What causes a "Return loss fault?"

Bill M

I was working FT8, and my aurora 510M stopped transmitting, with a notice of a "return loss fault." It had been transmitting perfectly, and the ATU showed an SWR of less that 1.5. What could have happened? I also noticed a faint electrical insulation burning smell….?

KD0RC

Hi Bill, I would submit a help desk ticket before operating it further.

Mark_WS7M

Hi Bill,

My 2nd replacement AU-510 did that 30 minutes after receiving it. Also doing FT8. I had run like 10 minutes at full power then backed the power down to 300w. A few minutes later no RF out, ATU would not tune etc.

This was a brand new radio that had gone through a burn on.

Flex was gonna replace it with another but they have some supply chain issues. So I sent it back for repair. It was at the shop over a month. Here is the report given by the tech in the ticket:

Findings:

• Confirmed the reported issue: the radio was not operating properly and was not outputting any power.
• Further inspection identified a faulty coaxial cable on the balun connecting the PA and LPF boards.
• The radio also required recalibration.

 
Actions:

• Disassembled the radio to access its modules.
• Performed a visual hardware inspection and removed dust from the radio.
• Replaced the RF coaxial cable on the balun connecting the PA board to the LPF board.
• Reassembled the radio.
• Performed the necessary factory calibration, including PA Soak, PA, LPF, ATU, and ADC board-level testing and calibration.
• Loaded firmware version 4.2.20.
• Performed functional tests.
• Left the radio running overnight in receive mode.
• Performed final tests and checks this morning.
• Performed a factory reset.

A couple of interesting notes on this report:

"The radio also required recalibration". This was new out of the box, run for only like 30 minutes. So I can only guess if the coax is replaced it needs re-calibration.

"Performed a visual hardware inspection and removed dust from the radio". I'm sure some dust could have accumulated, but it was basically sitting int he basement awaiting a replacement. So not sure how dirty it could really get.

Anyway I expect to receive it back today and will give it a test later or or early Tuesday AM.

Bill M

Thanks, Mark. That is a fair description of my problem. I am glad I am not alone. I really like the radio, and hope that it can be fixed quickly. I had a much smaller problem with it right away, and they shipped me a new one…which now won't transmit.

Bummer.

Trucker

It sounds like quality control is having a problem. I am surprised that they didn't do an extended key down test to make sure that the problem found actually did fix issue after an extended transmit time. I have not tried any modes that would stress the finals like the hours on end demonstration that Flex does to promote the Aurora radios. But, I would be pretty upset if my AU-520M wasn't capable of extended transmit times.

James

WD5GWY

David Decoons, wo2x

First, make sure you are setting TUNE power on Aurora to 3 (slider is in percent, which is 15 watts). To this for both internal and external tuners

Note on Return Loss. Unlike traditional class AB transmitters in the 100 watt Flex radios, the Aurora PA is more sensitive to the reactance the radios sees from the antenna and feelline. If you have an antenna analyzer that can show the complex (reactive) numbers, like R 35 X 24 then take a look at what the antenna shows on the band you are receiving the Return Laois failure on. If the reactive number (X) is poor, the ATU may still tune it but the radio will fail with High SWR or Return Loss errors. This is due to the design of the Polar Modulation transmitter being more sensitive to poor reactance (low reactive impedance, poor X).

I have seen this with customers using a V5RV antenna with very short lengths of coax. The design of the 102 ft G5RV calls for at least 50 feet of 50 Ohm coax.

if your antenna has a poor reactive impedance try adding some 50 Ohm coax between the radio and existing feed line.

Last, the ATU will tune to provide a good load for the transmitter. It can tune higher than 3:1 SWR but that condition presents higher voltage and currents in the TX band pass filter and ATU. This can cause heat build up in components.

73 Dave wo2x