Aurora - initial IMD Testing

Mike-VA3MW

Just ran an IMD test on the Aurora transmitter—results were excellent.

With IMD3 better than 50 dB down from the carrier, Aurora shows some of the cleanest transmit performance available. The spectrum was impressively quiet, with minimal adjacent signal artifacts—exactly what you want in a high-performance setup.

The top panadapter is the transmitted signal before final RF filtering. The lower is a separate receiver.

(not done with it yet —- still a work in progress)

As a comparison:

Transmitter / Rig	IMD3 Worst‑Case (ARRL Lab)
Typical HF transceiver	–25 to –30 dB
High‑end amateur gear	≤ –40 dB (rare)
Aurora transmitter	< –50 dB

Mick W8BE

What are the results if you disable APD?

Mike-VA3MW

I don’t have a slide for that at the moment, but it is still very good.

Trucker

I was under the impression that the Aurora transmitter needed APD to function properly and not generate unwanted spurs. And from what I "think " I remember from one of the videos, it cannot be disabled. I for one, wouldn't want it to be easily disabled if it will generate unwanted spurs. It would make it something that could possibly be disabled by accident.

James

WD5GWY

Mike-VA3MW

I actually have a seen it operating with it off and it is still about -40db down, which is still amazing.

Trucker

For a class D transmitter that is pretty good. I will have to go back and see if I can find the video that I thought mentioned that the Aurora transmitter needed Pre-Destortion to operate cleanly.

James

WD5GWY

Mike-VA3MW

No need to dig up that old email—those messages really just capture thoughts and ideas from the early stages of the design process.

As development moves forward toward production and shipping, a lot evolves. Requirements, priorities, and even features can shift based on daily discussions and ongoing evaluations. That’s actually one of the big advantages of working with a small, agile engineering team—we’re able to adapt quickly as things develop and improve.

Trucker

So, you are saying that the transmitter will be as clean as the 8600M I had without Pre-Destortion enabled? The "video " ( not email) I recalled was the one that you and Steve Hicks )along with several YouTube people), were in that was made shortly before the official announcement of the Aurora radios. Also, one of the documents on the Flex Radio website indicates that the Aurora transmitter needs Pre-Destortion in order to function properly and have a clean signal. Does that indicate a design change has been made to the transmitter since the announcement and demonstration at Xenia?

It is going to be interesting to see how well actual production radios preform compared to what has been shared so far. I am looking forward to receiving my AU-520M . Hopefully, it will not be a long wait. ( getting old you know)

James

WD5GWY

Mike-VA3MW

Hi James,

Great questions – and I appreciate your careful attention to the details and your memory of that early video with Steve and the crew. You're spot on that those were some very preliminary glimpses into what would eventually become the Aurora series, and like you said, things have evolved a bit since then.

At this stage, I wouldn’t hang my hat on anything as being final. 😊 All the information we’re sharing right now is simply meant to give a sense of the progress we’re making—no promises or guarantees just yet. The design and performance characteristics are still very much under active development, and naturally, that means things can and do change as we move closer to full production.

Regarding Pre-Distortion and transmitter cleanliness—yes, early documentation may have indicated certain dependencies, but that’s also part of the ongoing refinement. Our engineering team is continuing to evaluate what’s necessary to meet our performance goals without introducing extra complexity for the end user. Whether or not Pre-D is required for optimal transmit performance may still shift before final release. Again, it’s all in motion, and we’re taking a careful, measured approach as we work to ensure that Aurora lives up to expectations—especially for folks like you who know what clean TX should look like, having run a 6600 or 8600M.

We're just trying to be as transparent as we can along the way, even though it means sometimes saying, "this may change." I know that’s not always satisfying, but it’s honest—and we’d rather set realistic expectations now than walk anything back later.

Totally understand the excitement and the wait—especially with a radio like Aurora on the way. We’re eager to get it in your hands and truly appreciate your patience and continued support.

What order group are you in?

73,

Trucker

I returned my 8600M a couple of weeks after receiving it. I applied the refund and paid the difference in full just a few days after the official announcement at Xenia. The only thing I owe now is the sales tax that I was told would be collected upon notice of shipping. I think that puts me in the first group of buyers. I am hoping for an early Christmas present! If I get the urge to operate a Flex radio, I have a 5000A to hold me over till the Aurora finally ships. Thank you for the explanation. It really does help.

James

WD5GWY

Trucker

Mike, I placed my order on May 22nd the day after my 74th birthday. So, I hope that puts me in the first group as I received a paid in full notice a few days after my 8600M was evaluated for return and refund. Which I requested that the refund be applied to the AU-520M I ordered. Once that was completed, I paid the balance in full ( not counting sales tax as mentioned previously). Fun times ahead!

James

WD5GWY