EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: SaabFAN on September 08, 2016, 10:41:08 pm
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Since I have bought a PM6654C on ebay, I have had the idea of adding the Prescaler-module to it to give it the ability to detect frequencies up to 1.5Ghz or even higher.
The reasons behind this: My cheap 2.4GHz counter from ebay doesn't really fit into my setup on my bench and adding the functionality to the PM6654C would save one device. Also i don't like the fact that my device has the connector and the silk-screen for the RF-Option on the Front-Panel but no RF-Option installed :)
Fortunately, Philips provided full schematics for the options in the Service Manual, so I started remodeling the circuit in Circuit Maker with slightly different components:
- I'm using a BGA2869 MMIC from NXP instead of a 6-stage amplifier made out of discrete transistors.
- Instead of using one 1:2 Prescaler and one 1:8 prescaler, I use 2 MC12095D Prescalers that perform division by 4 and offer a shutdown-mode.
- Instead of the NE5512, I use a NE5535 Dual OpAmp for the Shutoff-Control (turns off the last prescaler-Chip when the input-signal is too weak.
- I am also using standard SMA-Connectors, so the connector on the Coax-Cable that is attached to the BNC-Connector in the Front-Panel needs to be replaced by an SMA-Connector.
The budget for this thing is less than 40€, which includes 10 PCBs from china.
What I need though, are the correct measurements for the board, as well as where to connect the little connector called BU2. The mainboard has no cutouts for it and there's nothing on the Input-Board either.
Could anyone with that counter and the PM9610 installed take some pictures? Google isn't too helpful in this regard unfortunately.
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Schematic for the Original Unit and the new Version with more modern components.
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I can't help with the photo, but I would love to buy a couple of boards when you have them.
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I have finished the layout of the PCB in CircuitMaker.
I have tried to avoid bends in the traces that carry high frequency-stuff and chose a Coplanar Waveguide for the 50Ohm trace that runs from the Input to the amplifier and into the Prescaler.
The board-size is 15cm X 4cm - the unit is rather small in terms of height.
I haven't put anything of that sort in the board yet, but I think that at least everything before the MMIC should be shielded - The Philips Engineers apparently didn't think so when they made the second generation of the board, despite the fact that it is right next to the Display, which does consume a bit of current :)
Btw. on the 3D-View the board has staight connectors - That's wrong. The Connector has to be angled, but was too lazy to search for a fitting model in the Circuitmaker-Database.
Ideas / Suggestions are welcome. I haven't calculated the signal-levels before and after the amplifier yet, but NXP offers quite a broad range of MMICs in the small 6-pad SMD-Package. So there is the possibility of using a different type if the one I have specified now doesn't work.
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I have just checked the signal-levels: The MMIC has a maximum rating of 10dBm Input-Power, which should be enough for the automatic attenuator, which should kick in once the voltage rises above 0,5V.
In the other direction the MC12095 has a toggle-sensitivity of 200mVpp, which is just above the signal-level if one puts 10Vrms into the Input-Connector.
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Hi,
That was very timely, I just "found" the PM6654 I bought on ebay 5 years ago that did not work this evening. I was looking for something else in the attic. I'd forgotten all about it. Anyway having fixed it this evening, I thought it would be nice to fit a prescaler, googed PM6654 and this popped up.
I would be very keen to have a PCB if you get a batch made.
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I also own this model of counter :)
If a prescaler PCB, unpopulated or populated, becomes available to purchase, I would love one for my unit.
Fraser
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Just to be on the safe side, I have added two Minimelf 1N4148 Diodes at the Input of the first Prescaler. I doubt that the MMIC will be able to dump too much voltage into the Prescaler and blow it up, but with RF and possible impedance missmatches, anything is possible :)
Anyway, if you guys think that there's nothing fundamentally wrong with the circuit I drew up, I'll check if it fit well into the counter (with a paper model^^) and then order the boards. I already have all the components, so once I order them it will be about 2 to 3 weeks until I can show some success, or some smoky stuff :D
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I just added the necessary Jumper-Links to make the use of MC12093 instead of the MC12095 possible because the latter one has been discontinued. The MC12093 ist still active and available on Digikey for quite expensive 4,50€. The MC12095 can be found on ebay for about 1€ in signle quantities or 5€ for 10 pieces.
This updates the design to REV. C.
I haven't checked how well the board fits yet and I'm not sure if I really want to or if I'll just roll with it now and later just buy some larger metal-pieces to form the retainers :)
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REV. D:
- Replaced the two LL4148 with one BAV99.
- Replaced the Bourns 3313S-1-102 Trim Pot by a Bourns 3296W-1-102LF - I have quite a few of these Trim-Pots here and I guess everyone else has at least a few of them too :)
- Complete rearrangement of the board to make the pot more accessible if the one with the top-screw has to be used instead of the one with the screw mounted at the side.
- Made it more clear that there is an inductor connected in parallel to C18 in the schematic.
I have also checked inside the Counter if it all fits and to verify that just shorting Pins 5 and 6 on the connector activates Channel C - It does :)
I'm now going to order the boards. I've checked the Footprints of all components (the Footprint of the Trim-Pot was wrong: The Wiper was on Pin 3 instead of 2, like it is specified in the datasheet - The database of Circuitmaker sometimes isn't too reliable in this regard...) and have made sure that the trim-pot is easily reachable. If there's no GPIB-Module installed, it can be reached rather easily with a screwdriver. If the pot with the side-mounted screw is used, there's no problem in that regard of course.
Once I have the boards here, I need something to verify their performance. Unfortunately, the fastest thingie I have here is a Si5153 on an Adafruit Board, which goes up to about 160MHz. I could try to build a fast enough oscillator, but given my history with VCOs and hand-made inductors, I see some problems ahead :)
Btw. once I have the boards, where would be the best place to put them up for sale? I'll order 10 and only need one of course. eBay?
