Hi timenuts, Here is an update for all of you interested by this project. According to the emails I got, you are a lot ;-) I spent the last 3 months trying to get rid of the self-oscillation of the prescaler. I tried nearly all possible solutions, from PCB reworking to every possible components placed everywhere. Without success. Even with both inputs grounded, the ADF4107 still oscillate at about 3.8 GHz. I switched the chip for an ADF4156. Everything worked but the damn oscillation remain. I even ordered the evaluation board from Analog in case I missed something. That board oscillate too. So I think there is no solution : the input stage oscillate for some unknown reason when the chip is used as a prescaler. I already spent too much money on this project and many other great PCB are waiting for my attention since too long. Nonetheless, that auto-oscillation is not a problem for me. After all, even my Keithley 2000 displays junk when no input is connected. So I will start taking preorders soon for the board. If you really don’t want that auto oscillation, you can add a Chebyshev Low-Pass Filter with 2 caps and 1 inductor. I tried this solution (there is room on the PCB for the filter) and the counter doesn’t display junk anymore when no input is connected. Of course, the board will be limited to ~3 GHz with the LC filter. So it’s up to you : 3 GHz without oscillation or 5+ GHz with. Here are the features : * 100 MHz to 5+ GHz Frequency * ADF4107 PLL chip used as a prescaler * PIC 16F636 (with ICSP header) to program the PLL * Sensibility up to -30 dB (graph will follow soon) * Board designed to fit the 53131A/53181A/53132A * All SMD, not less than 0805 for easy soldering * SMA input with internal SMA-BNC or SMA-TNC cable * Optional LC Filter to avoid auto-oscillation (~3 GHz limit) * Optional SMA output for a generic prescaler * Optional ratio (/256, /512, /1000) via jumper * Optional power header if used as a generic prescaler 3 options available : 1/ bare board 2/ bare board with ADF4107 (very fine pitch), PIC and other hard-to-find components soldered 3/ fully assembled board. Prices should be ~15-20€ for 1/, ~50€ for 2/ and ~200€ for 3/. I will build a final prototype soon and use it for final review of the specs. Then I’ll build a website with all pictures, technical informations, schematics and part list. Any question, just ask ;) --------------------- Samuel DEMEULEMEESTER Presse Non Stop - Canard PC <http://www.canardpc.com> http://www.canardpc.com MSN : <mailto:sam@x86.fr> sam@x86.fr

On 1/23/11 4:27 PM, Samuel DEMEULEMEESTER wrote: > Hi timenuts, > > > > Here is an update for all of you interested by this project. According to the emails I got, you are a lot ;-) > > What if both inputs are terminated into a load (e.g. 50 ohms) rather than a short? The input circuit in Fig 18 of the data sheet shows it going into a diffamp (which will be pretty Hi-Z differential) and tied through 500 ohms to the bias supply, which I assume would be (very) low Z to ground, so the input z is a few hundred ohms or so. Tying that straight to ground might not be the best way to put "no input" in. That is, the amplifier isn't stable with a mismatch on the input. Figure 27 shows a 51 ohm termination to ground (through a decoupling cap), fed by a resistive 2 way splitter. When you say the eval board also oscillates, is that with the VCO removed from the circuit, or what? >

> What if both inputs are terminated into a load (e.g. 50 ohms) rather than a short? I tried to terminate the inputs with 50 ohm between the pin and the DC block cap (and even 1 Kohm). auto-oscillations are gone, but the loss of sensibility is catastrophic. From -30 dB at 2 GHz, it drops down to +5 dB. Tried with and without amp input stage. > When you say the eval board also oscillates, is that with the VCO removed from the circuit, or what? I removed C18, so VCO was disconnected. The "best practice" for this chip seems to decouple the RFINB input from ground with a 100 pF cap and use a DC block cap on RFINA directly to the pin. In that configuration, the ADF4107 oscillate. -----Message d'origine----- De : time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] De la part de jimlux Envoyé : lundi 24 janvier 2011 02:02 À : time-nuts@febo.com Objet : Re: [time-nuts] Update on prescaler board for HP 53131A-like counters On 1/23/11 4:27 PM, Samuel DEMEULEMEESTER wrote: > Hi timenuts, > > > > Here is an update for all of you interested by this project. According > to the emails I got, you are a lot ;-) > > What if both inputs are terminated into a load (e.g. 50 ohms) rather than a short? The input circuit in Fig 18 of the data sheet shows it going into a diffamp (which will be pretty Hi-Z differential) and tied through 500 ohms to the bias supply, which I assume would be (very) low Z to ground, so the input z is a few hundred ohms or so. Tying that straight to ground might not be the best way to put "no input" in. That is, the amplifier isn't stable with a mismatch on the input. Figure 27 shows a 51 ohm termination to ground (through a decoupling cap), fed by a resistive 2 way splitter. When you say the eval board also oscillates, is that with the VCO removed from the circuit, or what? > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.