Powered by Invision Power Board


Forum Rules Forum Rules (Please read before posting)
  Reply to this topicStart new topicStart Poll

> Problem With Output Power-linear Amplifier
tzitzikas
Posted: May 20, 2010 04:27 pm
Reply to this postQuote Post


Newbie
*

Group: Members+
Posts: 7
Member No.: 29,521
Joined: May 20, 2010




hi, i have construct this linear amplifier for mw band: http://tzitzikas.webs.com/linear500w.jpg with 12 mosfets IRFP360.
some photos from my project here:
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 (photo of /t3 broadband transformer)

for ferrite beads i am using FB-43-7351 from https://www.amidoncorp.com/items/44 but i have also orderedFB-43-7352 and the FB-43-1020 ferrite beads.
The manufacturer claims that with only 2w input r.f power it gives 500w at the output at 110vdc (13A current). But with 5,5w input power at 106vdc my linear gives only 220w output r.f power (7A current) at dummy load 50ohm.
(here you can see a photo from prototype: http://tzitzikas.webs.com/linear_first.jpg )
Also, the other problem is that the T3 transformer and the resistors R9,R10,R11,R8 and the r.f choke VK200 are very warm when the linear operates.
But the basic problem is to increase the output power.
The mosfets are from Siliconix but i have ordered and i will try to use International Rectifier's IRFP360 mosfets.
Do you have any idea what is the problem for the low output power? Do you have to propose any change to broadband transformers to increase the output power? I tried to change the value of C4=3,9nf capacitor but the output power was more low.
Thank you.
PMEmail Poster
Top
tekwiz
Posted: May 20, 2010 06:13 pm
Reply to this postQuote Post


Forum Addict ++
Group Icon

Group: Moderators
Posts: 28,711
Member No.: 5,746
Joined: July 24, 2006




What are you using as a load? What are you measuring power with? What frequency are you using?
At this point, it looks like possibly T3 may be faulty, or has a winding that's out of phase. More when I get more info.


--------------------
Trouble rather the tiger in his lair, than the sage among his books.
For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

Fortuna favet fortibus.
PMEmail Poster
Top
tzitzikas
Posted: May 20, 2010 06:23 pm
Reply to this postQuote Post


Newbie
*

Group: Members+
Posts: 7
Member No.: 29,521
Joined: May 20, 2010




QUOTE (tekwiz @ May 20, 2010 08:13 pm)
What are you using as a load? What are you measuring power with? What frequency are you using?
At this point, it looks like possibly T3 may be faulty, or has a winding that's out of phase. More when I get more info.

the dummy load is an 50ohm 1kw dummy rf load and the frequency is 1431khz (mw band). To measure the r.f output power i am using a digital power/swr meter 5kw maximum 1-30mhz, from a Greek radio equipement corporation. It is a very good power meter, which is using many radio amateurs.
i am thinking to increase the turns of T3 transformer (the 5 turns with coaxial 25ohm cable) or to increase the secondary coil's turns of output transformer T1 from 6 turns to 9 turns. What do you think about this?
thank you

This post has been edited by tzitzikas on May 20, 2010 06:36 pm
PMEmail Poster
Top
Nothing40
Posted: May 20, 2010 10:27 pm
Reply to this postQuote Post


Forum Addict ++
*******

Group: Spamminator Taskforce
Posts: 3,565
Member No.: 181
Joined: October 05, 2002




My suggestion is to improve your construction technique. RF is a fickle b*tch.


--------------------
"we need an e-kick-in-the-nuts button" -Colt45
PMUsers WebsiteYahoo
Top
Sch3mat1c
Posted: May 20, 2010 10:28 pm
Reply to this postQuote Post


Forum Addict ++
Group Icon

Group: Moderators
Posts: 19,597
Member No.: 73
Joined: July 24, 2002




Ewww-www-www! Why are the transistors all the way on the side, with wires!? Get everything on a ground plane!