EDIT: 3D-View of the Board and BOM added.
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Hiya,
As previously stated, I would love to buy a board from you. You could place then in the Buy and Sell section of this forum for our fellow members. Set your price to that with which YOU are comfortable. I.e. I do not expect you to sell them at cost. Once you have fed the forum members with their needs you will get feedback on performance and any issues. You then have the option to sell PCB's and/or complete kits on eBay with Bona Fide quotes from happy members here who have built it. Such feedback is invaluable for sales. You can also reference this forum thread as part of the eBay auction.
I would buy a complete kit of parts if it were available so please consider me a very interested party.
Best Wishes
Fraser
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Hi
If a prescaler PCB, or PCB comes available to purchase, I would love one to.
Marc
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Short update:
- Boards are still listed as "Producing" on the ShenZhen2U Website
- If someone is interested, here is the Link to the CircuitMaker project: http://circuitmaker.com/Projects/Details/Thorsten-Schroeder/Philips-PM9610-Replacement (http://circuitmaker.com/Projects/Details/Thorsten-Schroeder/Philips-PM9610-Replacement) Maybe if there are enough "thumbs up" for it it gets to the main page with the features projects ;D
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The boards are here and my curse strikes again: They kinda work, but not too well -.-
As you can see on the attached pictures, there's alot of noise and oscillation in the signal after the first prescaler and it gets worse after the second prescaler.
As you can imagine, the counter doesn't really know what to do with such an unclean signal and displays higher frequencies than the one that is put in. With no input the counter counts about 1,21GHz, which is probably the noise that gets amplified and lowpass-filtered by the DC Block-Capacitors.
At the moment I have the following culprits:
- The Prescalers are capable of too high frequencies and are toggling on a harmonic as well as the fundamental frequency - They are capable of 2.5GHz and per datasheet their useful operation area starts at 500MHz. This would mean I need other prescalers.
- Noise gets amplified enough for the prescalers to toggle on them, which I would say is unlikely because I have to go down to 10mV/div on my scope to see noise on the supply-lines, which is probably already inside the noise-floor of the scope. This would mean bigger or more caps.
- The prescaler cannot be connected directly to each other and require DC-Blocks to work properly. This would mean I have to hack the board to get a DC-Block in there.
- The prescalers need larger output capacitances to suppress parasitic oscillations and harmonics. This could be fixed the easiest way: Just add a bunch of caps :)
Any other reasons for this behavior?
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I had this problem some years ago when I made a prescaler for another Philips counter. I didn't have the original schematic so I just adapted a prescaler from another design (an Elektor project that used an MB512).
In my case, it was OK when given a reasonable signal, but tended to read non-zero when disconnected. The problem is self-oscillation. If you google prescaler self-oscillation you'll find it's a common problem with most home made designs. I think one way of dealing with it on commercial designs is to block the divided signal if it's below the level the input can work reliably with.
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If you're looking for a different prescaler, check out the Fujitsu MB506. I've had very good results with it. On perfboard even.
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Well, I got it mostly to work now.
It took some cutting and component-acrobatics, but I finally managed to get a decent waveform at the output that the counter can use. I also discovered that the biggest problem wasn't the board itself, but the Si5351 Adafruit board I used as a signal generator. Using it at 120MHz caused the output to contain considerable jitter which made the output of the prescaler-board look a lot worse than it actually was.
Self-Oscillation and a lot of harmonics is riding on top of the output waveform, but at as there is a circuit on the board that shuts off the output if there is no input-signal, this is no problem as long as the input-signal is handled correctly.
Which brings me to the biggest problem I'm having at the moment: It does not handle the signal correctly! The second Prescaler performs the correct /4 division, but the first one doesn't.
I already changed the chip because I suspected a faulty one from the 5 piece lot I bought on ebay, but the problem remains: The first prescaler only does division by 2. Both ICs have basically the same connection with both SW-Pins grounded.
Btw. the datasheet specifies the SW-Pin to be open for a low-condition, but if I leave the pin unconnected the voltage at the pin rises to about 3,5V and it still keeps dividing just by 2.
The picture with the counter displaying 100MHz was taken with the math function active which added a multiplier of 0.5 to the counter-result.
When searching for other prescaler-chips I also found some interesting replacements (pin-compatible).
A suitable set of chips would be the MC12026 (both control Pins set to high) together with the MC12083 (/2 divider with standby). The MC12026 could also be used standalone with some board-hacking, but that would defeat the standby-control as this chip has no standby-input. This chip is compatible with the boards I have here now.
About building the board: I've specified BAT54JFilm and BAP50-03 diodes in several places, but with a cut off leg regular BAT54C or schottky diodes in a similar package will also fit.
I also used 0402 components in several places so components ranging from 0805 down to 0402-package fit on the footprints.
With board revision D some cutting of traces and mounting resistors and capacitors on top of each other is necessary.
I don't know yet if I'm going to order another batch, as this board seems to work except for the problem with the first prescaler mentioned earlier (anyone have an idea about that?).
EDIT: Was a bit late and forgot to add the picture of the counter with the prescaler in it :)
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Is there any chance your input signal isn't clean enough and the first prescaler is triggering on an undesired harmonic? Are you able to scope the input and output to see it really only dividing by 2? My only other thought is that the input signal is so noisy going into the first prescaler that it sees voltage on pin 6 even when it is grounded.
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The sine-wave at the input is pretty clean.
But as you can see in the attached pictures, there's excessive jitter on it at the output of the first prescaler.
When I look at the output signal of the first prescaler more closely, it seems as if there's some frequency-mixing going on...
