The AM Forum

I know that Ken KC2UDZ has put together a mobile linear using Mosfets... in the not to distant future I will be wanting to put together a linear with Mosfets, for the 80m band. It will need to "perk up" 25watts of carrier to a nominal ~200watts of carrier + modulation, or there abouts. Preferably "no tune", although it will likely suffice to have a broadband output matching section that covers the primary AM portion of the band, although I do operate sometimes down above 3.700... so that is a consideration.

Power supply voltage can be any - this is not for mobile operation. Fixed.

The closer to a "dumb block" with gain, the better.

Ideas, links to projects etc are all appreciated. Suggestions for devices too.

                       _-_-bear

here, try this. using 4 FETs instead of 2 should give you 200 watts.
http://amfone.net/Amforum/index.php?topic=27142.0 (http://amfone.net/Amforum/index.php?topic=27142.0)

Thanks,

I was unable to get a good download of the schematic in pdf format... :(

Only got 512kb and an error opening the file...

Would have like to look and see.

But so far the silence on the band is deafening on this topic. I am surprised.

                         _-_-bear

This time of year bears typically want to lay back and are kinda sleepy. However I did do an internet search on these things and it seems that the design of a single band Lin-eee-yar is fairly simple and straightforward. Especially for 80m.

In addition there are some 1kw class RF power Mosfets out there for <$100usd... to do the same power with discrete switching mosfets @ say $5 per device and using 8 or 12 devices will run between $40-60, and given that I saw one of the high power devices for $59.95 and they are good out to VHF, that is looking interesting because it will not be restricted to 160,80 and maybe 40...

I may get my feet wet on the switching mosfets, that way when I smoke them, it's cheaper! ;)

But broadly speaking the way to go seems to be with P-P using ~250w modules and a combiner...

This is looking very interesting indeed!

                    _-_-bear

Ok, admitting ignorance.

Can this device:

http://cache.freescale.com/files/rf_if/doc/data_sheet/MRF6S19140H.pdf?pspll=1

be used at HF??

Looks like it does 140w peak, and loafs at 25w... meaning x 8 = 200w carrier with >1kwpeak... also a nice low IMD @ higher currents... of course that is spec'd at GHz., thus my query.

Dunno if this is the sort of device to go with, just trying to determine the ins and outs...

                 _-_-bear

Sure is quiet on this frequency...














                               _-_-bear

A comment on MOSFETs such as those UHF power FETs. An applications guy told me that UHF MOSFETs have so much gain at HF that they may be unstable, are unstable and might take off oscillating. I am thinking it is an issue that could be worked with swamping and layout. He is not a ham and only thinks about their use at UHF. Wish I knew more.

Hello Bear,

I always liked Jay's (W1VD) approach:
Class D, torroid output xfmrs.  Simple, neat, efficient,compact, and sounds great.
He's done 100, 200 and 375 watt versions.
Probably the way I would go if I had more time...

http://w1vd.com/375wattclassD.html

Patrick, thanks  for that info...

Jim, that's Class D/E stuff. I am doing a Linear for 75m (maybe broadband), to amplify an existing AM transmitter's signal... similar design to the RF deck, but a different animal.

                  _-_-bear