Signal Generation

I have been watching Jeff's - KO7M Blog and his current QRSS/WSPR Transmitter project using the DDS-60 as part of the prototype. Jeff had previously done some work with the AD5330 8 bit DAC.

Jeff's efforts have inspired me to look at a previous purchased Si750 SDR-Kit, that I still had not built.

Without much difficulty, I now have put the Si570 SDR-Kit together (only the 3.3v Regulator went in backwards, which I fixed). Testing is still in progress.

While investigating; the kit's circuit and the Si570 datasheet, the DDS-60 and its AD9851 device, I have learned a lot more about micro-controlled frequency generators and DDS's in general.

This may be Old Stuff for some folks, but this is what I have learned, this info is saved here for my future use:

The Si570

The Si750 SDR-Kit is a real neat device with a very wide frequency range of 10MHz to >900MHz and can be controlled via a two wire computer connection (I²C). It's output is square-wave, which is ideal for a mixer LO of a receiver

But, the Si570 has some limitations for use as a general use signal source. The output (square-wave) would require difficult frequency sensitive filtering to obtain a clean sine wave over the entire frequency range.

Obviously for a single frequency, a filter can be easily created, but for that single frequency, a simpler crystal or oscillator circuit could be used instead. 

Once setup, the Si570 output is continuious, without assistance from the computer or micro controller. 

The DDS-60 

More information needed.

The AD5330 

The AD5330 8 bit DAC is a general purpose signal/wave-form source with a frequency range of 1kHz to 36kHz. It uses DDS processor to create the output wave form. Almost any shape of output can be created.

For use as a AF signal source, it's output is normally a stepped waveform, which normally needs a low pass filter to remove the steps.The output can be used with a mixer to create double sideband signals. 

A continuous use computer or micro controller is needed to generate the steps of the intended frequency or wave form.

I need to explore these circuits more, and will update as necessary.

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pQRP P&C Meeting

The following was reported by Wayne, after our Puget Sound QRP (pQRP) Pie and Coffee (P&C) Meeting, republished here as an archive.

Note: I did not invent the Toner Transfer Process to produce PCB's, I used a lot of information form the WEB, thanks to the many people that have gone before me.



Hello All,

We had a great turnout at P&C last evening, with fourteen of us around the table. Here's the list:

Roger, K7RXV
Jeff, KO7M
Rod, WE7X
Eldon, WA0UWH
Charlie, K7KN
Bob, W8MCJ
Rick, K7MW
Lyle, KK7P
Doug, W7RDP
Rich, AC7MA
Brendan, N0BML
Bill, WA7NCL
John, KC7NVE

Although most of us have been busy with summertime activities, there have been a few projects going on.

Eldon, WA0UWH, has worked out a method for producing PC boards, using an ink transfer method involving a laminating machine. He'll have to explain it in detail for us, but it looks very interesting.

He brought his 40 dB Tap project along for show and tell, also, having cut the PCB material to Roger's specifications and now getting ready to build it.

Eldon is making his shop available to any of us on the 3rd Saturday of each month, for radio or other types of building projects. He has everything from wood working equipment through metal working gear, including a lathe and milling machine.

Lyle has built his RF Test Set, and his lack of output from the DDS board was caused by the fact that his DDS60 is an older one with a different DDS chip and clock frequency. Rich is going to try to adjust the firmware so that Lyle will be able to use the older daughterboard.

I have been so busy with being the Commodore of my local yacht club, hosting company, and the usual summertime activities, that I have not been doing any building projects and have not been on the air, either. My time will free up a lot in late October, and the onset of the rainy and dark season will turn my interests back to the workbench and paddles.

Jeff, KO7M, brought his recently built HF Packer Amp, that he built from a kit, and it is very nicely packaged and will be a nice addition which will give his QRP RF output a good boost to help make contacts in this time of low sunspot activity.

Bob, W8MCJ, came with a box of free stuff like coax cables, some ham related books, and gave a copper ground strip with braided connecting wires to tie rigs together and to ground as a door prize. Lyle gratefully received this unit.

As usual, the discussion around the table was varied and lively, ranging from a little teasing towards Doug, W7RDP, about the recent docking mishap with the Wenatchee, the Washington State Ferry he works on, to various computer programs for MAC and Windows Vista, as well as QRP Radios and operating events.

Bill, WA7NCL, talked a bit about operating in a recent "Bumblebee" event, and made a suggestion for next Salmoncon, saying that since we tend to focus on building projects, we should have an operating event at Bowman Bay, where we each put together a portable QRP station, hike over to the point, throw an antenna over a tree, and operate for a while. Could be a lot of fun.

Rod, WE7X, brought in an award that he and Doug, W7RDP, had won in a recent VHF Contest. Roger, K7RXV, had been along on that trip as well, but didn't operate.

Brendan, N0BML, talked about his building project at Eldon's last shop gathering, which was a homebrew charger unit for his cell phone. Brendan is also practicing CW and getting ready for an upgrade to his license.

If I missed anything, it was simply because there was so much being discussed.

In short, it was another very enjoyable evening.

73,

Wayne NB6M