Hi Andrea
I built a Driscoll generator with an SC-cut oscillator. The nominal values of resistors, capacitors and inductances correspond to the latest version of the table on page 16 of the manual. I tried using transistor MMBT5179 and NE85633.
In all cases, a generator with an oscillator of 45.158 MHz operates at a frequency of 49.158 MHz.
Changing the value of the capacitor C3 in either direction does not change anything.
Please tell me what I need to do to get the correct frequency.
I built a Driscoll generator with an SC-cut oscillator. The nominal values of resistors, capacitors and inductances correspond to the latest version of the table on page 16 of the manual. I tried using transistor MMBT5179 and NE85633.
In all cases, a generator with an oscillator of 45.158 MHz operates at a frequency of 49.158 MHz.
Changing the value of the capacitor C3 in either direction does not change anything.
Please tell me what I need to do to get the correct frequency.
Hi,
it seems that your Crystal starts at unwanted B-mode, so you need some fine tuning to get it works at the right frequency.
Firstly keep the MMBT5179 in place.
First option with fixed components: you could install C3=5.6pF C2=2.2pF R1=1K R2=330R and check the frequency.
Second option: you could replace C1 and C3 with trimmer capacitors (2-15pF) and then you have to tune these to see if the oscillator starts correctly. Finally you can measure the capacitance of the trimmer capacitors and replace them with fixed type.
Third option: keep all original component values and place an inductor with a value around 1 or 1.2 uH in series between C2 and ground.
Anyway take care to set R11 to get half VCC at Q1 collector.
Hi all,
Well, summer is approaching yet I was thinking that I'd like to share some results I got the other day measuring a small inverter test PCB likely to be used for the output of the TWTMC.
As it is my DC-Receiver (courtesy Herbert Rutgers) hopefully soon will be ready to use and to this end I have made some small test PCBs: A clock divider PCB (a FF) and an inverter PCB where different options can be tried out.
In a first round I tried the inverter PCB and among other things paralleling or not paralleling the outputs (74HCU04). I.e. a single inverter or 3 paralleled inverters. I also tried to insert a resistor (40 ohms) between the squarer inverter and the output inverters.
The latter did not really cause much change in the measurements, whereas paralleling/not paralleling the outputs caused an appr. 100% difference in the noise amplitude on the VDD pin of the inverter. Paralleling the outputs caused this ~ 100 increase in the noise amplitude.
Also, measuring the individual outputs of the inverters, what I assume is a slight difference in trigger time between the individual inverters showed up clearly on the oscilloscope. This was not the case when only one inverter was used.
One remark here: I connected the 33 ohm resistors on the output of the inverters so that the paralleling took place after these resistors and not before. Thus each inverter did not "see" another two inverters' output directly but through 2 * 33 ohms. Paralleled it would give 11 ohms output impedance plus another 33 ohms connected in series with the three paralleled 33 ohms resistors (I hope this may be visualized ;-)).
Unfortunately, I didn't save any of the key measurements - so nothing to show - but thought that I'd share this anyway.
Cheers,
Jesper
Well, summer is approaching yet I was thinking that I'd like to share some results I got the other day measuring a small inverter test PCB likely to be used for the output of the TWTMC.
As it is my DC-Receiver (courtesy Herbert Rutgers) hopefully soon will be ready to use and to this end I have made some small test PCBs: A clock divider PCB (a FF) and an inverter PCB where different options can be tried out.
In a first round I tried the inverter PCB and among other things paralleling or not paralleling the outputs (74HCU04). I.e. a single inverter or 3 paralleled inverters. I also tried to insert a resistor (40 ohms) between the squarer inverter and the output inverters.
The latter did not really cause much change in the measurements, whereas paralleling/not paralleling the outputs caused an appr. 100% difference in the noise amplitude on the VDD pin of the inverter. Paralleling the outputs caused this ~ 100 increase in the noise amplitude.
Also, measuring the individual outputs of the inverters, what I assume is a slight difference in trigger time between the individual inverters showed up clearly on the oscilloscope. This was not the case when only one inverter was used.
One remark here: I connected the 33 ohm resistors on the output of the inverters so that the paralleling took place after these resistors and not before. Thus each inverter did not "see" another two inverters' output directly but through 2 * 33 ohms. Paralleled it would give 11 ohms output impedance plus another 33 ohms connected in series with the three paralleled 33 ohms resistors (I hope this may be visualized ;-)).
Unfortunately, I didn't save any of the key measurements - so nothing to show - but thought that I'd share this anyway.
Cheers,
Jesper
How much propagation difference did you measure on the inverter? That is usually a very small number.
There are techniques for measuring the phase noise contribution of stages in a system. They can be very sensitive and are simpler than measuring a source. This may be helpful: 74AC04 Residual Phase Noise Measurements
There are techniques for measuring the phase noise contribution of stages in a system. They can be very sensitive and are simpler than measuring a source. This may be helpful: 74AC04 Residual Phase Noise Measurements
@1audio:
I didn't as such measure the propagation difference other than noticing that using three or one inverter (input pins & output resistors lifted on the unused inverters) led to both more noise (glitch I believe) on the output of the inverter(s) and also on the PSU pin.
