Skip to main content

I want my lazy BLX15 back!

I did replace my old BLX15 power transistor with a modern Power MOS device.
The BLF177   the BLX15 has 6dB gain only at 70MHz.
While the BLF177 should have over 20dB.

After a few days  trying all I could think of to get stable power out of the BLF177 MOS   at 70MHz  the result was  2 melted tuning C's.
It sure can generate power this device  but I did not manage to let it  work at the wanted frequency.
Many combinations of L and C  where tested. The original circuit was  used for 50MHz relatively  close to 70MHz.  I did not expect major changes in the L and C's  in use.
The   2 stage low-pass filter should be almost the same.
Of course the bias circuit is different   but simple only a pot-meter to get about 3V at the gate for 500mA. The BLX15 needed the 0.7 PN diode in parallel to get a 500mA bias.
I have  edited  an input file with the scattering parameters from the specification data for  RFSimm99

I need a working circuit with practical L and C values to continue.
It is very strange that I can not find a tuning for this device.  Only oscillating ?  At one moment it looked ok  I could drive easy 150<  in the dummy. But then suddenly at switching in the tuning C burned out and fuses blown.   At lower Voltage I managed to get 20W with 1W drive but very unstable.


Victims of the shear oscillating power...  Arco type 406  80pF  and a smaller one



 

Comments

Archive

Show more

Popular posts from this blog

2011-01-22 DIAMOND 2m 70cm 1m30 Colinear inside

Having relative poor signals on the local 70cm / 2m channels using this X50 Diamond collinear 70/2  1m antenna at a height of 25m. I needed to investigate what could be wrong. Measuring the cable only 3W is left for the antenna of the 10W 435MHz output from a IC451E The cable is 30m type H100 Z50 10mm outside diameter it is semi air-spaced but has an impossible 4mm² solid CU inner conductor not much air left. I preferred the H43 Z75 cable having lower loss and mechanical better ratio in conductor size. My antenna uses SO239 connector UHF type semi air spaced isolator.  3W should be enough for a comfortable noise free FM signal. But only 27km away at PA0A the signal is weak too weak something must be wrong? I made a simple reference dipole of 2x17cm CU wire. With this dipole the signals where totally worse. So the Diamond does work? I got curious to look inside. Maybe moisture penetration degraded the antenna. This  antenna is rainwater close in its n...

SPF5189z Low noise preamp 23cm

 14-4-2018 updated Above the low noise  preamp 50 - 4GHz    ebay  6€ Tested  2 small porto antennas 1 Baofeng UV antenna left   2nd best signal on PI2NOS 2 eBay DIAMONDSRH805S  wide band 144/432/1200  it works for its size as expected 3 piece of wire :   best signal in the setup... Unit under test at workbench. It was stable  50mA  at 5V   few days,  but sudden the current went up to 100mA And i could  no longer adjust it with the negative bias Voltage. The - Voltage went to zero and the SPF input port became low Z. This SPF5189z was broken  no oscillations, no input overload just it broke while i was receiving the PI2NOS 430.125 using a small antenna at the workbench. The specs of  SPF5189z  say it has an internal circuit  regulating the bias current. Replaced . again   with an other of the 5 spare SPF i have. The new one again could be adjuste...

TS790 cat interface

A CAT interface  for the old TS790 144/432/1292 tranceiver to work with N1MM  including the internal CW keyer DTR and "PTT" RTS and WSJT MSHV with "PTT" control Using the 3€ FTDI USB serial interface picture bottom page first i bought the Kenwood USB serial interface cable that cable has the TS790 special 6 pin DIN plug this interface works well ...as long as you cut the 4-5  wire bridge on the ACC din.. with the wire bridge it did go offline after 30 seconds or so  Kenwood interface cable with CH330 eBay 15€    This type Kenwood interface cable uses a tiny 6 pin USB CH330 chip  The driver is CH340 known for Arduino it workes in W7/10 64  It has only TX RX Usart function no DTR RTS available  The TS790 settings are 4800b 8bit data 2 stop  default  N1MM does not list the TS790 it has the TS890  but that one does not support modes the TS2000 does support freq and modes and let you switch 2/70/23 it seem...