5364	2010-10-08 19:24:10	Jason W6IEE	simpler FET final Re: More thoughts on gate drive
Message	Date	From	Subject
Taking this off track a little bit, as its not class E, While having a look at EMRFD fig 2.99, I (re)noticed fig 2.98. Been trying to remember where I saw this simple little circuit! Could anyone shed some more light on the physical construction of the output transformer? Thanks and 73, Jason W6IEE More thoughts on gate drive Posted by: "Tim" timshoppa@yahoo.com timshoppa Thu Oct 7, 2010 9:29 am (PDT) Just as an aside on gate drive (having looked at some of the recommendations that popped up - wow, the NC7WZ16 IS THE SIZE OF A SPECK OF DUST!!!!), I'm playing around in LTSPICE with variants of the "W7EL direct coupled drive" circuit shown in EMRFD Fig 2.99 (a totem pole from bipolar transistors) and that's actually not too bad. A 2N3904/3906 pair isn't real low impedance by itself but perhaps paralleling these is a better approach than paralleling 74AC240 sections. Tim N3QE -- (Formerly KF6PQT) AMI #1625 SKCC #3768 GQRP #12446 http://en.wikipedia.org/wiki/Junk_box http://w6iee.dyndns.org http://www.flickr.com/photos/kf6pqt/
5365	2010-10-08 21:06:49	w7zoi	simpler FET final Re: More thoughts on gate drive
Hi Jason and group, This circuit is pretty generic and I suspect you have seen many variations just like this. The output transformer is a transmission like type consisting of about 10 bifilar turns on a ferrite core. About any core will work for the HF bands. #24 wire on a FT-37-43 would be a good start, and if you twist the wire with a drill to a few turns per inch, you will end up with a transmission line of around 50 Ohms. The more turns per inch and the lower the Z0 of the line. You want 25 Ohms ideally in this case, but if you don't hit that, the circuit will still work with reduced bandwidth. You should be able to drive the thing to an output of 5 W or so with about 0.1 W, although more may be needed at the high end of the HF spectrum. The linearity will be pretty poor with this part at this power level. Fortunately, with QRP you won't be bothering a lot of folks. If you neglect the transmission line character of the transformer, it still works because it degenerates into a simple center tapped toroid transformer. The 10 Ohm gate resistor enhances stability. However, it will soak up some of the drive. You may want to eliminate it on the higher bands. Come to think of it, I think that this circuit is used in Farhan's original versi
5366	2010-10-09 13:37:51	Jason W6IEE	Re: simpler FET final Re: More thoughts on gate drive
Wes, Thanks so much! This circuit has given me quite a few ideas for tinkering. One of which is to see first hand how much abuse an IRF510 final will tolerate working into various horrendously mis-matched antenna loads. Thanks again and 73, Jason W6IEE -- (Formerly KF6PQT) AMI #1625 SKCC #3768 GQRP #12446 http://en.wikipedia.org/wiki/Junk_box http://w6iee.dyndns.org http://www.flickr.com/photos/kf6pqt/
5367	2010-10-09 14:43:22	ehydra	Re: simpler FET final Re: More thoughts on gate drive
w7zoi schrieb: > The biasing is straight forward. Merely adjust the pot for a drain > current of about 100 mA without any applied drive. The current will > kick way up when you start talking or keying the drive. Use a heat > sink, for there will be some power to dissipate. Bob Kopski, K3NHI, > has a circuit in the files for this group for a slick circuit that > provides thermal feedback for MOSFET power amplifiers. Where is the circuit or link? Seems it is not there. regards - Henry -- ehydra.dyndns.info
5369	2010-10-09 16:37:45	Tim	simpler FET final Re: More thoughts on gate drive
I think the reference FETbiastempcomp3.PDF in the EMRFD files archive, http://groups.yahoo.com/group/emrfd/files/ The yahoo groups "files" and "photos" sections are wonderful ideas, but the way it's impossible to directly link to any of the documents is sucky and undermines the basic principles of the web.
5370	2010-10-09 17:04:30	ehydra	Re: simpler FET final Re: More thoughts on gate drive
Thanks Tim! - I even struggle with the Yahoo concept! But it is possible to directly define a link! But the user then need a yahoo account and read access to the specific group to access it. Groups are most often moderated and the moderator delays the activation... Complicated procedure! And don't forget that Yahoo killed Geocities with all the wonderful content! So I wait for the day all the groups with the non-profitable tag are gone ... - Henry -- ehydra.dyndns.info Tim schrieb: > I think the reference FETbiastempcomp3.PDF in the EMRFD files archive, http://groups.yahoo.com/group/emrfd/files/ > > The yahoo groups "files" and "photos" sections are wonderful ideas, but the way it's impossible to directly link to any of the documents is sucky and undermines the basic principles of the web. > >
5371	2010-10-09 17:10:36	ehydra	Re: simpler FET final Re: More thoughts on gate drive
Nice circuit idea! Here is the correct link: http://groups.yahoo.com/group/emrfd/files/FETbiastempcomp3.PDF But yahoo scrambles a simple link copy. So you have to merge the correct path. I think they plan to install a ad-server proxy page in the near future. thx - Henry -- ehydra.dyndns.info ehydra schrieb: > Thanks Tim! > > - > I even struggle with the Yahoo concept! But it is possible to directly > define a link! But the user then need a yahoo account and read access to > the specific group to access it. Groups are most often moderated and the > moderator delays the activation... > Complicated procedure! > > And don't forget that Yahoo killed Geocities with all the wonderful > content! > So I wait for the day all the groups with the non-profitable tag are > gone ...