Re: LF: RE: 500 kHz JT4A

[Andy Talbot <andy.g4jnt@googlemail.com>]

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

This email has been scanned for damaging side-effects by the health and safety police, is guaranteed to contain no substances hazardous to health, but may contribute to dissolving the nether and polar regions

2010/1/27 Rik Strobbe <Rik.Strobbe@fys.kuleuven.be>

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

---

Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.org] namens Gary - G4WGT [g4wgt@tiscali.co.uk]

Verzonden: woensdag 27 januari 2010 22:03
Aan: rsgb_lf_group@blacksheep.org
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 <andy.g4jnt@googlemail.com>

-24dB S/N (2.5kHz )  is usually guaranteed

Andy
www.g4jnt.com

This email has been scanned for damaging side-effects by the health and safety police, is guaranteed to contain no substances hazardous to health, but may contribute to dissolving the nether and polar regions

2010/1/27 Rik Strobbe <Rik.Strobbe@fys.kuleuven.be>

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: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.org] namens Gary - G4WGT [g4wgt@tiscali.co.uk]
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