On 3 feb, 07:37, "Suzy" not@valid wrote:
Looking for a website that gives comparative performance of diodes (max
frequency for UHF use)

Hello Suzy,

The type of diode that will be best for your application depends on
the type of application.

For high level detectors (above several volts of RF input power), the
BAT62 is a good one up to some GHz. It has low capacitance (at Vj=0V)
and a reverse voltage of 40 V (fourty V). You cannot use it in low
noise mixers because of high intrinsic resistance.

Most of the HP or equivalent "hybrid" Shottky detector diodes (with
70V reverse rating) have far higher capacitance then the BAT62. Check
the datasheets, the 70V diodes are measured at Vj = -0.5V. At Vj=0V,
capacitance will be 1pF. For mixers, the best are the pure Shottky
rectifiers (that have a reverse voltage of less then 4..6V). For
Zero IF systems (Doppler radar, movement detection), other type of
shottky diodes are used (with low 1/f noise).

When you want to make a (calibrated) low level RF detector (for RF
levels 10mV), you need to consider the so-called "video
resistance" (that is the differential resistance of the diode at 0V
bias). To get full benefit of a low level detector, the DC voltmeter
(or buffer amplifier) must have a Rin video resistance. Otherwise
you cannot convert the DC voltage back to an RF input voltage.

The video resistance varies from about 10 kOhm (special "zero bias"
detector diodes) to several Mohm (for high barrier mixer diodes). Main
advantage of zero bias detector circuit is that you do not need to
build a temperature compensation (for compensating the about 2mV/degr.
C).

For UHF mixer or low level detection I use BAT15 (Cj 0.35pF at
Vj=0V).


Best regards,


Wim
PA3DJS
www.tetech.nl