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By the way, this is the signal from the Si5351. It is not exactly clean, but I don't have any better signal source upwards of 10MHz here at the moment.
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I have looked at the difference between the connection of the first and second prescaler:
The only difference is that the first one has a trace running under it that is connected to the +5V supply.
Could that be enough to cause oscillation if there's some noise on this particular trace?
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I have looked at the difference between the connection of the first and second prescaler:
The only difference is that the first one has a trace running under it that is connected to the +5V supply.
Could that be enough to cause oscillation if there's some noise on this particular trace?
Hard to say for sure but having a solid ground plane under the IC is important and standard practice for the frequencies involved.
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I’ve had a brief look at your circuit and there are a few issues striking me immediately.
D2 and D3 are specified as BAT54? These are totally inadequate, with a capacitance of 10pF @ 1V, compared to the original BAT17, which is 1pF @ 0V.
This means that the input of the MMIC is loaded with ~20pF and the corner frequency is 318MHz, thus making the circuit very insensitive at high frequencies.
Furthermore, at higher frequencies like 1GHz, the input impedance seen by the MMIC is very low and almost purely capacitive, which might lead to stability issues.
Apart from the capacitive loading, these diodes appear to be part of an RF detector which produces the control voltage for the pin diodes. Therefore these diodes need to work up to several GHz, whereas a slow BAT54 will not be good for more than maybe 100MHz.
Then the output of the MMIC is loaded with 25 ohms, which means a major mismatch (C13, R11 in parallel with C14, R20).
BTW. What is that shorted C18? Even if it’s not shorted, it will still act like a short at 1GHz or above anyway. This again will not aid stability and clean signals.
So I recommend solving these issues first before looking any further.
BAT14 is still available, but of course any other UHF mixer diode will do the job, as long as the capacitance is <1pF and the max. forward current can be at least 30mA.
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I’ve had a brief look at your circuit and there are a few issues striking me immediately.
D2 and D3 are specified as BAT54? These are totally inadequate, with a capacitance of 10pF @ 1V, compared to the original BAT17, which is 1pF @ 0V.
This means that the input of the MMIC is loaded with ~20pF and the corner frequency is 318MHz, thus making the circuit very insensitive at high frequencies.
Furthermore, at higher frequencies like 1GHz, the input impedance seen by the MMIC is very low and almost purely capacitive, which might lead to stability issues.
Apart from the capacitive loading, these diodes appear to be part of an RF detector which produces the control voltage for the pin diodes. Therefore these diodes need to work up to several GHz, whereas a slow BAT54 will not be good for more than maybe 100MHz.
Then the output of the MMIC is loaded with 25 ohms, which means a major mismatch (C13, R11 in parallel with C14, R20).
BTW. What is that shorted C18? Even if it’s not shorted, it will still act like a short at 1GHz or above anyway. This again will not aid stability and clean signals.
So I recommend solving these issues first before looking any further.
BAT14 is still available, but of course any other UHF mixer diode will do the job, as long as the capacitance is <1pF and the max. forward current can be at least 30mA.
Thanks for pointing out the problems.
I completely missed the parallel connection of the termination resistors :)
I just replaced the resistors with 100Ohms each, which improved the sensitivity a bit.
The Diodes will have to stay the same for the time being, as I don't have any better ones, but I will try to get better ones on ebay (digikey requires 65€ order and I just ordered something about a week ago^^).
C18 is connected in parallel with an tiny microstrip-inductor on the board, forming a notch-filter at about 1,55GHz. My best guess is that it is supposed to stop RF-Power from reaching the detector if the input-frequency exceeds 1,5GHz and therefore the Prescaler is disabled - I haven't paid too much attention to that part though and just copied it from the original schematic :)
The biggest success I just had by inserting some copper foil underneath the first prescaler that I connected to ground. At least when connected on the bench, I now have the correct division ratio at the output. It seems to require some "warm-up" time, but after about 30 to 60seconds it shows the correct frequency (this might be a problem with the Si5351 though).
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So you’re making progress … :-+
Don’t you have a ground plane under the prescaler? If so, the copper foil shouldn’t make a difference. Sorry if this sounds daft, but I haven’t really studied your PCB design.
As for the diodes – for the time being, even a humble “computer diode” like 1N914 or 1N4148 would surpass the BAT54 by quite a margin. Even better would be 1N4151 or at least 1N4448.
Yes, these are no Schottky, but that doesn’t really matter for now.
Try to replace the BAT54 with the fastest Si diode (lowest capacitance) you have, and then compare the sensitivity at 1GHz or above – you should see a substantial improvement, even though quite obviously no Si diode can ever match a dedicated RF detector/mixer Schottky diode.
EDIT: oh, forgot to mention the notch filter at 1.55GHz - isn't your design meant to go higher than that?
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I actually thought about putting in some LL4148 but didn't do that because I though it was more important to use schottkys there.
Although at the moment it probably doesn't really make a difference because the highest frequency I can generate here is about 140MHz.
I have a solid ground plane underneath the second prescaler, but I have routed the +5V supply to the Standby-Pin on the top layer.
Interestingly, I have discovered that there seems to be a mechanical problem as well - If I put pressure on the board from the right side and at the correct spot, it suddenly puts out a perfectly clean ECL-Signal at 6,25MHz (Input = 100MHz). I have checked the signal at basically every place and it stays constant until the first prescaler. That one is the pressure-sensitive one...
I am now soldering another board with the copper-foil in place from the beginning and putting in 3,3nF coupling capacitors (easier to solder), as well as all the other hacks I have already employed to get it to work. Once I have it up and running I'll incorporate all the changes into the design and order another batch in China.
