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Replacement for the PM9610 Prescaler for Philips PM6654 High precision Counter
SaabFAN:
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.
SaabFAN:
Schematic for the Original Unit and the new Version with more modern components.
edavid:
I can't help with the photo, but I would love to buy a couple of boards when you have them.
SaabFAN:
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.
SaabFAN:
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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