Technical Articles:

1 KW 6 Meter LDMOS Amplifier
2 Meter 80W All Mode Amplifier
1 KW 2M LDMOS Amplifier
1 KW 222 MHz LDMOS Amplifier
500w 70cm Amplifier
1KW 70cm LDMOS Amplifier
A Big Power Supply for SSPAs
Low Pass Filter + Dual Directional Detector
Sampling RF Power
Amplifier Control Board
LNA Sequencing and Protection
LED Bar Graph Meter
Building UHF Antennas
MIcrowave Marker
Crystal Oven Controller
Microwave L.O.
Latching Relay Driver
12 to 28v
Relay Sequencer
High Current DC Switch
L & S Band LNA
Microwave L.O. Filters
Using Inexpensive Relays
PC Board Filters
600w 23cm LDMOS Amplifier
XRF-286 Amplifiers for 23cm
150W 23CM Turn-Key Amplifier
300w 23cm Amplifier
200w 23cm Amplifier
100w 23cm "brick"
100w 23cm Transverter
60w 23 cm Amplifier
23 CM Beacon
23cm Signal Generator
23cm Double Quad
23cm filters
13cm filter
13cm Signal Generator
13cm Transverter
120w 13 cm Amplifier
300w 33cm Amplifier
33cm filter
33 cm Crystal Source
33cm Signal Generator
9cm Transverter
Transverter Selector
12 AND 28 volts
Klitzing Amplifiers
IC-910H tweaks
Audio Files
Parts and Kits I Can Supply
Current Projects

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Relay Sequencer

A sequencer is the key to protecting those expensive microwave or other antenna relays from hot-switching (which destroys the contacts). There is an additional description of a sequencer in the 300w 23cm amplifier article listed on the left.

This sequencer is even better, and will handle up to 4 events; one output is able to sink up to 100v at several amps, and the remaining 3 up to 40v at about 500 ma each.

Typically, one would have the high-capacity port switching the antenna relays, and the others handling amplifier, transverter, or radio switching. The outputs are protected from transient spikes, and the delay is adjustable from a few milliseconds to about one second. LED indicators allow a visual indication of timing on initial set-up.

One additional capability is useful to anyone using a radio that has a transmit inhibit feature (like the FT-897 or FT-817). These radios will hold off RF while an accessory pin is held high. Any of the outputs on this sequencer will do that...the LED feed resistors supply a 12v pull-up potential until pulled low by the sequencer. This not only turns on the LED, it also supplies the required signal for the inhibit feature of the radio. If you have a radio without an inhibit feature, check the work of WA7TZY; he was able to adapt it to his FT736R, which does not have an inhibit feature.

This is the schematic (click the thumbnail to enlarge)