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).

8. Clock 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.

9. 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 myself.

Hope to see you in 2011 at the show. I appreciate all of your
feedback. Inquires are welcome at: