Softrock Lite 6.2
Adventures in Electronics and Radio
Elecraft K2 and K3 Transceivers
31 August 2007
I've added phase noise data for a Z90 operating in signal
generator mode. Since the Z90's AD9851 DDS circuitry is quite similar to the
DDS-60, the Z90 data can be taken as representative of a DDS-60. The data is at
the Canned Osc Phase Noise page.
30 August 2007
I've been intrigued with the small custom one-time
programmable oscillator modules, such as Cardinal Components' CPP series units.
http://www.cardinalxtal.com/docs/series/CPP.pdf. The CPP series is a
one-time programmable module, with 1 Hz steps and is modestly priced at $8.18
each from DigiKey, programmed to your frequency.
If, and it's a big if, these modules have acceptable phase
noise they would be extremely handy for BFO or 2nd oscillators in one-off or low
volume designs. A few months ago, I purchased several of these oscillators for
21.4 MHz and was disappointed at their broadband noise output. I've added a new
page to this site comparing the CPP oscillator with a standard canned oscillator
and a home brew crystal oscillator. You can view the new page by clicking
here or via the links at the top left of this
27 August 2007
I've finished laying out an interim printed circuit board
for the RF section of my next generation panadapter. It took a full week to
enter the schematic, make patterns for parts not in the stock libraries and lay
out the PCB. I plan to order prototype boards later today.
I've also laid out a test board for component measurement
with a VNA. The board has provisions for through measurements as well as
reflection measurements. I will have a few extra boards and can supply them to
interested readers while the supply lasts for $15.00 each, including domestic US
shipping. This price includes the PCB, and 1206 parts for the short and 50 ohm
load. The board also requires 8 "V-Bite" Teflon BNC connectors
available for purchase
from Mouser at about $3.50 each.
I'll post more details, including photos and test results
when the boards arrive and I verify the layout.
21 August 2007
I've looked a bit more at Vista support for the E-MU 0202
USB sound card. This is of academic interest to me at the moment because I don't
have a Vista machine, but at some point I will almost certainly be forced into
one as new XP installations will come to an end before long. The short answer is
that there's an existing work-around to install E-MU 0202's XP drivers in Vista
and the release data for real Vista drivers is 3Q 2007. I've added this data to
my Softrock page and provided links.
20 August 2007
My wife uses a Taylor digital oven thermometer (model 1470) to measure the
interior temperature of roasts and the like. The first one got a bit too close
to a hot stove burner and the case melted, so I replaced it with a new one
earlier this year.
Recently, she remarked that the new thermometer was reading differently than
the old one, so today I compared the old and new oven thermometers along with
two glass "laboratory" thermometers, two analog dial thermometers and my Fluke
189 Digital Voltmeter and 80PK-25 Type K thermocouple combination. I've added a
new page with the results of my comparison, viewable by clicking
here or via the links at the top left of this page.
If you don't have one, by the way, I recommend the Taylor 1470. As my
measurement data shows, both samples I tested agree well with my Type K
19 August 2007
The last few days have been occupied by entering a
schematic of the RF section of the "Z93" next generation panadapter into
DIPtrace's schematic capture program. This is a fairly time consuming process,
but not nearly as painful as doing the associated PCB layout. I hope to have a
PCB layout done by the end of the week and enter an order for a couple prototype
boards. This represents a modest step forward, and is mostly to verify the
breadboard work I've done this month in the areas of sensitivity, IP3 and IP2
performance, gain distribution and the like. I expect to make quite a few
changes in this design as the project goes forward. I can't start on the rest of
the work�the DSP section and the display/controller�with the RF as a selection
of Manhattan-style boards spread over the test bench, however. The next major
element of the project I will work on is likely to be the display and main
microcontroller, assuming the RF section is not in too bad a shape.