It is true that my design could go higher than 1,5GHz because I use 2,5GHz prescaler-chips, but the counter is only able to count up to 120MHz, which translates to 1950MHz at the prescaler-input. Changing the capacitor will pull the notch higher in frequency - I just assumed 1nH inductance of the short 6mil trace parallel to the capacitor btw.
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Regarding D1 and D4, at low frequencies the only difference between normal and Schottky diodes is the control voltage offset for the PIN diode attenuator/limiter. At 100MHz the difference is negligible in this application.
Much more important is that these diodes need to be fast enough to provide a proper detector function up to at least 2GHz. I’m not aware of any normal Si-diode that could do that, but an average Schottky diode won’t be any better either. You really need an ultrafast diode specifically designed for RF detector/mixer applications.
Just to illustrate the difference, I’ve simulated your input circuit with three different diodes for the RF detector: BAT15 (which is a proper RF mixer diode and roughly equivalent to BAT17, but appears to be more robust) BAT54 (which is not intended for HF) and 1N4148. See the results below:
(https://www.eevblog.com/forum/testgear/replacement-for-the-pm9610-prescaler-for-philips-pm6654-high-precision-counter/?action=dlattach;attach=263961)
As can be seen, with BAT 15 the input circuit works up to 5GHz within less than 3dB, no problem. Of course, the parasitic elements in a real world circuit would make the results worse, but we are just looking at the diodes right now.
BAT54 on the other hand causes 10dB attenuation at 1GHz due to its large capacitance already, and the automatic level adjust for input attenuation/limiting will not work at that high frequencies either. Ironically, the latter will most probably not even be a problem, as it merely causes additional attenuation at higher input levels.
1N4148 does a significantly better job than the BAT54 and causes little more than 3dB attenuation at 1GHz.
One more remark with regard to the input circuit. R10, L2 and C12 can be omitted, as this quite obviously is nothing more than a low frequency gain correction for the discrete amplifier in the original Philips design, not needed for the MMIC. This will further improve the overall frequency response, because less components in the signal path also means less parasitics.
Regarding the notch filter with C18, I don’t quite get it.
What’s the benefit of the prescaler turning off at higher frequencies?
And if there’s a benefit, wouldn’t be a lowpass filter be more suitable?
Finally for the ground plane. So I understand you only have a 2-layer PCB and there is no solid ground plane, i.e. other traces running on the same layer, thus disrupting it. Well, in this case, it’s not a ground plane any more. For a high frequency design like this, a 4-layer PCB with true ground (and supply) plane(s) would be clearly indicated.
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I don't know what the Philips-Engineers were thinking either when they put the notch-filter in there. Maybe it was smaller than using a low-pass on the crammed board... We'll probably never know because I doubt one of the designers of this board will come here and tell us :)
I have now ordered a few BAT17 from Conrad and a VCO to generate higher frequencies. But for the time the LL4148 will have to do. They are the ones with the lowest capacitance and specified reverse recovery time - some manufacturers specify it in the datasheet some unfortunately don't...
The ground planes on the top and bottom layer around the RF-Path is basically uninterrupted except for the supply of the MMIC and next to the Prescalers. The one mistake I probably made was that I routed the pullup for the first prescaler on the top layer underneath the chip instead of the bottom layer.
The updated PCB has the pullup-line for the standby-pin of both prescalers routed in a way that the RF-Path up to the second prescaler has an uninterrupted ground-plane beneath it.
A 4-Layer board seems like overkill to me and would also be prohibitively expensive (27€ vs. 84€ for 10 boards).
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I don't know what the Philips-Engineers were thinking either when they put the notch-filter in there. Maybe it was smaller than using a low-pass The updated PCB has the pullup-line for the standby-pin of both prescalers routed in a way that the RF-Path up to the second prescaler has an uninterrupted ground-plane beneath it.
That sounds good.
Basically, you're right, the ground plane is most important for the high frequency section of the PCB.
But behind the 2nd prescaler, frequencies up to 120MHz aren't exactly low either. More importantly, this is the output of a digital divider, hence a digital signal with steep edges, hence lots of strong harmonics. So you should try hard to get a true (uninterrupted) ground plane for the entire signal path from input to output of the entire circuit - where "ground plane" refers to a reasonable low inductance (hence as wide as possible, but never less than say 3mm) copper trace going straight from input to output. This is the only thing that really matters. All the other ground connected copper areas will give some shielding, but do not contribute to signal integritiy in any way.
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I'm pretty sure it is working now. The little piece of copper foil underneath the first Prescaler seems to have been the solution. The counter is now able to count 100MHz sent to the prescaler. Above 100MHz the output of the Si5351 gets really jittery and the frequency count jumps up and down several MHz at the prescaler-input and even worse at the normal Input (terminated with 50 Ohms of course).
I haven't checked or adjusted the Standby-Circuit yet because I'm currently using a LL4148 as the detector-diode and BAS70 Schottky-Diodes (those were the ones with the lowest capacity I could find in my part-box - Unfortunately without any information about reverse recovery in the datasheet) for the automatic Attenuator.
Now I have to wait for the diodes and build something that can generate higher frequencies. I have 2 GHZ VCOs in my part-box, as well as an ADF4351 Module intended for my Spectrum Analyzer. I'm still at least a little bit tempted to buy the 8922H that is offered on ebay for about a year now for 350€ - It has an RF-Generator in it that goes up to 1GHz. :)
Well, if someone want's one of these prototype-boards, you can have them for 5€ per board plus shipping. They require cutting one trace and soldering a 1nF cap manhattan-style to the first pin of the first prescaler, as well as the copper-foil underneath the first prescaler (see Screenshot of the 3D-Rendering of the board).
