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Re: Question about MMIC amp design for HP 8601a output replacement

Lothar baier
 

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I been looking at the schematic of the 8601A and have a few comments/notes on the subject of designing a replacement for this hybrid :

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I want to start with a short summary of the specifications for the device :

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  1. The output power of the amplifier is 20dBm at -30dBm Drive
  2. Amplifier has 2 stages , a driver/predriver with 30Db Gain and Power Amp with 22Db
  3. Power Supply available is 20VDC
  4. Power amplifier includes a detector with neg DC output of -1.2V at 10dBm and -3.3V at 20dBm
  5. Mechanical outline and interface TBD

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-Analyzing the requirements and looking at available parts as well as considering stability concerns it will be necessary to use a lineup with at least 2 or even better 3 stages !

- Pout specification of +20dBm narrows down useable parts quite a bit ,? since MMIC are specified using P1Db the power has to be at least 1Db higher than the output power of the module specified in the schematics

- power detector possibly using directional coupler and diode combination or Detector MMIC , scaling will be required

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For the output stage a CMA84 seems to be well suited , for the driver the MAR8A looks ok , one nuisance is that those parts just like most newer MMIC are parts running at much lower voltage than the 20V provided in the unit which mandates the use of a regulator !

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From: [email protected] <[email protected]> On Behalf Of DB via groups.io
Sent: Monday, March 21, 2022 2:58 PM
To: [email protected]
Subject: [HP-Agilent-Keysight-equipment] Question about MMIC amp design for HP 8601a output replacement

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Hi,

I've read that it may be possible to use a MMIC amp to replace the failed hybrid output amps in the HP 8601a sweep generator.? I have some MiniCircuits GALI MMIC amps and wanted to try one of these.?

I am using AppCAD for the design calcs for blocking caps but have a question about the RF choke that is in series with the 200 ohm resistor on the bias power lead.
The MiniCircuits data says the impedance of the choke should be ~500ohms at the minimum operating freq (which is 100khz for the HP 8601a).? This is giving me a value of 795uH for 500ohm impedance.

The other limitation for the choke is the SRF self resonant freq.? The chokes that I'm finding in the 795uH range all seem to have SRF much lower than the max 110Mhz freq of the 8601a.? (most of the 800uH chokes I've found have SRF around 20-50Mhz).

I would appreciate any assistance on selecting the proper choke value that will be adequate for 100khz to 110Mhz.

Thanks
DB

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