Keying an Amp with the SDR-1000 Using the X2 Connector Keying ...

Keying an Amp with the SDR-1000 Using the X2 Connector
Keying an Amp with the SDR-1000 Using the X2 Connector
System Dependencies
Minimum PowerSDR Version: 1.8.0
Applicable Hardware:
SDR-1000
Content provided by: Larry, K2LT
I am trying to key an amplifier with my new Flex. Pin 7 on X2 measures 60 ohms to ground on
standby and doesn't change much when I key the Flex. What am I doing wrong? Can someone
furnish a schematic? I have a 5VDC SPST relay that I would like to use to act as a buffer between
the Flex and my 4K Ultra.
Answer:
The X2-7 pin is driven by a darlington that goes to ground when activated. The easiest test is poke
a 1 K resistor into Vcc pin 14 and pin 7. Measure the voltage from pin 7 to ground. Standby is 5 V
and keyed is close to 0 V. A standard ohmmeter doesn't supply enough voltage to show a
meaningful test.
As long as the resistance of your 5 volt relay coil is 100 ohms or greater then the Vcc pin 14 can
operate it. Hook pin 8 to the Vcc pin 14 to provide a back diode protection across the coil. The coil
goes between pin 14 and pin 7.
You will need to spend quality time with grounding everything together and maybe a few ferrite
beads on the control cables too.
Wally M0ZAZ is working on a solid state driver interface called the Poor Mans Universal Control
Board.that will make it easy to hook amps to the SDR-1000. His email is wawatson@erols.com.
Follow Up Question:
I connected it just the way you you indicated above and when I connect it to my amp it
immediately keys it even though I have not keyed the SDR-1000. As indicated before, pin 7 is
only 60 ohms above ground and when I connect it to the coil of the 5VDC mini relay, the relay
keys immediately, which keys my amp. I am connecting pin 14 to the top of the relay coil, as well
as pin 8. The bottom of the relay coil goes to pin 7. Since there is always 5vDC on pin 14 and pin
7 is only 60 ohms from ground, the relay energizes. What is going on????
Follow Up Answer:
Content provided by: Jim, W6RMK
You have a "shortput" or shorted output caused by some previous event like trying to key an older
amp without a protection diode across the relay coil. Or maybe static electricity got the pin 7

darlington with the winter heating season low humidity.
Fortunately there is a way around the fault. Pick one of the X2 connector external control lines pins
1-6. These have the same output stages as pin 7.
You set up these pins in the Ext Ctrl Tab (Setup Program) and once programmed they act just like
pin 7. Even the "enable X2 TR sequencing" and the "X2 delay" settings in General/Options setup
work. So you have six more outputs.
Do the resistor test first on the pin of your choice to be sure it is working.
I am not a fan of hooking relays directly to the X2 connector. Too hard to replace that little surface
mount chip that is 3 boards down in the stack. If the relay has a GOOD back diode across the coil
then that should prevent the inductive kick from creating the HV spike that blows the output
darlington. The naked relay coil acts like a spark coil in an ignition system.
There was a great discussion a month ago about back diodes and Jim Lux came up with an
application note from Tyco that provided an improvement on the back diode by adding a zener to
the string. This gave the optimal control for the relay coil discharge time.
I quote without Jim's permission:
"I would suggest that before embarking on such a design that you read what the relay
manufacturers have to say about transient suppression (hint, a diode across the coil isn't the
recommendation)."
http://relays.tycoelectronics.com/appnotes/ has a series of app notes: The first one (application of
coil suppression with DC relays) is a good one, as is the "Coil suppression can reduce relay life"
They recommend either a suitable zener across the transistor (so that the voltage doesn't exceed
the Vceo breakdown) or a resistor. Typically a 20-30 V zener is appropriate. Some commercially
available driver devices include the zener, or have the output transistor designed to tolerate the
breakdown (the latter is particularly common in electronic ignitions, where you have a 400 V
transient to deal with)."
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Last Modified By: Administrator, Friday, August 08, 2008
http://kc.flex-radio.com/KnowledgebaseArticle50164.aspx
Thursday, July 23, 2009