Roger,
For measuring the output power take a 50 Ohm dummy load (50, not 55
Ohms or so) and measure the peak voltage with an oscilloscope. Type
this into the excel file and calculate the output power (P=(û)^2/(2*R)).
73, Stefan
Am 07.09.2010 21:32, schrieb Andy Talbot:
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.
On 7 September 2010 20:08, Roger Lapthorn <[email protected]>
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 <[email protected]>
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 <[email protected]>
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
--
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
--
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
G3XBM GQRP 1678 ISWL G11088
|
|
