RF Guru
RX Power Disconnect via RCA/PTT
RX Power Disconnect via RCA/PTT
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The RF.Guru RX Power Disconnect via RCA/PTT automatically removes DC power from a receive-only accessory whenever your transmitter keys. Place it between your 12–13.8 V supply and a Bias-T, active receive antenna, LNA, or preamp; connect its RCA control input to a compatible PTT output, and the accessory is powered down for the duration of transmit.
• PTT open / receive: the Powerpole output is powered.
• PTT grounded / transmit: the Powerpole output is switched off.
• PTT released: power returns automatically for receive.
The control input is active-low: it requires a contact, open-collector, or open-drain PTT output that closes to ground during transmit.
Why Disconnect RX Power During Transmit?
Some receiving setups use powered accessories close to a transmitting antenna. Switching those accessories off during transmit can prevent their active electronics from remaining energized in a very strong RF field, reduce unwanted interaction, and make station operation automatic—without a separate power switch to remember.
- Automatic operation: follows your station’s PTT state.
- Solid-state switching: a P-channel MOSFET switches the positive supply rail without relay chatter or contact wear.
- Receive-first default: with no RCA cable connected, power remains available at the output.
- Simple shack wiring: Powerpole DC input and output, plus an RCA PTT control jack.
Connectors & Typical Wiring
| Connection | Connect To | Function |
|---|---|---|
| DC Input | 12–13.8 V DC supply | Powerpole input for the source supply |
| Switched DC Output | Bias-T, active RX antenna, LNA, or preamp | Power is present in receive and removed while PTT is grounded |
| RCA/PTT Input | Compatible transmitter, transceiver, sequencer, or keying interface | RCA center contact to ground switches the DC output off |
1) With the station switched off, connect your 12–13.8 V supply to the DC input.
2) Connect the switched Powerpole output to the receive accessory you want to control.
3) Connect the RCA/PTT input to a control output that grounds during transmit.
4) Test at low power: confirm the accessory is powered in receive and switches off before transmitting at normal power.
The PTT input and DC supply share a common ground; the control input is not galvanically isolated.
PTT Compatibility
Use a PTT/keying output that behaves as a ground closure during transmit. Suitable sources normally include a dry relay contact, open-collector output, or open-drain output. The RCA sleeve is ground and the center contact is the active-low control input.
Protection & Switching
- Reverse-polarity protection: a series protection diode helps protect the unit from an accidentally reversed DC input.
- Resettable input fuse: a 0.75 A hold-class PTC helps limit sustained overcurrent; actual trip behavior depends on load and temperature.
- Protected control input: the RCA/PTT line includes transient clamping.
- Defined off state: the MOSFET gate is pulled to the supply rail so a grounded PTT command switches the output off cleanly.
- Input-power LED: shows that protected input power is present.
The LED monitors the protected input supply; it is not an independent indication that the switched output is on.
What This Unit Does—and Does Not Do
This unit controls DC power to a receive accessory. It does not switch or isolate the RF signal path, detect RF automatically, provide adjustable sequencing delays, or replace a proper T/R switch, receiver protector, RF limiter, antenna relay, grounding system, or lightning protection.
Because the output is normally on, a missing or unplugged PTT cable will not disconnect the receive accessory during transmit. Always verify PTT operation as part of your station checks.
Included
- RF.Guru RX Power Disconnect via RCA/PTT
- Powerpole DC input and switched output
- RCA/PTT control input
- Input-power LED
Specs at a Glance
| Parameter | Value |
|---|---|
| Application | Automatic DC power disconnect for receive-only accessories |
| Nominal Supply | 12–13.8 V DC |
| DC Connections | Powerpole input and switched Powerpole output |
| Output Voltage | Approximately the DC input voltage minus the series protection and switching losses |
| Control Connection | RCA, active-low ground closure |
| Receive State | PTT open; switched output on |
| Transmit State | PTT grounded; switched output off |
| Switching | High-side P-channel MOSFET |
| Input Fuse | 0.75 A hold-class resettable PTC |
| Isolation | Non-isolated; PTT and DC supply share ground |
| Protection | Reverse-polarity protection, resettable input fuse, and PTT transient clamp |
Use only with receive accessories whose voltage and current requirements are compatible with the supply and this unit. The resettable fuse is a protection device, not a precision current limiter.
Mini-FAQ
- What happens when I press PTT? ... A compatible PTT output grounds the RCA control input, and the unit removes DC power from the connected receive accessory.
- What happens when the RCA cable is unplugged? ... The switched output stays on. The unit is normally on in receive and requires a ground command to switch off.
- Can I feed a positive PTT voltage into the RCA jack? ... No. The input is designed for a contact or transistor output that closes to ground.
- Does it disconnect my antenna or RF cable? ... No. It switches accessory power only; RF-path switching or receiver protection must be provided separately where needed.
- Does it include a transmit delay or sequencer? ... No. It follows the external PTT signal directly, so any required timing must come from your station controller or sequencer.
- Is the PTT input isolated? ... No. The RCA/PTT ground and DC negative are common.
- Can I use it with a Bias-T? ... Yes. Place it in the Bias-T’s DC supply lead so Bias-T power is removed during transmit.
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Questions about PTT compatibility or installation? Feel free to contact RF.Guru before connecting the unit to an unfamiliar keying interface.
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