Softrock Lite 6.2
Adventures in Electronics and Radio
Elecraft K2 and K3 Transceivers
August 2008 Archives
30 August 2008
I've created a new page with Elecraft K3 audio output
measurements at Elecraft K3 Receive
27 August 2008
Last week, I purchased two
LF Converter kits
from Jackson Harbor Press,
run by Chuck Olson, WB9KZY. I've built both kits and have added a review of the
converter at Jackson Harbor
Press VLF Converter. These are inexpensive kits ($14.00 plus shipping) and
provide more than decent performance. I couldn't resist tinkering with the input
low pass filter, however, and those readers interested in frequency selective
filters may find the page interesting for that reason alone.
As part of the process, I also designed and built an AM
band band-reject filter. I'll write that up in the next few days as well.
25 August 2008
I'm temporarily out of stock of printed circuit boards for
the Z10000 buffer amplifier. I've ordered more boards with a September 11th
scheduled delivery date. Shipping will resume shortly after I receive the
25 August 2008
Dave, K4DGW, found another case where I had the wrong AGC
speed mention at my
http://www.cliftonlaboratories.com/elecraft_k3_agc_and_s-meter.htm page and
I've fixed that this morning. At his request, I've also added several paragraphs
describing the difference between fast and slow AGC in practical use.
24 August 2008
I corrected the AGC fast/slow graph caption on my
Thanks to Dave, K4DGW for catching my error.
23 August 2008
I made a small change in the
Noise Blanker and Crystal/DSP Filtering page to add response curves
for the 500 Hz crystal filter with the DSP set at 600 Hz.
21 August 2008
I've added a new page
Noise Blanker and Crystal/DSP Filtering presenting measurements of the K3's
IF noise blanker performance (have not yet looked at the DSP noise blanker) and
crystal filter and DSP filter performance, both in terms of bandwidth and also
time response due to DSP processing delays. I would like to measure group delay
but that's proving more difficult than I anticipated.
I'll be working on the page off and on a good part of the
day, so it will be published in an incomplete stage at times today as I
test the completed portions. [page finished at 1910 EDT.]
20 August 2008
I've been working on an automated method of looking at the
K3's filters (both the crystal roofing filter and the DSP filter). The plot
below shows the 500 Hz 5-pole crystal roofing filter and the DSP filter.
When the DSP is set to be significantly wider than the
crystal filter (DSP at 4000 Hz) the filter response is dominated by the crystal
filter's response. Even with the DSP set to 1500 Hz, however, the DSP response
contaminates the crystal filter data once we are 40 dB or so down on the filter
from the peak response.
This data was taken with only the K3 and an external
oscillator; no other test equipment. I also should note that this method does
not accurately show the K3's ultimate rejection. The dynamic range of this
method depends on the bandwidth selected, but is 70 to 80 dB, which is more than
enough to show the filter performance over the 6:60 dB "shape factor"
I'll write up the procedure and make available the
associated software sometime in the next week or two. I really dislike
programming a Windows computers and if someone who enjoys that process more
would like to work with me to develop a more refined version of my thrown
together code, please drop me an E-mail message.
20 August 2008
I received the following E-mail today from Doug, GM0ELP
reporting his success using a Softrock Lite 6.2 as a panadapter with his
Just a quick e-mail to thank you for the
info on your website and the Z10000 buffer amp. It's all working great here
with my K3:
19 August 2008
I've extensively expanded the
Elecraft K3 AGC and S-Meter page
to include the effects of changing the K3's AGC-F, AGC-S and AGC HOLD
19 August 2008
I received an update from Rick, VE7TK, concerning his
Ten-Tec Orion modification to extract a buffered 9 MHz IF sample for to use with
an external panadapter. Rick says that he has now extended his modifications to
include the Orion II (model 566) as well as the original Orion (model 565). I've
modified my Z10000 Buffer Amp page
accordingly. Rick's installation notes are available from his web site at
http://www3.telus.net/ve7tk/9MHz_IF.pdf (contents are subject to change, as Rick
18 August 2008
I've extensively revised the
Elecraft K3 and Panadapters page
to (a) reflect measurements for spurious signals into the KRX3 sub-receiver and
(b) add a modification developed by Larry, N8LP, to increase the K3's IF sample
I've also cleaned up a couple of sentences in the
K3 AGC and S-Meter page and
reformatted the two data tables.