I'm going to order the new design in 2 or 3 weeks I think. Still trying to get a HP Spectrum Analyzer and I need to save money^^
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Just to be clear: The 5€/PCB offer is for the unpopulated non-reworked PCB.
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I have just checked the lower end of the Prescaler-Board: It works down to at least 26MHz and about 5mVrms (measured by putting the output of a 26MHz TCXO through a 10dB and 14dB attenuator before feeding it into the counter).
I haven't gotten around to build a signal source that produces higher frequencies than 120MHz though, so I havent been able to check the performance at higher frequencies yet.
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Could I use Micrel prescaler SYS89875U for divider ?
There is reset as well, I enclose datasheet...
The PM9610 is divider 16?
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I don't think that that component is capable of producing the required signal-levels to drive the MC10102 NOR-Gate on the mainboard of the counter correctly.
It requires PECL-Levels and the chip you're asking about has LVDS-Outputs.
If you power it with close to +4V, it might work, but the chip is operating close to the maximum rating, which isn't recommended.
What you could do: Use a fast comparator at the output of the prescaler to produce the right signal levels for the ECL-Circuits on the mainboard.
But before that: Try to inject a 250 mVpp signal directly at the connector for the Prescaler-Module and measure the output of IC116 on the mainboard with channel C enabled. If there is a signal at pin 2 of IC116, your chip should work without a comparator.
With that in mind, every other 1:16 Prescaler should also work, provided that the output is PECL-Compatible.
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OK, Thank You much! The 1:16 dividers with LVPECL out
are reachable :) But there is connector BU2 and BU302
in elder version, but I don`t have it :( Where I can enable
input C on processor board? David
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No idea what Connector BU302 / BU02 does.
My counter has no holes in the mainboard at that location and the service-manual doesn't mention anything that would connect to this connector and the diode located there.
It might be possible that the PM9610 was used in other counters as well, though, and those needed that connector to enable the high frequency channel.
To activate channel C on the PM6652 and PM6654, the pins 5 and 6 on connector BU107 have to be connected. That sets the configuration-bit for the RF-Option.
Btw. when testing the ADF4351 at different frequencies, I discovered that my board is able to prescale a 2.4GHz signal at 0dBm - But there's a notch around 1.6GHz (displayed frequency jumps all over the place) and 3GHz is too much (counter only displays "0."
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It would be like this scheme? I have several MiniCircuits
MAR6, or ERA3 should be working up 2GHz, the divider
MC12095 is easy to buy on Ebay :) This scheme would
be produced noice and wrong counter`s display, but I think in cause "right signal" the counter should be displayed right value :) Thanks and Happy Easter
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Yes, in the absence of a strong enough signal, the counter "counts" the noise. Also the Prescalers tend to self-oscillate at a certain frequency.
That's why the detector-circuit with the OpAmp is in there. It turns off the prescalers if the input-signal isn't strong enough, preventing any signal from appearing at the output.
I have included the detector-circuit on by board, but at the moment I've turned down the sensitivity of the circuit so the prescalers are always on. In essence it works like the circuit you drew up.
Important is a 30dB gain at the input to be able to count a 10mVrms signal and the limiter to go up to 12Vrms without blowing the amplifier.
Edit: You need a termination-resistor between the MMIC and the Prescaler. It doesn't have a 50 Ohm Input-Impedance, so no termination will create reflections and all kinds of trouble. The Terminator must be on its own segment of the signal-path with DC-Blocks in both directions. You cannot connect it directly to the input-pin of the prescaler. It would eat up the bias-voltage at that pin and make the ECL-Circuit inside Prescaler "deaf".
Also keep in mind to have a solid ground-plane underneath the chip, or it WILL become an oscillator (see earlier posts).
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My idea is use RF detektor LT5538 with comparator, where You
can set needed GAIN,
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Why use such an expensive chip when you can do the same with a simple diode? You don't want to measure the RF-Voltage accurately over a huge dB-Range. You just need a rough value for the comparator to turn the outputs on or off.
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You have true, LT is expensive, in package exacting for soldering
:(
I don`t know, but AD8313 in CONTROLLER MODE would be
controll directly divider MC12095? The scheme will be plainer
with this chip from Ebay?
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Attempt for improve scheme
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It generally should work, but I see a few problems:
- The MC12095 has it's input loaded with 56 Ohms. I made that mistake too and it just doesn't work. The sensitivity of the chip is extremely low if you put a resistor there. You need to place a DC-Block capacitor between the terminator and the input-pin of the Prescaler. It is an ECL-Circuit and has bias-voltage at the input-pin. Disturb that bias-voltage and the chip stops working correctly.
Also the DC-Block capacitors at the inverting inputs of the prescalers should match the capacitance of the other DC-Block caps.
- What's the purpose of R13? At 10 Ohms it will load down the output significantly. To have 5V across it, there needs to be a current of 500mA flowing through it. Way more than such a tiny chip can handle. If used at all, you can put 1k or 10k there. The SB-Input is relatively high impedance (as high as ECL-Inputs can be) and the AD8313 has a totem pole output-stage. If it want's the standby-pin to go LOW, it will pull it actively low, so no actual need for a pulldown-resistor.
- The detector and the Prescaler both have 50 Ohms termination, which results in a 25 Ohm load for the ERA-3 Amplifier, resulting in reduced amplitude. Made the same mistake and was pointed towards it by another forum-member. Replacing the termination-resistors with 100 Ohms resistors made the circuit work a lot better.
Also not so much a problem, but unecessary: You don't need a DC-Block capacitor at the output of the second Prescaler-chip. At that point you're connecting digital circuits, which generally speaking like their signals at either 0V or as close to Vcc as possible (in this case 5V).
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Yes, R13 is mistake, I was thinking about 1K resistor. I will revork
output from MAR6. Thank You.
