Amplifiers by pass relays

High power amplifiers by pass relays

by F1FRV

Rev 2: november 2010

These relays are only to be used for output power which exceeds conventional antenna relays specifications. Unfortunately for us, the most powerful "plug and pay" we are able to find in amateur equipments supplies are the Tohtsu CZX-3500 (~145 Euro in germany), or the HCS_3000_144_2Z (~290 Euro in Hungary). Dont forget to chose the connectors adapted to your power, see HERE.

Up-to 5 kW @ 30 MHz or 2.5 kW @ 144 MHz, the B1B is an acceptable low cost solution to carry the power.

For more than 5 kW @ 30 MHz or up-to 5 kW @ 144 MHz, the B2B is the only one able to carry the power.

This universal version is for use either with my triode or tetrode logic boards, with transmit position by grounding a 24/27 V DC on the command terminal, OR for use in any other amplifiers, with transmit position by applying a +5V DC (minimum) to +50V DC (not critical) on the command terminal.

It is mandatory to have a permanent +24/27 V DC supply to operate. This is the major inconvenience, compared to conventional antenna relays, which can bypass the amplifier without any supply. But at more than 1.5 or 2 TRUE kW, it is not so easy to find fast switching and reliable antenna relays at affordable cost...

Printed circuit board is single side only, with large pads and traces, for easy realisation by the average amateur who knows that ferric chloride etchant is not made to be drinked, even shaked in exotic cocktails.

As relays are not "coaxial", SWR compensation in by pass line shall be made at the highest working frequency. This is done with a capacitor between the by pass branch and ground, which compensates relays inductance. This can be checked with a SWR meter or, better, with a network analyser.

NOTA: As 24/27V DC supply is with negative at ground, this is not applicable AS IT IS to R-140 amplifiers.

The vacuum relays used (SPST)

The "system"

Measurements

Real SWR is less than measured, as measurements where made with old very low quality PL259 connectors, and ~3 cm of unshielded cable at each relay terminal. These relays seemed usable up to VHF, tests with high power will have to confirm....

Alternative up-to 5 kW @ 50 MHz

Alternative up-to 5 kW @ 50 MHz or 2.5 kW @ 144 MHz is to use changeover vacuum relays, either russian, american or german made. With these relays, flexible connections are mandatory, to not break glass or ceramique casing. Coaxial used shall accept full power. It can be 1/4" or 3/8" flexible PTFE corrugated semi rigid, to reduce size, and have good flexibility. At low frequencies, copper braid of adequate C.S.A.is OK.