VFD Application Note - Options
INTRODUCTION
The purpose of this Application Note is to provide the user of the RF
Applications, Inc. VFD Series Wattmeter with information needed to use the various
options available for these Wattmeters. We provide information on the
installation of the Vanity Option, the VSWR Relay Option and the Power Monitor
Option.
The Vanity Option allows your VFD to be personalized with up to 12 (11 preferred)
characters that will be displayed when the VFD is idle (no RF is present.) Eleven
characters are preferred because the last four positions on the lower line of the
display are used (causing a twelve character personalization to run in to those four
positions.) The Vanity Option is available only from RF Applications,
Inc. There is no way to program the Vanity Option yourself.
Installation is simple. TURN OFF THE VFD. Open the VFD using a 1/16" hex
wrench. Do not lose the screws! Once open, locate the microcontroller. It is in an
18 pin DIP package and has a label on it. It is the only socketed component on the
board. Using care to avoid static discharge, carefully remove the old
microcontroller. Then, noting the orientation of the chip, install your Vanity
microcontroller. The notch on one end of the chip should be nearest the electrolytic
capacitor. Reassemble the VFD. No recalibration is required. Power up the unit to
verify proper operation, and be sure to store the old chip so you’ll have it if you
ever sell your VFD.
The VFD provides a visual indication (both with an LED and via the display) that
a preset VSWR limit has been exceeded. If you have purchase the VSWR Relay Option,
you can connect external devices to the VFD (such as your amplifier keying/ALC lines
or a bright indicator light) that will respond to your operating VSWR conditions.
The option is normally factory installed. If you are installing it yourself, this
process is relatively simple. TURN OFF THE VFD. Open the VFD using a 1/16"
hex wrench. Locate the VSWR Relay Option board and install it in the case (the hole
for this should be predrilled). The Option Board only installs one way. Once
installed, connect the Molex connector already present in the VFD to the Option
Board. If you are having trouble installing the connector, you are trying to put it
on backwards. It goes on VERY easily the right way and is VERY hard to install the
wrong way.
Once the Option Board is installed, put the VFD back together.
VSWR Relay Option Operation
A two wire cable is used to connect to external devices. Use the Common (usually
the shield) and the wire connected to the TIP of the 1/8" mini phone plug (usually
the white wire). The circuit is rated a 500 ma at 30 volts ac/dc maximum. Inductive
loads should be snubbed (usually done with a reverse biased diode). The relay is a
reed relay and the circuit is isolated (not connected to power or ground) so you can
connect to anything you need to without this concern.
You will find continuity between the two wires when the VFD is powered up and
there is no VSWR alarm condition. If you turn off the VFD, the circuit opens. If you
have a high VSWR condition, the circuit opens. The circuit closes again when RF is
removed.
In the following section we will discuss some ways to use the relay contacts.
VSWR Relay Applications
Amplifier Interruption
High VSWR can kill an amplifier (or traps). You can use the VFD to signal your
transmitting system to stop applying high power if you’ve got a VSWR problem.
The preferred method is to set up the relay to drive the ALC input of your
transmitter to its maximum (usually negative) input voltage, thereby causing it to
minimize its RF output to the amplifier. This method avoids potential "hot
switching" situations if the unit trips under high power conditions. Since the relay
is normally closed, you will probably need to drive an additional relay (or circuit
of some kind) to accomplish. RF Applications, Inc. can provide suggestions on
request.
The alternate method is to wire the relay contacts in series with the PTT line
between the transmitter and the amplifier. Under an alarm condition, the PTT line
will be interrupted and the amplifier will be taken off line.
External High VSWR Indicator
You can easily wire a lamp in series with the circuit using any voltage up to 30
volts ac or dc. This lamp will be on whenever your VFD is on and there is no VSWR
alarm. It will go out when you have an alarm. If you would like it to operate the
other way (on when the alarm condition happens), you can use an LED with the circuit
below, or use another relay with its normally closed contacts in series with the
lamp.
T
he Power Monitor Option offers you the ability to control your
transmitting system based on the power output levels from your transmitting system.