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reworked scheme
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Your schematic looks good, except for the terminators R9 and R10.
The way you have connected them, you have formed a voltage-divider with R1, resulting in a much lower DC-Voltage at Pin 3 of the MMIC.
You need to isolate the DC-Supply from the terminators by two additional DC Block-Capacitors (see attached picture)
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I will make test platine :) Thank You
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I'd put way more clearance between the HF traces and the ground pours. Say at least 2mm or so but there are online tools which can calculate the minimum clearance between a microstrip and ground pours.
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reworked platine
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I would also add Ground-Stitching Vias to the board to connect the top and bottom ground-plane.
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Thank You for Your idea.
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Yes, extra stitches are necessary and put an extra via (or two) at each capacitor in the RF path to connect the capacitor to the reference plane otherwise the current will flow along the edges of the copper ground pour on the top and the circuit won't work as expected.
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someone has any empy pcb's available ?
regards
Tom
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I placed board with prescaler in counter. I have tested 50MHz
sine signal, counter starts rightly count from 45mV RMS and
logaritmic detector works fine, and disable prescaler without signal.
It needs some test on UHF, but I don`t have gener :(
The output from AD8313 can`t be pulled to ground
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test UHF 1GHz, works well, level sinus signal 100mV RMS.
AD8313 volume to ground occurs noice, 30mV RMS signal,
is good with MAR6, original PM9610 has 10mV level.
Chanel A date is 120MHz, but counts up 200MHz
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My 6654C needs its powers supply refurbishing due to capacitor ageing. It has been on my to-do list for ages so I am going to rehome it. This also means that I no longer need my Prescaler upgrade PCB's. After reading this thread I purchased two of the PCB's and some of the key components from the OP.
I will sell the PCB's and parts for what I paid for them. PM me if interested.
Update : Just checked on pricing......
I paid 30 Euros for 2 boards, 2 MMICs and 3 Prescaler-Chips. IIRC, at least one of the prescalers had been used by SaabFan for testing but carefully removed afterwards.
Fraser
UK
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I've now updated the board to revision F.
Changes:
- Attenuator upgraded to handle up to 12 Vrms, as stated on the front panel of the instrument, and dissipate 5,9 dB of that power.
- Prescaler-Footprints reconfigured with Jumpers, so different types of Prescalers can be used.
- Removed the Notch-Filter for the Power-Detector.
- Switched the connections of the OpAmp (Input is pulled BELOW 5V once RF-Power is applied).
- Negative power-supply of the OpAmp is now regulated with a zener to -3,7V. (Suggestion by a User of the Circuit Maker-community)
I'm thinking about using the unused board-space to add an AD8307 or a similar chip, capable of measuring RF-Power. An ADC or Microcontroller would then measure the output-voltage and make the digital information available by some means. USB-Connector at the rear or OLED-Display to be mounted externally would be possible.
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If you have front panel connections, the rear BNC ones are not used.
Or the other way around.
The Philips mini-coax connectors are a bit of a mystery.
Either they are very obscure or a SMC type variant.
Checking around this week.
They seem to be used around the 80'ies / 90'ies.
Educational: https://ewh.ieee.org/r1/new_york/tz/2007/20070315presentation.ppt
and from the same site: Quartz Crystal Resonators and Oscillators
Picture is from the same site.
Regards,
Frans
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Yes, the connector on the coax-cable connected to the BNC-Connector in the front-panel is strange.
But there's just enough coax-cable available for 2 attempts to solder an SMA-Connector to it. So I think using SMA-Connectors is the best way to go :)
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Also for the +5V test connector?
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I've designed a new version. It still uses the MC12095 / 12093 Prescaler-Chips, but also adds a Power-Meter and an ADC to read the voltage coming from the chip measuring the RF-Power (about 36dB down from the actual input-power).
I have bought 5 boards and there are now 3 left, so if someone wants to get one of those, please PM me. :)
Attached are pictures of the new boards.
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The original 1.5 GHz input board had it's input part shielded with a ni-plated brass box, soldered over the pre-scaler part.
Frans
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The shields on the original units were most likely there because Philips had to build the RF-Amp with discrete components with the technology available. For the first Version they even had to use through hole-components.
With the Amp implemented as a single MMIC, I don't think its necessary to put any shield on the board. Especially given the fact basically nothing else inside the counter is shielded :)
I have had some time to measure the highest possible frequency at -20 dBm this weekend: 2070 MHz.
The Signal-Source I used was my DIY Signal Generator, which uses a ADF4351 for anything higher than 400 MHz.
At lower frequencies (1.5 GHz), I can go as low as -29 dBm.
The lowest frequency the board was able to count was 8 MHz btw.
Higher amplification on the board might help with these performance-figures, but might also cause other signals to become too strong - Might be worth some investigation, but for the moment I'm pretty happy with the results :)
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I have updated the Boards to Mk. II Rev. A
Changes:
- Replaced T-Junction at output of RF-Amplifier with Resistive Splitter
- Added second RF-Amplifier to compensate for losses in Resistive Splitter and increase sensitivity
- Replaced the MC12095 Prescalers with MC100EL33 (MC10EL33, SY10EL33 and SY100EL33 fit also), as these parts are listed as "Active" by the manufacturers
- Replaced the NE5532 with a LM258 OpAmp in SOIC-Package to save space
- Schottky-Diodes of the automatic limiter-circuit replaced by BAT15-04 (2 Diodes in one package)
- Removed unnecessary Filters (High Pass at input of first Amplifier and Notch-Filter for the Detector)
- Replaced Zener-Diode for the negative supply with LM79L05
- New Board-Layout with larger and less Vias, as well as additional mounting-holes for a standoff (this standoff can be glued to the Mainboard, which makes mounting easier)
- Removed RF Power-Measurement features (caused problems)
The additional amplifier, together with the new Prescalers should improve sensitivity (hopefully not so much that noise is being counted :) ) and increase the measurement-range up to 2.5 GHz (currently the counter loses the signal at about 2.1 GHz but if I remember correctly, the normal inputs could count up to 160 MHz which gives a max Frequency of 160 x 16 = 2560 MHz).
