Receive antenna on RX port (6600)

Iu4jnr

Hi all,

Is the RX-A Port muted (disconnected) when used on the same slice of TX Antenna?

I connected a Loop on the Ground to my Flex 6600 RX-A port for 160/80m reception but space constrains forced me to lay it down just 10m off TX antenna which is a 160/80m Inverted L.

How safe is the ADC from RF coming from RX antenna when using hi-power?

Max IU4JNR

Dan-N7HQ

Hi Max,

When the RX-A port is selected as the receive port for the same slice used for transmission (e.g., TX on ANT1 and RX on RX-A), the system operates as follows:

1. RX-A is Not Automatically Muted:
   • The RX-A port does not automatically disconnect or mute during transmission. This configuration is typical in configurations using separate receive antennas, such as low-noise loops, for enhanced RX performance.
2. Impact of High RF Power on RX-A:
   • With RX-A selected as the slice's receive antenna, it will remain active even during the transmission of the slice. If the RX antenna is physically close to the TX antenna (e.g., 10 meters away as you describe), the RX path is vulnerable to strong RF coupling, which could potentially overload or damage the ADC during high-power transmissions.
3. System Protection:
   • The FLEX-6600 has robust RF protection circuits, but in such a close proximity with high-power RF, relying solely on built-in protections is not advisable. RF energy coupling through the RX-A port could still exceed safe thresholds under these conditions.

Recommendations to Protect the RX-A Port and ADC:

• Add RF Protection Devices:
  • Use an RX-only RF limiter or RF protection device in the RX-A path. These devices prevent high-level RF signals from reaching the ADC and causing damage.
• Band-Pass Filters:
  • Implement band-specific receive filters to suppress out-of-band signals and reduce potential ADC overload.
• Enable RX-A Isolation (Manual Intervention):
  • While not automatic, you can configure TX inhibit or manually disable RX-A during high-power TX via software controls in SmartSDR to avoid ADC stress.
• Increase Physical Separation:
  • If feasible, maximize the distance between the TX and RX antennas to reduce RF coupling. Even small increases in separation can substantially reduce induced RF levels on the RX-A port.

✔ Pro Tip

Monitor the receiver's Signal Overload Protection status during transmissions using SmartSDR. If frequent overloads are detected, adjust power levels or incorporate additional RF isolation mechanisms. You can use this spreadsheet to determine your risk for overload.

Final Note:

This configuration (RX-A and TX on the same slice) requires careful management, especially with antennas in close proximity. While the FLEX-6600's design accommodates such use cases, safety measures are essential to protect the hardware.

Iu4jnr

Dan,

Thank you very much for your prompt and fully comprehensive answer.

I'm now well aware of risks and i will act accordingly.

I just tested rising up the power on 160m up to 500W and I didn't notice any overload, however as a safety measure i'm in the process of acquiring a protection device.

Thank you very much indeed and I wish you a happy new year.

Max IU4JNR

Dan-N7HQ

Glad to assist, Max. Happy New Year to you as well.

73,