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Author Topic: Question concerning Diversity sdr choice  (Read 1365 times)

sdruzer

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Question concerning Diversity sdr choice
« on: April 12, 2020, 1634 UTC »
I have a technical question and am looking for advice to decide which "path" to take:

First, the present "operating conditions":

I am currently using an Elad FDM-S2 sdr. My main interests with the unit is reception below 500khz, but I also enjoy HF. In my many years in this hobby, this Elad is the best rx I've owned. I'm very pleased with its performance. Here are the only listed specs on it I could find:

MDS: -132dBm@14MHz, Clipping level: -8dBm
FDM-S2 is a direct sampling receiver based on 122.88MHz 16bit single channel ADC converter

Ok, now I'll state what I'm looking for. I wish to experiment with diversity reception... mainly for use in noise cancellation. I have an excellent rx location, but it's plagued with severe powerline "buzz". It's not an option to get the utility company to fix it. The blankers in the hdsdr software clean up 95% of it but then cause problems when there are strong signals on a nearby freq. So, I'd like to use noise cancellation to avoid the use of blankers.

I understand that Afedri makes a nice dual input sdr that can be used in dual channel mode to cancel noise. That unit runs approx. $360. Here are the specs I found on it:

Dual 12- bit 76.8 MSPS A/D conversion
Sensitivity -  MDS -136 dBm at 500Hz bandwidth

At just a "glance", it would seem that the Elad would be an overall better performer since it's 16 bit compared to the Afedri at 12 bit. Of course, I know that things in the technical realm aren't that simple and that other factors come into play.

Everyone in the hobby tries to "save a buck", and of course, I'm no exception. Here's what I'm getting at:

I could purchase the Afedi and accomplish the noise cancellation goal, but then I may not experience the overall performance that the Elad has. I had an idea. I could also purchase a used Elad just like the one I'm presently using, and if possible "lash up" the two receivers software-wise into the pc to accomplish the noise cancellation goal. I could probably get the used Elad for roughly $250 thus saving roughly $100 over the Afedri purchase. Of course, this path is dependent on the ease or the possibility of actually making the dual Elads accomplish the task.

So that's the two paths ... anyone care to add input on this situation?

 

Offline Josh

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Re: Question concerning Diversity sdr choice
« Reply #1 on: April 12, 2020, 2141 UTC »
The 16bit will have it all over the 12bit rx. As to the noise, is there a local ambc station you can complain to about the power line noise covering their signal? If so, they will have a lot more pull at getting things fixed than you might.
:D
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sdruzer

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Re: Question concerning Diversity sdr choice
« Reply #2 on: April 12, 2020, 2207 UTC »
Josh, I wasn't sure if the higher bit rate was the absolute standard of performance for an sdr. The design of this Elad is probably 5 yrs or more old, and I was considering if the Afedri may have done things a different way with newer technology/hardware to "make up the difference". In any case, I sure don't want to give up performance in any area of specifications.

On the line noise, I feel that it isn't really the time to complain about noisy radio reception given the current medical situation. Besides, I'd like to be able to control a noise problem from my end of things no matter if they fix the problem or not. There will always be another source of noise to deal with if one is fixed. Thanks for your idea though.

I had looked into simple circuits posted on the 'net to cancel noise, but have always felt that it would be best not to use an "outboard"  method, and that the dual rcvrs would probably provide better cancellation.
« Last Edit: April 12, 2020, 2237 UTC by sdruzer »

sdruzer

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Re: Question concerning Diversity sdr choice
« Reply #3 on: April 13, 2020, 1719 UTC »
Well, I've found the answer to the question:

Can you simply use two receivers "slaved" together for noise cancellation? The short/uncomplicated answer is no. One must use an sdr capable of coherently using two ports together such as the Afedri mentioned or the RSPduo.

So, here's the direction I'm going to take at this time:

I'm not satisfied that either of these two sdr's offer the over-all performance of what I'm currently using (the 16-bit Elad), so I don't want to compromise in one or more areas of reception to gain the noise cancellation feature. I'm going to hold off purchasing another sdr until the technology advances somewhat... offering at least a 16-bit unit with the noise cancelling ability, at a price-point of the Elad. May have to wait a few years or so.

I can inexpensively experiment with an "outboard" noise cancelling kit such as offered by VK5TM. I'm sure it won't deliver the cancelling performance of the previously mentioned sdr's, but if it gives me just a few S-units of noise reduction, the low cost will make the investment worthwhile.