Symmetrical High Power 50-144MHz Relay
Intended to switch two equal antennas to QRO. Possible use is as H / V switch.
Although relay will be perfect to switch antenna to QRO and preamplifier. Intention of High Power 50-144MHz Relay is for switching equal power on “NC (Normally connected)” and “NO (Normally open)” sides. On any place where both sides need to pass high power.It has excellent isolation. Good enough to protect any sensitive device on “other” side.But if you intend to use this relay as switch between QRO and preamplifier i suggest to use more simple design described in this text. You can buy better relay for 5 to 10 times more money, but intention is not to compete with industrial relays. Just homebrew that will do excellent job.
How to make High Power 50-144MHz Relay:
This is about 1 – 2 day task. To make this H/V relay you need: 200 W soldering iron. 60 – 100W to help soldering big surfaces and 30 W soldering iron. Basis is 1 mm copper 145 x 41 mm. Distance between connectors is 55 mm. Although on pictures is unusual combination of connectors it is possible to use any combination of “N” male/female and 7/16 DIN male/female connectors. For instance, we will use cheap Finder or Schrack 12V 16A relays.
You can find Finder 41.61 12V relay here or Schrack RT314012 here. Similarly, you can find Digi-Key relay here.
Mechanical configuration – schematics from Symmetrical High Power 50-144MHz Relay:
How does Symmetrical High Power 50-144MHz Relay – H/V Switch it work?
Most important is to set all capacitors and inductors. Without inductors signal passes through wires and reduces possible isolation between “NC (Normally connected)” and “NO (Normally open)” sides. On every side signal passes through 2 peaces of 16A relays in parallel. Open and short circuits enables very high isolation even with that relays with high capacitance between contacts. Copper parts:
Measured Characteristics using HP8753ES Network Analyzer:
Before the measurement, we performed a full 2-port calibration to make the measurements accurate.
1. S21 (Isolation) measurements and graph – NC (Normally connected) isolation.
| Frequency | Isolation |
|---|---|
| 14 MHz | 100 dB |
| 28 MHz | 95 dB |
| 50 MHz | 90 dB |
| 144 MHz | 75 dB |
| 146 MHz | 75 dB |
2. S21 (Insertion loss) and S11 (Return loss)
| Frequency | S21 | S11 |
|---|---|---|
| 14 MHz | 0.01 dB | – 39 dB |
| 28 MHz | 0.01 dB | – 33 dB |
| 50 MHz | 0.02 dB | – 28 dB |
| 144 MHz | 0.1 dB | – 19.5 dB |
| 146 MHz | 0.1 dB | – 19.5 dB |
3. S21 (Isolation) measurements and graph – NO (Normally open) isolation.
| Frequency | Isolation |
|---|---|
| 14 MHz | 100 dB |
| 28 MHz | 90 dB |
| 50 MHz | 87 dB |
| 144 MHz | 75 dB |
| 146 MHz | 75 dB |
S21 (Insertion loss) and S11 (Return loss)
| Frequency | S21 | S11 |
|---|---|---|
| 14 MHz | 0.01 dB | – 40 dB |
| 28 MHz | 0.01 dB | – 37 dB |
| 50 MHz | 0.01 dB | – 32 dB |
| 144 MHz | 0.06 dB | – 22 dB |
| 146 MHz | 0.06 dB | – 22 dB |
Finished relay may be placed in a waterproof plastic case for outdoor use.
You can find link to outdoor plastic box here.
Measured characteristics are amazing good. Super high isolation and very low losses enables this homemade relay to be used in any high power demand. This cheap 50 / 144 MHz relay as seen has very good characteristics adjusted for amateur use on EME and HF – VHF. There are no need for another isolation relay. This presentation is for amateur use only.
If you are not sure if you can make it you can order from us via e-mail: [email protected]
73 Goran YU1CF
