Raspberry Pi Wobbulator - UK Vintage Radio Repair and Restoration Discussion Forum

David Goodall · 2nd Jan 2014, 9:54 pm

Hello all. Has anyone seen, or built this wobbulator? I don't have a wobbulator, and I'm looking to build one.

http://asliceofraspberrypi.blogspot....lator-kit.html

Radio Wrangler · 3rd Jan 2014, 12:53 am

It looks good, and quite sensibly done. With one of the ADI loggers for a detector, it's really a scalar network analyser and not just a wobbulator. The DDS approach allows wide down to very narrow sweeps, and the designer even shows plots of crystal responses. I think the DDS looks like an AD9850 which will clock to 125MHz,and so give normal use to about 50MHz.

I've used those parts before and they'll do very nicely. The computer will also give you digital trace storage which is much nicer for the slow sweeps needed to plot narrow filters.

I'd go for it.

David

David Goodall · 3rd Jan 2014, 9:21 pm

Thanks David. It will be fun to play with, so I shall give it a go for £40.

Radio Wrangler · 3rd Jan 2014, 11:02 pm

You'll need to build a well-screened multi-section attenuator to go with it to get the level down to what would suit a radio input. Working at low level stops the AGC trying to 'correct' what you're trying to see.

I buit myself spectrum analyser with a tracking generator some years ago, otherwise I might just be building one of these.

David

dominicbeesley · 6th Jan 2014, 7:04 pm

I built a prototype of something similar, with microcontrollers to make a vector display on a scope, a few years ago and still use another wobbulator using an AD9851 DDS and PIC controller nicely boxed up - great fun and I still use it. I've got a pair (or maybe three) of those modules kicking around and was going to make a simple VNA - maybe I'll just crib this one - looks interesting

Dom

mole42uk · 9th Jan 2014, 9:32 am

Quote:

Originally Posted by David Goodall

Hello all. Has anyone seen, or built this wobbulator?

I have just built one. Early testing as yet but it looks good so far. The kit is excellent (but not for the faint-hearted - it's mostly surface mount soldering so you'll need a steady hand, a magnifier and the correct soldering iron!).

A surprise yesterday was that I got the frequency output down to 440Hz - I'll be trying to get down to about 20Hz if possible then the wobbulator will be useful as an audio amp frequency response tester!

I'll update the forum as more results come in.

Richard

2nd Jan 2014, 9:54 pm	#1
David Goodall Pentode Join Date: Mar 2006 Location: North Norfolk, UK. Posts: 181	Raspberry Pi Wobbulator Hello all. Has anyone seen, or built this wobbulator? I don't have a wobbulator, and I'm looking to build one. http://asliceofraspberrypi.blogspot....lator-kit.html __________________ David Goodall

3rd Jan 2014, 12:53 am	#2
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,876	Re: Raspberry Pi Wobbulator It looks good, and quite sensibly done. With one of the ADI loggers for a detector, it's really a scalar network analyser and not just a wobbulator. The DDS approach allows wide down to very narrow sweeps, and the designer even shows plots of crystal responses. I think the DDS looks like an AD9850 which will clock to 125MHz,and so give normal use to about 50MHz. I've used those parts before and they'll do very nicely. The computer will also give you digital trace storage which is much nicer for the slow sweeps needed to plot narrow filters. I'd go for it. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

3rd Jan 2014, 9:21 pm	#3
David Goodall Pentode Join Date: Mar 2006 Location: North Norfolk, UK. Posts: 181	Re: Raspberry Pi Wobbulator Thanks David. It will be fun to play with, so I shall give it a go for £40. __________________ David Goodall

3rd Jan 2014, 11:02 pm	#4
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,876	Re: Raspberry Pi Wobbulator You'll need to build a well-screened multi-section attenuator to go with it to get the level down to what would suit a radio input. Working at low level stops the AGC trying to 'correct' what you're trying to see. I buit myself spectrum analyser with a tracking generator some years ago, otherwise I might just be building one of these. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

6th Jan 2014, 7:04 pm	#5
dominicbeesley Octode Join Date: Nov 2004 Location: Hebden Bridge, West Yorkshire, UK. Posts: 1,885	Re: Raspberry Pi Wobbulator I built a prototype of something similar, with microcontrollers to make a vector display on a scope, a few years ago and still use another wobbulator using an AD9851 DDS and PIC controller nicely boxed up - great fun and I still use it. I've got a pair (or maybe three) of those modules kicking around and was going to make a simple VNA - maybe I'll just crib this one - looks interesting Dom