FYI my oscilloscope has a 200 MHz bandwidth.
I haven't yet come to that as the DC-Receiver is not yet ready but hopefully soon ...
Cheers,
Jesper
I didn't as such measure the propagation difference other than noticing that using three or one inverter (input pins & output resistors lifted on the unused inverters) led to both more noise (glitch I believe) on the output of the inverter(s) and also on the PSU pin.
FYI my oscilloscope has a 200 MHz bandwidth.
I haven't yet come to that as the DC-Receiver is not yet ready but hopefully soon ...
Cheers,
Jesper
Hi ..
@Andrea: I am now laying out the 98.304 MHz oscillator (Driscoll; SC-Cut), however, neither Mouser nor Digikey have the NE85633 anymore.
Can you recommend a just-as-good-or-even-better
alternative that is available from either of these companies (mouser preferred)?
Have a good summer ;-)
Jesper
@Andrea: I am now laying out the 98.304 MHz oscillator (Driscoll; SC-Cut), however, neither Mouser nor Digikey have the NE85633 anymore.
Can you recommend a just-as-good-or-even-better
alternative that is available from either of these companies (mouser preferred)? Have a good summer ;-)
Jesper
Hi ..
@Andrea: I am now laying out the 98.304 MHz oscillator (Driscoll; SC-Cut), however, neither Mouser nor Digikey have the NE85633 anymore.
Can you recommend a just-as-good-or-even-better
Have a good summer ;-)
Jesper
Hi Jesper,
you could try the MMBT5179, usually it has enough gain to overcome the losses due to the high ESR of the crystal. Otherwise you can use the BFR182.
You can source both from Mouser.
Andrea
Hi again Andrea.
While working on the PCB layout a question more has popped up which I hope you may help with: When I look at Herbert's webpages about the Clapps oscillator I notice that the crystal casing is connected to the oscillator PCB ground:
https://www.by-rutgers.nl/rutgerS-Clock.html ... a bit down the page.
Normally I would consider this a good idea because EM noise in the air would not cause the case to change potential. Might you (or somebody else) have tried this?
Also, to this end, what is the reason there is an crystal isolator between the crystal case and the PCB (Mouser 749-CI-192-028).
Cheers,
Jesper
While working on the PCB layout a question more has popped up which I hope you may help with: When I look at Herbert's webpages about the Clapps oscillator I notice that the crystal casing is connected to the oscillator PCB ground:
https://www.by-rutgers.nl/rutgerS-Clock.html ... a bit down the page.
Normally I would consider this a good idea because EM noise in the air would not cause the case to change potential. Might you (or somebody else) have tried this?
Also, to this end, what is the reason there is an crystal isolator between the crystal case and the PCB (Mouser 749-CI-192-028).
Cheers,
Jesper
I have never tried to short the case of the crystal to ground, you need a clip such as that used by Herbert to do the job and tie it to ground, for example to the left pad of C3.
Since under the crystal there are tracks connected to different voltage, the isolator avoids any short circuit caused by the crystal case.
Onboard power supply oscillation
Hello,
Onboard power supply on D&D board oscillates when Driscol boards are connected (SC cut 45 & 49). I'll try to capture wave from the scope today. Oscillation occurs even with only one Driscoll board, otherwise it's clean. Both supplies, 6V and 3,3V are affected. I measured them first without boards attached and they were spot on but when I connected driscol boards ocillator outputs were kind a wobbly in amplitude with about 400 mVp-p 84 kHz. Then I suspected power supply as problem. Also, on 49 Mhz board I couldn't get middle point 3V with trimmer pot with mmbt5179.
Hello,
Onboard power supply on D&D board oscillates when Driscol boards are connected (SC cut 45 & 49). I'll try to capture wave from the scope today. Oscillation occurs even with only one Driscoll board, otherwise it's clean. Both supplies, 6V and 3,3V are affected. I measured them first without boards attached and they were spot on but when I connected driscol boards ocillator outputs were kind a wobbly in amplitude with about 400 mVp-p 84 kHz. Then I suspected power supply as problem. Also, on 49 Mhz board I couldn't get middle point 3V with trimmer pot with mmbt5179.
If you have on the shelf a pair of 47uF capacitors you could try to place them at the output of each regulator to understand if they suppress the oscillation.
About setting of the half Vcc at Q1 collector you have to replace R11 with a 100k one.
Thanks Andrea.
In the mean time I used external regulators and after tryouts with several mmbt's I've settled with bfr afterall on 49 clock to achieve half voltage dc output. Still didn't finish oven boards, ie only left is to prepare and solder copper tube and accompanying resistors.
I'll try 47uf. Does ESR of this capacitor matter?
Hi,
you should avoid very low ESR capacitor, you could use the Panasonic FC for example.
One more thing, thinking to the ESR of capacitor: the oscillation could also come from the output of the pre-regulators U9/U10, followed by low ESR capacitors. You could replace these capacitors with higher ESR type like this:
667-EEE-FC1E101AP from Mouser.
I tried the single buffer by blocking the contact of pin10~13 on 7404 and there is definitely some improvement on the sound. The high & extreme high is more smooth now. I think the parallel output somehow impacts the performance of the clock. I have no equipment to prove it, but I can hear it.
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