, measurements and real data. Lord Kelvin said, as
restated by Prof. Michael Sherba, my transmission line professor in electrical
engineering at Wayne State University many years ago, "if you can't measure it,
it's not worth a damn." What Lord Kelvin actually said was:
When you can measure
what you are speaking about, and express it in numbers, you know something
about it; but when you cannot measure it, when you cannot express it in
numbers, your knowledge is of a meager and unsatisfactory kind: it may be
the beginning of knowledge, but you have scarcely, in your thoughts,
advanced to the state of science.
Along these lines, I've read today an on-line book
Sustainable Energy � without the hot air, written by David J.C. MacKay of
the Department of Physics University of Cambridge. The book may be downloaded or
read on line without charge at
What makes this book worth reading for me is the author's
attempt to quantify current energy consumption and possible long-term
sustainable replacements with hard numbers, or at least as hard as the numbers
can be given our current information. I don't agree with the author's viewpoint
when he veers away from the physics of his topic and enters the political realm,
but he has well separated opinion from fact. The book is still in progress so
you'll find a few gaps and notes to "fill this section in" here and there.
19 June 2008
My wife has spent a a couple weeks in the Greek islands
studying painting and whilst she was away, I visited my friend Mike, from
Charlottesville VA, W4XN Monday and Tuesday this week. My wife returned last
night after what turned into a long flight from JFK to Dulles so things will
return to normal around Clifton Laboratories World Headquarters.
One thing I did while visiting with W4XN was help
him install a
Z10000-U buffer amplifier into his FT-1000MP transceiver, to obtain a sample of
the 70.455 MHz first IF ahead of the crystal filter. The photo on the right
shows Mike working on the FT-1000MP.
It took both of us close to a full day to install the
Z10000-U buffer amplifier. Electrically, the installation was simple enough. We
found a point to connect the amplifier in the schematic. Mechanically, however,
it was a different story. First, in order to reach the high IF PCB, the
FT-1000MP must be disassembled, including removing the power amplifier module
and the cooling fan module. Then, you must devise a mounting arrangement for the
Z10000-U board. We spent a couple of hours debating various mounting approaches,
as all the normal methods, such as using a threaded standoff, would have
required much more disassembly than either of us cared to do. Ultimately, we
attached it to the power supply enclosure with tape. Not the most elegant mount,
but it avoided further disassembly.
The Z10000-U buffer amplifier's purpose is to provide an
IF sample to be used with a Z90 digital spectrum analyzer. 70.455 MHz is
considerably out of the Z90's normal operating range and we found that
although the Z90 has adequate sensitivity, it has some undesirable spurious
responses. I'm working on a solution for that.
Because there may be wider interest in obtaining an IF
sample from the FT-1000MP, I've added a new page discussing the installation.
Read the page by clicking here,
or via the navigation bar at the top right.
13 June 2008
A long time friend, K8AQC, asked about the AC current and
power characteristics of the compact fluorescent lamps he uses.
I've made measurements of the AC current and power and
also looked at the broadband and line spectrum noise coupled back into the AC
line by a Sylvania 100 watt (equivalent) 23 watt actual screw-in CCFL. The data
is presented at a new Compact Fluorescent Lamp
12 June 2008
I've tried several ways to store multi-meter cables,
ranging from plastic Zip-lock bags to a small tool chest. A couple days ago, I
stopped at the local Office Depot to purchase supplies and ran across an
inexpensive ($2.99) nylon pencil holder that makes a great test lead holder.
The pencil holders are available in several styles and
colors, and the one pictured below best fits my needs. The front is clear
plastic so you can see which leads are in the bag. Additional protection is
provided by the black nylon mesh. The pouch has two compartments, each with a
separate zipper. I've placed the test leads in the main compartment.
The three grommet protected holes are spaced for a 3-ring
binder, but could also be used to hang the bag from a hook, or to attach the
pouch to the multi-meter.
09 June 2008
Below is 24 hours of line frequency data, taken with a
Racal 1992 frequency counter. I've also plotted a 15 minute moving average to
better illustrate changes and suppress the sample-to-sample noise. The plot has
about 35,000 data points, taken 2.33 seconds apart.
The moving average data seems to show peaks and valleys
with about a 1 hour period. It also shows a major drop in line frequency at 18
hours into the collection, corresponding to 7 AM EDT.