Attached is a 3D-Rendering of the new board. I tried to avoid having to route stuff on the bottom side, but a few traces had to go down there. Undivided RF-Path is undisturbed though. I again went for a Coplanar waveguide-design but with larger Vias this time.
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SaabFAN,
Thanks for the continuing effort improving your PM9610 replacement! I'm looking forward to trying this out on my recently acquired PM6652.
- George
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Small update here to Rev. B (which I'm actually going to order):
- Coplanar Waveguide Vias now 0.5mm hole and placed in a denser pattern.
- Added a 0 Ohm resistor as a jumper in the +5V rail
- Replaced D4 and D7 with 1N4148 (before LL4148)
The addition of the jumper link and replacing the 2 SMD Diodes with Through hole basically adds a "3rd Layer" to have a completely uninterrupted GND-Plane underneath the RF-Traces (before the divided signal had to cross these 3 signals) :)
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Well, new boards are ready to order, but I since I discovered the opportunity to buy them ASSEMBLED from JLCPCB, I'm considering to do just that :)
Does anyone have any experience about buying them assembled from them? The Previewer sometimes shows (especially on larger chips) the chips to be in the wrong orientation. Wouldn't really make sense to have them assembled and then have to redo all the chips if they're in the wrong orientation.
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SaabFAN,
Is it possible to ask them to run a test batch of one to see if all components are oriented correctly?
Perhaps with the understanding that you won't pay for their errors?
- George
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I went ahead and asked JLCPCB after making sure that my files are correct and they replied with the statement that their previewer has a bug and they have an engineer checking the rotation and correcting it if necessary.
BUT The parts I want to use aren't in their parts-catalogue and similar parts are "extended parts", which cost 3€ each to change the reels. So the boards will only be partially assembled (only 0603 and 0805 Capacitors and Resistors will be on the board) with "Some Assembly Required" :)
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I can't wait to see what the partially assembled boards will look like when you get them!
- George
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New boards are here.
Assembly turned out to be quite good. Especially the 0402 Capacitors - Hard to solder those by hand and have it look good :)
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The board looks great! Really looks pro. And I agree, no matter how you try to solder 0402 parts (which are evil small), they never come out looking good.
I already PMed about the boards.
- George
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Btw. these are the parts that are missing and have to be hand soldered:
U1, U2: NXP BGA2869 RF Amplifier
U3: LM258T OpAmp (basically any dual OpAmp will work, but the ones with high bandwith might be prone to potentially damaging oscillations)
U4, U5: SY100EL33LZG-TR (Prescalers)
U6: LM79L05ACZ
D1: Bat15-04W
D2, D3: Bap50-03 PIN-Diodes
D4, D7: 1N4148 (Leaded diode)
D5: Bat15
L1: 680nH 0603-Package Inductor
VR1: Bourns 3296W-1-102LF (10k 10-Turn Pot)
C28: 47uF/10V Tantalum Capacitor - "C" or "D"-Package
R3: 352236RFT
R6, R7: 3522150RJT
P1: SMA-Connector (The ones that can be mounted at the edge of a PCB)
P2: 2,54mm Pin Header, 12 Pins, 90 Degree - I recommend ones that have longer pins, as the typical 90degree pin-headers with 6mm long connector-pins tend to be a bit too short. It is possible to solder a straight connector SMD-Style to the board, however. That way the pins should reach the contacts in the slot.
Jump_1: Any kind of wire that is flying around on the bench :)
The only ones that are a little tricky are the two MMICs U1 and U2. I recommend hot air or a magnifying glas and a small soldering tip for those.
Caps should be far enough away from the chips to avoid blowing them off the board if the airflow is not set too high.
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I just realized something: D2 and D3 must of course have their Cathode on the RF-Trace and the Anode connected to GND.
There's a small dot on the RF-Trace noting pin 1 of the diode, but it's a bit hard to see.
Unfortunately there was a screw up with the shipping labels where the chinese apparently forgot to put my name on the label. Just the street and the city. So I'm still waiting for the parts, hoping the chinese are able to straighten this out quickly with DHL. Otherwise I would be testing the prescalers right now. :)
Same issue happened with the boards btw., but they were shipped via UPS and it took one phone call with their customer service to clear it up. A day later I was able to pick up the boards at a UPS Access Point.
DHL is a bit more... "German" in that regard it seems (rigid and inflexible, with a fanatical adherence to protocol) and I had to mail LCSC and ask them to fix the problem :)
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A big thanks to SaabFAN for sending me a pair of his new Philips prescaler boards. (Some assembly required!)
- George
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Btw. Here's the schematic for the newest version. :)
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I finally got around to building up the new version after I had ordered the wrong chips (MSOP instead of SOIC).
Results so far:
- I goofed up the input of the first prescaler (again) |O : C22 has to be replaced with a solder bridge and pins 2 and 3 of U4 have to be connected with a 1 kOhm resistor. I have soldered a 0603 resistor across the legs, but soldering a resistor to C21 and the solder bridge that replaces C22 works too.
