Topband: Pro III rx jack and SEND relay- issues on Top Band-

[Ian & Nerida Miller]

Hi Paul,

I had trouble with the my Icom 746pro send relay when using the rig directly with an amplifier or receive preamps, changeover tx/rx followers that use relays for switching.

The send relay in the rig is a delicate reed relay. It seems to not handle the make and break currents of driving the inductive load of a slave relay in an attached device. I haven’t looked at the circuit of your rx antenna input protector, but if it has a relay coil on it’s control input, that may be the problem.

My send relay would stick permanently closed after a tx over, randomly.  The contacts seem to micro weld themselves closed in this situation. Giving it a physical tap with a screwdriver would release the contact. I replaced the reed relay and the same thing happened with the brand new one.

I cured the problem by building a fet relay switching circuit that drives the amp etc control inputs from the rig send relay. The input current controlled by the send relay is now only a few microamps and I have had no further problems. A 2N2222 fet relay switching circuit, (switching 500mA max) is easy to build and will isolate the send relay from the attached device’s higher input switching currents.

I hope this helps you Paul.

73’s,

Ian VK2BJT