Re: Need help with technical question


Stephen Melachrinos
 

Rick -

That's an interesting topic. I hadn't ever paid attention to this type of device, but you ask a very good question.

First of all, I looked at all of the reviews of the product on eHam, and I found very few mentions of any specific modulation type at all. And when a modulation was mentioned, it was either CW or SSB--amplitude modulations. No one reported using the -1026 on any phase or frequency modulation, let alone one of the PSK variants.

Second, I looked at the MFJ product page on their web site. It says "It works on all modes -- SSB, AM, CW, FM". PSK is conspicuous by its absence.

Third, I reviewed the -1026 Instruction Manual from the MFJ web site. It says there are two operating modes of the device--one to null out noise or an interferer, and an alternate to improve the reception of a desired signal. I haven't studied the theory of operation, but it sounds to me like the nulling process adjusts the phase and amplitude of the noise/interferer without concern to the primary signal. The only objective in this mode is to zero out (as much as possible) the offending source. That mode is likely to distort a PSK signal, though the amount of distortion would depend on the strength of the interferer being cancelled. I was going to say that it might be like multipath distortion, but that would include changes in path delay, and I doubt if the -1026 makes that adjustment. Perhaps it might be more like the phase distortion we sometimes get with pure polar paths, where the PSK signal seems strong enough to be decodable but the phase is floating all over the place.

In the "improve the reception of a desired signal", it's possible that the operator may be able to adjust the phase of the combining in a way that preserves the phase of the PSK signal. You might not null out the interferer completely, but the phase and amplitude settings that optimize the desired signal are likely to be at least partially destructive to the interferer.

Fourth, I looked through the entire Instruction Manual and found no reference to modulation types. 

So I don't have a real answer for you. I am concerned enough, though, to be skeptical. I'd suggest two things:

- Send a question to MFJ, asking about operation with PSK31. Page 14 of the Instruction Manual lists ways to contact MFJ with technical questions (email, phone, fax, paper).
- Also, post a question on a larger forum, like QRZ or eHam. I think the fact that no one on this reflector has said anything yet is an indicator that none of us in 070 have any experience with the -1026. It can't hurt to ask a larger audience--you might find someone.

And let us know what you find out.

Steve
W3HF



-----Original Message-----
From: Rick - N7WE <n7we1980@...>
To: 070Club <070Club@groups.io>
Sent: Thu, Apr 11, 2019 8:16 am
Subject: [070Club] Need help with technical question

They say there are no "dumb" questions, but this is probably very close!  I need help from someone who has a lot more technical understanding than me!

There are RF noise cancelling devices on the market like the MFJ 1026, that supposedly reduce RF noise (both local and distance) by using two antennas and shifting the phase between them to null out the noise before sending the "processed" signal into your transceiver.  And I'm talking RF, not the audio frequency DSP stuff like ClearSpeech and bhi. 

I think I understand the basic concept of operation.  But here's what I don't know.  Will that phase processing alter Phase Shift Keying modulation on the desired signal making PSK undecodable?  I understand how it can work on Amplitude or Frequency modulation. But before I plunk down $200 to try one of these devices, I'd like to make sure it is suitable for use with PSK.  And I just don't know enough radio theory to have a guess!  

Any experience, thoughts, advice?

--
Rick - N7WE
070 - #1602

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