Sequencers

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Sequencers Tower Mounted Preamps

• Presented by
• Charlie Betz N0AKC

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What is a sequencer?

• A sequencer is a circuit that is used to key
  multiple devices (transverter, amp, relays) on
  and off in a specific order.
• A TR time delay generator

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Why Sequence?

• To prevent RF from being applied to a relay
  before it is fully closed, or opening the relay
  prior to removing RF power. Failure to avoid
  these conditions can result in burned relay
  contacts
• Prevent preamp failure caused by RF leaking into
  it due to relay contacts not being fully closed.

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When Should the Use of aSequencer be Considered?

• When using high powered amplifiers with external
  relays.
• When using mast mounted or other external preamps
  that do not use RF-sensed switching.
• When you need a convenient means of switching
  multiple devices from one key line.

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A Sequencer is Probably Not Required in These
Cases

• Your station consists of a simple setup, such as
  a transceiver and antenna.
• Your station uses brick amplifiers with built
  in preamps.

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The N6CA Sequencer
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Station Block Diagram
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N6CA sequencer potential problems

• If all the devices being switched through the
  sequencer are not running off the same power
  supply, ground loops can result.
• The circuit limits the types of relays that can
  be keyed. 28V relays can be switched, but
  probably marginal. Cant switch AC relays.

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A fix for the N6CA sequencer

• Add a relay stage to the sequencer. The
  sequencer outputs keys an intermediate set of
  relays and the relay contacts are then in turn
  used to control the outside devices.

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To RX ISOLATION RELAY
To TR RELAY
To AMP CONTROL
To XVERTER CONTROL
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Mast Mounted Preamps
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Why Mast Mount a Preamp?

• Mast mounting a preamp preserves the S/N ratio by
  amplifying the signal prior to introducing cable
  losses.

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Remote Preamp Block Diagram
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Mast Mounted Preamps

• The configuration shown in the previous slide
  uses two separate feedlines to the tower
• One feedline for TX
• A separate feedline for RX

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Cable management can become a BIG issue!
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