6300 Transverter port status while TX on ANT1?

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  • Updated 3 years ago
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Using a 6300 and SmartSDR 1.3.8 , what is the status of the XVTR port **when transmitting** via the ANT1 port and using the XVTR port for the receiving antenna?

I've been using the XVTR port for my low-band receiving antennas, and also using a PTT-switched preamp that shorts the far end when PTT is engaged. I'm about to change that to a resonant shielded loop with no preamp, which means RF will couple from the transmitting antenna to the loop, then back down to the XVTR port. Is that port shorted or opened (or something) during TX, or left connected to the ADC?

Long story short, I obviously don't want to damage the receiver. I do run QRO, and the loop will definitely be in the near field of the TX antenna on 160 meters.

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Jim - N7CXI

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Posted 3 years ago

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Steve - N5AC, VP Engineering

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Official Response
Several points here: The internal isolation is sufficient to keep RF from causing any issues IN THE RADIO (when you transmit, nothing in the radio will hurt itself).  If you are running a full 1500W and you have an antenna connected to the XVTR line, you should expect that it will be live during transmit (expect it to be connected to the receiver), because even if this isn't the case right now, it could be at some point.  So what you really need to do is measure the coupling between your antennas.  You could put a power meter on your antenna (loop) and measure what is coming back towards the receiver when you are transmitting.  The FLEX-6300 overloads at +7dBm as I remember and can take something around +16dBm before it disconnects the antenna.  

If you're seeing a lot of power come back to the radio during transmit, I would do something to reduce that power level -- moving the antenna, putting a T/R relay in line with it, etc.

There is a power sense/disconnect feature in all the FLEX6000s that prevents receiver damage in most situations.  The test criteria for this feature is to inject 1W into the receiver and have the radio disconnect the antenna and protect itself.  We recently had a radio hit by lightning that shorted the T/R relay and fed 100W into the receiver every time that the radio was keyed (first time we've ever seen a failure like this).  The circuit operated as designed and disconnected the antenna every time the radio was transmitted.  In the time it takes the circuit to disconnect, it also fired the ESD diodes which are inline to protect the ADC from very rapid transients on the antenna, typically caused by electrostatic discharge (ESD) and so they sustained damage also.  The relays and diodes are all cheap so it was a very inexpensive repair -- this is why we put these components into the radio: to protect the expensive $100+ ADCs.