Intermittent REF UNLOCK error message on 8591A Spectrum Analyzer
开云体育Hi, ? I tested this with my 8591A. I used an external generator for the 10 MHz reference. I measured the 300 MHz signal returning to the A15 COUNTER LOCK module. This way, I tested the path from the 10 MHz IN to A15, and the return from A9 THIRD CONVERTER at 300 MHz. ? I measured the 300 MHz return at the spectrum, but kept the PLL closed loop using a T-connector. ? The maximum range of the VCXO was 299.976-300.087 MHz, or 300 MHz -24/+87 kHz, but this is doubled if you measure the 600 MHz output. The RF amplitude of this signal was approximately -4.5 dBm upon arrival at the A15 COUNTER LOCK module. The DC control voltage coming from the A15 COUNTER LOCK module (J4-40) to A9 was -0.253/-13.2 Volts, and -4.645V was the voltage for an accurate input 10 MHz reference. ? For adjustment, you can see from the wiring diagram that R68 presumably allows for range centering. I haven't checked the manual yet, but I did check this potentiometer, as I've had several issues with defective potentiometers in this Spectrum series. ? Yves ? ? De?: [email protected] <[email protected]> De la part de Anders L??v via groups.io ? After further digging into my Ref Unlock error message on the HP8591A Spectrum Analyzer I have found the following. The 600 MHz SAW oscillator on A9 Third Converter assembly seems to oscillate at only 599.744 MHz on its own (without 10 MHz reference connected). With the 10 MHz reference connected, the frequency only comes up to 599.920 MHz - It does not reach 600 MHz. The VTO_TUNE signal between the Counterclock assembly and the A9 Third Converter assembly is maxed so it can not tune the 600 MHz SAW oscillator any further. ? Can the 600 MHz SAW oscillator be tweaked in some way or is the next step to replace the A9 Third Converter assembly? |
开云体育Anders, ? So, in green is the active bias stage, R66 serves as the current sense. In my case, I have 5.186V, which means that the collector current of Q13 is about 9.8mA. ? In blue is the oscillator with CR1 as a varicap for frequency control. Now, the frequency range of your circuit is too low, I would be tempted to try adjusting with R68, but make a mark on R61 to note the current state of the adjustment, because if it doesn't work, you can reset it to its original position. Since the frequency is lower than expected, and if R68 doesn't change anything, then the capacitive load is too large, I would suspect the varicap CR1 as the first suspect. ? You can always experiment by disconnecting C81; the frequency should rise higher. ? Yves ? ? De?: [email protected] <[email protected]> De la part de Anders L??v via groups.io ? Thanky you for the valuable information Yves!
? My 300 MHz VCXO range is 299.872 MHz (10 MHz Ref disconnected) to 299.959 MHz (10 MHz Ref connected) - A total range of 88 kHz which is a bit smaller than yours 111 kHz. This time I have meassured the frequency at the Cal Out to make the meassurement easier. ? I have desoldered and checked the R68 potentiometer and it was fine. |