[GreenKeys] Selective Fading Experiment

[Harold Hallikainen]

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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