# Replacing relays with solid-state devices at RF?

#### kevinz

Joined Oct 26, 2022
2
Hello,

I'm working on a microprocessor controlled antenna matching system, or tuner. It consists of a number of inductors and capacitors switched in and out of the signal path with relays. See the attached file.

The advantage of relays is that they add almost no inductance, capacitance or resistance to the signal. The disadvantages are that they're electromechanical devices with moving parts that can fail. They also cost about $2USD each. Could the relays be replaced in this circuit with semiconductor components, and still work at the 3-30MHz frequencies required? If so, where would I go to learn about the techniques of designing such a circuit? Thanks for your help and advice. -Kevin #### Attachments • 57.6 KB Views: 33 #### sagor Joined Mar 10, 2019 786 You could look up PIN diodes, but I suspect the circuit to run those and the overall cost may be even more than relays. A lot depends on how much power you plan to pass through the relay. In the milliwatt range, PIN diodes may be effective. #### ZCochran98 Joined Jul 24, 2018 221 PIN diodes, like what was said, or SPDT RF switches designed for a minimum frequency <3MHz may satisfy what you need (maximum frequency doesn't matter as much). Depending on the switch (especially based on frequency or power requirements), they can be super cheap or rather expensive. That "low" of a frequency range is going to be a bit hard to find nowadays, unless you find one with a low frequency cutoff <1MHz. #### Gussie60 Joined Oct 7, 2022 2 Hello, I'm working on a microprocessor controlled antenna matching system, or tuner. It consists of a number of inductors and capacitors switched in and out of the signal path with relays. See the attached file. The advantage of relays is that they add almost no inductance, capacitance or resistance to the signal. The disadvantages are that they're electromechanical devices with moving parts that can fail. They also cost about$2USD each.

Could the relays be replaced in this circuit with semiconductor components, and still work at the 3-30MHz frequencies required? If so, where would I go to learn about the techniques of designing such a circuit?

-Kevin

#### Gussie60

Joined Oct 7, 2022
2
I’m not an expert, but would a CD4066B CMOS Quad Bilateral Switch work as your relay replacement? I’ve used these with PWM signals for controlling stepper motors, and the signals seem to get through without any problems or distortions

#### kevinz

Joined Oct 26, 2022
2
I’m not an expert, but would a CD4066B CMOS Quad Bilateral Switch work as your relay replacement?
@Gussie60 , thanks for your reply. I wasn't able to read the datasheet throughly, but typically, these devices don't work well for connecting high frequencies (3-30MHz) through the switch. I'll read the datasheet in depth when I have time.
Thanks, again.
-Kevin

#### drjohsmith

Joined Dec 13, 2021
546
Hello,

I'm working on a microprocessor controlled antenna matching system, or tuner. It consists of a number of inductors and capacitors switched in and out of the signal path with relays. See the attached file.

The advantage of relays is that they add almost no inductance, capacitance or resistance to the signal. The disadvantages are that they're electromechanical devices with moving parts that can fail. They also cost about \$2USD each.

Could the relays be replaced in this circuit with semiconductor components, and still work at the 3-30MHz frequencies required? If so, where would I go to learn about the techniques of designing such a circuit?

-Kevin
suggest that you spend more than 2 dollars on a relay to get one thats more reliable,

#### Ian0

Joined Aug 7, 2020
6,706