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From: RC on 21 Jul 2010 10:25
why microwave applications need devices with negative resistance?
From: Tim Wescott on 21 Jul 2010 12:18
On 07/21/2010 07:25 AM, RC wrote:
> why microwave applications need devices with negative resistance?

They don't. But treating a device as a one-port network with a negative
resistance makes a tractable way to design an oscillator. And there are
devices that are useful at microwave frequencies that exhibit a negative
resistance effect.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html
From: John Larkin on 21 Jul 2010 12:25
On Wed, 21 Jul 2010 09:18:58 -0700, Tim Wescott <tim(a)seemywebsite.com>
wrote:

>On 07/21/2010 07:25 AM, RC wrote:
>> why microwave applications need devices with negative resistance?
>
>They don't. But treating a device as a one-port network with a negative
>resistance makes a tractable way to design an oscillator. And there are
>devices that are useful at microwave frequencies that exhibit a negative
>resistance effect.

I really miss tunnel diodes. Sob.

John


From: Tim Wescott on 21 Jul 2010 12:58
On 07/21/2010 09:25 AM, John Larkin wrote:
> On Wed, 21 Jul 2010 09:18:58 -0700, Tim Wescott<tim(a)seemywebsite.com>
> wrote:
>
>> On 07/21/2010 07:25 AM, RC wrote:
>>> why microwave applications need devices with negative resistance?
>>
>> They don't. But treating a device as a one-port network with a negative
>> resistance makes a tractable way to design an oscillator. And there are
>> devices that are useful at microwave frequencies that exhibit a negative
>> resistance effect.
>
> I really miss tunnel diodes. Sob.

I missed out on it -- to young (except for my Heathkit "Tunnel Dip
Meter", which will need a complete rebuild if ever the tunnel diode
craps out).

http://en.wikipedia.org/wiki/Gunn_diode
http://en.wikipedia.org/wiki/IMPATT_diode

I believe that reflex klystrons and magnetrons also exhibit an apparent
negative resistance (or at least negative absorption) at their working
frequencies; this is what makes them oscillate.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html
From: JW on 22 Jul 2010 06:07
On Wed, 21 Jul 2010 09:25:21 -0700 John Larkin
<jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in Message id:
<nq7e46h4lum2916sdsra0qe2vcst6n43nb(a)4ax.com>:

>I really miss tunnel diodes. Sob.

You got me curious. Taking a look around the net I only found a hand-full
of companies who still manufacture them, and the prices are outrageous. Is
there a reason why they are not so popular anymore? Were they always so
expensive?

I think they were more popular once but I guess that was before my time...
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