Monday, November 12, 2012

VK7DIK 80M back in


Have been busy  this afternoon went shopping got a FTDI US232  USB-RS232 (39€)
interface hopefully to solve the communication problem with N1MM.
It did run immediate the driver was found in the system already.
But... DTR/CW is not driven on my Notebook on my other Laptop it works normal
Latest FTDI driver. DTR is only short active at init of the port. Seems a software problem.

So still not a solution hardware and software is resisting to cooperate . 

Same time purchased some extra high grade capacitors  WIMA FKP1 to tune the QTX 501kHz  down to 474.2kHz  I was testing my M.W. QTX again at 474.2 kHz.  our new M.W. allocation in 2013.
Before even thinking of building a bigger MW PA  I should at least be capable to get this small PA working stable.
Now at reduced power  20V  5A limited  to keep the IRF540 save.
Also used the IRL540  designed for logic level that one worked in the 500kHz version 2010 okay but could not get this one to work at 474kHz for unknown reason.
Meantime it became a graveyard for FET's here.. 5 blown up.

I experienced  that the IRF540 was latching up when reducing the drive or  after power boot.
Normally the drive level must be kept at fixed level for class-D operation but the PA should not trip when the drive is reduced.  
The effect is high current it jumps sudden from 2,5 to over 5A limit while the output drops. it is like oscillating effect.
I found I had used 22k instead of 12k R   gate to ground.
Also did I never use a ferrite bead at the gate.
With 3 beads and 12k it was more stable already but still at some lower drive levels the IRF
latched at 5Amps  a short-circuit  that sure would destroy if the current was not limited.
Not sure if the beads are really needed since there seems no self oscillating problem but it will not harm anyway.
Earlier this year in January with my 4M XVTR project.  
When trying this small ferrite bead at the gate to stop oscillation of the BLF177 at 4m  I found the power was complete gone. And the small bead was heating up so the effect of these small ferrite cores is not to be underestimating as I did before.

Now I am testing with 1k gate R4 (for diagram see previous post)   it seems to be stable now.
No need to keep the gate impedance high with the totem-pole low impedance driver stage here.
Possible this 12k was designed for the original logic level drive stage.

Doing  2,5A at 20V   running cool fttb... no latch-up  and more output then I got in 2010 at 500kHz  a picture of then showing the power meter at full power. Now I have more and not even running at full 24V.  Still after power up the FET can latch at current limit. I will need to have a current limit at my heavier supply.   Now it runs at 24V  3,8A  and staying cool after 2minutes carrier.
My power meter say 35W  before I could  reach 12W only  so much more.
The Daiwa NS660P is not designed for this low frequencies.  I thought at 500kHz I could multiply the reading roughly  about 9x   so 12W would mean about 100W  RF    that  was also matching the input power and the estimated >80% efficiency  the small heath-sink stayed cool  at 4,5A 24V input.
But now with optimised output on a 50 Ohm load  it deflects 35W  at 24V 3,8A  at 475.7 kHz
it is more output but it can never be more than  80W with n=90%
Just have to measure the  Voltage on my dummy load of coarse.
  

After yesterday's evening short 160m SS/SR peak exchange  RST at 160m with Greg ZL3IX
at 1831.5kHz  not new but the ultimate DX  at topband  that was a highlight .
This morning 10m was good to ZL2IT  2 decodes  PA was having the best DX of EU today at 10
It is not a competition WSPR but still it is a thrill with 5W  could have been 0.5 too at -12dB.. 

As extra goody tonight's surprise at 80m

After months and months  zip DX suddenly  tonight 5 decodes by VK7DIK

Normally  DK4XI is the only EU one being decoded by VK7DIK.

 2012-11-12 18:16  PA0O  3.594089  -24  0  JO33hg  5  VK7DIK  QE28sf  16731  84 
 2012-11-12 18:24  PA0O  3.594089  -23  0  JO33hg  5  VK7DIK  QE28sf  16731  84 
 2012-11-12 18:28  PA0O  3.594089  -22  0  JO33hg  5  VK7DIK  QE28sf  16731  84 
 2012-11-12 19:16  PA0O  3.594089  -14  0  JO33hg  5  VK7DIK  QE28sf  16731  84 
 2012-11-12 19:28  PA0O  3.594089  -12  0  JO33hg  5  VK7DIK  QE28sf  16731  84 
 2012-11-12 18:58  PA0HCK  3.594038  -16  0  JO33ld  5  VK7DIK  QE28sf  16711  84 
 2012-11-12 19:18  PA0HCK  3.594038  -19  0  JO33ld  5  VK7DIK  QE28sf  16711  84 
 2012-11-12 19:28  PA0HCK  3.594038  -18  0  JO33ld  5  VK7DIK  QE28sf  16711  84 
 2012-11-12 19:40  PA0HCK  3.594038  -22  0  JO33ld  5  VK7DIK  QE28sf  16711  84 

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