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----- Original Message -----
From: "Craig Sawyers" <c.sawyers@...>
To: "TekScopes" <TekScopes@...>
Sent: Tuesday, July 06, 2004 8:25 PM
Subject: [TekScopes] 1N21 etc

Thanks to Benoit and Vladimir, I have quite a lot of information now on

the

1N21 and 1N23 series of diodes.

There is a good amount of information on this site
, along with loads of
other interesting information about step recovery diodes (snap-off diodes

in

Tek-speak) and other microwave and high frequency components.

But here is an interesting thing - the 1N21 and 1N23 series have a

burn-out

threshold quoted in ergs - which is a unit of energy, not power. In fact

it

is a small number - between 2 and 5 (1 erg = 10^-7 Joules). Now the local
oscillator power for these mixer diodes is quoted at 1mW (in other words
10^-3 Joules/second) - so how do these figures stack up?

Or is the 2 - 5 ergs a statement of the static damage threshold? Since

they

have a point-contact junction capacitance of about 1pF or less, 2 ergs
implies a static discharge of less than 450V or so to zap the diode. That
would seem reasonable, and would explain why very early diodes were

supplied

in lead tubes (radiation hardening too?), and later ones in conductive
packets (like a few I have from Microwave Associates). It also implies

that

they ought to be handled on an antistatic bench.

The other problem is that the NTE equivalent to the 1N21 series is the
NTE112, which is actually a schottky diode (and not physically compatible,
BTW - it is wire ended) - and they state that the forward voltage drop of
0.55V at 10mA is measured with a 300us pulse length at 2% duty cycle -
implying that there is also a power damage threshold at the few mW level -
which I haven't seen quoted elsewhere. Or it could just be intended to
reduce Joule heating of the junction, which effects the forward drop. It
also doesn't quite stack up with the set-up that GR suggest using their

unit

oscillators as the Local Oscillator - and they shove out 400mW into 50

ohms.

In fact they state that 1V ought to be adequate as a local oscillator
level - and since the 874MR includes a 250 ohm series resistor indicates

at

least several mA of drive current, up to 16mA at higher drive levels.

Any further thoughts folks?

Craig





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