17 August 2008
I've written before about automatic gain control in
receivers at Receiver AGC Curves but none
of the receivers examined there had the flexibility of Elecraft's K3 for
user-adjustable AGC slope and intercept.
I've added a page
Elecraft K3 AGC and S-Meter
documenting how the K3's parameters AGC THD (threshold) and AGC SLP (slope),
accessible from the Configuration Menu, alter the receiver's AGC performance.
I've run audio out versus RF input plots for varing AGC THD settings and AGC SLP
While I had the equipment set up for these measurements, I
also ran an S-meter calibration curve, comparing the K3's S-meter with RF signal
levels. (Actually, "S meter" is a misnomer as the signal strength indication is
part of the main LCD display.)
16 August 2008
I've finished several days of measurements on my K3. These
will lead to two new pages, one of which is now ready:
Elecraft K3 and Panadapters
The new page discusses several issues related to the K3's
IF sample output and how one might go about making the signal level more usable.
In addition, if you plan to or are using a Z90 or
Z91 with a K3, please read this page. Jump to the marker concerning the Z90.
11 August 2008
I received a shipping notice from Elecraft today�my K3 is
scheduled to arrive on Wednesday, the 13th. Original order date May 27, 2007, so
the total wait has been 14.5 months. The main delaying factor has been the
10 August 2008
The last week has been devoted to more active
antenna work, this time on the coupler end. The coupler injects 24V DC onto the
coaxial cable and picks off the returned signal. Ideally, the DC power is
sufficiently decoupled from the signal so that (a) no appreciable signal loss is
caused and (b) no appreciable power supply noise is injected into the signal
Objective (a) is not too hard to accomplish, and I have
that working well. Part (b), on the other hand, is proving a bit more
challenging than I thought. After the usual tricks with bypassing, chokes and
the like, I still see excess noise injected from the power supply. My current
assumption is that the transformer I am using has sufficient capacitive coupling
between the primary and secondary windings to allow noise from the power mains
to be coupled into the receiver path. I'll order a couple of split-bobbin
transformers tomorrow, as that design results in much better primary/secondary
isolation than the transformer I'm currently using.
On a completely different topic, I'm occasionally asked
"which PIC programmer and development board should I purchase"? I've added a new
page PIC Development Boards
and Programmers to address these questions. This page presents my limited
exposure to several boards and programmers and is not intended to be a
comprehensive of the field.
04 August 2008
The image below shows the signal level of WWVB at 60
KHz over nearly three days taken with the same conditions as previously
02 August 2008
As usual, I've moved the July 2008 updates to an archive
page, viewable by clicking on the July 2008 link at the top of this page or by
mentioned in July updates, I've started work on a broadband (10 KHz to 30+ MHz)
The photograph to the right shows one prototype mounted in
my back yard. The whip portion is a low-band mobile radio antenna, about 50
inches (1.25 m) long.
In addition to the antenna, I've added a common mode choke
with ground about 20 feet (6 m) from the antenna. The theory is that power line
and computer hash noise is coupled to the braid's exterior and travels along the
braid to the antenna where it is picked up by the antenna. This theory says that
a choke (with ground rod) located near the antenna will reduce the noise
The choke is wound with a dozen turns of coaxial cable
around a double stack ferrite core of Steward Type LF material. The choke
impedance is at least several hundred ohms at 25 KHz, and rapidly increases to
several thousand ohms by 500 KHz.
I've only started performance measurements, and I've
noticed differences in both signal and noise amongst the possible combinations:
- Ground at choke, none at antenna
- Grounds at choke and antenna
- Ground at antenna, no choke installed
My subjective impression, backed up with a quick
measurement comparison is that mode (1) provides the best signal to noise ratio
in the VLF and LF range. But, this conclusion may change with more data,
particular when I look at higher frequencies.
