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Old 19th Jan 2018, 12:15 am   #52
Bazz4CQJ
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Join Date: Apr 2009
Location: Oxfordshire, UK.
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Default Re: The Best GDO Ever Made?

Quote:
Originally Posted by G0HZU_JMR View Post
The modern ON Semi datasheet for the 2N3819 has s parameter measurements up to 900MHz and the gm holds good up past 500MHz and only really fades badly towards 900MHz. I've not tried to get a 2N3819 to oscillate at 1GHz but I think I could get fairly close...
Yes, perhaps one problem that many/all GDO's have to deal with is finding circuits/components that will enable them to operate over a range that's often 100kHz to 300MHz(?). Perhaps that's a requirement where a valve does well? That said, I have an old Taylor workshop sig gen that has one valve VFO for the LF end of the range, and a completely separate VFO for HF/VHF. Of course the Model 59 GDO was designed 'simply' to cover 2-400MHz. Could it be that by not needing (trying) to cover low frequencies, they could focus on doing the more limited job really quite well and that is a significant factor which helped it achieve some acclaim? Later on, of course, they were able to go a step further and supply a completely separate oscillator unit, using a different type of valve, which covered 400-940MHz.

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