[GreenKeys] Selective Fading Experiment

[W2HX]

 Yeah, I was just wondering if any one of the streaming guys tried to "sum" two streams, and if I pointed my TU to a stream with both 170 and 850Hz shift audio in the same stream, what would happen? Could I use one stream and just select the shift on the TU and would it work? This would seem different from multiple channels where the audio frequencies are separated and never use the same audio spectrum. Whereas my question the two channels share the same audio spectrum. Just a thought experiment, really.


73 Eugene W2HX
My Youtube Channel: https://www.youtube.com/@w2hx/videos
 

-----Original Message-----
From: Harold Hallikainen <harold at w6iwi.org> 
Sent: Sunday, January 12, 2025 7:11 PM
To: Jeff G <jeffg at junknet.net>
Cc: W2HX <w2hx at w2hx.com>; harold at w6iwi.org; Green Keys <greenkeys at mailman.qth.net>
Subject: Re: [GreenKeys] Selective Fading Experiment

That's an interesting system with multiple channels each with pretty narrow shift. Another one is at https://www.navy-radio.com/rtty/ucc1/ucc1-sys-101.jpg which uses wide shift (about 1.5 kHz). Based on my experiment, I don't think anything within the FCC allowed 900 Hz shift will do much as far as frequency diversity. Everything fades almost simultaneously. So, space diversity or redundancy with error detection seem to be the best approach. To maintain compatibility with standard heavy metal RTTY, space diversity seems best.
And, since the multipath signals are not identical level, there is not a complete cancellation of the receive signal. The near cancellation just takes the received signal below the noise. More transmit power can make the near cancellation be above the noise.

Harold
https://w6iwi.org

On Sun, January 12, 2025 3:54 pm, Jeff G wrote:
> At the ship, we have at least one 16ch multiplexer that still seems to 
> be intact enough that it might do something. I'd have to go back 
> through my pics to see what the ID on it is, but it has 16 "cards" 
> each with adjustable m/s freq.
>
> Found it - this guy: https://www.navy-radio.com/rtty-mux-ucc1.htm
>
> Jeff KC3GJX
>
> On Sun, Jan 12, 2025 at 5:22 PM W2HX <w2hx at w2hx.com> wrote:
>
>> Has anyone ever tried combining two different shift streams into one? 
>> In other words, four tones in one audio stream? Would it allow one 
>> stream to work for two different audiences (say 170 shift audience 
>> and 850 shift audience)?
>>
>>
>> 73 Eugene W2HX
>> My Youtube Channel: https://www.youtube.com/@w2hx/videos
>>
>>
>> -----Original Message-----
>> From: greenkeys-bounces at mailman.qth.net 
>> <greenkeys-bounces at mailman.qth.net>
>> On Behalf Of Harold Hallikainen via GreenKeys
>> Sent: Saturday, January 11, 2025 10:14 PM
>> To: Green Keys <greenkeys at mailman.qth.net>
>> Subject: [GreenKeys] Selective Fading Experiment
>>
>> I ran an experiment comparing signal levels and fading with 850 and 
>> 170 Hz shift by transmitting four frequencies at once and seeing if 
>> they all faded together. My notes are at 
>> https://w6iwi.org/rtty/SelectiveFading/ .
>>
>> Harold
>> https://w6iwi.org
>>
>>
>>
>>
>> --
>> Not sent from an iPhone.
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