Its a common issue that you have a lot of excess gain at lower frequencies and then roll off at higher frequencies normally you can combat this by using resistive feedback between drain and gate , it will change your input impedance and drop gain at lower frequencies!
I think the best approach would be to find a MMIC that will work , i looked through offerings from different companies and nobody seems to make discretes in SOT89 anymore?
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On May 28, 2022, at 03:13, Peter Hansen via groups.io <oz1lpr@...> wrote:
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Hello Lothar I do not need 27dBm output. As it is not the final Fet. but I think the gain of the SHF-0189 is too little. It has around 20dB at low freq but only 10 to 12dB at 4Ghz. so I might need more gain
best regards Peter
The problem is finding a HEMT in SOT89 with 27dBm ,? used to those parts were made as driver or pre-driver for Power amps but this is all done with MMIC now ,? I remember seeing a GaN HEMT made by MACOM that was SOT89 but I believe it
was a 28V part !
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As far as MMIC you can try the TQP7M9103 , its specified 400-4000MHz but you can use it at lower frequencies , this part does require external matching and only produces 13-14Db gain at 4GHz but can drive 27dBm
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Hello Lothar It is a Fet. I does have a biasing system where is measures to drop over the Drain supply and then give bias to the Gate. The circuit does include matching network. I added a SHF-0189
in the circuit and it works but too low output for the High output option mounted. I can find traces on the Net over the M11X but only that it is a HFET.
The Fet is in the ALC loop so the amplitude is not really a problem as long as there is enough. I am afraid that is not the case. I wonder if a MMIC would work in the spot. I need one working
from 250khz to 4Ghz. the 4 to 6Ghz path is another board so the Part only need to go to 4Ghz.
sorry no schematics over the E44XX series
best regards Peter OZ1LPR
Do you have the schematic of the stage ?? if so can you share it ?
Let me render a few comments / thoughts on this :
- The first thing that needs to be established is whether the original part is a FET or a MMIC amplifier ,? you can tell by looking at the schematics , if there is a bias applied to both input and output
or just the output of the block , if bias is only applied to the output than its more than likely a MMIC amplifier if bias exists on both gate and drain than it¡¯s a FET/HEMT !
- If the part is a FET than there should be matching as well as feedback networks present , since this is a stage operating over a wide frequency range resistive feedback between gate and drain will most
certainly be required in addition to lumped input and output matching circuits
- Based on the gain and output power estimate you provided as well as the frequency range of the generator I question the assessment of this part being a FET and rather assume this being a MMIC as it would
be hard to reach 20Db gain and 27dBm P1Db up to 4GHz
- If the part is a FET using matching networks it will be hard to find a drop in replacement , if you were to find a part in a SOT-89 package you will most certainly have to re-design the matching networks
as S-parameters will be different
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I am rapiring a E4438C generator. There is a FET shorted in the output of chain of the 4Ghz path. The FET is called M11X1005. I can see traces of it existing
but no data. The SHF-0189Z can be used but not directly. The M11X1005 is using 6.5V on the drain but the SHF-0189 uses 8V and has higher gain and higher output.
Does anyone have either a M11X1005 Fet, data or a suitable repleacement.
I would assume something having 20dB of gain and +27dBm output.
best regards Peter
