At driver linear: http://tzitzikas.webs.com/irf640-1.JPG i am using for outupt
transformer the BN-43-3312 double ferrite (see here:
https://www.amidoncorp.com/items/62 ) not 2 FB-43-7351 (see here:
https://www.amidoncorp.com/items/44 ) like the original design. Do you think
this change makes problems like output r.f power reduction and not good
modultion? thank you
--- On Sat, 4/24/10, sasas asasas <tzitzikas_ee@yahoo.com> wrote:
From: sasas asasas <tzitzikas_ee@yahoo.com>
Subject: 160m linear amplifier with mosfets low output at some frequencies
To: amps@contesting.com
Date: Saturday, April 24, 2010, 10:11 AM
hi, i have construct this linear amplifier 500w with 12 mosfet irfp360 for 160m
band:
http://tzitzikas.webs.com/linear500w.jpg (schematic)
The manufacturer and other amateurs who have construct the follwing set, claims
that the linear
provide in output at 110vdc 450-500w carrier (13A current), at 55vdc 100w and
at 75vdc 200w carrier and the
requirements for r.f driving power are only 2w (Also he claims that is
broadband at frequencies between 1000-2000khz)
The PLL which i use to drive the linear 500w, consists of:
pll: http://tzitzikas.webs.com/pll-1.JPG (schematic)
oscillator: http://tzitzikas.webs.com/oscillator-1.JPG (schematic)
modulator: http://tzitzikas.webs.com/modulator-1.jpg (schematic)
linear 2-10w with 2 irf640 mosfets: http://tzitzikas.webs.com/irf640-1.JPG
(schematic)
the block diagram is
pll-oscillator-->modulator-->linear 2-10w with 2 irf640 mosfets-->linear
amplifier 500w-->dummy load
50ohm 1kw
I do all test in dummy load 50ohm/1kw.
I took these measures:
at 1450khz at 65V(voltage to drains of irfp360): 103W output power current 4.8Α
and driving power 2w
at 1700 at 65V 60W output power current 3.3Α (i don't change the driving stage
settings (like voltage e.t.c)
at 1200 at 65V 183W output power current 7.8Α
(at 1850khz! the output power was only 50w!)
swr=0 (all frequencies)
After, i connect only the linear with 2 irf640 (driver) to the dummy load and i
took these measures at 20v (voltage to drains
of irf640):
1431khz 2w
1700khz 1.9w
1200khz 4w
So, you can see that the driving power was increasing when the frequency was
decreasing.
After these measures i gave to linear 500w, 3.6w of driving r.f power at
1450khz and it gave only 130w at 65v
(current was
5,5Α and the modulation in this test wasn't very good- AM modulation).
So, it is clear that at lower frequences linear 500w, and the other circuits
give the maximum r.f power.
The designer claims that this linear amplifier is broadband for 160m and mw
band (1000-2000khz)
I would like my linear to give 185w at 65vdc at high frequencies between
1400-1900khz.
What changes do you propose to do at linear amplifier 500w, linear 2xirf640,
modulator or oscillator
to give at output 185w at 65v? Maybe some changes in transformers or
capacitors??
Moreover, the one heatsink was colder than the other one.
some photos from my constructions:
linear
500w:
http://tzitzikas.webs.com/linear_photo_1.jpg
http://tzitzikas.webs.com/linear20.JPG
http://tzitzikas.webs.com/linear20a.JPG
http://tzitzikas.webs.com/linear21.JPG
http://tzitzikas.webs.com/fet21.JPG
http://tzitzikas.webs.com/pompos20.JPG
http://tzitzikas.webs.com/T3.JPG
linear 2xirf640:
http://tzitzikas.webs.com/linear2xirf640-1.jpg
oscillator-modulator:
http://tzitzikas.webs.com/oscillator-modulator_photo_1.jpg
http://tzitzikas.webs.com/pll-modulator-oscillator-filter-1.jpg
thank you very much!
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