Hi Mike, KB8ZGL
A sequencers provides that preamp switchover occurs before power amplifier turn on by first removing the preamplifier control voltage and then providing a relay closure to key the PTT line of your linear amplifier. This insures that hot switching which could damage the preamp relay contacts or destroy the GaAsFET does not occur.
In other words when you are receiving the antenna is connected to the preamplifier input.
When you push the PTT to transmit first of all the antenna must be switched to the TX line and only then after a 1/2 second delay time the transceiver and the amplifier must go ON
Doing that no sparks of RF can occur on preamplifier and linear amplifier relays contacts during the sequence RX to TX switching and TX to RX switching.
The above delay time of about 1/2 second allow the antenna and amplifier relays to switch ON and OFF in about 20 milliseconds without RF current applied to the contacts.
Without the delay time provided by the sequencer the RF current applied to relay contacts during closing and opening will burn the relay contacts itself and will destroy the GaAsFET preamplifier.
http://www.ssbusa.com/seqcon.html
A description to fully understand how to build a good sequencer how it works and how it must be connected to antenna- preamplifier- driver and power amplifier has been published in THE ARRL HANDBOOK for Radio Amateurs 1991 by Chip Angle N6CA Chapter 31 " TR Time-Delay Generator " pages 9 to 12
I have built it and I am using it with great results to switch the antenna from my GaAsFET preamplifier to a 600 watt power amplifier for 1296 MHz
73" de
i8CVS Domenico
----- Original Message ----- From: "Michael J. Wolthuis" [email protected] To: [email protected] Sent: Sunday, May 01, 2011 2:45 AM Subject: [amsat-bb] Question on layout for new preamps
I am adding UHF and VHF preamps to my Satellite setup and I am trying to make sure I know the right order of components...
Here is what I think is right for VHF:
FT-847 --> VHF AMP --> SWR Meter --> SEQUENCER --> PREAMP --> Antenna
Is that right or does the SEQUENCER go before the AMP?
For UHF, pretty straight forward I think:
FT-847 --> SWR Meter --> SEQUENCER --> PREAMP --> Antenna
Note the SSB Sequencers provide power to the SSB Preamps also, which is why I guessed on V it went after the AMP and the SWR Meter.
Thanks for checking it out before I wire it all up.
Thanks, Mike kb8zgl