[Fourlanders] FW: W8ISS Group Purchase: SGA-3586AZ MMIC for 900 and 1300 MHz

[Jim Worsham]

This is for folks who bought the microwave transverter kits from W8ISS.  It
turns out that he made a substitute for one of the MMICs but didn't think to
check to see if the supply voltage or bias resistor value would need to
change so read the following.

73
Jim, W4KXY

It doesn't matter how beautiful your theory is, it doesn't matter how smart
you are.  If it doesn't agree with experiment, it's wrong.
Richard P. Feynman

-----Original Message-----
From: James French [mailto:w8iss at wideopenwest.com] 
Sent: Thursday, January 07, 2010 10:24 AM
To: Kevin Hobbs; David Palm; wb8tgy at yahoo.com; Jim Forsyth; David McKenzie;
Tom Sneden, K6VCR; Jack Davis; Jim Worsham; Simon.Bosworth; Bart Jahnke;
Dean Denter; Jim N7TCF; whensley11 at comcast.net; James Duffey;
WA4GHK at aol.com; 'Bill Pence'; 'Tom McElroy'; 'Bob Lear'; Frank Alwine;
walnuthil at juno.com; e.krome at comcast.net; Matt Patterson; Ellen;
jarritt at vt.edu; Todd Dravland-WD0T; David Muller; HDale77067 at aol.com; Andy
Lokken; WILLIAMS MICHAEL; Doug Allen; John (JK) Kalenowsky, K9JK; Jeff Pahl;
Buchanan Bill; Ethan Miller K8GU; JAY HOPPA; Steve Bunch; Scott Armstrong;
Gene; Eric Watkins; cqdx at sonoratx.net; Jill Wadsworth; David R. Hassall;
SAS-EMRS
Subject: W8ISS Group Purchase: SGA-3586AZ MMIC for 900 and 1300 MHz

This from Ben N3Um that purchased some of the boards and found something
that 
I would not have caught unless I was an engineer. 

I am passing this along so that everyone knows about this. Also, PLEASE read

the last portion of this message as it makes mention of a Arkansas group
that
has been supplying a emailer reflector as support for questions and answers
about the W1GHZ boards and parts.

=====
Hi Jim,

Just got started today actually soldering SMT components for the  
first time, after assembling all the required stuff like small  
solder, headband magnifier, fine tweezers, etc.  I was immensely  
relieved to find I could do it.  Put half or more of the SMT  
components on the 1152 MHz LO board, so it should soon be up and  
working.

Looking ahead a bit, I downloaded a data sheet for the SGA-3586Z MMIC  
amp which you sent as a substitute for the INA-10386 initially used  
by W1GHZ for the receive preamp A1 in the 900 and 1300 MHz  
transverters.  That SGA is one hot amp: I was impressed with its  
performance.  Good for you for finding it.

BUT: it is clear from page 5 of the SGA-3586Z data sheet that the  
total value of bias resistance must be 136 ohms for use with an 8  
volt power supply, or else a 5 volt supply must be used with a total  
bias resistance of 51 ohms to get the required 35 ma current.

This resistor, R3, is 51 ohms on the W1GHZ parts list, AND on the  
schematic which shows an 8 volt receive power supply.  I assume this  
was appropriate for the old INA-3086, though I couldn't easily find a  
data sheet for that part to confirm this.

By my calculation, the combination of an 8 volt supply and R3 = 51  
ohms would give 95 ma of current through an SGA-3586Z amp, very  
probably leading to cremation of the MMIC since its absolute maximum  
device current is 70 ma.

It's pretty simple to either supply 5 volts for receive, as is done  
in the 2304 transverter, or just add 86 ohms in series with the  
receive supply lead for the 900 and 1300 MHz transverters.  Doing  
neither seems likely to result in SGA-3586 destruction.

You may wish to consider disseminating this cautionary info.

73, Ben N3UM
=====
Here's the information about the 4Smicrowave groups website and discussion 
list:
4-State Microwave Discussion List
List Info:
http://lists.ae5k.us/listinfo.cgi/4smicrowave-ae5k.us
Post message: mailto:4Smicrowave at ae5k.us
Archives: http://lists.ae5k.us/pipermail/4smicrowave-ae5k.us/
4Smicrowave web page: http://4smicrowave.ae5k.us

The 4Smicrowave group did the first group purchase of parts and boards last 
April and have been supplying the discussion list there with very useful 
infomation and support for the W1GHZ boards.

This is were I also got the modified parts list along with suggestions on
where
to procure parts for the boards. I was also using the original parts list
from 
W1GHZ as reference so I may have crossed parts and not caught the dis- 
crepencies in values and question them.

I am on that list also so if anyone has questions about the boards, I will
see 
them posted.

Here's to hoping this information helps out. PLEASE join the 4Smicrowave
list
so that your questions can be answered by those more qualified and to offer
suggestions that would benefit everyone that is using these boards.

James W8ISS