[sci.electronics] HP Spectrum Analyzer 8558B Part Question

john@qip.UUCP (John Moore) (09/19/90)

I have an HP 8558B Spectrum Analyzer that has a blown first mixer diode.
Does anybody know which diodes would be suitable replacement. HP gets
big $$ for a replacement pair.

I believe the diodes are germanium because of their low (.34V) forward
junction voltage. They also have to be microwave, since the mixer 
operates around 2GHz.
-- 
John Moore HAM:NJ7E/CAP:T-Bird 381 {ames!ncar!noao!asuvax,mcdphx}!anasaz!john 
USnail: 7525 Clearwater Pkwy, Scottsdale,AZ 85253 anasaz!john@asuvax.eas.asu.edu
Voice: (602) 951-9326         Wishful Thinking: Long palladium, Short Petroleum
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jws@thumper.mlb.semi.harris.com (James W. Swonger) (09/20/90)

 Probably a Schottky diode. We use some from HP.

whit@milton.u.washington.edu (John Whitmore) (09/21/90)

In article <4574@qip.UUCP> john@qip.UUCP (John Moore) writes:
>
>I have an HP 8558B Spectrum Analyzer that has a blown first mixer diode.
>Does anybody know which diodes would be suitable replacement. HP gets
>big $$ for a replacement pair.
>
	HP makes a large line of Schottky diodes at all sorts of prices;
matched pair "5082-2306" for $30, "5082-2351" for $50, and "5082-2804"
for $1.31, according to Almac-Stroum's catalog (a few  years old now).
	Unless you know exactly what to get, performance will likely
suffer.  Do these numbers look familiar?  HP dealers can get you the
parts in small quantity at (perhaps) better prices than HP's repair
depot will offer.
	Don't even consider germanium, by the way; the turnon
characteristics of a diffused diode are not nearly as controllable as
those of a Schottky barrier, so matching is far worse.  This causes
some odd effects (like amplifying noise in the LO and shifting it
to the IF frequency...).

	John Whitmore

john@qip.UUCP (John Moore) (09/21/90)

In article <7899@milton.u.washington.edu> whit@milton.u.washington.edu (John Whitmore) writes:
]	Don't even consider germanium, by the way; the turnon
]characteristics of a diffused diode are not nearly as controllable as
]those of a Schottky barrier, so matching is far worse.  This causes
]some odd effects (like amplifying noise in the LO and shifting it
]to the IF frequency...).
Does a Schottky diode have a .34 Volt forward voltage drop (in a
diode tester)? I tested the surviving diode and that's what I found.
My Schottky diodes that I have in stock have a significantly higher
voltage drop.
-- 
John Moore HAM:NJ7E/CAP:T-Bird 381 {ames!ncar!noao!asuvax,mcdphx}!anasaz!john 
USnail: 7525 Clearwater Pkwy, Scottsdale,AZ 85253 anasaz!john@asuvax.eas.asu.edu
Voice: (602) 951-9326         Wishful Thinking: Long palladium, Short Petroleum
Opinion: Support ALL of the bill of rights, INCLUDING the 2nd amendment!

whit@milton.u.washington.edu (John Whitmore) (09/22/90)

In article <4615@qip.UUCP> john@qip.UUCP (John Moore) writes:

>Does a Schottky diode have a .34 Volt forward voltage drop (in a
>diode tester)? I tested the surviving diode and that's what I found.
>My Schottky diodes that I have in stock have a significantly higher
>voltage drop.

	Without knowing the test current, I couldn't say; all
Si diodes have about the same forward voltage drop, but Schottky
diodes are half-Si, half-metal, and there's a large variation
in the metals used.
	HP's 5082-2800 has Vf of 0.34 V at about 0.5 mA, according to
the data sheet, so the number looks about right.

 Part number      Matched pair           Vf at 1 mA

 5082-2800        5082-2804              0.40
 5082-2810        NA                     0.39
 5082-2301        5082-2306              0.36
 5082-2303        5082-2308              0.36
 5082-2811        5082-2815 (quad)       0.37

 5082-2835        5082-2080 (batch)      0.30
 5082-2200        5082-2201 (batch)      0.22
 5082-2520        5082-2521              0.36

 5082-2817        5082-2818              0.36
 5082-2400        5082-2401              0.36
 5082-2350        5082-2351              0.36

	Those last three are specified for noise figure at 2.0 GHz;
from the looks of it, they are your most likely candidates.
The packages should be glass, wires .015 +/- .001 inch diameter,
glass diameter .072+/-.004 inch, glass length .160 +/- .010 inch.

	All Vf's are approximate (read from small 'typical' graphs).
The '-2351' pair runs about half a decabuck.

		John Whitmore