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Author Topic: Integral Cycle CW transmission on 2200 meters  (Read 6331 times)

KL7AJ

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Integral Cycle CW transmission on 2200 meters
« on: June 28, 2017, 10:53:57 AM »

One of the neat things about low frequencies like 2200 meters is that you can do some interesting things you can't do at "normal" radio frequencies.   If you key a CW signal PRECISELY at the zero crossing point (integral cycle keying), you don't need to do any waveshaping to restrict the bandwidth.   This is a bit tricky to pull off at higher frequencies, but any decent function generator can perform an integral cycle burst mode at 137 Khz.   I will be experimenting with this as soon as we get our frequency allocation approved.

Eric
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WB8LZR

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RE: Integral Cycle CW transmission on 2200 meters
« Reply #1 on: July 01, 2017, 12:05:31 PM »

One of the neat things about low frequencies like 2200 meters is that you can do some interesting things you can't do at "normal" radio frequencies.   If you key a CW signal PRECISELY at the zero crossing point (integral cycle keying), you don't need to do any waveshaping to restrict the bandwidth.   This is a bit tricky to pull off at higher frequencies, but any decent function generator can perform an integral cycle burst mode at 137 Khz.   I will be experimenting with this as soon as we get our frequency allocation approved.

Eric

That IS neat.   That's exactly what the front-end of the Loran-c 100 KHz receiver has to do (crossover point), as I mentioned in another thread.

A little OT, but I mentioned in yet another thread in this sub-forum that I think SDR will start to be used for low frequency bands like the 2200 meter band.  QRP-Labs has a transmitter good for 2200 meters, that uses the Si5351A synthesizer chip.  The Synthesizer chip is not SDR in the way we normally think about it.  But that same site has an amplifer that uses an ATtiny84 MCU waveshape controller, and that IS SDR (or SDA).   Neat stuff coming up lately ...

Let us know how your experiments work out ...

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G8HQP

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RE: Integral Cycle CW transmission on 2200 meters
« Reply #2 on: July 18, 2017, 12:24:58 PM »

Quote from: KL7AJ
If you key a CW signal PRECISELY at the zero crossing point (integral cycle keying), you don't need to do any waveshaping to restrict the bandwidth.
I'm not certain this is true. You might get a superficially cleaner looking sideband spectrum, because all the components are sub-harmonically related to the carrier frequency, but I don't think it will be narrower.

A gated sinewave has infinite bandwidth, whatever the phase or frequency relationship between the sine and the gating function.
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KA0HCP

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RE: Integral Cycle CW transmission on 2200 meters
« Reply #3 on: July 19, 2017, 10:59:53 AM »


A little OT, but I mentioned in yet another thread in this sub-forum that I think SDR will start to be used for low frequency bands like the 2200 meter band.  QRP-Labs has a transmitter good for 2200 meters, that uses the Si5351A synthesizer chip.  The Synthesizer chip is not SDR in the way we normally think about it.  But that same site has an amplifer that uses an ATtiny84 MCU waveshape controller, and that IS SDR (or SDA).  
This is not SDR at all.  It's a DDS with analog modulation (sound card emulator).

Thanks for the point to QRP-Labs. They have a very exciting collection of offerings, that amazingly low priced.  cheers, bill.
« Last Edit: July 19, 2017, 11:02:17 AM by KB4QAA »
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KA0HCP, ex-KB4QAA Relocated to Ks. April 2019.
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