Re: AD9850 module pc board
Hi Jim,toggle quoted messageShow quoted text
The PHSNA project hardware has a a lot of variants. The main one used a DDS60 module from AmQRP. This used the AD9851 DDS and it is sold assembled or in kit form at http://midnightdesignsolutions.com. When I built mine the kit did not included the DDS chip because you could order free samples from Analog Devices as I did. This module is quite better than the Chinese ones, but it is far more expensive.
I can't speak by the designer, but I think that the main reason for using the Chinese modules in later versions of the PHSNA was price. When the project appeared and even several years after, these modules were far cheaper than buying the chip itself even directly from Analog Devices. I don't know the reason why these modules were so cheap, but I suppose that they began as excess inventory purchased from a manufacturer who used them as a part of other equipment (antenna analyzer perhaps?) and the module manufacturer could continue production after seen how well they were selling them. Two main versions were available with two different pinouts that were named Type I and Type II, there were PHSNA boards designed for each version. Also were modules with the AD9850 and the AD9851, the same PHSNA firmware and software could be used with both. The current price of these Chinese modules is probably due to a reduced supply. Offer and demand.
The reason for using an Arduino was in the the same line. The first version used and Arduino One and later it was changed to Arduino Nano that was cheaper, better and smaller, and directly pluggable on the main board. These micros were so cheap that it was no reason to include the chip in the main board. In fact you need other components such as the crystal, the serial to USB converter and others which added complexity to the building and purchasing. Also the Arduino has an IDE that is free and very easy to use. Even if you don't do any development, it is needed to load new versions of the firmware in the chip. I know that the Arduino IDE can be used with the AtMega chip without being mounted in an Arduino board, but you need to duplicate the environment in your board and the most difficult part for the standard user is to load the Arduino bootstrap in the virgin chip, you need a programmer for it (even other Arduino can be configured as a programmer). By the way, if you study the main board, it is nothing more that an interconnection board with some regulators, connectors and provision for options, extremely simple.
There is a big difference if a project is intended to become a manufactured product to be sold ready to use, a kit or just leave to the builder the task of procuring the parts. The PHSNA project provided a lot of information such as schematics, BOMs and provided the PCBs. The builder had to purchase the components from the usual sources. The designer also provided free the firmware, the software and the manuals.
Other projects, such as the now popular nanoVNA, are intended to be sold as a manufactured product. Everything is integrated in a compact PCB and sold assembled, but this project could be not made as a kit or a PCB, it would be difficult for the user to get the parts, difficult to assemble, and certainly more expensive.
About using a Si5351: there is a version of the PHSNA that can use this synthesizer in a plugin module and these modules are very cheap (about $8 or less) and you avoid the task of soldering the tiny chip. I do not recommend using this kind of synthesizer for this project because its output is a square wave, so plenty of odd harmonics. The PHSNA detector is a wide band one, it goes up to 500 MHz so if you are measuring some thing, say a filter, the readings are the sum of the desired frequency component plus all its harmonics winch are indistinguishable and can not be separated by the detector. for this kind of signal source you need a tuned detector, normally based in a superheterodyne receiver. The DDS is a sine wave generator, a much better option for using it with this type of detector. The Si5351 is advantageous used in the nanoVNA, but there the detector is a superheterodyne SDR receiver.
Best regards and 73,
El 14/05/2020 a las 7:44, Jim Pruitt escribió:
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