Re: LF: FET RDS

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

An interesting circuit, but there is one thing that puzzles me.  There is a lot of open loop gain as well as non-linear discontinuity in the drive that would contribute audio distortion.   Just like crossover distortion in a class B audio stage  

 

It could be completely solved by adding negative feedback into the audio path from the output - same as any Hi-Fi amp - but I don't seen any.   Is it elsewhere and just doesn't appear on that schmatic?

 

For general EER type modulation techniqes, a phase/amplitude generator module would be useful, giving  Pythagoras and arctan outputs from baseband audio in.   A ideal task for a DSPic

 

Andy

www.g4jnt.com

 

2011/1/13 Stefan Schäfer <schaefer@iup.uni-heidelberg.de>

Hi Minto,

Am 13.01.2011 23:09, schrieb Minto Witteveen:

Stefan,

You mentioned the IXDD414 in a previous message here on the reflector, and I immediately downloaded the datasheet. The IXDD414 certainly looks very promising and I plan to experiment with it as soon as we are allowed back on 500....

I've used them successfully up to 10 MHz, driving about 2 nF.

Now if I can just find a supplier here in PA who stocks this chip.

Yes, that's the problem. I've got 5 of them as a sample part but later i needed more. So i've ordered at digikey in USA. If you find a cheeper distributor, please tell me (quantity below 10000000000000) :-)

My original 500 KHz design was for linear operation (so I could use psk31) but I only made one qso in PSK, the rest in ordinary CW. A new design can and will be much simpler.

Have you heared about a class H modulator? This is a circuit that separates AM and FM. The FM and PA can be done by a class E design and the AM is applied by modulating the supply voltage by a step down converter (the class H modulator). I've never built one but there are some interesting examples at http://www.classeradio.com/classh.htm
This would be a good combination to push-up a class E PA for linear mode. Since i do nothing more than CW/QRSS/DFCW i actually do not need one ;-)

73, Stefan/DK7FC

Thanks for the info.

Regards,
Minto pa3bca


--------------------------------------------------
From: "Stefan Schäfer" <schaefer@iup.uni-heidelberg.de>
Sent: Thursday, January 13, 2011 22:49
To: <rsgb_lf_group@blacksheep.org>
Subject: Re: LF: FET RDS

Minto,

14 nF gate capacity can easily be driven by a IXDD414, at 500 kHz and even at 1800 kHz. I've built a 600W class E for 160m running at 36 VDC (for /p, 3 car batteries in series ;-) ), using 4xIRFP260N. Efficiency is above 90% but mostly due to losses in the coils ( i like to built it compact :-) ).

73, Stefan/DK7FC