On 01/19/2012 09:31 PM, Don Latham wrote:
Oh dear I had the wrong idea. Thought PIN's were designed for switching.
There is a breed of "ultra-fast" diode for protection in MOSFET
switching circuits like h-bridges. Any better?
I'll replace the PIN diodes in our optical receivers at work, obviously
they can't handle the gigabits we pass through them.
Cheers,
Magnus
Don
Bob Camp
Hi
PIN = designed to be slow (not so good an idea)
Avalanche = reverse breakdown (not a good conduction mode, noisy)
Bob
-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Don Latham
Sent: Thursday, January 19, 2012 2:22 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] mixers for frequency measurement
Soooo, PIN diodes? avalanche?
Don
Bob Camp
Hi
Complicating the matter - the time it takes for the junction to go
from
full
on to full off also contributes to the noise. An ideal mixer would
switch
instantaneously.... It's always a tradeoff between various noise
sources.
Bob
-----Original Message-----
From: [email protected] [mailto:[email protected]]
On
Behalf Of ed breya
Sent: Thursday, January 19, 2012 12:36 PM
To: [email protected]
Subject: [time-nuts] mixers for frequency measurement
Yes, they are Schottkys, just like the ones used in most mixers - but
much bigger and slower. They would have to be properly impedance
matched, and could be driven to higher power levels, with higher
diode conductance, so (I think) much lower noise. Of course,
amplifying up to higher power will add noise, so it's not "free" in
that respect.
Ed
Stefan wrote:
1N5817 are schottky diodes. Wouldn't they saturate much earlier than
a 2N2222A? If saturation is the right word with a schottky diode...
I wrote:
> 5 or 10 MHz could be made even better. I wonder how a ring of
matched
> 1N5817s would work at saturated power levels - maybe +20 dBm or so.
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--
"Neither the voice of authority nor the weight of reason and argument
are as significant as experiment, for thence comes quiet to the mind."
R. Bacon
"If you don't know what it is, don't poke it."
Ghost in the Shell
Dr. Don Latham AJ7LL
Six Mile Systems LLP
17850 Six Mile Road
POB 134
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VOX 406-626-4304
www.lightningforensics.com
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