07 June 2008
The plot below is 3.5 hours of line frequency data taken
with both a Racal 1992 frequency counter and the 18F4620 PIC circuit I've
been working with. Racal data is captured once every 2.3 seconds whilst the
PIC data is once every 550 milliseconds. Data capture started around 1310
hours today and ended about 1640 hours.
The data agrees quite well, although the Racal has
greater excursions positive and negative. The PIC data is the moving average
of 8 instantaneous measurements, as I've added a moving average smoothing
algorithm to the PIC firmware. I don't know what algorithm Racal uses, but
if it is a true single measurement, it will exhibit greater extremes than
data subject to moving average smoothing.
06 June 2008
After a bit of tinkering with the hardware and
software, I have an 18F4620 PIC reading the AC line frequency with reasonable
The image below is the line frequency taken over a period
of about 1000 seconds with a Racal 1992 frequency counter. As you can see, it
isn't exactly 60 Hz at any given instant, although a long term average shows it
quite close to 60.000 Hz, and if it wasn't electric clocks would not keep
During a 100 minute sample period, I found the Racal 1992
Projected over 24 hours, this slight deviation of 0.0138
Hz from 60.0000 Hz would cause an electric clock to run 19.7 seconds slow.
That's much worse than experience shows, so we can expect the local power
company to offset this slow period with a slightly higher frequency later.
The image below is data from my PIC-based line
frequency monitor, taken over the same period. Racal data is captured at one
second intervals, whilst the PIC data is a bit faster, around 600 ms or so. I've
adjusted PIC data's horizontal scale to bring the two graphs into better
alignment. My adjustment factor distorts the PIC data's horizontal scale legend,
so it looks as if the Racal data is taken over 1000 seconds and the PIC data
over 2000 seconds. That's not the case - both data sets show the same interval,
1000 seconds more or less.
All in all, the agreement
05 June 2008
I've been working
on my power line frequency and voltage project intensively over the last several
The photo shows the PIC controller board (small board at
right center), a board with the master power supply and squarer circuit (the
board made from PCB material) and a A/D converter with optical isolation from
the PIC (the large plug-in board).
This represents about 75% of the total required circuitry.
Missing is the anti-alias filter, which is reasonably straightforward but needs
to be breadboarded.
At this stage of development, I'm concentrating on proper
functioning, not size, as should be obvious. It's much easier to work on a large
layout than with parts jammed together. It's also easier to work with single
op-amps than quad packages during the breadboard stage. When transferred to a
PCB layout, multiple section op-amps may make space and cost sense.
I'm now reading 60 Hz powerline frequency within 0.005 Hz
based on a single cycle of data.
02 June 2008
I've added a new page, (click
here to read it,) still under
development, discussing a few issues related to measuring 50/60 Hz power line
frequencies accurately and quickly. Or, click on the
Measuring 60 Hz Frequency link in
the navigation bar.
This is a project under development, so it is necessarily
incomplete. I plan to update it as my project progresses.
01 June 2008
As usual at the first of the month, I've moved May's
updates to an archive
page, viewable by clicking here or via the navigation
table at the top of this page.
May has been a wet month in northern Virginia - clocking
in with more than twice the normal rainfall. My backyard weather station shows
8.28 inches of rain during May, with 1.25 inches of the total falling in less
than one hour yesterday afternoon.
May is the wettest month in Fairfax County, with an
average of 4.60 inches of rain, so we are not quite twice average. It's going to
take several months of well over average perception to offset the the drought
we've been in for the last year.
Today's Washington Post has the official figures,
taken at National Airport, about 15 miles east of Clifton:
Yesterday afternoon, wind-driven rain hung a gray
curtain across the horizon, as a downpour left 1.45 inches of rain at
That brought the month's total in Washington to
within .03 inches of the record for May of 10.69 inches. The average l for
May is 3.82 inches. Last year's figure was 1.75 inches.
My 4.60 inch May average is from
http://www.erh.noaa.gov/marfc/Climatology/vappn.htm and is for Vienna VA,
which is perhaps half the distance from Clifton as is National Airport. The
MARFC data also represents a shorter time span, 1971-2000.
As far as radio projects go, I've been working with the
color LCD I mentioned last month, with some associated measurement hardware and
software. I'll have more to say about it in a couple weeks, I hope.