555 Super-Regenerative IF Spectrum Analyser

My relatively unconventional, but simple design for a toy (but still useful) HF spectrum analyser using a VHF super-regenerative detector as a logarithmic IF.

http://www.vk2zay.net/article/256

Fits in an Altoids tin, runs from 9 volts, and pulls 21 mA. Front-end is a JFET cascode mixer, the LO a JFET Hartley. Log IF is self-quenched common-gate JFET oscillator. Uses LM555 IC with PNP current source and LED modified threshold point for the linear sawtooth VCO tuning/X sweep voltage generation. Another (7)555 implements a frequency to voltage converter that resolves the log detector's quench signal. An LM358 op-amp level shifts and amplifies the output of the F2V converter to something more convenient for a CRO Y channel input.

Sweeps 22 MHz chunks of spectrum to beyond 55 MHz (limited largely by front-end LPF, IF is around 150 MHz), and gives a resolution bandwidth of about 250 kHz. Log range is better than 50 dB and quite linear. Frequency sweep is a bit compressed at the bottom end because of VCO varicap non-linearity. Tolerates 10 dBm signals, but IP3 is not expected to be very good as mixer stands only 2 mA.

Category:

Science & Technology

Tags:

• vk2zay
• super-regeneration
• super-regenerative
• spectrum analyser
• log detector
• log IF
• 555
• 555 contest

[bkelektronik]

A great Idea. I like tha way you get your log scale. Simple and effective. Looking forward to see the diagram on your web site.

[vk2zay]

@bkelektronik I wrote it up last night, link is in description bar...

[ea3ghs]

very nice!

[randomgarfield]

Very nice work AY!

[Canzona01]

Alan, excellent job.. I look forward to the details on your website.

[orbiter8]

Thanks vk, very interesting indeed. I'm definately gunna give this project a go.

Thank you.