EMRFD Message Archive 2248
Message Date From Subject 2248 2008-10-14 21:19:27 Kevin Wheatley VCXO problems Hi to the group and help!
I have a Valpey Fisher VCXO here and can't seem to get the beast
The specific part number is VFVX321-DGEC- 125Mhz.
I believe the issue is the output impedance (although I'm usually
wrong with my hunches).
The current set-up is:
---------- 3V3 3V3 -----
2249 2008-10-14 23:47:26 brainerd@wildblue... Re: VCXO problems On 14 Oct 2008 at 18:33, Kevin Wheatley wrote:
> Hi to the group and help!
> I have a Valpey Fisher VCXO here and can't seem to get the beast
> The specific part number is VFVX321-DGEC- 125Mhz.
> I believe the issue is the output impedance (although I'm usually
> wrong with my hunches).
> The current set-up is:
> ---------- 3V3 3V3 -----
2250 2008-10-15 07:20:54 Kevin Wheatley Re: VCXO problems 2255 2008-10-15 18:50:38 wimmie262000 Re: VCXO problems 2265 2008-10-16 18:13:04 Kevin Wheatley Re: VCXO problems 2267 2008-10-16 21:24:05 Andy Re: VCXO problems Your load (130/81 ohms) is a typical ECL or PECL 50 ohm thevenin load.
Maybe you should have used a VFVX321-DGEL instead? (If that's the kind of
load you need to drive.)
Is there any reason why you can't connect that Tristate pin directly to 3V3?
If it's not truly high you're never going to see any significant output.
Your second circuit (with the transformer) is OK, but you only need one of
those two coupling capacitors.
Since you aren't getting significant output yet, disconnect the transformer
and just look at pin 4. It doesn't need a load. Do you get any output? If
yes, go from there. If no, consider that your oscillator might be
You say you see 10 mV p-p; but what are the actual high & low voltages at
Any chance the problem is in your test equipment? Does it have the
necessary bandwidth, low capacitance, and short leads?
2307 2008-10-22 08:11:05 Kevin Wheatley Re: VCXO problems