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Author Topic: Open Source HW RF Signal Generator  (Read 5569 times)

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Online chrisl

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Re: Open Source HW RF Signal Generator
« Reply #25 on: September 06, 2017, 06:34:39 PM »
A couple of quick comments:

Looks like all the RF switches  have DC block caps at the GND pin (2).  You want to ground this pin directly to the board GND.

Do not expect that the fab house can control and hold the tight tolerance on the DK and 4 mil trace width - especially the low coast PCB houses.
Simulate your filter design to make sure that your design can tolerate +/- 10 to 20% of variation.
It would be much easier and cleaner to use SMT filters at 1.5 and 3 GHz.

 

Offline SaabFAN

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Re: Open Source HW RF Signal Generator
« Reply #26 on: September 09, 2017, 02:23:18 AM »
A couple of quick comments:

Looks like all the RF switches  have DC block caps at the GND pin (2).  You want to ground this pin directly to the board GND.

Do not expect that the fab house can control and hold the tight tolerance on the DK and 4 mil trace width - especially the low coast PCB houses.
Simulate your filter design to make sure that your design can tolerate +/- 10 to 20% of variation.
It would be much easier and cleaner to use SMT filters at 1.5 and 3 GHz.

Yes, they do have DC Blocks at the GND-Pin. The reason behind this: I've used some attenuators from MaCom in a previous design that required exactly that: DC Blocks at the GND-Pin if driven by only positive voltages.
To avoid having to respin the board if that's the case with these switches too, I've but the DC Blocks in there. If they work without those caps, I'll replace them with 0Ohm Resistors or solder-blobs.

I'm currently using 6mil traces, as that's the smallest ShenZhen2U or EasyEDA can manufacture without massive cost increase.
SMT-Filter available from digikey unfortunately don't really have the features I require. There are filters available that could replace the 3GHz Filter, but a Filter for 1.5GHz isn't really available.

Offline SaabFAN

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Re: Open Source HW RF Signal Generator
« Reply #27 on: September 10, 2017, 10:23:14 AM »
I've just finished the controller-board. I don't have a block-diagram yet, but it is pretty straight forward:
A NodeMCU-Board with an ESP-12E contains the micro, as well as the 3.3V-Converter and the USB-Connection.
Attached to that are 3 PCF8574. One for the Keyboard (Address 0x21), One for the ChipSelect-Signals for the ADF4351 and AD9910, as well as two Interrupt-Inputs - one for the Keyboard, one for the Touch-Controller (Address 0x22), and One PCF8574 for the Attenuator-Control (Address 0x20).
Because the Attenuator requires 5V TTL-Levels, I've added what I had in my parts-drawers to do the level shifting: 74HCT14 and a 74LS00 (Both have a Positive Threshold of about 2V).
To use the TouchScreen, I've installed the STMPE610 Module from Adafruit and the Display is the 3.5inch 480x320 TouchScreen-Display-Module from Adafruit.

The MCU-Board is socketed by the way, because I had problems uploading a new Firmware when I had it soldered in. Really strange - GPIO-Pins 0 and 2 were showing a 0.5Vpp oscillation at about 2V DC-Offset when the Reset came and the bootloader was supposed to start and accept a new Upload.
Did anyone of you guys had similar problems with that board? Or do you have an idea what could have caused this behavior? Installing a socket made with female 2.54mm headers and plugging the MCU-Board into that solved the problem...


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