Digital Drive & New Rigs

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Re: Digital Drive & New Rigs

Postby Gilly » Thu May 22, 2014 5:44 pm

OK well thats about the end of this post I suppose......
Let us know how it all goes Bill....

OK too Bruce on your thoughts regarding N3ZI DDS ......
Actually have built 3 of his and they all worked first go....
The first one was very slow and thats now used as the VFO of my new 40M Transmitter.
Its not on air yet....works well up to the gates but have yet to apply Drain voltage....

Will read up on K5BCQ web site as has a lot of stuff there......

Best of luck all round....


Wayne
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Re: Digital Drive & New Rigs

Postby W1AC » Thu May 22, 2014 10:39 pm

kf1z wrote:I am a big fan of taking on a project that I have never done before following the 'proven method' FIRST.


That's a good policy, and I like to follow it. "Tried and True", and just follow the schematic, that's me. I always loved the Heathkit and Knightkit rigs, because they had such great directions.

My chief concern with the current deck is that I don't want to turn a Ford into a Chevy just because I've always driven Chevy: if "sine wave" drive is reliable, I'd be happy to use it, but I was advised to use a more conventional design, so I'm going to add driver chips and maybe a DDS VFO. I want to save as much of the existing deck as I can, consistent with good design, and then get the Class H modulator and power supply ready to go.

Later on, I might experiment with sine-wave input. For now, I'm playing it safe.

Bill
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The trick is to avoid the hot spots!
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Re: Digital Drive & New Rigs

Postby Gilly » Fri May 23, 2014 12:46 am

Good idea Bill......

If you need help squaring up the Sinewave from the DDS or anything else just let us know... :D

It will work fine...


Wayne
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Re: Digital Drive & New Rigs

Postby Mark_WB2ERS » Tue Dec 22, 2015 7:17 pm

Brent, I built a new transmitter with 4 CREE Fets based around the 24 FET design with 4 output transformers and 2000 pf shunt per device.
Unit makes plenty of power but I can't get beyond 50 % efficiency. Some discussion on the air seemed to point to incorrect drive duty cycle.
I didn't find anything on Steve's site related to scope pics on proper drive setup.
Do you or anyone here have an A-Z procedure on setting up proper duty cycle for the two phase drive?

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Re: Digital Drive & New Rigs

Postby Gilly » Thu Dec 24, 2015 5:08 pm

Hi Mark

Have not been on the Forum for a while now .....
Its Christmas day at the moment but will reply to your post tomorrow if you like...


Wayne
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Re: Digital Drive & New Rigs

Postby steve_qix » Thu Dec 31, 2015 6:28 pm

The drive waveform should achieve a steady-state value (for those particular CREE MOSFETs) of 20V. This is the manufacturer's recommended operational value, and I have found this to be correct. You are allowed some SHORT spikes on the drive waveform that go above 20V, as there is an R/C time constant formed by the gate resistance and the gate input capacitance.

The waveform should be a trapezoid with a single IXDD414 or IXDD614 driver on 80 meters. You can get pretty close to square, but not quite.

The duty cycle should be such that the rising edges do not overlap at all. This is very important to the efficiency of the RF amplifier.

Hey, it's new year's eve so Happy New Year !!

Regards, Steve
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