On 13 Apr 2022, at 22:34, Tom Lee <tomlee@...> wrote:

? What you say is largely true for the 1/f^2 part of the spectrum, but for close-in (1/f^3) phase noise, the device itself makes a large difference.

--Tom

-- 
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070

On 4/13/2022 18:32, Patricio A. Greco via groups.io wrote:

Phase noise is a characteristic of high Q resonant cavity . Or course the transistors incides but more the resonant circuit .?

Ing. Patricio A. Greco
Taller Aeronáutico de Reparación 1B-349
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On 13 Apr 2022, at 22:16, Lothar baier <Lothar@...> wrote:

?

For best phase-noise I would recommend finding a SiGe Device like the BFP740 or similar , Infineon and NXP both make great devices

?

From: [email protected] <[email protected]> On Behalf Of Tom Lee via groups.io
Sent: Wednesday, April 13, 2022 7:15 PM
To: [email protected]
Subject: Re: [HP-Agilent-Keysight-equipment] HP8640B RF Fails Several Seconds After Power Up

?

Re: Ft overhead: Keep in mind that you need more gain than the minimum that sustains oscillation in the absence of a load -- you need enough to support the power delivered to a load. On top of that, you don't want the frequency of oscillation to be affected too much by the transistor's own phase shift -- you want the resonator to control it. All those considerations argue for a healthy ft margin. I'm sure you could sub a somewhat slower transistor and still get output, but you will sacrifice some of the famous (and hard-fought) stability for which the HP8640B is prized.

-- Cheers
Tom

-- 

Prof. Thomas H. Lee

Allen Ctr., Rm. 205

350 Jane Stanford Way

Stanford University

Stanford, CA 94305-4070

On 4/13/2022 16:44, Flannel Tuba wrote:

Thank you, Arie for finding a link to the actual scanned? article! Having the pictures along with he text is quite a nice addition.

Meanwhile, I have ordered a smattering of VHF and UHF transistors from Mouser with marginally similar ratings to those Tom provided. I do wonder about the fT of 5GHz though. The oscillator's range is from 230-550MHz, so I wonder why the extreme frequency overhead margin. I went ahead and ordered a dozen or so potential replacements having at least the Vcbo of 30v, Vceo of 20v, Vebo of 4v and fT of over 600MHz with several in the 1-5GHz range. A couple are TO92 packages, which I envision just folding the base lead across the top to make contact with the grounding hex cap nut/cover, but most are SOT-23, which I'll have to come up with an adapter of some sort for. Any ideas on this are more than welcome.?

Well, if I'm lucky I'll have some time in the next few weekends to experiment with possible replacements for the rare and venerable HP 5086-7082.

I'll let you know what I find.

-Scott?

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