Simple Radio Project: Part One

The basis for the start of the “simple radio project”. A zp-1-s+ ring mixer with an attached zfbt-4r2gw+ Bias T. RF & DC side connected to IF out, and the RF dumped into a 50ohm terminator while the dc pass will bring audio to an lm386-4 to a speaker. For testing I used my Koolertron DDS since this is a zero IF / no conversion setup it can be driven with one LO.

I re-used one of the amplifiers from the LBS project and with no filtering had promising results. I ordered the zx75lp-30-s+ low pass filter last night. And Monday once Ar2 is open I will call in an order for the p.1-30/20vd wideband preamp (sma of course). I’m still contemplating whether to use the Arduino Mega 2560 or to run the Arduino Uno with the si5351 clock board for this project. I feel like saving the mega for something that needs more inputs and memory than this likely will so it looks like the uno will be back in the game once again.

Originally I decided to go with sma as these were the headers that I had installed on various boards for the LBS project; as well as, the si5351 clock 0,1,2 out headers. If I had it to do over again I would have just went BNC such as Glen did with his projects. For now though I’ll be sticking with sma. These parts may remain together as a unit indefinitely, and the triple conversion transceiver will likely go all bnc for simplicity and fiduciary’s sake.

I drove the lo with a .47v p2p drive level and I have to say this mixer performs very well. I may buy a band reject filter for the broadcast am area depending on results once the basic design is assembled. I had quite a lot of overpowering AM signals but for now I’m going to blame the mixed bag amplifier for that, or that I was feeding this with an 80m skyloop.

It is most likely as well that I will switch to a mixer similar to what Glen used for this project in my triple conversion design. Getting the widest coverage possible with a stack of bandpass filters / low pass filters should make for some great reception and transmission capabilities. Hopefully the si5351 is up to the task as I am no where near ready to tool up and design a dds from scratch for a high end home built radio.

I did find conclusive proof in regard to phase noise from another blog though which has been the first time I’ve seen it tested at least as well as the author did.

Courtesy of Ripples In The Ether : Full article located here:

The first two plots were taken at 3 MHz, first with 2 mA output current then at 8 mA output current. Then you will find 10 MHz, 13.371 MHz (in both fractional and integer divider modes), 14 MHz, 100 MHz, and then a composite plot of all of the different traces.

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I believe that the plots speak for themselves fairly well. If you compare these results to the receivers in the Sherwood Engineering receiver table, I think you’ll see that the Si5351 acquits itself quite nicely for such an inexpensive part. Personally, I think the Si5351 is eminently usable for many receiver applications, except perhaps the most high-performance. Certainly for the price, it’s going to be extremely hard to beat. I hope this motivates those sitting on the fence to decide if the Si5351 will meet their needs.


As you can see it will work well enough. So for the time being until I am in a place where I can take the time to acquire the necessary skills to tool up and build a dds from scratch this will have to work. Multiplying the clocks by 4 and using a flip flop to divide back down would create a 6-12db gain improvement in phase noise as well. Several options to attack this issue, but for now I am just focusing on the receiver project here.

And as always

73 Ben N4AXE

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