Notes from 2009 Dayton Hamvention®. Based on conversations with
users, here is a list of the most frequent requested custom features
and topics of interest.
1. Buffer Amplifier. I offer a buffer amplifier
kit for $7.00 postpaid that includes another
AD8005 output stage and its associated resistors and capacitors.
Gain is about 15 dB (R12 is increased
to 100 ohms to prevent saturation). This provides enough to boost
the output of the VFO up to several
volts peak output. This is a sufficient level to drive a passive
mixer or a 1-watt amplifier. Several
amateurs have already built this gain buffer and used it with
success. The circuit is the same as the
original one, with no output filter needed. It merely provides
gain. If you would like to add extra
filtering, feel free as this is encouraged.
2. TCXO (Temperature Compensated Crystal Oscillator) option.
I have sold all the C/W TCXOs and am investigating other options. Contact WA1FFL
for latest details.
3. Band-limited version. I can ship a VFO software
version that only covers a portion of
the HF band (i.e., 1.8-2.0 MHz, or the like). Reverse tuning
(5.5-5.0 MHz, for example) is also available.
4. Six Meter Option. I now have boards that will go up to 6 meters (54 MHz Chebychev filter) and am ready to ship; add $10.00 extra to kit price.
5. Rotary Switch
Control. I now have an option to control the VFO with a 9-position
rotary bandswitch. This circuit utilizes a 74HC147 priority encoder.
Instead of switchable offset control
at pins 1-4 of the microprocessor, the 4-bit priority encoder
output is routed to pins 1-4 and used to
decode nine bands. Typically I have programmed the lower band
edge of Amateur Bands 1-9 (1.8 MHz,
3.5 MHz, 7.0 MHz, etc.) into the nine memory locations. Please
contact me for details in setting up this
option. If an offset is desired, each band can contain its own
combination. For example, for a user with
an Atlas transceiver, I had bands 1-4 give the desired 5.595
MHz offset (positive), switching to a negative
offset (still 5.595 MHz) in bands 5-9.
6. Frequency Step Word Truncation
Effects. It turns out that, if a DDS clock
frequency of 134.217728 MHz is used (rather than the standard
150 MHz oscillator that I ship), the step
constants come out to be perfect integers. Then there is no finite-word
or truncation error (which is
normally so small with the fixed 150 MHz clock that it is unnoticeable
to most users). This clock oscillator
(134.217728) is not shipped in the standard kit because not everyone
has a frequency counter or the
ability to trim it to this close precision. K2AOP’s voltage-controlled
oscillator circuit (see application
note on this site) using an International Crystal IC1100FRSV2
voltage controlled oscillator, set for this
frequency using a trimpot, makes it possible to set this up.
I have the VFO software program for this
clock frequency if anyone wishes to explore this option. Thanks
to John Clark and Mitchell Lee for
encouraging me to investigate this.
7. Non-Detente Shaft Encoders. I have found two excellent ones made by Bourns, part numbers EM14A0D-24-L008N, and EM14A0D-24-L032N, both available for about $18.00 from Mouser Electronics. Be careful of the small pins- I used #24 solid wire to hook these up, bending them at right angles (the middle two are not used).
error. With a 50 ppm clock oscillator (i.e., standard 150 MHz
Connor-Winfield unit) you
will typically measure about 30 Hz/MHz step error in the 1 MHz
steps. This is why I encourage users to
set up sub-bands in the flash memory and calibrate those bands
individually. If you stay within the sub-
band after calibration, errors of less than 10 Hz. are typical.
Driving Vacuum Tube Rigs. The best article on this subject that
I am aware of is
the DeMaw Article listed on this web site. I got permission from
CQ Magazine to post it here. One detail:
the article is ambiguous about certain toroid cores used in the
transformers shown in the article. I would
use the Amidon FT37-43 cores for T1 and T2; they are used in
many other HF transformers that I have
seen and seem to be very suitable. In fact, I have used them
Hope to see you in 2011 at the show. I appreciate all
feedback. Inquires are welcome at: