6300 Transverter port status while TX on ANT1?

N7CXI

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.

Thanks,
Jim N7CXI

Jim Gilliam

I was told by the engineer that there was a 60 dB isolation between the ports but no mention was made of the consequences with large amounts of RF coming into the receiving port. This was discussed in another thread regarding the use of full duplexing with a transverter.

N7CXI

Thanks, Jim. 
I'm wondering if the ADC stays hooked to the port during RX when not in a duplex situation. The use cases are similar, but I'd like to get a response on this specific one.

73,
Jim N7CXI

Jim Gilliam

Hopefully Tim or Steve will read this and give you an answer. I have wondered the same thing and expressed my worry regarding this near field problem. No one else seemed to think it would matter. I think your question is a good one and deserves some thought.

Jim

pa0bie

As far as I know , the XVTR port will always give a +/- +6dBm output signal during transmission.

Jan , pa0bie 

N7CXI

Hi Jan,
I'm using the XVTR port to receive. My question has to do with near-field RF from a TX antenna on ANT1 feeding back into the XVTR port from a dedicated RX antenna. I want to make sure the ADC is protected.

I could use ANT2 instead of the XVTR port - the question remains the same: Is the receive antenna port protected while the radio is in TX mode?

73,
Jim N7CXI

Steve-N5AC

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.

N7CXI

Thanks, Steve.
Would it be ok to have my sequencer simply short the RX port during TX? 
I don't currently have a simple means to break-and-switch to a 50-ohm termination, although it's beginning to sound like that would be a good feature for the next rev of the sequencer.

Considering the new 160m RX loop is resonant, 14 feet across and only 30 feet or so from the vertical part of the TX radiator, I would rather be safe than sorry. 

Steve-N5AC

That should be fine, from what I see in the schematic, Jim.

N7CXI

Thanks, Steve.
... and try to get an answer like that from one of the "Big Three".  :-)

73,
Jim N7CXI