Re: LF: 137.5kHz WSPR Tuesday evening - reports appreciated

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

Take a look at G3NYK's Class E design page http://www.alan.melia.btinternet.co.uk/classepa.htm

 

Don't even try biassing the FET with a pot.  You must use a squarewave drive- preferrable from a proper MOSFET driver like an ICL7667 or TC4426 type, or at a push a stack of paralleled 74C drivers will do. 

 

I measured somewhere between  85 - 103% efficiency for a 20 Watt design running from 12V on 1.9MHz.  Its very difficult to measure PA efficiency properly at low frequencies as the HP432  power meter doesn't go below 10MHz    Judging by how not-hot the device got, looks to be around 90%.    See the next RadCom for more details.

 

Andy
www.g4jnt.com

On 7 September 2010 20:08, Roger Lapthorn <rogerlapthorn@gmail.com> wrote:

Stefan/Mal,

Clearly my design was not working in class E properly as the PA was dissipating a fair amount of heat and it was taking about 0.8A to produce 40V p-p output from a 13.8V supply which is about half as efficient as it should be. I took a PA design start from a design program I found on the net by Tonne Software called "Class E" and the values seemed to be close to optimum when I adjusted caps and L up and down a small amount, but the dissipation seems miles off what a good class E design should take. The IRF510 gate voltage is set just below 3V with a resistive pot. The drive is not a square wave though, so I suppose this could be part of the issue?

Stefan, if you have a better class E PA circuit for 137kHz suitable for around the 10-20W out region I'd be interested in seeing it. I would prefer to use toroid inductors because of size. I have several T106-2 cores to hand as well as several 16mm diameter 3C90 cores.

I'm still learning..... and not too proud to ask for help from those with more experience.

73s
Roger G3XBM

2010/9/7 Stefan Schäfer <schaefer@iup.uni-heidelberg.de>

Hello Roger,

Maybe you can send us a circuit with its values. I have built class E PA for 2200/160/80/40/30/17/10m and have some experience. If you are using a IRF510 and stay in the QRP range (< 10 W) at 137 in a class E stage you wouldn't even need a heat sink at all if well dimensioned!

See the infos at http://www.classeradio.com/  This is most useful if you are starting with that design. On 137 kHz problems are much smaller than on HF :-)

Best 73, Stefan/DK7FC

Am 07.09.2010 20:17, schrieb Roger Lapthorn:

Just hit a bit of a snag and blew up my (last) IRF510 PA because of totally inadequate heatsink. So, I'm on 137.5kHz WSPR but only with about 1W from the simpler PA at present, so ERP low uWs.  I need to get some heatsink and more FETs!

Any reports (now less likely) still appreciated.

[Mal - it started out as a Class E design attempt but hadn't been optimised, so I guess this counts as class D. ]

73s
Roger G3XBM

On 7 September 2010 17:34, Roger Lapthorn <rogerlapthorn@gmail.com> wrote:

My 137.5kHz WSPR TX transverter is now working fine, so I'll be on-air with WSPR tonight (Sept 7th) from 5.30pm - 11pm UK time.

After my success on QRSS3 with G3XIZ I'm hopeful he'll now decode my WSPR signal tonight, assuming Chris can take a listen. If anyone else within, say, 100km of Burwell, Cambs JO02dg cares to take a look for the WSPR beacon (running around 35% TX time) I'd be most grateful.

Not sure if anyone else has had this problem, but I was using the small 16mm 3C90 cores (cream colour) as the PA bifilar output transformer and I had all sorts of issues with the darn thing overheating and even one cracking. I replaced this with a choke wound on a T106-2 core and made the output network work in class D/E and now everything is working very predictably. The larger diameter 3C90 cores seem fine in the step-down transformer matching the "in the air" loop.

The WSPR beacon is now going ON.....

73s
Roger G3XBM


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G3XBM   GQRP 1678    ISWL G11088

--
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
G3XBM   GQRP 1678    ISWL G11088

--
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
G3XBM   GQRP 1678    ISWL G11088