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Re: Fw: Drake 2880 additional mod




That is an interesting idea to trim out the shorting bar.

I left the hairpin loop for its inductance to get a better noise figure.  
The spec for the MGA-86563 says its typical noise figure is 2 dB with a 
50-ohm input, and 1.6 dB with an inductive input.  I left the hairpin to get 
the inductance, but without knowing whether it is the correct amount.  I may 
use an RF CAD program to look at the effects of the hairpin before I start 
cutting!

Thanks for the suggestion.

73,
Ward


>From: Bill Hurlock <bill@hurlock.net>
>To: wc0y <wc0y@msn.com>
>CC: amsat-bb@AMSAT.Org
>Subject: Re: Fw: [amsat-bb] Drake 2880 additional mod
>Date: Thu, 22 Feb 2001 12:32:15 -0500
>
>Looking at your pix you can trim out the little shorting bar on the input
>"hairpin loop" and see a bit more gain. Gives you a bit better match at 
>2401.
>
>wc0y wrote:
>
> > Several people kindly wrote me that the link to the photo showing Drake 
>2880
> > mods that I provided does not work.  I have been working on a web page 
>that
> > has the photo and more details.  Please try:
> >
> > http://communities.msn.com/wc0y
> >
> > 73,
> > Ward - WC0Y
> >
> > ----- Original Message -----
> > From: "wc0y" <wc0y@email.msn.com>
> > To: <amsat-bb@AMSAT.Org>
> > Sent: Tuesday, February 20, 2001 10:21 PM
> > Subject: [amsat-bb] Drake 2880 additional mod
> >
> > > I did one more mod to my Drake 2880 and will now quit while I am 
>ahead.  I
> > > had reported a gain of 38 dB and a 1.9 dB noise figure achieved by
> > replacing
> > > the first amplifier stage with a MGA-86563 MMIC and doing the other 
>mods
> > > described at the G3PHO site.  The next step was to protect this IC 
>from
> > > static on the input connector without loosing performance.  I plan to 
>use
> > > this converter with a helix that is not DC grounded.
> > >
> > > A photo of my modified input circuit can be found at:
> > > http://www.msnusers.com/wc0y/files/LNA.jpeg
> > >
> > > You will see two chip inductors, one in the MMIC bias circuit, and one 
>at
> > > the input connector, from the input trace to ground.  The chip 
>inductors
> > > have blue markings.
> > >
> > > These inductors are Coilcraft 0805CS-220X_BC part number.  I chose 
>this
> > one
> > > because it is designed to have a series resonant frequency (SRF) 
>around
> > 2400
> > > MHz.  It is a wire-wound chip inductor, so it should help with static
> > > discharge.  I am happy to report that placing it across the input 
>circuit
> > to
> > > ground had no measurable effect on gain or noise figure.
> > >
> > > Coilcraft has a good web site at www.coilcraft.com, and they do direct
> > > sales.
> > >
> > > If you downloaded the photograph, you will see the MMIC placed between 
>two
> > > "huge" eyelets that I inserted to get a low impedance path to the 
>ground
> > > foil on the underside.  These eyelets are 0.055 inches in diameter on 
>the
> > > body, and 0.10 inches in diameter at the collar that is visible.  That
> > shows
> > > how tiny the MMIC IC is.
> > >
> > > Hope this helps some of you with your plans.
> > >
> > > 73,
> > > Ward - WC0Y
> > >
> > > ----
> > > Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> > > To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
> >
> > ----
> > Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> > To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
>
>----
>Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
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