Larry, N8LP, purchased an E-MU 0202 USB sound card at my
recommendation a few days ago and a comment he made alerted me to something I
had overlooked. The E-MU 0202 ships with only Windows XP drivers, and has no
support for Windows 2000. It also does not support Vista, but that's a
short-term issue as far as I can tell. I'll add a note to my
Softrock page noting the E-MU 0202's
If you are interested in WW II era aircraft radio
communications gear, take a look at
http://aafradio.org/ . I spent a couple of hours looking at the
photos. I still have somegear from that era around here, including a BC221
frequency meter (but without the calibration book), a Command Receiver for the
150 - 550 KHz band and a 1020 Hz "range filter."
13 August 2007
In addition to my ferrite rod article, I received an
acceptance letter for an article on the Z100 CW tuning aid. It will also appear
in QEX over the next few months.
I've finished the article on resistors and submitted the
manuscript to QEX today. It's about 30 double spaced pages and 35 illustrations.
It includes the material on my Carbon
Composition Resistor page, but goes way beyond that, as I've provided
extensive RF measurements over the range 300 KHz - 500 MHz for carbon
composition, carbon film, metal film and thin film parts. The following
illustrations may provide the flavor of the article.
In case anyone wonders, writing an article like this
requires a great deal of work. The measurements are a fraction of the total
effort, with most of the effort being in research and writing, drawing graphics
and double-checking and triple-checking the text. The resistor article,
for example, required more than 120 hours. That's about four hours for each
08 August 2007
I will have another article in QEX concerning ferrite rods
and their perversity, as I've recently received a letter accepting my
manuscript. I use the term "perversity" only semi humorously, as they have
some of the most non-linear relationships I've run into. The inductance depends
on about everything, including where the winding is with respect to the rod
center, the percentage of rod length covered by windings, the ratio of the rod
diameter to length and the rod permeability to just name the most important
I hope to finish another manuscript this week, concerning
resistors. A few weeks ago, I measured a stash of new old stock 1/2 watt carbon
composition resistors I ran across in a distant corner of my garage,
report here. Those measurements
lead me to further explorations in the world of resistors, and I hope to finish
a draft of the article and get it off to QEX by Monday.
04 August 2007
I've added a section to my
Prototyping page showing Teflon push-in pins, and a simple home made
insertion tool. These pins are available at modest cost on the surplus market
and offer a useful solution to those portions of a circuit that can't be
adequately built with conventional Manhattan-style construction. The section can
be found on the Prototyping Page by clicking on the Teflon Pin Inserts link. Or,
some browsers will take you there directly by clicking
02 August 2007
I've received a question about the compatibility of 50 and
75 ohm BNC connectors, as the Extron ADA 6 300MX video distribution amplifier is
equipped with 75 ohm female BNC connectors. I've confirmed my understanding that
50 and 75 ohm BNC connectors are mechanically interchangeable. Amphenol's web
site notes the following:
Two distinct types of 75 Ω
BNC's are available, and both mate with each other and with 50
Ω BNC's. Type 1 is designated 75
Ω BNC-T1 and provides constant 75
Ω performance with low VSWR DC 4 GHz. Type 2 is
designated 75 Ω BNC-T2 and is usable with low
reflection DC - 1 GHz. For applications above 1 GHz, Type 1 is recommended.
Interchangeability is definitely not the case with Type N
connectors, as a male 50 ohm N connector has a larger pin diameter than a 75 N
connector. Hence, mating a 50 ohm N male connector with a 75 ohm N female
connector will damage the female connector's spring fingers. Likewise, a
precision 75 ohm N male connector mated with a 50 ohm female N connector will
not make reliable contact.
In the BNC case, however, the pin's mating end diameter is
identical in both the 50 and 75 ohm versions. The impedance difference is
accommodated by reducing the plastic insulation diameter, which raises the
connector impedance by making part of the connector structure air. (Air has a
lower dielectric constant than the plastics used in the connector. Since coaxial
cable impedance is proportional to 1/square root (C), decreasing C increases the
connector impedance.) There's also a difference in the pin shank diameter
between 50 and 75 ohm BNCs, but the critical dimension is the mating section
diameter, identical in both 50 and 75 ohm BNC connectors.
As a final check, I measured the tip diameter of the 75
ohm BNC connector on the video cable supplied with the ADA 6 300MX and compared
it with the diameter of a 50 ohm BNC's pin. To my ability to measure, they have
the same diameter.
