#rfbiscuit – Use Case 1: Dummyload

In this first example I would like to design a 50Ohm-Dummyload capable to dissipate 10 Watts – the resistor I have chosen for this task is a Bourns PWR263S-35-50R0F – which is specified for 35 Watts (with proper cooling). This resistor is a thick-film resistor, because we want to keep parasitics inductances low and has a tolerance of 1%.

IMG_4681

To measure the performance I attached the DIY-Dummyload to a VNWA3E Networkanalyzer

IMG_4682

In the frequency range from 1-500Mhz the DIY-Dummyload shows up as a dot in the Smith Diagramm. Exactly what we want.

50Ohm_RFBiscuit_DUMMYLOAD_500Mhz

above 500Mhz the parasitic capacitance of the RF Biscuit starts to show – but depending on your application such a result might be considered still as good-enough.

50Ohm_RFBiscuit_DUMMYLOAD_1000Mhz

Let’s compare this result to a commercial 50Ohm-Termination

IMG_4675

The following Smith Diagramm shows the 50Ohm-Termination in the Frequencyrange of 1-1000Mhz:

50Ohm_termination_1000Mhz

In this Diagramm you can see that the dot is a bit broader – which can be explained as the VNWA3E is less accurate above 500Mhz . You can also see spurs which are releated to the measurement device and which are not part of the characteristics of the 50Ohm Termination.

I will update this part with an evaluation of the thermalperformance of the DIY-Dummyload.

#rfbiscuit – Welcome to RF Biscuit

Hello, World!

This blog is dedicated to research the possibilities of low-cost prototyping of RF gear using the RF Biscuit platform. RF Biscuit is a OSHW project aiming to provide a small, simple, low-cost but yet versatile PCB that can be used to make filters, attenuators, dummyloads and even amplifiers (using gainblocks) the DIY-way. It current features include SMA PCB-edgeconnectors, a prototyping signalpath and the option to use a RF-shielding can.  The creation of the RF Biscuit follows the principle of “release early, release often” and heavily relies on feedback from the community to evolve into an even better protyping platform.

Let me invite you to use and experiment with RF Biscuit – if you are interested to join the circle of Beta-Testers feel free to contact me:

email_egen

You feedback is highly appriciated 🙂

Thanks, Georg

PS: PCB-Design is done in KiCad and the GitHub-Repo is here.