[amsat-bb] Re: ARR Preamp Documentation

[Edward R. Cole]

At 03:15 PM 1/2/2007 -0800, Mark Brueggemann K5LXP wrote:
>
>
>Poked around the web for a while and didn't see any downloadable 
>data on ARR preamps.  I am trying to find out what the exact 
>DGFET/BPT/GaAsFET the 144 and 430 models use, and if the 
>DGFETs/BPT/GaAsFET's are interchangeable.  I anticipate blowing 
>them up when I get my sat setup going soon, and I would like to order 
>up some spare devices (exact replacements or suitable substitutes).  
>I have the PxxxVDG's but I'm reading that the DGFET and bipolar 
>versions are less ESD fragile than the GaAs ones albiet less gain.  
>Is there an advantage to one over the other in practical ham 
>satellite applications?
>
>Thanks, 
>
>Mark K5LXP
>Albuquerque, NM

Mark,

I have had several P144VDG preamps and used mgf-1302 or 1402's for
replacement.  However, these devices are difficult to find nowadays (I
scored several away for spares).  I have a P144VDA that is used as a second
preamp after my mast mounted 2m-eme preamp.  I uses a 3SK48 MosFet.  It is
used as a line amp so its 1 dBNF is sufficient.  The MosFet is less
susceptible to overdriving by the 1st preamp.  I bought a spare 3SK48
directly from ARR after accidently transmitting into the preamp.

Although the GasFet is static (ESD) sensitive, I have not had any problem
damaging them while replacing them in the preamp.
The issue of the Fets or BPT devices is they are higher noise figure
devices, not that they are less gain.  It is true the mgf-1302/1402 will
produce 22-25 dB gain at about 0.5 dBNF.

The devices are not interchageable, though.  Bias circuitry and operating
voltage vary by device.
73's,
Ed - KL7UW 
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