And, the impedance mismatch from using a 75 ohm source
with 50 ohm connectors and cable is unimportant when routing 10 MHz frequency
data short distances around my basement lab.
I also looked at the waveform out of the ADA 6 300MX video
DA when connected to my HP 5065A Rubidium frequency standard. The image below
shows the waveform when connected to the oscilloscope's high impedance input.
The peak-to-peak level is 4.6 V and the waveform generally looks good.
When terminated with 50 ohms, the waveform drops in
When terminated with 50 ohms, the waveform drops in
amplitude, as expected. Don't pay attention to the oscilloscope's
frequency measurement in the image below. It's really 10.000000 MHz as shown in
the first image.
01 August 2007
As usual, I've moved the July 2007 Updates page to
archives. It may be reached by clicking here, or via
the link table at the top of this page.
Most recent test equipment has an option for synchronizing
its time base to an external standard. Some receivers also have this option, and
Elecraft's K3 transceiver provides external synchronization as well.
I have an HP 5065A Rubidium frequency standard, but it has
only a single output for each frequency (10 MHz, 5 MHz, 1 MHz and 100 KHz), so a
distribution amplifier is normally used to connect multiple pieces of test
equipment to a single time base standard. HP's 5087A distribution amplifier is
commonly used, but can be difficult to find configured in the way that best
meets your test bench. The 5087A uses a separate plug-in card for each output
port, and the cards are frequency specific, although it isn't too hard to make a
5 MHz card into a 10 MHz card. Other distribution amplifiers are available,
including a kit from TAPR, as well as commercial products.
A recent posting on the Agilent mailing list, however,
suggested using an inexpensive video distribution amplifier, an Extron ADA 6
300MX, for example. This video DA has three independent channels (red, green and
blue), each with 6 isolated outputs. (There's also a synchronization channel,
but that is more difficult to use for this purpose.) This allows, for example, 6
outputs at 10 MHz, 6 outputs at 5 MHz and 6 outputs at 1 MHz. Or, the output of
one channel may be connected to the input of another to give, e.g., 11 outputs
at 10 MHz.
I found a number of ADA 6 300MXs on E-bay and purchased
one for $49.95, which is about one-tenth of the price of a test equipment type
time base distribution amplifier. It arrived today and I've made a few quick
measurements and installed it in my basement shop. It seems to work well.
My current configuration is:
Red input = 10 MHz, with 6 outputs
Green input = 5 MHz with 6 outputs
Blue currently unused.
The video DA is 75 ohms input/output, but for distributing
10 MHz and lower time base signals around my basement shop, this mis-match is
not important. Furthermore, although the video DA is equipped with 75 ohm female
BNC connectors, the connection end of 50 and 75 ohm BNC connectors is
identical, so 50 ohm male BNC connectors may safely be used with these DAs.
(There's a difference in the insulation diameter between 75 and 50 ohm
I understand from the Agilent mailing list that it is
possible to change the input/output impedance from 75 ohms to 50 ohms via
resistor changes. Since this is not necessary, I have not further explored the
Front view of the ADA 6 300MX.
Rear view. The unit is powered via a 120V mains connection.
The output BNCs are 75 ohm female type. The connecting
portion of center pin's diameter is identical in 75 and 50 ohm BNC connectors,
so no damage will result using 50 ohm male BNC connectors with 75 ohm female
These video amplifiers have excellent high frequency
response, and are usable to nearly 400 MHz. The response will change depending
on two option switch settings, AC/DC coupled and 1V/0.7V. The frequency sweep
below shows the flattest response, obtained with AC coupling / 0.7V gain. Marker
1 at 1 MHz is set to be 0 dB relative, so marker 2 shows point at which the
output is -3 dB with respect to a 1 MHz input.
don't know what the noise figure of the amplifier is, so I don't necessarily
recommend one as a DA for VHF signals, but this shows the amplifier to have more
than enough frequency response for timing signal distribution.
The next plot sets Marker 1 to absolute mode, and marks the spot at which the
next gain is 0 dB, 368 MHz. The peak gain is about 2.5 dB.