Re: One question only...

Timothy Fidler
 

one 74LS42 with bcd firing from the three output ports assuming they are TTL compatible  and  say 5 BS250s P channel (or four given the number of  relays now available)  say 80 40 20 and 10 mtr  BPF drivers) small signal Mosfets for switch on zero, (or a ULN 2003 (30c US at Futurlec.com in one off qty)..

Say total cost $1.50 could have put a stake thorough this demon...KISS ?? of course it is board space and cost that drives these decisions.

Alternative for physical relays for switching RF up to say 6W level in 50 z impedance circuits...

 a possibly foolish thought for likes of Kees and Ashar F  for any weakware rework concept.. if you fire the gate of a 2N7000 N mosfet  and drive it hard on from an isolated 10V dc supply* with a limiting resistor and a decent say 1mH mini inductor in both the  supply and return legs of the 5V psu - will the thing pass RF as if it were a small signal relay contact ?  RDS fully on for above part approx 1.2 ohms.

* homemade with a Hartley osc design to reduce the snap and crackle.

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