Hi guys, The 200 MHz. frequency synthesizer thread got me thinking. I could use a 200MHz VFO (say 150 to 250 MHz or something like that) I don't need much stability, a part per thousand for a several minutes would be enough. So what's the simplest way to get there? An LC oscillator (I've got some nice tunable few pF caps) There's also a VCO from Maxim. (max2607) that looks easy.
Would the manually tunable cap be more stable than the VCO?
In general a manually tunable cap is more stable, yes.
Maxim used to suck at delivery, I've avoided them for so long that I don't know if they still do.
Basically they denied that they ever discontinued parts, but on the other hand they'd only make a run of a particular chip when they got enough orders to make up a batch. So if you're a low-volume customer and you want something that doesn't move fast, you're screwed.
That was a decade ago -- people with current experience are welcome to speak up.
Do you need turn-on to turn-on stability, just something that keeps on frequency once it's tuned, or what? If you want to tune it mechanically and you care at all about getting it dead nuts on then the mechanical design can get painful -- that's part of the reason why everyone uses synthesizers these days.
An FM broadcast tuner with 100 MHz +/-10 % tuning range would be a good reference. 1000 ppm would mean 100 kHz error, which is comparable to FM frequency raster (200 kHz), thus without AFC things would work and if AFC is used, it would not jump to the wrong station.
FM broadcast receivers have achieved such stability with simple mechanical LC local oscillators for at least 60 years.
Check if Mini Circuits would have some usable VCO modules.
However, there are issues like microphonics.
There are issues with the slip ring connectors, so if you have a dual section variable capacitors, connect the sections in series, i.e. connect the stators into the resonance circuit and no connection to the rotor. Any two section BC FM variable capacitor should be ideal for 200 MHz, however the large tuning range might be an issue.
They don't deny it (better not). They discontinued an amplifier on me, after I'd built and tested the prototypes. Nice part but they decided to get out of the market. When my boss told me that they'd dropped it, the first words out of my mouth were "I told you so".
A lot of other engineers use their stuff but I've always found something else that works. We're not low volume, so not everyone has been burned. Yet.
I never had ***any*** problems with Maxim. The only downside to their avail ability is /sometimes/ you need to go with MIL or industrial grade for quic k delivery, and of course that costs more, but not really a whole lot more, won't amount to a hill of beans in small quantity. If you go with a propri etary part, one that no one else makes, you're taking a risk no matter whic h semi you go with. There are vendors out there who can dig up parts from a nywhere if you really need them, so discontinued is never a catastrophe.
I have experienced exactly such examples. The first one right after getting my degree. Due to my hobby I could hit the ground running but that was not at all the case for most of the mates there. Most could solve anything back to the Maxwell equations, strictly on paper, but not even repair their own TV set. By chance I met one of them during a business trip. "Hey, how's it going? Where did you end up?" I asked. "Oh, I started at [insert major semiconductor manufacturer here]" ... "Interesting. So what are you doing there?" ... "Writing application notes". I could not believe it.