Stabilize YIG oscillator
This YIG generator runs from 2 GHz to 8 GHz but is highly unstable (old Marconi type generator) and often drifts several MHz in a few seconds.
Fortunately, it has an external tune voltage (0 - 10 V DC) so I'm looking for a way to phase lock the output and then output a proper tune voltage.
I've thought of the ADF4108 PLL and such but am still wondering if there's another way to stabilize this YIG before getting into that CSP SMD mess.
I was thinking of something like SRD diode, generating harmonics of a stable TCXO but inputting a specific frequency might be hard since I'd have to map a tuning voltage/frequency curve and program it into an EEPROM or something like that.
Any thoughts?
Are you using it cw at ONE frequency, or are you trying to sweep it?
I want to use it for one frequency at the moment. CW signal is more important to me then the sweep
Hello there:
I have used an old-style microwave counter to stabilize a YIG oscillator at X-band.
The old HP counters had a microwave plug-in unit in which a manually tuned resonator was used, with a discriminator output. An internal precision quartz oscillator at 100 MHz generated harmonics through a comb generator, to which the resonator was tuned. Then an input signal with unknown frequency generated a beat which was counted by the lower-frequency counter.
I adopted such HP counter, so I could generate the discriminator output voltage which was used as FM input to the YIG generator. By this I locked my YIG frequency to a selected multiple of the 100 MHz precision signal.
Or, like it is done in all modern phase-locked oscillators, one can generate a comb output harmonics from any stable quartz oscillator. A diode phase detector should be used to generate the error voltage proportional to the frequency (phase) difference between the YIG output frequency and a selected harmonic. This error voltage, after a low-pass filter, can hold YIG frequency stable. I used an "ordinary" diode discriminator to stabilize a VCO at ~ 3 GHz to a stable signal.
yes, you can stabilize the yig with some sort of harmonic mixer. The only problem is that you can only use the yig with the frequency spacing of the reference frequency....so if you drive the harmonic mixer with a 100 MHz LO, you are only going to be able to tune the yig as 2000, 2100.....7900, 8000 MHz. If you can't find a harmonic mixer, you can use one of those old harmonic samplers in the HP network analyzers, you know, the ones with two apc-7 connectors on them.
If you just want it to stabilize in FM noise, but not necessarily lock the frequency tightly, you can build a simple delay line frequency discrimnator. Ideally, you would couple off some power, amplify it, to around +15 dbm, split it, send one arm to a mixer LO, and send the other arm thru perhaps 10 feet of low loss cable. The mixer IF output is a voltage +/- 200 mV that correspond to changing frequency. You can them DC connect the IF to the FM tune bnc connector input on the sweeper, and it will stabilize it. Once again, there are only certain frequencies that will lock, but you can fine tune where they will lock by adding a line stretcher of crank phase shifter to reset the zero crossing of the mixer (phase detector) IF output.
Another thing you could try is to just add a big cap across the tuning coil of the yig. You might have a noisy drive circuit that could be filtered out. Of course, you will not be able to sweep quickly after adding the cap.
G'day mate,
yup a very good suggestion .... have a look here ... http://www.thegleam.com/ke5fx/stellex.htm
John has done a lot of work with PLL/Synth controlling of YIG osc's
the PLL/Synth board is available from several ebay sellers like ....
http://cgi.ebay.com.au/2GHz-12GHz-PL...item255adb2336
I have bought several of these boards for YIG controlling
cheers
Dave
VK2TDN
Dave thanks for the link. I'll keep this in mind and I'll look over the schematics in a bit. I think I've got a few of those LMX2326 lying around here somewhere. (For a microwave counter project)
I'll try adding that large cap over the tuning coil first because I noticed some odd behavior in the YIG. At 3 GHz it was remarkably stable for about three minutes, after which it became unstable again. Almost seems like the heater is causing the instability.
they do have heater coils inside. Also, make sure the case is heat sunk to the chassis, as the current in the tuning coils can generate considerable heat.
Most of the yig coil drivers have a current feedback loop...they sense the yig coil current in a small resistor to ground. Make sure that resistor is not fried, and that the ground connection is not noisy, as that would make the driver go nutz.