- Frequencies up to 2.89 GHz can be measured at input-levels of -30 dBm. :-+
- Frequencies lower than 290 MHz cannot be measured reliably and anything lower than 350 MHz requires at least -10 dBm to be measured reliably. :--
My investigation so far points to 3 possible causes:
- Signal Source. I'm using the ADALM Pluto in CW-Mode and the spectrum looks horrible with powerful wideband spurs close to the CW-Signal, as well as strong harmonics. The output has massive jitter which gets really bad at
frequencies below 280 MHz. At 100 MHz the jitter takes up almost 25% or a full period.
- Oscillations in the second amplifier: I noticed 1.2 GHz parasitic oscillations that become quite strong and frequency stable when a finger is placed over U2, the output-trace of U2 and the Bypass-Caps C4 and C5. This is rather
surprising,
since until now I never had any oscillation-problems with the BGA2869 Amplifier and used it in several projects without any problem. Even mounted dead bug-style on a vero-board it didn't oscillate.
- A problem with the splitter (R2, R4 and R5 arranged in a Delta-Configuration) and/or reflections from the RF-Detector for the standby-Circuit.
I've also noticed a tendency to count harmonics if the input-signal has a frequency of less than 100 MHz. Interestingly, I've had absolutely no issues when I fed the prescaler a 24 MHz-Signal from my FeelTech DDS-Signal-Gen...
So 2 steps forward (higher sensitivity, frequency-range extended), one step back (Problems with the Divider-Chips again). >:(
Sorry @ geostep and everyone else who bought one of the new boards. I really thought I had nailed it this time :(
Any ideas on how to fix or how to tackle this problem?
My big problem is that I don't have a good working signal source for frequencies between 24 and 900 MHz.
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Okay, I managed to get it working with a DDS Sine-Wave from my AD9910-Module (part of my Signal-Generator Project - yes, it is kinda working :) ).
The changes I have done so far:
- Connected Pins 2 and 3 of U4 with a 1k Ohm Resistor
- Replaced C22 with a Solder-Blob
- Removed U2 and connected the input and output-pads with a 2 Ohm 0805 Resistor (fits almost perfectly and I was able to solder it without my magnifying glas)
- Removed C23
With these modifications, a clean Sinewave works down to 80 MHz with Input-Power from 0 dBm down to -26 dBm. At 50 MHz the Output was rather jittery and the count was off, but the prescaler isn't supposed to cover anything below 50 MHz anyway. That's what Channel A and B are for :)
The reason for the removal of U2 is twofold: First the amp is oscillating (now there's no output even without diode D7 disconnected if there's no input), and second it is completely overdriven unless the input-signal is extremely weak. The result of the amp being overdriven is a horribly clipped signal that has a ground bounce-component that triggers the prescaler, resulting in jitter and counting frequencies twice as high as the input-frequency.
Standby-Circuit is still not working, though. And I don't have a second LM258 here to replace the OpAmp. I might have damaged it by powering the board with just positive voltage and leaving the negative supply unconnected - The Output of the OpAmp isn't changing at all regardless of the input-voltage. It's just driven against the positive rail all the time.
Also the SY100EL33 chips I am using (Mouser didn't have the MC100EL33) appear to be recognizing only the rising flank of the reset-signal and are not level controlled (datasheet isn't really clear about it and surprisingly rudimentary in general).
So since the outputs stay silent even if there's no input-signal most of the time, I would recommend to just leave D4, D7 and U3 unpopulated.
Tomorrow I'll repeat the measurements at higher frequencies with my HP8614. I expect it not to go all the way to almost 2.9 GHz any longer due to the amplification of U2 missing from the signal chain and also to have less sensitivity above 2 GHz.
I was expecting to run into a wall due to the limitations of the original hardware on the counter-board, especially the COAC-ASIC by Philips, at about 2.3 to 2.4 GHz, but that part is apparently capable of a lot more than advertised :)
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Any update on this project ? :)
Specifically regarding the latest mentioned issues
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I am thinking to do a same project for another similar counter (PM6665/PM6669). Slightly different board but very similar architecture.
What does B and TEST GO lines do ? I'm having some problems understanding what they are doing with the RF detection stuff
Thanks
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I've found some time to work on this again.
The boards I have work pretty well with the workarounds I've detailed in the last post when I use pure sine wave generators.
The ADALM Pluto unfortunately is completely useless as a signal source as there's always some kind of modulation on the signal, so I have no means to test the device with sine waves in the frequency range 400 to 900 MHz until I have my Signal Generator working.
The latest Revision has only one RF Amplifier and I'm revising the Standby-Circuit in a way that the board doesn't need the negative supply anymore, so no more damaged OpAmps when I supply only the positive voltage during testing :)
The "B"-Signal and "TEST GO" disable / enable the Output of the Prescaler-Board.
"B" adds a Bias-Voltage to the detected RF-Voltage or subtracts it from the RF-Voltage - I'm not entirely sure anymore ;) In any case, it turns off the output of the Prescaler when the Prescaler is not needed (in the PM6654C this is the case when Channel C-Mode is not selected).
"TEST GO" on the other hand pulls the other input of the comparator in the standby-circuit to a value that ensures the Prescaler-Output to be on under all circumstances for testing purposes.
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I just checked the Schematic of the PM6654C Mainboard again.
The B-Signal is left floating on that board, so it's not actually needed. It either is used when installed in a different instrument, or just there for testing purposes.
The TEST GO-Pin connects to the "DATA OPTIONS"-Connector "BU108" on Pin 24, but is not used by any Option that is listed in the Service Manual. So it was probably only there for testing during manufacturing.
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Hi, nice project, I have a PM6652 that would need a prescaler. Are you still selling pcbs? Otherwise, would you share the fabrication files? Thanks
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I also need a prescaler for my 6654c. Any way I can get the PCBs or the gerber files ?
Thanks you,
-George
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Just wondering are there older versions pcb files available for download or someone have spare board for version with MC12095 prescaler?