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Re: LF: RE: 500 kHz JT4A

To: [email protected]
Subject: Re: LF: RE: 500 kHz JT4A
From: Andy Talbot <[email protected]>
Date: Wed, 27 Jan 2010 21:56:58 +0000
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I was looking at driving push-pull transmitters from fundamental drive signals quite recently.  
 
How about a frequency doubler?    The output doesn't have to have 1:1 mark-space ratio as it only clocks a flip-flop.   And simple doubler can consists of a delay line (CR network with around 0.5us time constant) followed by a squarer to give a resulting waveform shifted in phase from the 500kHz drive signal.  Then apply this one,  along with the original to a two input XOR gate whose output will then consists of a 1MHz train suitable for dividing by 2 for a perfect 1:1 squarewave drive.
 

Andy
www.g4jnt.com

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2010/1/27 Rik Strobbe <[email protected]>
Gary,
 
the SNR values over the last hour or so varied between -2 and -13dB.
Assuming a -24dB limit and your current power (50W) anything above 5W would provide solid copy and 0.5W occasional copy.
Impressive.
I should get QRV on JT4A, but I blew the transformer of my "straight" 100W PA, and my 250W G3YXM-clone PA needs 1MHz drive (at TTL level), so I cannot use that with my HF/500kHz transverter.
 
73, Rik  ON7YD - OR7T

Verzonden: woensdag 27 januari 2010 22:03
Aan: [email protected]
Onderwerp: Re: LF: RE: 500 kHz JT4A

Rik, & Andy,

Thanks for your report & comments & Andy for answering Rik's query.

Well there has not been any response to my CQ call so I will change the text to beacon & continue to see if there is a report from further afield.

If you want to try for a weak decode I can reduce the power for a short period say 30 minutes, my power is 50 watt RF (200 mW ERP) at the moment so in view of your good report I could take it down to 10 watts RF.

Let me know.

73, Gary - G4WGT - IO83qo

2010/1/27 Andy Talbot <[email protected]>
-24dB S/N (2.5kHz )  is usually guaranteed

Andy
www.g4jnt.com

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2010/1/27 Rik Strobbe <[email protected]>

Gary,
 
solid copy here, SNR -5 to -7dB.
But the signal is clearly audible, CW would be armchair copy.
Any idea down to what SNR values JT4A produces a usable decoding ?
 
73, Rik  ON7YD - OR7T

Van: [email protected] [[email protected]] namens Gary - G4WGT [[email protected]]
Verzonden: woensdag 27 januari 2010 20:33
Aan: Rsgb_Lf_Group
Onderwerp: LF: 500 kHz JT4A

LF,

Running JT4A this evening on 503.600 kHz, dial frequency 502.300 kHz USB.

73, Gary - G4WGT - IO83qo



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