There are two contacts available to you that have various functions based on jumper
settings on the Power Monitor Option Board (which is the same board as the VSWR
Relay Option board). As with the VSWR Relay Option, the Power Monitor Option is
normally factory installed. Refer to the installation instructions in the VSWR Relay
Option section (above) if you are installing it yourself.
Power Monitor Option Operation
The Power Monitor Option has two relay outputs. These outputs are available on
the 1/8" phone jack on the rear of the VFD. The relays are connected as shown below.
For the purpose of this discussion, we will refer to the relays as "White" and
"Red". The White relay is connected to the tip of the plug and the Red relay is
connected to the ring. These color designations also correspond to the cable shipped
with the VFD. The relays share the common, which is the shield in the supplied
cable. The circuit is not connected to power or ground (it is floating). The relays
are rated at 30 volts ac or dc at 500 mA maximum.
CONFIGURATIONS
There are four jumpers used to set up various configurations for the operation of
the Power Monitor Option. These jumpers are located on the Option Board as shown
below:
Jumpers JA and JB are used to select four power levels at which you have contact
closures. Jumper JC controls the operation of the Red relay, and Jumper JD selects
whether or not there is a delay on release of the relay after RF is removed. All
jumpers are installed from the factory.
In general, the White relay is on when no RF is present. When the power level
selected by jumpers JA and JB is exceeded, the White relays is de-energized, opening
the circuit. The Red relay is configured using jumper JC (described below.) The
White relay circuit is useful to interlock two radio PTT arrangements and to disable
antenna selectors during transmission. The Red relay is useful to control indicator
lamps that let you know RF is present (and present above the predetermined level.)
Jumper Details
Jumper JD
If installed (the factory default), the relay(s) respond immediately to the
removal of RF. If removed, the relay(s) will hold for about 1 second after the
removal of RF. The system is designed for SSB and CW operation and will not pulse
(unless extremely slow CW or long voice pauses are encountered.)
Jumper JC
If installed (the factory default), the Red relay operates as the complement
(reverse) of the White relay. In effect, you have a SPDT contact arrangement. If
removed, the Red Relay is open when no RF is present and closed when more than 1400
watts are present. This is handy for those operators that would like a separate
signal that lets them know they are operating near the legal limit.
Jumpers JA and JB
These jumpers program the power level that trips the White relay. When the power
level selected is exceeded, the White relay is de-energized. If selected by jumper
JC being installed, the Red relay is energized based on these settings as well.
The available power levels are:
JA In and JB In: 24 watts (default)
JA In and JB Out: 96 watts
JA Out and JB In: 192 watts
JA Out and JB Out: 1400 watts
POWER MONITOR OPTION APPLICATIONS
Second Radio and Peripheral Protection
Configure the Power Monitor Option (PMO) so that the White relay opens when above
24 watts with no delay (the factory default.) Then wire the PTT from the second
radio in series with this circuit. When this unit detects power above 24 watts, the
other radio cannot transmit. By using the White relay circuit in series with the
power to the antenna switch (watch the voltage/power limit of 30 volts at 500 ma),
you prevent the possibility of hot switching your antennas.
On-The-Air Indicator
Use the factory default settings and the Red relay to control your "On-The-Air"
sign. It will light up when you are transmitting (and only when you are really
putting RF out!) Again, watch the voltage/power limitations. An external relay can
be used if you need to control higher power.
Near Legal Limit Indicator
Pull out Jumper JC and wire a light in series with the Red relay. This light,
when lit, will tell you that you are putting out more than 1400 watts, making it
easy for you to know when you’re station is operating at its peak. Also great for
multioperator installations where operator changes and unfamiliarity with equipment
can cause extended periods of time operating without and amplifier or with a
mistuned amplifier – if everyone has their green lights on, they’re operating "in
spec".
4 Square Vertical Array problem indicator
4 square arrays using a dummy load to balance a hybrid coupler relay on minimal
power being sent to the dummy load while transmitting and operating normally. If a
failure of the antenna system occurs large power is suddenly sent to the dummy load.
This option can detect when that happens and shut off the amplifier, and alarm the
operator that something is wrong. The sensor can be remote located at the
hybrid coupler with the dummy load.
Please contact Array Solutions for further information if required. In some cases
customization can be performed.