I've taken some signal strength and noise data in the 20 KHz
- 70 KHz range in recent days, and Ron, K8AQC, who has another of my prototype
antennas has also taken similar data. Ron uses an HP 3585A spectrum analyzer,
while my data is taken with an HP3562A dynamic signal analyzer. The 3562A is an
FFT-based device and looks at a very narrow slice of spectrum, 9.5 Hz bandwidth
for the particular configuration I've collected data with.
Ron's data is limited by the 3585A's resolution, which is
1,000 data points, so over a 4 hour period, a measurement is taken once every
My 3562A's data is taken at about 5 minute intervals, with
each data point being the average of 16 readings. I've plotted both the
individual 5-minute values and a smoothed average (adjacent average of 5 values
on either side).
It's not possible without a lot of extra work to directly
compare signal strength taken by Ron (located in suburban Detroit MI) and my
data in suburban Washington DC. The relative changes are directly comparable,
but not the absolute levels.
Ron provided the two images below illustrating WWVB's
signal level (60 KHz) over two four-hour periods. The first is from 8 PM -
midnight 01 August, whilst the second is 4 AM - 8 AM today, 02 August 2008. (All
times are EDT).
Studies of VLF/LF propagation have long showed anomalies
at sunrise and sunset. (Local sunset at Ron's is 8:50 PM EDT this time of year.)
The studies usually show a dip in signal level, followed by an increase at local
(receiver) sunset. In some cases, a second dip is seen at local sunset at the
transmitter location, in this case in Colorado, near Ft. Collins. Local sunset
at WWVB is 8:13 MDT, or 10:13 EDT. At sunrise, the reverse effect is seen.
In the 8 PM - 12 midnight plot below, local (receiver
site) sunset is approximately 2.5 divisions from the left edge, and increased
signal levels are seen shortly after sunset. Transmitter sunset is essentially
mid-screen, at which point the signal level flattens and exhibits a dip of
perhaps 1 to 1.5 dB.
Sunrise at the receiving site is 6:27 AM EDT and at the
transmitter site 5:55 AM MDT, or 7:55 EDT.
Receiving sunrise corresponds to 6 divisions from the
left, and we indeed see a major drop in signal around local sunrise, with a 10
dB decrease in signal level over 30 minutes or so. Sunrise at the transmitter
occurs at the end of the data, so we can not say too much about it.
It's also apparent that Ron's local noise dropped
considerably between midnight and 0400�the "fuzz" on the data plot is noticeably
reduced in the plot below.
The plot below shows data I took over the same time, with
local sunrise and sunset in Clifton VA added. My plot runs for a longer time and
shows similar behavior to Ron's data.
Ron's data shows a 10 dB increase in signal level over the
space of about 2.5 hours. I see a similar signal increase over about a 2 to 2.5
hour period. Our sunrise observations are similar as well.
I observed three peaks during the hours between sunset and
sunrise, with about 5 db peak/valley changes. Ron's data also shows peak/valley
changes of about 4 db, with perhaps a slightly shorter peak-to-peak time.
My data is taken with a control program I wrote that looks at
eight VLF/LF stations and four unoccupied frequencies for noise reference.
The strongest VLF station on the east coast is NAA's 1
megawatt ERP signal at 24 KHz. Over the same period, it shows faster
increases/decreases at sunrise/sunset. Of course, sunrise/sunset at NAA's Maine
transmitter is within 30 minutes of sunrise/sunset in Clifton VA, so a more
rapid rate of change in signal level makes sense.
I've not been successful at observing the US Navy's Holt VLF
facility at Exmouth, Australia, callsign NWC, at 19.8 KHz, but I can observe
station NPM, at 21.4 KHz in Hawaii, day and night. The daytime signal is only a
few dB above local noise, but it's distinctly observable.
This path also shows similar characteristics, with a slow
increase at sunset and a rather fast drop at sunrise.