At this frequency and power level, expect core loss, even from a mix 43 core. Only thing you can do is add more turns or use bigger cores = lower Bmax.

Tim


--------------------
Answering questions is a tricky subject to practice. Not due to the difficulty of formulating or locating answers, but due to the human inability of asking the right questions; a skill that, were one to possess, would put them in the "answering" category.
PMEmail PosterUsers Website
Top
CWB
Posted: May 21, 2010 12:24 pm
Reply to this postQuote Post


Forum Addict ++
*******

Group: Spamminator Taskforce
Posts: 21,463
Member No.: 15,154
Joined: May 15, 2008




yeah man ... the layout is bad . have you looked at the output with a spectrum analyzer ?
you say this is for 1.4 MHz ?
i have worked on commercial BCB transmitters (1.4MHz is towards the top end of your "MW" reference) here in the states .
nothing personal here ... but ... i would not allow an amplifier that looked like that (design wise) on the site .


--------------------
"Know how to solve every problem that has been solved"
R. Feynman '88
PM
Top
tzitzikas
Posted: May 21, 2010 01:04 pm
Reply to this postQuote Post


Newbie
*

Group: Members+
Posts: 7
Member No.: 29,521
Joined: May 20, 2010




Could i increase the output transformer T1 number of turns, but keep the ratio 1:2 constant, to increase the output power? It will help? (4 turns primary and 8 turns secondary or 5 turns primary and 10 turns secondary)
Or to increase the secondary number of turns of T3 (with 25ohm coaxial cable)?
If i use bigger ferrite beads?

This post has been edited by tzitzikas on May 21, 2010 01:05 pm
PMEmail Poster
Top
CWB
Posted: May 21, 2010 02:13 pm
Reply to this postQuote Post


Forum Addict ++
*******

Group: Spamminator Taskforce
Posts: 21,463
Member No.: 15,154
Joined: May 15, 2008




your biggest problem seems to be the amount of current you are trying to pass through the winding(s) .
you will need a physically larger core and larger gauge wire to wind them with .

with most "linear" amplifiers there will be a de-rating between operation as a CW , SSB , FM and AM amplifier .
most of these are labeled "PEP WATTS" and "AM/CW WATTS" (etc) .
in most cases the de-rating between AM and SSB is quite considerable .

just out of curiosity , what are the band allocations/rules in greece ? i don't recall an amateur band around 1.4 MHz .
that amplifier most likely will not meet commercial spec .


--------------------
"Know how to solve every problem that has been solved"
R. Feynman '88
PM
Top
tzitzikas
Posted: May 21, 2010 03:47 pm
Reply to this postQuote Post


Newbie
*

Group: Members+
Posts: 7
Member No.: 29,521
Joined: May 20, 2010




this transmitter is an educational university project. All test are in dummy load 50ohm (no antenna)
PMEmail Poster
Top
tekwiz
Posted: May 21, 2010 05:39 pm
Reply to this postQuote Post


Forum Addict ++
Group Icon

Group: Moderators
Posts: 28,711
Member No.: 5,746
Joined: July 24, 2006




QUOTE (CWB @ May 21, 2010 05:13 am)
your biggest problem seems to be the amount of current you are trying to pass through the winding(s) .
you will need a physically larger core and larger gauge wire to wind them with .

with most "linear" amplifiers there will be a de-rating between operation as a CW , SSB , FM and AM amplifier .
most of these are labeled "PEP WATTS" and "AM/CW WATTS" (etc) .
in most cases the de-rating between AM and SSB is quite considerable .

just out of curiosity , what are the band allocations/rules in greece ? i don't recall an amateur band around 1.4 MHz .
that amplifier most likely will not meet commercial spec .

Look at the schemmy...that 500W rating is the derated AM figure. PEP power is listed at 2KW.


