Continuation of the thread "Diversity Reception for the 6700".

  • 1
  • Question
  • Updated 3 years ago
The way I understand the diversity reception in the 6700 is that it is an analog process relying on an individual’s brain to combine two analog signals (one in each ear) to produce a perceived signal amplitude improvement. This seems to work as designed for SSB and CW signals, that are decoded by the listener’s ears but does nothing to improve the decoding of digital signals like RTTY, JT65, JT9, etc. With all the processing power in the 6700 would it be feasible or reasonable to do digital diversity reception by summing the two SCU digital outputs into a single analog audio signal and a DAX data stream for the digital data decoders (MMTTY, Wsjt-X, etc.). If not possible in the 6700 then maybe it could be accomplished externally using the DAX IQ data streams, and then sent to the decoder programs. If digital summing can be accomplished then it seems to me that you could also take the difference of the two SCU data streams and cancel the local ambient RF noise by limiting one SCU’s antenna reception to the local area (very poor antenna, dummy load, long lead to a ground, anything except a good “distance” antenna). I have a very high RF noise floor here and would like to be able to control it if possible.
I know the government and some commercial companies do active RF noise canceling mostly on targeted interference signals, so it is possible to accomplish. I just don’t know if it can be done with the 6700. I’m also pretty sure the Flex coding engineers can handle this problem, but there has not been much talk about this for more than a year. (Or maybe I missed it, getting old does funny things to the brain).
I also know that this is not easy to do. I’m just thinking out loud here, does anyone have any comments or suggestions along these lines.
Photo of Al

Al

  • 160 Posts
  • 9 Reply Likes

Posted 3 years ago

  • 1
Photo of Ken - NM9P

Ken - NM9P, Elmer

  • 3823 Posts
  • 1164 Reply Likes
There are many, many, things that CAN be done with a 6700. They just have not written the software yet. Stay tuned! The future holds a lot of interesting things. But we can't have it all at once.

A member of our local ham club is in IT. One of his mottos is: " You can have it fast, good, or inexpensive...pick any two!"

My guess is the same is true in the world of SDR.

Ken - NM9P
Photo of Walt - KZ1F

Walt - KZ1F

  • 3040 Posts
  • 640 Reply Likes
It's called 'the golden triangle' Ken.
For any software release an organization can control
Features included
Number of people working on it
Release date

But not all three
Popularized in the Agile development process as development managers have long held the notion they somehow could control all three
Actually in Agile the managers are largely removed from the process.
There is a very good chapter on DR in the new ARRL publication 'Propargation and Radio Science'.
(Edited)
Photo of Ross - K9COX

Ross - K9COX

  • 334 Posts
  • 100 Reply Likes
(Edited)
Photo of Walt - KZ1F

Walt - KZ1F

  • 3040 Posts
  • 640 Reply Likes
Here's what I don't understand, maybe it is as simple as I am describing. In the aforementioned book and chapter, the argument is made that at any given reception site, regardless the polarity of the transmitted signal, the received signal has both a vertical as well as horizontal polarization component. That the receiving antenna is vertical or horizontal means part of the received signal is lost. Therefore, the DR that the 6700 addresses is diversity polarization, as opposed to, largely what the book talks about, geographic DR.

Whether one transmits on a tribander, LP, trapped dipole, the section that is resonate on that frequency will radiate the signal, those parts not resonate, won't. Therefore:

If you had a monobander, trapped dipole, LP or whatever and T'd it with an antenna of the opposite polarity and ran it to the radio with a single coax, wouldn't the net effect be DR? One might say, of course but that would be for receive only. My question is this, much as the LP, trapped dipole, tribander, with any given transmitted frequency would have non-radiating sections, if you had an LP T'd with a vertical wouldn't the radiated signal be from the LP and the beverage simply would be passive, however, in receive mode you'd hear the circularly polarized product of the two different polarization antennas?

As I mentioned in a separate thread, what I am waiting for is for FRS to implement geographic diversity, which should work on a 6500 as the second signal would be arriving via UDP, not a second, receive only, antenna.
Photo of Mark Erbaugh

Mark Erbaugh

  • 371 Posts
  • 32 Reply Likes
I am reading the new ARRL book, Propagation and Radio Science, and the author, a plama physicist, argues that radio waves refracted by the ionosphere are actually circularly polarized, due to interaction with the earth' magnetic field, which is why they can be received by either horizontal or vertical polarized antennas. What is important is the direction of rotation. Depending on the phasing between your horizontal and vertical antennas, the antennas circular (or eliptical) polarization could match or be opposite the incoming wave, resulting in enhanced or degraded reception. The suggestion in several places in the book is that as amateurs we should experiment to see what is actually going on.
Photo of Walt - KZ1F

Walt - KZ1F

  • 3040 Posts
  • 640 Reply Likes
Yes Mark, that is why I said, seems to me 2 in-phase antennas, one vert one horizontal, should do precisely what the 6700 DR does except it would be in both ears not stereo in each ear. But it was an experiment. Plus a simple switch could change the phase just as in satellite work.  I posted a thread about it after I downloaded it, that was several weeks ago. I don't mean that to sound snarky Mark, I just ponder the downside of mating the two antenna with a T, two coax in, one coax out. I am thinking the initial reaction will be that will completely screw up your swr, but LPs and trapped dipoles seem to resonate fine. I recall when I was interested in satellites back in the late 80's, you could switch polarity to whichever sounded 'better'. So the essential question was, can one accomplish pretty much precisely the same thing with a 6300 or 6500? (with or without a polarity reversing switch).
(Edited)