Automated Transverter Band Switching
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.
The decoder I used to test the software is the Top Ten Devices band decoder [for a
Yaesu rig]. 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.
Wiring choices:
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
to ground.
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).
Alternate interface:
Steve Kerns, N3FTI designed the 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. LPT decoder kits are available from Steve Kerns -
N3FTI on qsl.net or n3fti at yahoo dot com
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 leaves the station `hanging` and 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.
5). Problems getting the decoder to switch?
Most PCs built today have LPT and COM interfaces that provide port voltages ~5V. If you
experience problems interfacing to the N3FTI decoder board, ie: the unit does not switch,
verify that it works with 5V connected to the BCD inputs. ex: 144MHz = BCD A at LPT Pin2.
See truth table and other info. Then connect the PC, run the logger and measure the voltage
at the BCD inputs.
No LPT port on new PCs:
This is a problem as the USB to LPT adapters and cables only work on hardware like USB
printers. BCD and multi-function outputs on LPT cannot be transferred to USB ports. Use
a PCI LPT board or save that old PC to run the older applications!