Automated Transverter Band Switching in VHFLOG and KM Rover
Frequently asked question:
Why not have an interface between the station and VHFLOG to automatically change bands?
A: Done! Stations may have multiple radios and multiple transverters with or without
transverter switchboxes. Stations may have separate radios for FM or single band
stand-alone radios that don`t get switched.
I decided to provide computer control in the direction that would get the widest
usage, from the computer to the station. The easiest solution is to use a band decoder,
connected to LPT, that `switches in` the transverter of choice. When you change bands
in VHFLOG (or KM Rover logger), the decoder`s output will also change. This type of
switching is used by HF operators to automatically switch to the proper antenna when
changing bands. Important note: See #4 below.
At this time, LPT I/O is not supported in Win7 Win8.
The decoder I used to test the software is the original Top Ten Devices band decoder [for a
Yaesu rig, not the newer Band Aide]. See alternate interface by N3FTI below. Once you get the
decoder wired into your station, it can be used in the manual mode to select transverters without
using the computer. This type of computer control does not care what IF radio(s) you have or what
the switching configurations are.
Regardless of the configuration, you need an `auto position` added to your current
setup, so the decoder can take control.
1). If you have a transverter switch box that uses a wafer switch going to ground to
activate each transverter, the output of the band decoder can provide the same ground.
The decoder is wired in parallel with your existing wafer switch.
2). If you have control relays doing the switching from toggle switches, you can wire
the decoder outputs in parallel with the toggle switches.
3). The TopTen decoder box only has 6 positions manually selectable from the front panel.
Wire the decoder in parallel with your existing system. Then add an auto position to your
existing switch system. It would be easy to replace the wafer switch with a 3 section
wafer switch with 3 more positions, so you can select the other 3 bands not available
in the manual mode. For the added 3 positions, just wire the decoder output lines
7, 10 & 11 directly to the wafer switch, with the common leg of that wafer connected
The TopTen decoder connects directly to the PC`s parallel port with a standard 25-pin
printer cable, and receives BCD band data generated by the logger. The decoder circuitry
converts the 4-input lines to 9-NPN outputs that can sink 500mA to ground. The nine
160-10m positions of the decoder are equivalent to the VHF/UHF bands from 50-5760 MHz
(or 144-10368 MHz), user selectable in the logger. If you use the logical 0 condition of
the logger in the 144-10368 MHz mode, you can have 10 bands controlled by the logger. Your
control circuitry would select 6m as the default band. My new loggers have encoded
outputs on all bands.
VHFLOG and KM Rover can key CW to LPT1-17, which is decoded to the RCA jack on the back
panel of the Top Ten decoder. Top Ten Devices (N3RD & W2VJN).
4). Important consideration: Keep in mind that when you are talking on a band and
you type a new band in the logger, this will cause your switchbox to change bands. When
moving stations up the bands, it is easy to forget and change bands before we are done
talking. This not only leaves the station `hanging` - but also moves your signal to
another frequency where a QSO may be in progress.
This also causes Hot RF switching that can cause damage to amplifiers, relays and preamps.
A lock-out circuit using a data latch chip and transistor latch enable circuit must be
added to your auto transverter switchbox to prevent the transverter band switching unit
from changing states if one of your transverters is keyed. The lock-out chip is a BCD latch
that stores the BCD input data when a transverter is keyed. If only one IF rig is used, then
only one +V signal (from the IF radio) is required into the latch transistor. Back to top.
Steve Kerns, N3FTI designed a VHFLOG LPT Interface (BCD to relay contacts) that allows
10 bands to be controlled by the logger. The state of the LPT port is logical 0 (6m) when
the PC is turned off. N3FTI is on qsl.net or n3fti at yahoo dot com.
Problems getting the decoder to switch? Use LPT1 pin 18 for the ground connection.
If you have problems interfacing to a decoder (the unit does not switch), verify that it
works with 5V connected to the BCD inputs. The connections and truth table are here.
No LPT port on new PCs:
USB to LPT converters only work on `printer class` hardware. BCD multi-pin outputs on
LPT cannot be transferred to USB ports. Use a PCI LPT board (supported by VHFLOG and KMRover)
or save that old PC to run the ham applications!