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Hi Stefan,
I thought the power was the RMS voltage squared
(i.e. peak voltage X 0.707) divided by the resistance.
Chris, G4AYT.
----- Original Message -----
Sent: Tuesday, September 07, 2010 9:31
PM
Subject: Re: LF: 137.5kHz WSPR Tuesday
evening - reports appreciated
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
--
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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
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