--------------------
Trouble rather the tiger in his lair, than the sage among his books.
For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

Fortuna favet fortibus.
PMEmail Poster
Top
CWB
Posted: May 22, 2010 01:22 pm
Reply to this postQuote Post


Forum Addict ++
*******

Group: Spamminator Taskforce
Posts: 21,463
Member No.: 15,154
Joined: May 15, 2008




i seen the ratings ... something is not quite right between the construction (basically) size of the output transformer and the power rating for AM .
it may be that the OP is testing with a constant level (say 95%) modulated signal as opposed to a varying modulation level (as in a "real" audio source) .
or ... feeding it a FM signal ... this would be almost the same as "brick on key" CW situation .

however ... these are secondary considerations ... the first order of business would be to make sure that the amplifier is not whistling .
a spectrum analyzer would quickly show if this were the case .
even if the idle current drops dramatically with no signal applied this does not mean that the amplifier is stable and clean while under actual operating conditions .


--------------------
"Know how to solve every problem that has been solved"
R. Feynman '88
PM
Top
tekwiz
Posted: May 22, 2010 06:24 pm
Reply to this postQuote Post


Forum Addict ++
Group Icon

Group: Moderators
Posts: 28,711
Member No.: 5,746
Joined: July 24, 2006




Well, he is getting near half of the design power, which means it's working, sort of. You should be able to detect oscillation by checking for output with no input signal, I would think.
I agree that the construction could be a lot better. Those MOSFETS should be as close to the transformers as possible, not hanging out on several inches of wire. The stray capacitance from them is likely responsible for some of the loss.


--------------------
Trouble rather the tiger in his lair, than the sage among his books.
For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

Fortuna favet fortibus.
PMEmail Poster
Top
CWB
Posted: May 23, 2010 02:28 am
Reply to this postQuote Post


Forum Addict ++
*******

Group: Spamminator Taskforce
Posts: 21,463
Member No.: 15,154
Joined: May 15, 2008




i have seen amps that turned into garbage generators when the meat was thrown to them .
spurs all over the place .
heh ... with one memorable amp the display on the SA looked like a picket fence .


--------------------
"Know how to solve every problem that has been solved"
R. Feynman '88
PM
Top
tzitzikas
Posted: May 23, 2010 09:47 am
Reply to this postQuote Post


Newbie
*

Group: Members+
Posts: 7
Member No.: 29,521
Joined: May 20, 2010




i am thinking to change the ferrite beads with bigger to reduce the losses and to increase the number of turns at T1 and T3 transformers but i will the ratios constant.
I am thinking at T3 to put 2 turns primary and 10 turns secondary (coil with 25ohm coaxial cable) and at T1 to put 4 turns primary and 8 turns secondary or 5 turns primary and 10 turns secondary. What do you think? These changes will help to increase the output power?
PMEmail Poster
Top
CWB
Posted: May 23, 2010 12:22 pm
Reply to this postQuote Post


Forum Addict ++
*******

Group: Spamminator Taskforce
Posts: 21,463
Member No.: 15,154
Joined: May 15, 2008




try it ...
ramp up the drive carefully and in stages ...
measure the parameters and temps at each level .


--------------------
"Know how to solve every problem that has been solved"
R. Feynman '88
PM
Top
tekwiz
Posted: May 23, 2010 06:25 pm
Reply to this postQuote Post


Forum Addict ++
Group Icon

Group: Moderators
Posts: 28,711
Member No.: 5,746
Joined: July 24, 2006




It should help, but you should do something about all that stray capacitance that's coming from your transistor wires. If you can't eliminate the wires, then make them as short & thick as possible. This will also improve performance. Make sure your heatsinks are completely grounded to the board, too. Preferrably in several spots along their lengths.


--------------------
Trouble rather the tiger in his lair, than the sage among his books.
For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

Fortuna favet fortibus.
PMEmail Poster
Top
0 User(s) are reading this topic (0 Guests and 0 Anonymous Users)
0 Members:

Topic Options Reply to this topicStart new topicStart Poll

 


:: support us ::




ElectronicsSkin by DutchDork & The-Force