Forum - Recent Threads

How to compute the required length and turns for a air cored antenna

obones — Sat, 20 Mar 2021 14:13:43 GMT

Hello,

While experimenting with various designs for the 433MHz antenna to be used with my RFM69 receiver, I stumbled across step by step instructions created by Ben Schueler in 2013 and republished a large number of times since then, such as here: https://arduinodiy.wordpress.com/2015/07/25/coil-loaded-433-mhz-antenna/

It works quite well for my application, but now I would like to dabble into the 868MHz range and I was wondering how I can calculate the appropriate dimensions/number of turns to replicate the above design, but tuned for 868MHz reception.

Would you have the link to a reference document so that I can compute it myself? Or should I just go ahead and divide every value by two as 868 is roughly 433 multiplied by two?

Thanks for any pointers.

What SDR software do you use?

colporteur — Wed, 10 Mar 2021 01:10:52 GMT

What is your go-to SDR software?

I'm thinking about pitching an application for the Digilent 1x1 USB Software-Defined Radio Platform RoadTest Review. Part of my research is to investigate what software is available for SDR. Here are some SDR application I have used GQRX, CubicSDR and GNURadio. I dabbled in RTL-SDR some two years ago. I recall at that time SDR#(SDRSharp) was popular but I seem to recall it was limited to Windows PC's. Being a Linux user Windows only applications are not something I look at.

I would like to investigate a few SDR applications but avoid the rabbit holes, application you discover after much research they are no longer supported.

What is your software pick for SDR? In your response can you indicate your operating system preference and what frequency band you focus your SDR efforts on? Three responses:

What SDR application?
What operating system?
What frequency band of interest?

Question on Harmonics and Filters

kmikemoo — Mon, 27 Jan 2020 16:31:04 GMT

A discussion going on about filters at Episode 355: Raspberry Pi Pirate Radio has me wondering. I have always thought about harmonics (and the need to filter them out) as things that happen above the base frequency; 3rd, 5th, 9th, etc. Is there such a thing as sub-harmonics?

If my primary issue is harmonics (bit banged Raspberry Pi RF output), why go for a bandpass filter over a lowpass filter? Thanks in advance.